Glossary of Terms - UNIPOWER LLC

Some common (and less common) terms that are used in the Power Conversion industry.

Use the search box below right to find the term you are looking for.

Term	Definition
A	Symbol for ampere.
ac	Alternating current. In text, use lower case. See alternating current.
ac brownout	See brownout.
ac line	The set of conductors that route a supply voltage from one point to another.
ac line filter	A filter circuit placed in the ac line to attenuate the frequency components that are higher in frequency than the line frequency.
ac loss detector	A power-fail detector circuit that monitors the status of the ac lines.
accumulator	See secondary cell.
activated cell	A cell containing all components in a charged state ready for discharge (as distinct from unactivated cell).
activated shelf life	The period of time, at a specified condition, that a cell can be stored on open circuit in the charged condition before its capacity falls below a specified level.
activation	1. Polarization resulting from the rate-determining step of the electrode reaction. 2. The difference between the total polarization and the concentration polarization. See polarization.
active material	The material in the electrodes of a cell or battery that takes part in the electrochemical reactions of charge or discharge. See battery.
active material shedding	Physical separation of active material from battery plates due to corrosion or other chemical processes.
Ah	Ampere-hour. See ampere-hour.
alarm fuse	A fuse designed to provide a remote indication upon operation.
alive (live)	Electrically connected to a source of voltage difference or electrically charged so as to have a voltage different from that of earth. Synonym: live.
alternating current (ac)	A periodically varying current whose average value over a period is zero. Unless distinctly specified otherwise, the term refers to a current which reverses at regularly recurring intervals of time and which has alternately positive and negative values. Contrast: direct current.
ambient temperature	1. The average temperature of the environment immediately surrounding the power supply or device. For forced air-cooled units, the ambient temperature is measured at the air intake. 2. For self-ventilated equipment, the ambient temperature is the average temperature of the air in the immediate vicinity of the equipment. 3. For air- or gas-cooled equipment with forced ventilation or secondary water cooling, the ambient temperature is taken as that of the ingoing air or cooling gas. 4. For self-ventilated enclosed (including oil-immersed) equipment considered as a complete unit, the ambient temperature is the average temperature of the air outside of the enclosure in the immediate neighborhood of the equipment. See also: operating temperature, storage temperature, and temperature coefficient.
American wire gauge (awg)	A standard for sizing cross-sectional areas of wire, and for measuring sheet-metal thickness. Also known as the Brown and Sharpe gage, AWG was devised in 1857 by J.R. Brown. This gage has the property such that its sizes represent approximately the successive steps in the process of wire drawing. Also, its numbers are retrogressive; a larger number denotes a smaller wire corresponding to the operations of drawing. These gage numbers are not arbitrarily chosen, but follow the mathematical law upon which the gage is founded.
amp	Common abbreviation for ampere or amplifier. Not recommended for use, due to this ambiguity, especially where it may be subjected to a translation from English to another language. See ampere; amplifier.
ampacity	Current carrying capacity of electric conductors expressed in amperes.
ampere (a)	A unit of measurement for electrical current or rate of flow of electrons (coulombs per second) through a wire. If a group of electrons whose total charge is 1 coulomb passes a point in a conductor in 1 second, the electric current is 1 ampere. Its mathematical symbol is "I".
ampere hour efficiency	The ratio of the number of ampere-hours delivered during the discharge of a secondary cell or battery to the number of ampere- hours necessary to restore the initial state of charge under specified conditions.
ampere-hour (Ah)	A measurement of charge capacity computed as the product of current (in amperes) and time (in hours).
ampere-hour capacity	The number of ampere-hours that can be delivered by a cell or battery under specified conditions.
anion	A negatively charged ion or radical that migrates toward the anode during operation of the cell.
anode	1. The electrode at which an oxidation reaction occurs. During discharge, the negative electrode of the cell is the anode. During charge, the situation reverses and the positive electrode of the cell is the anode. 2. (thyristor) The electrode by which current enters the thyristor, when the thyristor is in the ON state with the gate open- circuited. Note: This term does not apply to bidirectional thyristors. 3. (semiconductor rectifier diode) The electrode from which the forward current flows within the cell to the cathode.
anode terminal	In semiconductors, the terminal by which current enters the device. The positive terminal, such as the plate in an electron tube.
anolyte	The portion of the electrolyte in a galvanic cell adjacent to the anode; if a diaphragm is present, the electrolyte on the anode side of the diaphragm.
apparent power	Power value obtained in an ac circuit as the product of rms current times rms voltage. Note: It is a scalar quantity equal to the magnitude of the phasor power.
attenuation	Decrease in amplitude or intensity of a signal.
autoranging	A feature on some ac-input power supplies where internal circuitry senses the input voltage and automatically selects 115 V or 230 V operation by using a relay, thyristor or other switching device.
autotransformer	A single-winding transformer with one or more taps.
auxiliary power supply	A power source supplying power other than main load power as required for the proper functioning of a device.
availability	The fraction of time within which a system is actually capable of performing its mission.
available capacity	The total capacity, in Ah or Wh, that can be delivered by a cell or battery at defined discharge rates and other specified discharge or operating conditions.
average drain	The average current withdrawn from a cell or battery during discharge.
average value	The value of a repetitive waveform that is found by dividing the area under one cycle by the distance along the X-axis corresponding to one cycle.
averaging filter	See L-C filter.
awg	See American Wire Gage.
backup power supply	A power supply used to provide alternate system power in the event the primary power source fails or is unable to continue providing adequate system power.
bandwidth	Based on the assumption that a power supply can be modeled as a linear control system, the bandwidth is defined by the upper and lower frequencies at which the voltage is -3 dB from a reference frequency within the bandwidth. Bandwidth is an important determinant of transient response, output impedance and stability.
battery	Two or more electrochemical cells electrically interconnected in an appropriate series/parallel arrangement to provide the required operating voltage and current levels. Under common usage, the term "battery' is often also applied to a single cell.
battery backup	A power supply system where if the ac line fails, a battery will provide input energy to keep the dc outputs from failing. A battery connected in a system to provide power in the event of failure of the main power supply.
battery charger	Electrical equipment designed to restore capacity to a rechargeable battery.
battery crate	A container with frame walls for holding several groups of cells or batteries. Usually used in railroad applications.
battery disconnect	A circuit that disconnects the battery from the load to prevent excessive discharge of the battery.
battery plant	A complete power conversion and standby system, including battery charging rectifiers that normally supply the load and also float and recharge the batteries, one or more strings of secondary cells, load distribution and protection devices and monitor and alarm facilities.
battery rack	A rigid structure of one or more levels to support a group of stationary cells. Also called a battery stand.
battery voltage	The total voltage between the positive and negative terminals of the battery. See also nominal voltage, voltage, and working voltage.
Bellcore	Abbreviation for Bell Communications Research. The name was changed to Telcordia in 1997. See Telcordia.
bipolar	Having two poles, polarities, or directions. Note: Applied to amplifiers or power supplies, it means that the output may vary in either polarity from zero.
bipolar plate	An electrode construction where positive and negative active materials are on opposite sides of an electronically conductive plate.
blackout	A total loss of electrical power.
bleed	A low current drain from a power source.
bleeder resistor	A resistor that allows a small current drain on a power source to discharge filter capacitors or to stabilize an output.
bonding	A low impedance path obtained by permanently joining all metallic parts to form an electrically conductive path that will ensure electrical continuity and have the capacity to conduct safely any current likely to be imposed on it.
boost charge	A charge, generally at high rate for a limited period, to restore capacity in all cells of a battery. Synonym: quick charge.
boost converter	A dc-dc converter that supplies a low voltage output that is added in series with the battery supply to provide a regulated output.
boost regulator	One of several basic families of switching power supply topologies.
boundary layer	The volume of electrolyte solution immediately adjacent to the electrode surface in which concentration changes occur due to the effects of the electrode process.
branch	The current path between two voltage nodes in a circuit.
branch circuit	That portion of the wiring installation between the final overcurrent device protecting the circuit and the load.
branch circuit protection	An overcurrent protection circuit or device that protects the branch circuit.
break before make	Disconnecting the present circuit before connecting a new circuit. Also known as Break/Make.
brownout	The condition created by system overload or during peak usage periods when electric utility companies intentionally reduce their line voltage by approximately 10 to 15 percent to counter excessive demand.
built-in test	The capability of a power supply to monitor its own vital functions and to identify potential or actual failures.
bulk capacitor	The energy storage capacitor at the front or load end of a regulator.
bulk voltage	The voltage across a bulk capacitor.
burn-in	The process of operating a newly manufactured power supply, usually at rated load, for a period of time in order to force component infant mortality failures or other latent defects before the unit is delivered to a customer.
bus	1. The common primary conductor of power from a power source to two or more separate circuits or loads. 2. A conductor, or group of conductors, that serves as a common connection for two or more circuits.
C	Variously, the symbol for capacitance, capacitor, Celsius, centigrade or coulomb.
C rate	1. Discharge or charge current, in amperes, expressed in multiples of the rated capacity of an energy storage cell. A cell's capacity is not the same at all discharge rates and usually increases with a decreasing rate of discharge. See hourly rate. 2. CIX Rate The current which would be necessary to discharge or charge a cell of a given rated capacity (C) in X hours if the cell maintained the same rated capacity at all discharge rates. For example, a 2.5 ampere-hour cell, rated at the 10-hour rate, will provide 250 milliamperes for 10 hours. In the real world, however, a cell does not maintain the same rated capacity at all discharge rates.
C5	Symbol for ampere-hour capacity at the five-hour discharge rate to an end voltage.
cache	A section of a computer’s memory that retains recently accessed data in order to speed up repeated access to the same data.
capacitance	1. The property of an electric circuit or device to store electrical charge.
capacitance, distributed	The capacitance in a circuit resulting from adjacent turns on coils, parallel leads and connections.
capacitive coupling	Coupling of a signal between two circuits, due to discrete or parasitic capacitance between the circuits.
capacitive effect leakage current	The voltage and frequency dependent current flow between galvanically isolated metal parts.
capacitive reactance (Xc)	Opposition to a changing current as a result of capacitance.
capacitor	A device that stores electrical charge. A simple capacitor consists of two conducting surfaces separated by a dielectric.
capacitor input filter	Filter employing a capacitor at its input.
capacity	1. The ability of a component, battery or other device to store and deliver a given quantity of current (A) or power (W) over a specified period of time (Ah or Wh). 2. The total number of ampere-hours that can be withdrawn from a fully charged battery at a specific discharge rate and electrolyte temperature, to a specific cutoff voltage.
capacity current	The fraction of the cell current consumed in charging the electrical double layer.
capacity retention	The fraction of the full capacity available from a battery under specified conditions of discharge after it has been stored for a period of time. See also: charge retention.
carbonization	The formation of carbonate ions in an alkaline electrolyte owing to absorption of carbon dioxide from the air or from the topping-up water or to oxidation of carbonaceous matter within the cell. The carbonation can be expressed in % or in grams of potassium carbonate per liter of electrolyte.
carbon-zinc	A generic term for primary dry batteries of the Leclanché or zinc chloride system.
card edge connector	See edge connector.
carry-over	See holdup time.
cassette	Power supply package format used for mounting power supplies on a DIN rail. See DIN rail.
cathode	The electrode in an electrochemical cell where reduction takes place. During discharge, the positive electrode of the cell is the cathode. During charge, the situation reverses, and the negative electrode of the cell is the cathode. In diodes and thyristors, the terminal by which current leaves the device.
catholyte	The portion of an electrolyte in a galvanic cell adjacent to a cathode; if a diaphragm is present, the electrolyte on the cathode side of the diaphragm. See also: electrolytic cell.
cation	A positively charged ion or radical that migrates toward the cathode during operation of the cell.
cell	1. The basic electrochemical unit used to generate or store electrical energy. A cell consists of two electrodes of dissimilar material isolated from one another electronically, in a common ionically conductive electrolyte. 2. An electrochemical system which converts chemical energy into electrical energy and also the reverse for rechargeable units.
cell oil	A pure mineral type of oil used on top of the electrolyte in large, non-sealed alkaline cells to minimize electrolyte creepage.
cell polarization	See also: polarization.
cell reversal	Reversal of polarity of a cell due to over discharge or forced discharge.
cell voltage	The dc voltage potential between the individual positive and negative terminals of a cell in a battery. See also nominal voltage, voltage, and working voltage.
centering	See also: tolerance.
charge	1. The conversion of electrical energy provided in the form of a current from an external source, into chemical energy within a cell or battery. 2. The potential energy stored in a capacitive electrical device.
charge acceptance	The ability of a battery to accept charge under specified conditions.
charge coefficient	The factor by which the quantity of electricity delivered during discharge is multiplied to determine the amount necessary for recharge.
charge equalization	Bringing all of the cells in a rechargeable battery to the same state of charge.
charging rate	The current applied to a secondary cell or battery to restore its capacity. This rate is commonly expressed as a multiple of the rated capacity of the cell or battery. For example, the C/10 charge rate of a 500-Ah cell or battery is 50 A.
charge retention	The ability of a battery to retain capacity on open circuit under specified conditions of temperature. See capacity retention.
charge voltage	The voltage applied to a cell during charge.
charge, state of	Condition of cell in terms of the rated capacity remaining in the cell at a given point in time.
charge/discharge cycle	A sequence of a charge and subsequent discharge under specified conditions.
charger	Device used to charge a cell or battery.
charging	Process of restoring electrical energy into a rechargeable cell or battery. See also: charge.
charging temperature coefficient	The factor by which the charge voltage must be adjusted for a given change in temperature.
chassis	The structure supporting or enclosing a power supply or other electrical circuit.
chassis ground	The voltage potential of the chassis or other reference point in a unit with a non-conducting chassis.
circuit breaker	A mechanical device designed to open the circuit automatically on a predetermined overload.
circuit input filter	A filter employing an inductor (L) or an inductor-capacitor (LC) as its input.
circular mil	Cross-sectional area of a circular conductor one thousandth of an inch in diameter.
circulating current	See also: ground loop.
cold switching	Closing the relay contacts before applying voltage and current, plus removing voltage and current before opening the contacts. (Contacts do not make or break current.) See also: dry circuit switching.
common-mode noise	The component of noise voltage that appears equally and in phase on conductors relative to a common reference.
common return	A return conductor common to two or more circuits.
communications port	A standard communications interface, such as an IEEE 488 or RS-232, which provides information flow between a processor and a peripheral device such as a power supply.
compensation	The addition of circuit elements to assist in stabilization of a control loop. Compensation is frequently qualified as series, parallel, feedback, etc., to indicate the relative position of the compensating element. See also: feedback; equalization.
compliance	Indication that a product meets its standards. See also safety compliance.
compliance current	The range of current over which the load regulation is within specified limits is called compliance current. There can be compliance current problems at high and/or low currents.
compliance range	Range of voltage needed to sustain a given constant current throughout a range of load resistance.
compliance voltage	The range of output voltage (in a constant current power supply) over which the load regulation is within certain limits.
component	An element in an electrical circuit.
concentration polarization	Polarization caused by the depletion of ions in the electrolyte at the surface of the electrode. See also polarization.
conductance (g)	A measure of the ability to conduct current. It is equal to amperes per volt, or the reciprocal of resistance, and is measured in siemens (S).
conductor	A device made from conducting material, which permits free motion of electrons; for example, a metal wire.
conformal coating	An insulating layer that can be applied by spraying, dipping or vapor deposition that covers and protects the components on a circuit board.
conformance test	A test specifically made to demonstrate conformance of equipment with specified standards.
connector	A mechanical device used to connect conductors.
constant current charge	Note: For some types of lead-acid batteries this may involve two rates called the starting and finishing rates. See also: charge.
constant current limiting circuit	Current-limiting circuit that holds output current at some maximum value whenever an overload of any magnitude is experienced.
constant current load	An electronic load with a control loop to regulate the current drawn from the power supply.
constant current power supply	A power supply that regulates its output current, within specified limits, against changes in line voltage, load, ambient temperature and time.
constant voltage charge	A charge during which the voltage across the battery terminals is maintained at a constant value.
constant voltage power supply	A power supply that regulates its output voltage within specified limits, against changes in line voltage, load, ambient temperature and time.
constant voltage transformer	A transformer that maintains approximately constant voltage ratio over the range from zero to rated output.
contact bounce	The intermittent and usually undesired opening of mechanical relay contacts during closure, or closing of contacts during opening. The duration of contact bounce depends upon the relay mechanism, and can vary from as little as 0.5 ms for small reed relays to 10-20 ms or more for larger solenoid types. Solid-state and mercury-wetted contacts typically do not have contact bounce.
contact life	The maximum number of expected closures before failure. Life is dependent on the switched voltage, current, power, and reactive transients. Failure is usually defined as a contact resistance that exceeds an end of life value. The common failure mode is non closure of the contacts, as opposed to contacts sticking closed.
contact potential	A voltage produced between contact terminals due to the temperature gradient across the relay contacts, and the reed to terminal junctions of dissimilar metals. (The temperature gradient is typically caused by the power dissipated by the energized coil.) Also known as contact offset voltage, thermal EMF, and thermal offset. This is a major consideration when measuring voltages in the microvolt range. There are special low thermal relay contacts available to address this need. Special contacts are not required if the relay is closed for a short period of time where the coil has no time to vary the temperature of the contact or connecting materials (welds or leads).
contact rating	The voltage, current, and power capacities of relay contacts under specified environmental and load conditions. See also: carry current, switched current.
contact resistance	The resistance in ohms or milliohms across closed contacts. See also: path resistance.
continuous duty	A requirement of service that demands operation at a substantially constant load for an indefinitely long time. See also: intermittent duty.
continuous test	A test in which a cell or battery is discharged to a prescribed end- point voltage without interruption. See also: battery; cutoff voltage.
continuous wave (CW)	Uninterrupted sinusoidal RF wave with all wave peaks equal in amplitude and evenly spaced along time axis.
control	The means of regulating the operation of a piece of equipment.
control circuit	The circuit that carries the electric signals directing the performance of a control device, but that does not carry the power which the device controls.
control coefficient	A ratio of an incremental change in a stabilized output signal to the incremental change in the input control signal that causes it.
control deviation	The difference between the actual value of a controlled output quantity and the control quantity, divided by the control coefficient. The control deviation includes nonlinearity, calibration error and offsets.
control loop	A feedback circuit used to control an output signal. See also loop.
control range	The parameters over which the controlled signal may be adjusted and still meet the unit specifications.
control rate	The maximum rate at which the stabilized output can be varied as a result of control signal changes without exceeding the control deviation.
control section	In a closed-loop system, the circuitry which maintains the control loop is referred to as the control section.
control, remote	Control over the stabilized output signal by means located outside or away from the power supply.
control, resolution	The smallest increment of the stabilized output signal that can be reliably repeated with a given accuracy.
controlled ferroresonance	A circuit that uses semiconductor devices to simulate saturation in a ferroresonant transformer to provide closed loop control.
convection, natural	The transfer of thermal energy between a moving fluid and a solid object. Fluid motion results from nonuniform fluid temperature.
convection-cooled power supply	A power supply cooled exclusively from the natural motion of a gas or a liquid over the surfaces of heat dissipating elements.
converter	A machine or device for changing dc power to ac power, for changing ac power to dc power, for changing ac power from one frequency to another, or for changing dc power from one voltage to another. This definition covers several different power conversion functions, each of which is known by a separate term. See also: dc-dc converter; flyback converter; forward converter; frequency changer; inverter; rectifier.
cooling	The process of removing heat dissipated by a power supply or device. Methods include radiation, convection, and conduction, or combinations thereof.
copper loss	Heat loss in motors, generators and transformers and other devices as the result of wire resistance. Joule's Law mathematically describes the heating effect of the flow of current as a result of losses. Sometimes called l2R loss.
cord set	An assembly of a suitable length of flexible electrical cable provided with an attachment plug at one end and a connector at the other.
core	Magnetic material serving as a path for magnetic flux.
core loss	Power dissipated by a magnetic core due to hysteresis and eddy currents.
core saturation	The tendency of magnetic domains in a magnetic material to orient in one direction due to the application of a magnetic field.
coulomb	The unit of electric charge in SI units (International System of Units). The coulomb is the quantity of electric charge that passes any cross section of a conductor in one second when the current is maintained constant at one ampere.
coulombic efficiency	See also: ampere-hour efficiency.
counter emf (cemf)	Voltage induced in a conductor that opposes the passage of current in a specified direction. See also: electromotive force (emf).
counter emf cell	An electrolytic cell or semiconductor device used to reduce the voltage of the main battery. See also: battery.
coup de fouet	A short duration (minutes) dip in output voltage of a lead acid cell when a load is first connected after having been on float for an extended period.
coupled choke	An inductor with two or more windings placed on a common core. Energy storage is still the principal requirement, but some "transformer" coupling is utilized to maintain a voltage balance or ratio between the windings. Often used in dc-dc converters with multiple "batch regulated" outputs. See also: integrated magnetics.
coupled inductor	See coupled choke.
coupled magnetics	Two or more transformers and/or inductors are wound on a common magnetic core such that some or all of the flux produced by one device flows through another, requiring similar voltage waveshapes on all windings. Advantages are reductions in size and weight, and the ability to "steer" ripple currents from one winding to another through adjustments in volts/turn and leakage inductances. The classic example is a Ćuk converter with input and output inductors coupled to the transformer, with "zero" ripple current in the two inductors.
coupling	The ability of isolated circuit elements to transfer energy between them via electromagnetic fields. See also: coefficient of coupling.
cpu	Central processing unit. The main processing section of a computer.
creepage	The movement of electrolyte onto surfaces of components of a cell with which it is not normally in contact. See also: electrolytic cell.
creepage distance	The shortest distance separating two conductors as measured along an insulating surface touching both conductors.
crest factor	In an ac circuit, crest factor is the mathematical ratio of the peak (maximum) to the root-mean-square value of a waveform. Crest factor is sometimes used for describing the current stress in an ac mains supply, since for a given amount of power transferred, the rms value, and hence the losses, become greater with increasing peak values.
crest value	Maximum repetitive value (excluding transients) of a waveform.
cross regulation	In a multiple output power supply, the percent voltage change at one output caused by the load change on another output.
crossover frequency	The frequency on a Bode plot at which the loop gain drops to zero decibels.
crossover point	The resistance value (E/I) defined by this intersection is the matching impedance for the power supply, which will draw the maximum output power. See also: automatic crossover.
crossover voltage/current	Voltage/current crossover is that characteristic of a power supply that automatically converts the mode of operation from voltage regulation to current regulation (or vice versa) as required by preset limits.
crosspoint switch	A switch that, when closed, connects the signal on an input bus to one or more output buses. Also referred to as a matrix switch or switching array.
crosstalk, crosstalk isolation	Unwanted interference in an output resulting from other input and output signals, measured in dB below the nominal signal level, and is expressed in decibels (dB) at a specified load impedance and over a specific frequency range or ranges.
crowbar circuit	An overvoltage protection circuit which rapidly places a low resistance shunt across the power supply output terminals if a predetermined voltage is exceeded. Also used to de-energize stored energy in capacitors for safety or nuclear event detection.
crowbar protection	A fail-safe mechanism that shorts the outputs of the power supply under failure conditions such as overvoltage. Crowbar protection can also refer to a circuit that has its sole purpose to cause a fuse to blow by subjecting it to high current.
CRT	Cathode ray tube.
current	The flow of electricity within a conductor, expressed in amperes. Current refers to the quantity or intensity of electricity flow, whereas voltage refers to the pressure or force causing the electrical flow.
current (i)	The rate of transfer of electrical charge measured in amperes. One 'international" ampere will deposit silver from a specified silver nitrate solution at the rate of 0.00111800 grams per second. An "international' ampere, in turn, is defined as 0.99985 "absolute” amperes, one coulomb per second.
current collector	An inert member of high electrical conductivity used to conduct current from or to an electrode during discharge or charge. See also: collector.
current control	See: current stabilization.
current density	The current per unit active area of a conductor or electrode. The preferred unit is amperes per square meter (A/m2).
current doubler	A secondary-side rectifying circuit for a high-frequency dc-dc converter that uses two inductors in series across the power transformer secondary and a pair of diodes also in series across the transformer secondary that doubles the output current from the transformer but produces only half the output voltage.
current foldback	See: foldback current limiting.
current limit knee	The point on the plot of current vs. voltage of a supply at which the current starts to foldback. See also: foldback current limiting.
current limiting	An overload protection feature that limits the maximum output current to a preset value, to prevent damage to the power supply and the system in which it is used.
current mode	The functioning of a power supply so as to produce a stabilized output current.
current-mode control	A control method for a switched-mode power converter in which the current (usually through one of the power switches) is compared to a variable threshold to determine the amount of power delivered to the output. 1. Peak current mode control works on a cycle-by-cycle basis, terminating each power pulse when the current rises to the threshold usually provided by an integrating error amplifier. 2. Average current mode control works on the average of the current pulses, rather on each individual pulse.
current monitor	An analog power supply signal which is linearly proportional to output current flow.
current sensing resistor	A resistor placed in series with another device to develop a voltage proportional to current through the device.
current source	A power source that tends to deliver constant current.
current stabilization	The process of controlling an output current.
current surge limiting	The circuitry necessary to protect relay contacts from excessive and possibly damaging current caused by capacitive loads
current transformer	A transformer that is intended to have its primary winding connected in series with the conductor carrying the current to be measured. The primary winding may be single turn or bus bar. In window-type (non-contact) current transformers, the primary winding is provided by the line conductor, and is not an integral part of the transformer.
cutoff voltage	The cell or battery voltage at which the discharge is considered complete. The cutoff voltage typically varies with the type of battery, the rate of discharge, the temperature, and the kind of service.
cw	Continuous wave.
cycle	The period of time in which one set of events is completed.
cycle life	The number of cycles under specified conditions before a device fails to meet specified performance criteria. For example, the number of cycles (discharges and recharges) under specified conditions that a battery can undergo before failing to meet its specified end-of-life capacity.
cycle service	A duty cycle characterized by frequent and usually deep discharge-charge sequences, such as motive power applications.
cylindrical cell	A cell whose shape is that of a cylinder. The term cylindrical is also used to describe batteries made up of cylindrical cells.
D	Variously, the symbol for diameter, drain, deuterium, duty ratio (used often in switched-mode power converter circuits---see: duty ratio.)
D2D	Dc to dc, usually referring to a dc-dc converter.
D/A	Digital to analog.
DAC	Digital to analog converter. An electronic circuit that converts digital information into analog signal levels.
daisy chaining	The sequential connection of two or more devices.
dB	Abbreviation for decibel.
dc	See: direct current. In text, use lower case.
direct current	Electrical current that flows in one direction.
dc component	The average value of a waveform.
dc transformer	A simple dc-dc converter that typically uses a self-resonant square wave generator without a voltage or current feedback loop.
dc-dc converter	A circuit or device that changes a dc input to a dc output of a different voltage.
debug	The process of detecting and correcting errors.
decay time	The time interval during which the value of a variable decays to a stated fraction of its initial value. See also: fall time.
decibel (dB)	The numerical expression of the relative magnitude of two signals, such as sound.
dedicated	Set aside for a special purpose.
deep discharge	Discharge of a battery to the specified voltage cutoff before the battery is replaced or recharged.
density	The ratio of mass of material to its own volume.
depolarization	A reduction in the polarization of an electrode.
depolarizer	A substance or means used to prevent or decrease polarization. The term “depolarizer” is often used, albeit incorrectly, to describe the positive electrode of a primary cell.
depth of discharge	The ratio of the quantity of electricity (usually ampere-hours) removed from a fully-charged cell or battery, expressed as a percentage of its rated capacity.
derating	1. The practice of applying a component or device at a lower stress level than its capacity, in order to reduce the probability of stress-related failure. 2. A reduction in the power output of a power supply due to its external environment such as altitude, airflow or ambient temperature. See also: reliability.
design life	The expected length of time a device or system will operate within specifications under specified conditions.
destructive testing	A test to determine the point in time at which a device catastrophically fails. The device is irreversibly damaged by the test.
diaphragm	A porous or permeable means for separating the positive and negative electrode compartments of a galvanic cell to prevent the admixture of catholyte and anolyte.
dielectric	An insulating material between conducting materials.
dielectric constant (k)	A material property that determines the electrostatic energy stored per unit volume for a unit potential gradient, relative to a vacuum.
dielectric withstand voltage	The voltage an insulating material will withstand before flashover or puncture. See also: hi-pot test, isolation.
differential amplifier	An amplifier, usually configured as an integrated circuit element with two inputs, an inverting input and a non-inverting input, with high amplification gain that is used with additional circuit components such as resistors and capacitors as a basic building block in designing functional signal-processing circuits.
differential gain	The difference between (a) the ratio of the output amplitudes of a small high-frequency sine-wave signal at two stated levels of a low frequency signal on which it is superimposed, and (b) unity. Notes: 1. Differential gain may be expressed in percent by multiplying the above difference by 100. 2. Differential gain may be expressed in decibels by multiplying the common logarithm of the ratio described in (a) above by 20.
differential input	An input circuit that actively responds to the voltage difference between two terminals rather than the difference between one terminal and ground.
differential mode noise	1. In a power supply, the conducted noise of an output as referenced to its return path. This is typically how "ripple and noise" specifications are defined. 2. (normal or transverse noise) The noise voltage that appears differentially between two signal wires and acts on the signal sensing circuit in the same manner as the desired signal. Normal mode noise may be caused by one or more of the following: Electrostatic induction and differences in distributed capacitance between the signal wires and the surroundings; Electromagnetic induction and magnetic fields linking unequally with the signal wires; Junction or thermal potentials due to the use of dissimilar metals in the connection system; Common mode to normal mode noise conversion.
differential output	An output circuit where the output voltage appears between two active output terminals rather than between one terminal and ground. Normally associated with balanced circuitry. See also: differential input.
differential phase	The difference in output phase of a small high-frequency sine- wave signal at the two stated levels of a low-frequency signal on which it is superimposed.
differential voltage	The difference in voltages at two points as measured with respect to a common reference.
diffusion	Gradual mixing of the molecules of two or more substances due to random thermal motion.
digital control	Using digital techniques and calculations in a power converter to determine when the power switches should turn on or off.
digital power	A general term that refers to the use of digital circuitry, such as digital control or digital power management, in a power converter.
digital power management	Using digital techniques, including serial communication and microcontrollers, to configure, control and monitor power converters.
DIN	Deutsche Institute fur Normung. German organization responsible for standards.
DIN rail	Standardized mounting scheme for electrical, electromechanical and electronic components.
DIN rail power supply	Power supply that can be mounted on a standard DIN rails.
diode	A two-element device containing a cathode and an anode that permits current flow from anode to cathode and blocks flow in the reverse direction.
DIP	Dual inline package.
dip	A short-term voltage decrease.
direct current (dc)	Flow of electrons in one direction. In text, use lower case: dc.
direct off-line	A switching power supply that is isolated by the high frequency transformer and has no 60 Hz transformer at the front end.
direct plug-in	A device that engages a receptacle without a cord.
discharge	The conversion of the chemical energy of a cell or battery into electrical energy and the movement of the electrical energy into a load.
discharge rate	The rate, usually expressed in amperes, at which electrical current is taken from the cell or battery.
distortion	An undesired change in a waveform. Common sources of distortion are: a nonlinear relation between input and output at a given frequency; nonuniform transmission at different frequencies; phase shift not proportional to frequency.
distortion, source	The departure of the source ac waveform from sinusoidal form. Some types of power supplies induce distortion in their source by imposing a nonlinear load impedance on the nonzero impedance of the source line.
distributed power architecture (DPA)	A power system architecture characterized by two elements: 1. Distribution of the system power at a voltage other than that used by the principal loads and 2. Conversion of the system power to the voltage needed by loads near the loads. Typical voltages for distribution of the system power are 48 V and 12 V. There may be multiple levels of power distribution buses. See, for example, intermediate bus architecture.
double insulation	An insulation system comprised of basic insulation and supplementary insulation, arranged so that they are not simultaneously subjected to the same deteriorating influences (temperature, contaminants, and the like) to the same degree, in order to reduce the risk of electric shock in the event of a failure of the basic insulation
double layer	The region in the vicinity of an electrode-electrolyte interface where the concentration of mobile ionic species has been changed to values differing from the bulk equilibrium value by the potential difference across the interface.
double plate	A pocket plate design where the plate consists of two plate blanks clamped together in the same frame.
double-layer capacitance	The capacitance of the double layer.
DPA	Distributed power architecture.
drain	1. With regard to cells or batteries, the withdrawal of current. 2. In field-effect transistors (FETs), the terminal that receives carriers (electrons or electron holes) from the source, in accordance with the gate bias conditions.
DRAM	Dynamic random access memory
drift	The change in an output, after a warm-up period, as a function of time when all relevant variables such a line, load, and operating temperature are held constant.
driver	An amplifier used for control of another device or circuit.
droop	1. The decrease in amplitude of the flat top of a square pulse. 2. A method of passive current sharing in which the output voltage is decreased with increasing output current, mimicking the effect of a resistor in the output.
dropout	The lower limit of the input voltage where the power supply just begins to experience insufficient input to maintain regulation.
dry battery	A battery in which the electrolyte is immobilized, being either in the form of a paste or gel or absorbed in the separator material.
dry cell	A cell with immobilized electrolyte. The term "dry cell" is often used to describe the Leclanché cell.
dry circuit switching	Switching below specified levels of voltage and current to minimize any physical and electrical changes in the contact junction. See also: cold switching.
dry reed relay	A hermetically sealed, magnetically actuated contact pair with which no mercury or other wetting material is used.
dry-charged battery	A battery in which the electrodes are in a charged state, ready to be activated by the addition of the electrolyte.
DSC	Digital signal controller, a device that combines the calculation capabilities of a digital signal processor with the peripheral capabilities (serial communication A/D and D/A converters, timers) of a general purpose microcontroller.
DSP	Digital signal processor, a specialized microprocessor for calculations related to signal processing, such as filtering or noise reduction.
duplex	Simultaneous independent two-way data transmission over a path.
duration	The time interval between the first and last instants at which the instantaneous amplitude reaches a stated fraction of the peak pulse amplitude.
DUT	Device under test. See also: UUT.
duty cycle	1. The time interval occupied by a device on intermittent duty in starting, running, stopping, and idling. 2. The operating regime of a cell or battery, including factors such as charge and discharge rates, depth of discharge, cycle length and length of time in the standby mode, to the total elapsed time.
duty ratio	The ratio of the sum of all pulse durations to the total period. In power electronic circuits, there is usually only one pulse per period, and the duty ratio is simply the ratio of the pulse duration to the total period.
dynamic load	A load that rapidly changes from one level to another. To be properly specified, both the total change and the rate of change must be stated.
dynamic regulation	The characteristic of a power supply that describes its ability to maintain a constant output in the presence of a rapidly changing load.
e	Symbol for electron.
E	Symbol for voltage (electrode potential) or an electric field.
earth	An electrical connection to the earth frequently using a grid or rod(s). See also: ground.
ECL	Emitter coupled logic, a very high speed digital circuit technology.
eddy current loss	Energy loss resulting from eddy currents induced to flow in a conducting material. Note: The eddy-current loss of a magnetic structure includes the eddy-current losses in the core, windings, and case.
eddy currents	A circulating current induced in a conducting material by a varying magnetic field.
edge connector	Female receptacle that mates with contacts on the edge of a printed circuit board.
edge insulator	Material that insulates the plate edges from each other and/or from the container sidewalls of a cell or battery.
effective value	The root mean square value of a waveform that is the equivalent heating effect of a direct current.
efficiency	1. The ratio of total output power to total input power, expressed as a percentage, under specified conditions, normally at full load under nominal input voltage. 2. The ratio of the output of a secondary cell or battery on discharge to the input required to restore it to the initial state of charge under specified conditions. See also: ampere-hour efficiency, voltage efficiency and watt-hour efficiency.
electricity	Property of fundamental particles of matter that have a force field associated with them to gain or lose electrons.
electrochemical couple	The system of active materials within a cell that provides electrical energy through an electrochemical reaction.
electrochemical equivalent	Weight of a substance that is deposited at an electrode when the quantity of electricity that is passed is one coulomb. See also: Faraday.
electrochemical series	A classification of the elements according to the values of the standard potentials of specified electrochemical reactions.
electrode	The site, area, location or material at which electrochemical processes take place.
electrode potential (Eo)	The voltage between an electrode and its surrounding elements. See also: standard electrode potential.
electrolysis	The electrochemical decomposition of an electrolyte.
electrolyte	The ion-conducting medium within an electrochemical cell that provides the ion transport mechanism between positive and negative electrodes.
electrolytic capacitor	Capacitor that contains two electrodes separated by a dielectric electrolyte.
electrolytic cell	A cell in which electrochemical reactions are caused by supplying electrical energy or which supplies electrical energy as a result of electrochemical reactions; if the first case only is applicable, the cell is an electrolysis cell; if the second case only, the cell is a galvanic cell.
electromagnet	A device consisting of a ferromagnetic core and a coil that produces appreciable magnetic effects only when an electric current exists in the coil.
electromagnetic interference (EMI)	Any electronic disturbance that interrupts, obstructs, or otherwise impairs the performance of electronic equipment.
electromotive force (emf)	1. Force that causes free electrons to move in a conductor. Unit of measurement is the volt. 2. The standard potential of a specified electrochemical action.
electromotive series	See Electrochemical Series.
electron (e)	Negatively charged elementary particle. The mass of the electron is approximately equal to 1/1837 of the mass of the hydrogen atom.
electron volt	A measure of energy. The energy acquired by an electron passing through a potential difference of one volt.
electronic industries association (EIA)	Trade group headquartered in Washington, DC, that establishes and maintains standards for the electronics industries in the United States.
electronic load	A test instrument designed to draw various and specified amounts of current or power from a power source.
electrostatic discharge (ESD)	The flow of current that results when objects having a static charge come into close proximity, causing a discharge between them.
electrostatic field	Electric field around a charged body.
electrostatic shield	A conductive screen that shunts induced electrical energy to ground.
element	1. A distinct functioning device in an electrical circuit. 2. The negative and positive electrodes together with the separators of single cell, It is used almost exclusively in describing lead-acid cell and batteries.
EMC (electromagnetic compatibility)	The requirement for electromagnetic emissions and susceptibility dictated by the physical environment and regulatory governing bodies in whose jurisdiction a piece of equipment is operated.
emf	Electromotive force.
EMI	Electromagnetic interference. A term that defines unwanted electromagnetic radiation from a device that could interfere with desired signals in test or communication equipment.
EMI filter	A circuit composed of reactive and resistive components for the attenuation of electromagnetic interference being emitted from a power supply. See also: electromagnetic interference.
enclosure	A housing for an electronic device designed to separate and protect the internal components from the outside environment.
end voltage	The prescribed voltage at which the discharge (or charge, if end- of-charge voltage) of a cell or battery may be considered complete. See also: cutoff voltage.
energy	The capacity for doing work, usually measured in watt-hours.
energy density	The ratio of the energy available from a cell or battery to its volume (Wh/L) or weight (Wh/kg).
energy management	The monitoring, analyzing and controlling of energy usage.
engine alternator	An internal combustion engine driving an AC generator, often used to supply long term backup power.
Eo	Variously, symbol for Electrode Potential or Standard Electrode Potential.
EPE	European Power Electronics And Drives Association
equalization	1. The process of restoring all cells in a battery to an equal state of charge. 2. Selective amplification (signal restoration) applied to a signal in order to compensate for high frequency attenuation and other distortions encountered in long lengths of cable.
equalizing connector	A device which connects points of the same theoretical potential in a battery to ensure that there will be no potential difference between these points.
equilibrium electrode potential	The difference in potential between an electrode and an electrolyte when they are in equilibrium for the electrode reaction that determines the electrode potential.
equivalent circuit	An electrical circuit that models the fundamental properties of a device or circuit. The equivalent circuit may replace, for convenience of analysis, a more complicated circuit or device.
equivalent load	An electrical circuit that models the fundamental properties of a load.
equivalent series inductance (ESL)	The amount of inductance in series with an ideal capacitor that exactly duplicates the performance of a real capacitor.
equivalent series resistance (ESR)	The amount of resistance in series with an ideal capacitor that exactly duplicates the performance of a real capacitor.
error amplifier	An operational amplifier, or differential amplifier, in a control loop that produces an error signal whenever a sensed output differs from a reference voltage.
error signal	The output voltage of an error amplifier produced by the difference between the reference and the input signal times the gain of the amplifier.
error voltage	The output voltage of the error amplifier in a control loop.
ESD	Electrostatic discharge.
ESL	Equivalent series inductance.
ESR	Equivalent series resistance.
ETSI	European Telecommunications Standards Institute
European Telecommunications Standards Institute	An independent, non-profit, standardization organization of the telecommunications industry (equipment makers and network operators) in Europe
exchange current	Under equilibrium conditions, the forward and backward currents of an electrochemical process are equal. This equilibrium current is defined as the exchange current.
exciting current	See magnetizing current.
explosion proof	Encased in an enclosure capable of withstanding without damage, the explosion within it of a specified gas or vapor, and capable of preventing a specified gas or vapor surrounding the enclosure from ignition due to sparks, flashes or an explosion of the specified gas or vapor within it.
F	Symbol for farad.
°F	Abbreviation for degrees Fahrenheit.
failsafe	1. In terms of relay technology, when power is lost, the relay contacts fall back to a default position. 2. A system or component that automatically places itself in a safe operating mode in the event of a failure; for example, a traffic light that reverts to blinking red in all directions when normal operation fails.
failure mode	The manner in which a device has ceased to meet specified minimum requirements.
fall time	The time required for a pulse to decrease from 90 percent to 10 percent of its maximum amplitude.
fan cooling	See forced convection cooling.
fan rating	Airflow in cubic feet per minute under specified conditions.
fanout	Distributing the same signal to multiple destinations.
farad	Unit of measurement of capacitance. A capacitor has a capacitance of one farad when a charge of one coulomb raises its potential one volt.
faraday	One gram equivalent weight of matter is chemically altered at each electrode of a cell for (approximately) each 96,500 international coulombs, or one faraday, of electricity passed through the electrolyte. See also: coulomb.
Faraday cage	A grounded metallic screen completely surrounding a space to protect it from external electrostatic influence.
Faraday shield	An electrostatic shield between input and output windings of a transformer. Used to reduce coupling capacitance, which in turn reduces output common mode noise. See also: electrostatic shield.
fault mode input current	Input current drawn by a power supply with the output short circuited.
fault tolerant	Capable of providing continued operation following specified failures.
Faure plate	A plate consisting of electroconductive material, usually consisting of lead-antimony alloy covered with oxides or salts of lead that is subsequently transformed into active material. See also: battery.
Fe	Chemical symbol for iron.
feedforward	A control technique whereby the line regulation of a power supply is improved by directly sensing the input voltage.
feedthrough	1. A plated through hole in a printed circuit board which electrically connects a trace on one layer to a trace on another layer. 2. A low impedance, high frequency capacitor used in EMI filtering.
feedback	The process of returning part of the output signal of a system to its input.
ferrite	A ceramic ferromagnetic material that exhibits low loss at high frequencies, which may contain iron oxide mixed with oxides or carbonates of one or more metals such as manganese, zinc, nickel or magnesium.
ferroresonance	A method of voltage regulation that employs a capacitor and a ferromagnetic inductance. An alternating voltage applied to the circuit causes changes in the inductance that result in regulation of the output.
ferroresonant power supply	A regulated power supply that uses a resonant circuit, with a capacitor in one of the secondary windings that resonates with the inductance of the transformer. Ferroresonant power supplies are designed to operate at a given input frequency.
FET	Field effect transistor.
field effect transistor (FET)	Transistor in which the resistance of the current path from source to drain is modulated by applying a transverse electric field between two electrodes.
filter	One or more discrete components positioned in a circuit to attenuate signal energy in a specified band of frequencies.
final charging voltage	The voltage that a battery reaches at the end of a charging operation. In the case of constant voltage charging, this voltage is determined by the setting of the charging equipment.
firmware	A stored program in semiconductor memory.
FIT	The basic unit of component failure. One FIT equals one failure in a billion (109) unit hours.
flag signal	See status signals.
flame arresting vent	A special design of a wet cell vent that provides protection against internal explosion when the cell or battery is exposed to a naked flame or external spark.
flat plate cell	A cell fabricated with rectangular flat-plate electrodes.
flatness	The constancy of signal amplitude across a frequency range, usually expressed in dB; example, the measured flatness was ±1.0 dB from 20 Hz to 20 kHz.
float charge	A method of maintaining a cell or battery in a charged condition by continuous, long-term, constant-voltage charging, at a level sufficient to balance self-discharge.
float voltage	The voltage required to maintain a charged battery in a fully charged condition.
floating	The condition where a common mode voltage exists, or may exist between earth ground and the instrument or circuit of interest.
floating output	An ungrounded output of a power supply, such that either output may be referenced to a specified voltage.
flooded cell	A cell design that incorporates electrolyte in excess of that required based on chemical interactions.
flux (φ)	Total number of lines of magnetic force passing through a given area.
flux density (b)	Number of lines of flux per cross-sectional area of a magnetic circuit expressed in gauss or tesla.
flyback	When the current flowing through an inductor is cut off, the energy stored in the magnetic field is released by a sudden reversal of the terminal voltage. A diode to conduct the stored energy is called a flyback diode. The inductor with one winding is called a flyback transformer. Energy is transferred to the secondary side of the power supply when the primary switch is turned off. Such switch mode power converters are called flyback converters.
flyback converter	A switched-mode power supply circuit in which a transistor is on and energy is stored in a transformer primary during the first part of each cycle. During the second part of the cycle, the stored energy is transferred to the load.
foldback current limiting	A power supply protection circuit whereby the output current decreases with increasing overload, reaching a minimum at short circuit, to minimize internal power dissipation under overload.
forced convection cooling	Heat transfer by moving a cooling medium (usually air) though the use of a fan or pump.
forced discharge	Discharging a cell or battery to the point of polarity reversal.
formation	Electrochemical processing of a battery plate or electrode, between manufacture and first discharge, which transforms the active materials into their usable form.
forward converter	A switch mode power supply circuit that transfers the energy from the primary to the secondary while the switching element is "on" which is the opposite of a flyback converter. Vout Vin i 1 n 1 Load (R) iRESET D m Vout = n Vin A popular variant of the forward converter is the two-transistor forward converter shown below. In this case the two switches are driven simultaneously. The advantage is that each switch is subjected to only the input voltage (maximum) in its off condition.
free wheel diode	A diode in a pulse-width modulated switch mode power conduction path for the current in the output choke to decay during the commutation or “free-wheeling” period.
frequency (Hz)	The number of periods per second.
frequency changer	Power conversion equipment that transforms ac electric power from one frequency to another.
frequency modulation	A variation in frequency about a specified mean frequency, caused by a change in a control signal.
frequency range	The two frequencies at which the output amplitude falls by a specified amount (often specified as -3 dB) below the average amplitude between the frequencies.
frequency response	The ability of a circuit or device to operate within specifications over a frequency range, for example, the gain-frequency or phase-frequency characteristics of an amplifier.
fuel cell	An electrochemical cell that can continuously change the chemical energy oxidant to electric energy.
full load	The maximum specified output load for a converter under continuous operating conditions.
full-bridge converter	A power switching circuit in which four switches connected in a bridge configuration drive the load.
full-bridge rectifier	A rectifier circuit that employs four switches to rectify single- phase or polyphase ac power.
full-wave rectifier	Rectifier circuit that produces a unidirectional, pulsating waveform that is a representation of a full ac wave.
fuse	An overcurrent protective device that permanently opens an electric circuit when overloaded.
g	Variously, the symbol for gram, conductance, or acceleration due to gravity.
gain	Ratio of an output signal to an input signal. See also: closed loop gain, gain margin, and open loop gain.
gain margin	The reciprocal of the gain of a control loop at the frequency for which there is 180 degrees of phase shift around the control loop.
galvanic	Pertaining to the flow of electrons due to chemical action.
galvanic cell	An electrolytic cell that converts chemical energy into electrical energy by electrochemical action.
ganged control	A method that allows the concurrent control of multiple circuits or devices.
gap	See Airgap.
gassing	The evolution of gas from one or more of the electrodes in a cell. Gassing commonly results from local action (self-discharge) or from the electrolysis of water in the electrolyte during charging.
gate	1. A circuit element with multiple inputs and an output that implements a logical operation such as AND or OR for the inputs. 2. A control electrode in a semiconductor device such as a triac or FET that has the ability to permit or inhibit the passage of current.
glitch	1. An undesired transient voltage spike occurring on a signal. 2. A minor technical problem arising in a system.
grid	In batteries, a framework for a plate or electrode which supports or retains the active materials and acts as a current collector.
ground	A conducting connection to earth, or to some conducting body that serves in place of earth.
ground bus	A bus to which individual grounds in a system are attached, and that in turn is connected to ground.
ground fault	An unintentional electrical path between an energized conductor or component and ground potential.
ground grid	Interconnected bare conductors arranged in a pattern over a specified area, laid out on or below the earth's surface.
ground loop	A loop formed when two or more points in a electrical system that are intended to be at ground potential are connected by a conducting path such that the points are not at the same potential.
ground rod	A metallic rod, commonly copper clad, driven into the earth to serve as a ground terminal.
grounded	Connected to or in contact with earth, or connected to some extended conductive body which serves instead of the earth.
grounding	A permanent and continuous conductive path to earth with sufficient capacity to carry any expected fault current, and of a sufficiently low impedance to limit the voltage rise above ground potential.
GUI	Graphical user interface.
h	Variously, the symbol for height or hour.
H	Variously, the symbol for henry, magnetic field strength, or magnetomotive force.
half-bridge converter	A switch mode power converter in which two power switching devices are used to drive the load. See also: bridge rectifier Vin Vout Load 1 (R) n 1 D Vout = Vin 2 n
half-cell	An electrode (either the anode or cathode) immersed in a suitable electrolyte.
half duplex	Data transmission a single direction.
half-wave rectifier	A circuit element, such as a diode, that passes only one-half of each cycle. The output consists of a single half-sine pulse for each input cycle. Input + t Input Output - Output t
HALT	Highly accelerated life test, a method of design qualification testing of product robustness by increasing stress, such as temperature, beyond specification limits and to the point of failure.
harmonic	A sinusoidal component of a periodic wave, having a frequency that is an integral multiple of the fundamental frequency. For example, the frequency of the third harmonic is three times the fundamental frequency.
harmonic distortion	The distortion of a sinusoidal wave characterized by the presence of harmonics of the fundamental frequency. Harmonic distortion is the ratio of the square root of the sum of the squares of all rms harmonic voltages (or currents) to the fundamental.
HASS	Highly accelerated stress screening, a method of production testing intended to detect weak units by testing products at high stress levels.
headroom	The difference between the input and output voltages in a regulator. See also: Differential Voltage.
heat pipe	A device using a fluid in a sealed capillary network to conduct thermal energy away from a heat source.
heat sink	The mechanical structure through which thermal energy is transferred between a device and an external cooling medium.
henry (H)	Unit of measurement of inductance. A coil has one henry of inductance if an EMF of one volt is induced when current through an inductor is changing at rate of one ampere per second.
hertz (Hz)	The SI unit of measurement for frequency, named in honor of Heinrich Hertz who discovered radio waves. One hertz equals one cycle per second.
hiccup	(slang) A transient condition that momentarily confuses a control loop.
hiccup mode	An operating mode of a power converter in which the converter cycles on and off, usually after being triggered by an output fault condition.
high line	Highest specified input operating line or mains voltage.
hi-pot (high potential) test	A dielectric test performed by applying a high voltage for a specified time to two isolated points in a device to determine adequacy of insulating materials.
holding time	See holdup time.
holdup time	The time under worst case conditions during which a power converter's output voltage remains within specified limits following the loss or removal of input power.
hostile crosstalk	See Crosstalk.
hostile input	An input signal which causes unwanted interference and coupling to a desired output.
hot pluggable	The ability to add or remove an element from a system while energy is being supplied or dissipated by the element.
hourly rate	A discharge rate, in amperes, of a cell or battery which will deliver the specified hours of service to a given discharge voltage.
hum	Audible noise from a magnetic device due to magnetostriction of the core at twice line frequency.
hybrid	The combination of different component technologies on a single substrate.
hybrid magnetics	Two or more magnetic devices combined into one structure. The most basic approach increases the magnetizing and/or leakage inductance energy in a transformer, in lieu of adding a discrete inductor in parallel or in series with a transformer winding. When such extra inductance is useful, the hybrid approach reduces the total size, weight and power loss over the used of a separate transformer and inductor.
hybrid supplies	A power converter that combines two or more different regulation techniques, such as ferroresonant and linear or switching and linear, or one that takes advantage of hybrid technology.
hydrogen electrode	An electrode of platinized platinum saturated by a stream of pure hydrogen.
hydrogen overvoltage	The activation overvoltage for hydrogen discharge.
hysteresis	1. The property of a magnetic substance that causes magnetic flux density to lag behind the magnetomotive force that produces it. 2. A variable input voltage threshold determined by the logic state of the output of the circuit.
hysteresis loop	A closed curve that shows, for each value of magnetizing force, two values of the magnetic flux density, B, in a cyclically magnetized material: one when the magnetizing force, H, is increasing (3), the other when it is decreasing (2). The initial magnetization, starting from the origin, is shown in (1). +B 2 1 -H +H 3 -B
hysteresis loss	Energy dissipated due to molecular friction as domains move through cycles of magnetization.
Hz	International symbol for hertz, the unit of frequency.
I	SI unit symbol for electric current.
I2R loss	Heat loss in a resistance.
IBA	Intermediate bus architecture
IBV	Intermediate bus voltage
IC	Integrated circuit.
IEC	International Electrotechnical Commission
impedance (Z)	1. Opposition to the flow of an alternating current as a result of a combination of resistance and reactance. 2. The ratio of the phasor equivalent of a steady-state sine-wave voltage to the phasor equivalent of a steady-state sine-wave current.
impedance matching (Z match)	1. Adjusting the output impedance of a sourcing device to equal the input impedance of a receiving device to maximize the transmission of power (or vice versa) 2. Using a circuit or device in between a sourcing device and a receiving device, such as a transformer, so the load impedance of a sourcing device equals its output impedance and that the source impedance presented to the receiving device equals its input impedance
IMS	Insulated metal substrate.
indicator fuse	A fuse that provides a visual indication that it interrupted current flow.
induced current	Current in a conductor resulting from the application of a time- varying electromagnetic field.
induced EMF	Voltage induced in a conductor by a varying electromagnetic field.
induced failure	The failure of a component resulting from an induced condition that causes a malfunction of the device.
induced noise	Noise generated in a circuit by a varying magnetic field produced by another circuit.
inductance (L)	The property of an electric circuit by virtue of which a varying current induces an electromotive force in that circuit or in a neighboring circuit.
inductive reactance (XL)	The scalar reactance XL (ohms) due to an inductance (henries) at a frequency (Hz) is calculated as (2πf)•L.
inductor	A two-terminal component consisting of one or more associated windings, with or without a magnetic core, which introduces inductance into an electric circuit.
initial voltage	The no-load voltage at the beginning of a discharge.
input bus	A circuit path on the input side of a switching array that connects to the inputs of one or more crosspoint switches.
input current	The current that a device draws from the input power bus under nominal operating conditions.
input impedance	The (open circuit) impedance at the input terminals of a circuit or device.
input line filter	A low-pass or band-reject filter at the input of a power supply, that reduces noise input to the supply or created by the supply. The filter may be external to the power supply.
input pi filter	See also: Pi filter.
input surge	See also: Inrush current.
input transient	A step change or spike in a power converter’s input line. Damage to sensitive components due to transients can be prevented by using input transient protection devices or circuits.
input voltage range	The range of input voltage values for which a power supply or device operates within specified limits.
input-output isolation	Circuit techniques that provide dc isolation between input and output circuitry of a power supply.
inrush current	The peak instantaneous input current drawn by a circuit or device at turn-on or application of input power.
inrush current limiting	The characteristic of a circuit that limits inrush current when a power supply or other circuit is energized.
insertion loss	The attenuation of signals in decibels (dB) at a frequency or over a frequency range as they pass through a circuit or system.
instantaneous value	The measured value of a signal at a specified time.
insulation	Non-conductive materials used to separate electric circuits.
insulation resistance	The resistance offered, usually measured in megohms, by an insulating material to the flow of current resulting from an impressed voltage.
integrated circuit (IC)	A combination of multiple active and/or passive circuit elements contained on a single semiconductor substrate.
integrated magnetic	A magnetic component in which separate magnetic circuit elements share a common core segment.
interleaved transformer windings	The segmentation of portions of one winding by another, usually to improve or control inductive coupling and to reduce ac resistance due to skin and proximity effects.
intermediate bus architecture (IBA)	A power system architecture characterized by: 1. Distribution of the system power at one voltage to the system’s circuit boards or subassemblies, 2. Conversion of the system level distribution power to another distribution voltage that is used to distribute power on the circuit board or within the subassembly, and 3. Conversion of the local distribution bus power to the voltages needed by the loads on the circuit board or within the subassembly.
intermittent duty	A requirement of service that demands operation for definitely specified alternate periods of: a) Load and no load; b) Load and rest; or c) Load, no load and rest. See also: Continuous duty.
intermittent test	A test during which a power source is subjected to specified alternate periods of loading and rest.
internal impedance	The impedance exhibited by a circuit element or component.
internal power dissipation	The power that a power supply or converter module dissipates (as heat) during its operation. Internal power dissipation is usually stated as a maximum specification that cannot be exceeded without risk of damage to the converter.
internal resistance	1. The resistance exhibited by a circuit element or component. 2. The opposition to the flow of an electric current within a cell or battery; the sum of the ionic and electronic resistances of the cell components.
internal resistance (apparent)	Quotient of the difference of voltage across battery terminals to the corresponding difference of current. It should be observed that the internal resistance is not constant but varies with state of charge, temperature and the testing method.
International Electrotechnical Commission (IEC)	An organization that produces safety standards and recommendations for electronic products and components.
inverter	A power supply which produces an ac output, usually from a dc input.
IP	Intellectual property.
IR drop	1. Voltage developed by current flowing through a resistance (typically parasitic, such as the resistance in a wire or printed conductor) 2. (electrolytic cells) The drop equal to the product of the current passing through the cell and the resistance of the cell.
iron core	A general class of magnetic cores that contain iron. Sometimes used to refer to cores made only from steel laminations. See also: Core, ferrite, powdered Iron core.
iron poisoning	In nickel alkaline cells a process by which the nickel electrode performance is impaired owing to the presence of excessive amounts of iron species in the nickel active material.
isolation	The electrical separation between the input and the output of a circuit or device. Power converters that have common grounds are not isolated. The measure of isolation is resistance and/or capacitance between the input and output.
isolation transformer	A transformer in which one or more output windings is electrically separated from the input winding and all other output windings by an insulation at least equivalent to double insulation or reinforced insulation.
isolation voltage	The level of ac or dc potential that can be applied to the various portions of a power converter, such as input-to-output, output-to- ground, primary-to-secondary, etc. The rating is important when power supplies are connected in series.
Jensen circuit	A full-wave transformer-coupled power converter circuit that utilizes the saturation of the gate drive transformer core to cause the switches to reverse their alternate conduction states, producing a square-wave output.
JFET	Junction field effect transistor
joule (j)	Unit of energy equal to one watt-second.
junction field effect transistor (JFET)	A low power semiconductor having a conductive channel whose resistance is controlled by the reverse voltage on the gate channel junction.
K	Variously, the symbol for coefficient of coupling, potassium, or Kelvin.
KCL	Kirchhoff’s Current Law
KVL	Kirchhoff’s Voltage Law
kelvin (K)	Unit of thermodynamic temperature in the International System of Units (SI), equal to the fraction1/273.16 of the thermodynamic temperature of the triple point of water. The kelvin temperature scale uses Celsius degree intervals with the scale shifted so 0 K is at absolute zero. Add 273.16 to any Celsius value to obtain the corresponding value in kelvin.
Kelvin bridge	A technique using 4 terminals to isolate current carrying leads from voltage measuring leads.
Kirchhoff’s current law	At any junction of conductors in a circuit, the algebraic sum of the currents is zero.
Kirchhoff’s voltage law	In a circuit, the algebraic sum of voltages around a closed loop is equal to zero.
kVA	Symbol of kilovolt-ampere.
kW	Symbol for kilowatt.
kWh	Symbol for kilowatt-hour.
l	The symbol for liter.
L	Variously, the symbol for inductance or length.
lag network	Resistance-reactance circuit arranged to control phase-gain roll- off versus frequency. It reduces gain at lower frequencies.
lagging angle	The phase angle by which current lags voltage in an inductive circuit.
laminations	Thin sheets of coated steel or alloys used in cores of transformers, motors and generators.
land	A terminal point on a printed circuit board.
latch	1. A logic circuit that, once set, maintains the output at some fixed state until reset. 2. An attachment used to hold a fuse or switch in the closed position.
latch up	A part of the control circuit for a power supply that goes into a latched condition.
latching	In relay switching, the ability to not change contact status (open or closed) when the coil is de-energized.
latching relay	A relay that mechanically latches until mechanically or electrically reset.
layer winding	The method of winding a transformer or choke whereby conductors are layered one on top of another, commonly separated by an insulating layer.
LC filter	A low pass filter that consists of an inductance (L) and a capacitance (C). Also known as an averaging filter.
LDO	Low drop out, a linear regulator with low input-to-output voltage differential
lead network	Resistance-reactance components arranged to control phase- gain roll-off versus frequency, typically used to assure the dynamic stability of a power converter’s comparison amplifier. The effect is to introduce a phase lead at higher frequencies, near the unity gain frequency.
lead resistance	The resistance in the conductors of a circuit element or device.
lead-acid cell	Secondary cell which uses lead peroxide and sponge lead for plates, and sulfuric acid and water for the electrolyte.
leading angle	The phase angle by which current leads voltage in a capacitive circuit.
leakage current	1. The ac or dc current flowing from input to output and/or input to chassis of an isolated device at a specified voltage. 2. The reverse current in semiconductor junctions.
leakage flux	Any magnetic lines of force that do not link all turns of all windings of a transformer.
leakage inductance	Self inductance within a transformer caused by leakage flux.
Leclanché	A carbon zinc battery with a slightly acidic electrolyte consisting of ammonium chloride and zinc chloride in water.
LED	Light-emitting diode.
LGA	Land grid array
Li	The chemical symbol for lithium.
life test	A test in which a device is subjected to actual or accelerated use to obtain an estimate of life expectancy.
light-emitting diode (LED)	A semiconductor device that radiates in the visible spectrum when energized by an electric current. Color is determined by the electroluminescent characteristics of the materials used in fabricating the devices, and by the addition of various dopants. For example, copper-doped zinc sulfide emits light in the 555 nanometer (green) range, the area of peak sensitivity of the human eye.
limiting	The process of providing an electrical limit to various quantities. Fuses, circuit breakers and current limiters, as well as overvoltage crowbars, spark gaps and voltage limiters, are all examples of limiting devices or circuits.
line	1. Medium for transmission of electricity between circuits or devices. 2. The voltage across a power transmission line.
line conditioner	A circuit or device designed to improve the quality of an ac line, such as reducing electrical noise.
line effect	See line regulation.
line frequency regulation	The change in power converter output for a specified change in the line frequency, at specified loads with all other factors constant, usually expressed as a percentage.
line regulation	The change in power converter output for a specified change in the input voltage, at specified loads with all other factors constant, sometimes expressed as a percentage.
line regulator	Power conversion equipment that regulates and/or changes the voltage of incoming power.
line transient	A perturbation outside the specified operating range of an input or supply voltage.
linear	A mathematical relationship in which quantities vary in direct proportion to one another.
linear pass	See series pass.
linear regulation	A regulation technique wherein the control device, such as a transistor, is placed in series or parallel with the load. The output is regulated by varying the effective resistance of the control device to dissipate unused power. See also: linear supply.
linear regulator	An active device connected in series or shunt with the load of a power supply to maintain a constant output voltage or current.
linear supply	A power converter employing linear regulation techniques.
linearity	When the change in the value of one quantity is directly proportional to the change in the value of another quantity, the quantities are in a linear relationship. A linear relationship, when plotted on a graph with linear axes, is a straight line.
linearity error	The deviation from perfect linearity in the relationship between two quantities. See also: linearity.
Litz wire	Wire that consists of a number of separately insulated strands woven together so each strand successively takes up all possible positions in the cross section of the entire conductor, to reduce skin effect and thereby reduce RF resistance.
load	Any combination of capacitance, resistance, and inductance which, when connected between two terminals of a source, determines the power used.
load decoupling	The practice of placing filter components at the load to attenuate noise.
load impedance	See load.
load line shaper	See snubber.
load regulation	1. Static: The change in output voltage when a load is changed from one specified steady-state value to another, with all other factors held constant. 2. Dynamic: The change in output voltage expressed as a percent for a given step change in load current. Initial and final current values and the rates of change must be specified. The response time and requirement to be damped must also be specified. The rate of change is expressed as current change per unit of time, such as 20 amperes per microsecond. The dynamic regulation is expressed as a +1- percent for a worst case peak-to-peak deviation for dc supplies, and worst case rms deviation for ac supplies.
load transient overshoot	See overshoot.
load transient response time	See transient recovery time.
local action	Chemical reactions within a cell that cause self-discharge, converting the energy stored in active materials to a discharged state without supplying energy to a load via the battery terminals.
local control	Control over the stabilized output signal by means located within or on the power converter.
local sensing	Using the power converter output voltage terminals as the error- sensing points to provide feedback to the voltage regulator.
logic ground	The common return or reference point for logic signals.
logic high	A voltage representing a logic value of 1 in positive logic.
logic inhibit/enable	A referenced or isolated logic signal that turns a power converter output off or on.
logic low	A voltage representing a logic value of 0 in positive logic.
long-term stability	The output voltage change of a power supply due to time only, with all other factors held constant, usually expressed as a percentage of nominal output voltage. Long-term stability may be a function of component aging.
loop	A set of branches forming a closed current path.
loop gain	The gain of a signal passing around a closed control loop.
loop response	The speed with which a control loop corrects for specified changes in line or load.
loop stability	A term describing the stability of a control loop as measured against some criteria, e.g., phase margin and gain margin.
low line	The lowest specified input operating voltage.
low voltage disconnect	A device that disconnects a battery or batteries from the load being powered when the battery voltage is at a predetermined threshold to protect the battery from overdischarge.
L-section filter	A fitter consisting of at least two components, one of which is reactive (inductive or capacitive) connected in an "L" configuration,
LVD	Low voltage disconnect
M	Symbol for mutual inductance.
magnetic amplifier	A magnetic device employing dc current in a control winding of a saturable reactor, to vary the magnetic core saturation, thus varying the output voltage of the main winding to secure power gain. The saturation may also be controlled by inserting reset current into the main winding during the absence of excitation, thus eliminating the control winding.
magnetic field strength	The magnitude of the magnetic field vector H.
magnetic flux (φ)	A condition in a medium produced by a magnetomotive force such that, when altered in magnitude, a voltage is induced in an electric circuit linked with the flux. See also: Flux.
magnetic flux density	The amount of magnetic flux per cross-sectional area of a magnetic circuit, expressed in gauss or tesla.
magnetic gap	See Air gap.
magnetic induction	The use of a magnetic field to generate currents or voltages in a conductor.
magnetizing current	The no-load current in a transformer primary winding that is required to magnetize the core, sometimes called exciting or excitation current.
magnetomotive force (H)	The line integral of the magnetizing force around a path.
mainframe	1. A rigid framework that provides mechanical support for modules inserted into a backplane, ensuring that connectors mate properly and that adjacent modules do not contact each other. It may provide cooling airflow, and may ensure that modules do not disengage from the backplane due to vibration or shock. 2. A very large computer
maintenance-free battery	A battery that does not require periodic addition of water to maintain proper electrolyte volume.
margining	The ability to temporarily shift output voltage by a specified amount for system testing.
master mainframe	A mainframe that has control of other mainframes (slaves) in a serial chain that appears as one mainframe with increased capacity.
master/slave operation	Interconnection of two or more regulated power converters in which one (the master) controls all others (the slaves).
maximum load	The highest allowable power output specified for the outputs of a power converter under specified conditions including duty cycle, period and amplitude.
maximum operating temperature	The highest ambient temperature at which a power supply will continuously operate safely and within specifications.
maximum power transfer	Condition that exists when impedance of load equals the conjugate of the source impedance.
maxwell (Mx)	The cgs unit of magnetic flux equal to 1 gilbert/cm2, or to one line of magnetic force. The SI unit for magnetic flux, the weber, is preferred. One weber equals 108 maxwells.
Mbps	Megabits per second (millions of bits per second), a measure of digital data transmission rate.
MCM	Multi-chip module
mean time between failure (MTBF)	The mean length of time between device or system failures, exclusive of infant mortality and rated end-of-life. One method of calculating MTBF is described in the most recent edition of Mil Handbook 217.
mean time to repair (MTTR)	The mean time required to repair a device or system that has experienced a failure.
mechanical recharging	Replacing a spent or discharged electrode with a fresh one to restore the capacity of a cell.
memory effect	The tendency of a cell to adjust its electrical properties to a certain duty cycle to which it has been subjected for a large number of times. For instance, if a cell has been cycled to a certain depth of discharge for a large number of cycles, then on a subsequent normal discharge the cell may not give more capacity than that corresponding to the applied cycling regime.
mercury wetted relay	A reed relay in which the contacts are wetted by a film of mercury (Hg) to reduce contact bounce. May have a required operating position to avoid liquid mercury from shorting the contacts.
metal oxide semiconductor field effect transistor (MOSFET)	See field effect transistor.
metal oxide varistor (MOV)	A device having nonlinear resistance that is intended to be used as a surge protective device or voltage limiter.
mho	Unit of measurement of conductance (obsolete). The mho has been replaced by the international unit, siemens (S). It is the conductance of a conductor such that a constant voltage of one volt between its ends produces a current of one ampere in it.
midpoint voltage	The voltage of a cell or battery midway in the discharge between the fully charged state and the end state.
migration	The transportation of ionic species in an electrolyte due to the presence of an electric field.
miniature cell	A button- or coin-shaped cell whose diameter is greater than its height. The term “Miniature" is also used to describe batteries made up of miniature cells.
minimum load	1. The lowest specified current to be drawn on a constant voltage power supply for the voltage to be in a specified range. 2. For a constant current supply, the maximum value of load resistance.
minimum operating temperature	The lowest ambient temperature at which a power supply or other device will continuously operate safely and within specifications.
minimum starting temperature	The lowest ambient temperature at which a power supply or other device will turn on and operate safely.
minus (-)	Negative terminal or junction of a circuit, circuit element or power supply.
mismatch	Incorrect matching of load and source impedance.
MLCC	Multi-layer ceramic capacitor
MLF	Multi-lead frame
mobile battery	A battery used in mobile applications.
modified constant voltage charge	A constant voltage charge where the initial current is limited.
modular	1. A physically descriptive term used to describe a power converter or other system made up of a number of separate subsections, such as an input module, power module, or filter module. 2. An individual power converter patterned on standard dimensions and capable of being integrated with other parts or units into a more complex and higher power system.
modulator	The control element of a switched-mode power converter.
monoblock battery	A battery in which the plate packs are fitted into a multi- compartment container.
monoblock container	A container with several compartments each of which can hold one or more plate packs.
MOSFET	Metal oxide semiconductor field effect transistor.
motive power battery	A battery designed for the propulsion of electric vehicles or electrically operated mobile equipment operating in a deep-cycle regime.
MOV	Metal oxide varistor
MTBF	Mean time between failures.
MTTR	Mean time to repair.
multimeter	A meter capable of measuring current, voltage and resistance.
multiple output power supply	A power converter with two or more outputs.
mutual inductance (M)	The common property of two electric circuits whereby an electromotive force is induced in one circuit by a change of current in the other circuit.
Mx	Maxwell, the cgs unit of magnetic flux.
n+1 redundancy	The ability to have one extra element in a system act as an on- line replacement for an element that fails.
Na	Chemical symbol for sodium.
natural-convection cooling	A cooling process using a fluid medium such as air that relies on the buoyancy of the medium when heated to create an upward flow to remove heat from a surface such as a hot part. Distinguished from “forced air cooling” which relies on a fan to provide the flow mechanism.
NEBS	Network Equipment-Building System, a set of standards and design guidelines created by Bellcore (now Telcordia) to standardize equipment installations in telephone central offices in the United States.
negative electrode	The electrode acting as an anode when a cell or battery is discharging.
negative rail	The more negative of the two conductors at the output of a power supply.
negative regulator	A voltage regulator whose output voltage is negative compared to the voltage at the common or ground terminal.
negative temperature coefficient	A decreasing function with increasing temperature. The function may be resistance, capacitance, voltage, etc.
negative-limited	A condition of a cell in which the operating characteristic (performance) of the cell is limited by the negative active material.
network	Two or more components connected in series, parallel or a combination thereof.
neutral	The ac return that is connected at some point to ground, but which should not be used for safety ground because it is a current-carrying path.
nicad battery	Nickel cadmium battery.
NiCd	Chemical symbol for nickel-cadmium.
nickel-cadmium (NiCd) cell	Alkaline cell using nickel and cadmium as active materials and an electrolyte.
no-load voltage	Terminal voltage of battery or supply when no current is flowing in external circuit.
node	The junction of two or more branches in a circuit.
noise	1. Any unwanted electronic signal superimposed upon a signal of interest, or an unwanted audible sound (from fans or cooling devices). 2. The aperiodic random component superimposed upon a power source output. Unless specified otherwise, noise is expressed in peak-to-peak or rms units over a specified bandwidth.
noise figure	An expression of noise generated with in a device specified in dB. This parameter is important in RF application such as a receiving antenna switching system and IF signal routing.
no-load voltage	The voltage of a power supply at its output when no current is flowing in the external output circuit (load).
nominal value	The specified normal value of a quantity.
nominal voltage	A specified value assigned to a circuit or system for the purpose of conveniently designating its voltage class (as 120/240, 480Y/277, 600 etc.) The actual voltage at which a circuit operates can vary from the nominal within a specified range that permits satisfactory operation of equipment.
normal mode inductor	Similar to filter inductors in design and function, but may be optimized for high impedance at frequencies above the conversion frequency (in a power converter). HF ac currents are negligible, and ac winding and core losses are of no concern, and either may in practice be increased to provide damping of spurious resonances.
O	Chemical symbol for oxygen.
OC	Overcurrent
OCP	Overcurrent protection
OEM	Original equipment manufacturer.
off-line power supply	1. A power converter in which the ac line voltage is rectified and filtered without using a line frequency isolation transformer. 2. A power supply switched into service upon line loss to provide power to the load without significant interruption.
off-load voltage	The output voltage of a power converter with no external load applied.
offset current	The direct current at either input terminal of a dc amplifier when the input source is disconnected.
offset voltage	The dc voltage that remains between the input terminals of a dc amplifier when the output voltage is zero.
ohm	The unit of resistance (and of impedance) in the International System of Units (SI). The ohm is the resistance of a conductor such that at a constant current of one ampere a voltage of one volt appears between its ends.
ohmic overvoltage	Overvoltage caused by the ohmic drop at an electrode- electrolyte interface.
ohm's law	The fundamental mathematical relationship between current (I), voltage (E) and resistance (R). The passage of one ampere through one ohm produces one volt.
on-load voltage	The difference in potential between the terminals of a cell or battery when it is discharging at a specified rate.
op-amp	Abbreviation for Operational Amplifier.
open loop	A signal path without feedback.
open loop gain	Ratio of output signal to input signal without feedback.
open-circuit voltage	The voltage between two terminals of a circuit when no external load is applied.
open-frame construction	A construction technique where the device (i.e. power supply) is not provided with an enclosure.
operating temperature range	The range of ambient, baseplate or case temperatures through which a power supply is specified to operate safely and to perform within specified limits.
operational power supply	A power supply whose control amplifier has been optimized for signal-processing applications rather than the supply of steady- state power to a load. A self-contained combination of operational amplifier, power amplifier, and power supplies for higher-level operations.
optocoupler	A package that contains a light emitter and a photoreceptor that is used to transmit signals between electrically isolated circuits.
optoisolator	See optocoupler.
ORing diode	A diode used to isolate parallel connected power supplies from one another. Under a fault condition, the faulty supply is isolated from the rest of the power supply system.
OT	Overtemperature
OTP	Overtemperature protection
outage	The state of a component or system when it is not available to perform its intended function.
outgassing	1. The discharge of gas due to subjecting a material or component to high temperatures, low pressures, or radiation effects. 2. The release of gas from a cell during operation.
output	The energy or information delivered from or through a circuit or device.
output choke	See output inductor.
output current limiting	A protective feature that keeps the output current of a power converter within predetermined limits during overload to prevent damage to the converter or the load.
output filter	One or more discrete components used to attenuate output ripple and noise.
output filter capacitor	The capacitor(s) across the output terminals of a power supply.
output good signal	A power supply signal indicating that the output voltage is within its specified tolerance.
output impedance	The impedance presented by the output terminals of a power supply to a load.
output inductor	The inductor in the LC filter at the output of a power converter.
output LC filter	The low pass filter at the output of a switch mode power converter that smoothes the rectified output to its average value. Also called an averaging filter.
output power	The specified power output that a power converter can deliver. Power converters may have a continuous rating, and a peak rating at a specified ambient temperature and duration.
output range	The specified range over which output voltage or current can be adjusted.
output rectifier	Devices in the output stage of a power converter that convert ac from the input-output transformer to pulsating dc.
output ripple and noise	See periodic and random deviation.
output voltage	The voltage measured at the output terminals of a power converter.
output voltage accuracy	The tolerance of the output voltage, sometime expressed in percent.
OV	Overvoltage
overdischarge	Continued removal of charge from a cell after the useful capacity has been exhausted, and which may result in damage to the cell.
overcharge	The forcing of current through a cell after all the active material has been converted to the charged state. Charging in excess of that needed to return full capacity to the cell.
overcurrent device	A device capable of automatically opening an electric circuit, both under predetermined overload and short-circuit conditions.
overcurrent protection	A circuit or device that reduces or interrupts the current to a load when a specified maximum current is exceeded.
overload protection	A feature or device that senses and responds to current or power overload conditions.
overshoot	A transient change in output voltage in excess of specified output regulation limits, which can occur when a power supply is turned on or off, or when there is a step change in line or load.
overvoltage	A voltage that exceeds specified limits.
overvoltage protection (OVP)	A circuit or device that limits the output of a power converter to a specified maximum voltage.
OVP	Overvoltage protection.
oxygen index	The minimum concentration of oxygen, expressed as volume percent, in a mixture of oxygen and nitrogen, that will just support flaming combustion of a material initially at room temperature, referred to in battery manufacturers’ flammability designations for battery cases.
oxygen recombination	The process by which oxygen is generated at the positive plates and ultimately recombined with hydrogen ions at the negative plates and converted back to water. In this process, hydrogen gas formation and evolution are suppressed.
P	Variously, the symbol for power or pressure.
pad	A conductive area on a printed circuit board used for connection to a component lead or terminal area, or as a test point.
paper-lined cell	Construction of a cell where a layer of paper, wetted with electrolyte, acts as the separator.
parallel	Term used to describe the interconnection of power sources (or loads) in which like terminals are connected such that the combined currents are delivered to a single load (or drawn from a single source).
parallel operation	The parallel connection of two or more power sources of the same output voltage so that their individual output currents are summed to a common load. Several methods for parallel connection of constant voltage sources are: spoiler resistors; master/slave connection; parallel programming; parallel padding.
parallel port	A port that transfers data one byte at a time, each bit over its own line.
parallelability	Common usage term to describe power sources that may be connected in parallel.
paralleling diode	A diode connected between the output of a power converter and a load bus that is energized by paralleled power converters, to isolate the load bus from internal converter faults.
PARD	Periodic and random deviation.
partial load disconnect	A device that disconnects non-critical loads when the battery voltage is at a predetermined threshold.
pass element	A controlled variable resistance device, either a vacuum tube or semiconductor, in series with the dc power source and used to provide voltage regulation.
passivation	A surface condition enabling a metal to remain chemically stable.
pasted plate	A plate, usually for a lead-acid battery, manufactured by coating a grid or support strip with active materials.
paste-lined cell	Leclanché cell constructed so that a layer of gelled paste acts as the separator.
path resistance	The resistance of a complete signal path, including the switching element's contact resistance, any PC board circuit resistance and connector terminal resistance and or cabling.
Pb	Chemical symbol for lead.
PCB	Printed circuit board
peak	Maximum value of a waveform reached during a particular cycle or operating time.
peak charging	A rise in voltage across a capacitor caused by the charging of the capacitor to the peak value of the input voltage.
peak current	The maximum amount of current that an output is capable of sourcing, or a load is capable of sinking, for a short specified period of time.
peak inverse voltage (PIV)	Maximum value of voltage applied in a reverse direction.
peak inverse voltage rating	The maximum rated voltage that can be applied in the reverse direction across a semiconductor.
peak output current	The maximum current delivered to a load under specified conditions such as duration and repetition.
peak power	The maximum output power that a power converter can deliver without immediate damage under specified conditions.
peak-to-peak	The measured value of a waveform from peak in a positive direction to peak in a negative direction.
periodic and random deviation (PARD)	The sum of all ripple and noise components measured over a specified bandwidth and stated, unless otherwise specified, in peak-to-peak values.
PFC	Power factor correction.
PGH	Power good high.
PGL	Power good low.
pH	Negative logarithm of the hydrogen ion concentration.
phase angle (θ)	The angle that a sinusoidal voltage waveform leads or lags the current waveform.
phase controlled modulation	A regulation technique where operating frequency is held constant (typically at line frequency) and the phase angle at which the control elements are turned on is varied, controlling both line and load changes with minimal dissipation.
phase margin	180 degrees minus the absolute value of the loop phase angle at a frequency where the loop gain is unity. Notes: Phase margin is a convenient way of expressing the relative stability of a linear system under parameter changes, in Nyquist, Bode, or Nichols diagrams. In a conditionally stable feedback control system where the loop gain becomes unity at several frequencies, the term is understood to apply to the value of phase margin at the highest of these frequencies.
phase shift	The difference between corresponding points on input and output signal wave forms (not affected by magnitude) expressed as degrees lead or lag.
photovoltaic cell	A semiconductor device that converts light to dc electricity.
pi filter	A filter consisting of two line-to-line capacitors and a series inductance used to attenuate noise and ripple.
piezoelectric currents	The current caused by mechanical stress to insulating materials or connectors.
pilot cell	A representative cell of a battery utilized to assess the average state of the battery or a somewhat undersized cell that is used as an indicator of the depth of discharge.
pin out	The pin assignment of a device package.
PIV	Peak inverse voltage.
planar winding transformer	A transformer in which the windings are flat spirals in parallel planes, instead of coaxial solenoids. Windings are typically fabricated of multi-layer PCBs, flexible PCB material (which may be "fan folded" for multiple layers), or copper sheet.
plante plate	A plate for a battery in which active materials are formed directly from a lead substrate by electro-chemical processing.
plate	An assembly for an electrochemical cell of active materials on a supporting framework grid, frame or support strip.
plate group	An assembly of plates of the same polarity connected together.
plate pack	An assembly of the positive and negative plate groups with separators.
plated through hole	A conductive material deposited on the walls of a hole in a printed circuit board is called a plated through hole.
PLD	1. See Partial Load Disconnect. 2. Power line disturbance.
plus (+)	Positive terminal of a circuit, circuit element or power source.
PMBus™	An open standard for power system management.
pocket plate	A plate for a battery in which active materials are held in perforated metal pockets on a support strip.
POL	Point of load.
polarity	Property of device or circuit to have poles such as north and south or positive and negative.
polarization	The change in potential of a cell or electrode from its equilibrium value caused by the passage of an electric current.
pole	1. A value in the s-plane where the denominator of the transfer function is equal to zero. 2. The positive or negative terminal of a cell or battery.
pole frequency	The frequency associated with a downward break in the gain plot portion of a Bode plot.
POS	Power operating system, a term used occasionally to describe a system or software that manages system power either at the unit or facility level.
positive electrode	The electrode acting as a cathode when a cell or battery is discharging.
positive rail	The most positive of the two output conductors of a power supply.
positive-limited	The condition where cell performance is limited by the positive active materials.
post regulation	The use of a secondary regulator on a power converter output to improve line/load regulation and to attenuate ripple and noise.
potentiometer	An adjustable tap on a resistor.
potting	An insulating material for encapsulating one or more circuit elements.
powdered iron core	Magnetic core material that contains iron particles held together with a high resistance binder to reduce eddy currents.
power (P)	The rate of generating, transferring or using energy, measured in watts. 1 watt = 1 joule/second 1 joule = I watt-second.
power architecture	The technical description of power supply devices and power usage devices that represents a power system.
power density	The ratio of the power available from a power source to its weight, e.g., watts/pound, or to its volume, e.g., watts/cubic inch.
power factor	The ratio of total active power to total apparent power in volt- amperes in an ac circuit where voltage and current are rms values that include the effects of harmonics as well as the effects of phase displacement. If both voltage and current are sinusoidal, power factor is the cosine of the angle between them.
power factor correction	The technique of changing the power factor so that the current is sinusoidal and the phase angle between the voltage and current approaches zero in an ac circuit.
power failure signal	A signal from a power supply that provides advance notice that the output voltage is about to fall out of specifications due to loss of input voltage.
power FET	Specialized field effect transistor designed for high current or high power applications.
power foldback	A protection feature that reduces the input to a power supply under output overload conditions.
power good signal	A logic signal from a power supply indicating that outputs are within predetermined specifications.
power grid	A distribution network connecting power generating systems and local utilities.
power limiting	The limiting of the total output power of a power supply.
power line disturbance	A disturbance in the input power source such as a sag, brownout, dropout, or surge. Often used in conjunction with testing for the ability of a power converter to withstand such events.
power rating	Power available at the output terminals of a power source based on the manufacturers specifications.
power source	Any device, that furnishes electrical power, including a generator, electrochemical cell, battery, power pack, power supply, power converter, photovoltaic cell, etc.
power supply	A device for the conversion of available power of one set of characteristics to another set of characteristics to meet specified requirements.
power supply cord	An assembly of a suitable length of flexible cord provided with attachment connector(s) at free ends.
power transformer	A magnetic component that transforms the impedance (V/I) of electrical power and/or provides isolation. High efficiency is a principle requirement. Minimization of the power transformer’s leakage inductance is often important in HF dc-dc converters.
ppm	Parts per million
preload	A small amount of current drawn from the output of a power supply in order to stabilize its operation at light loads.
preregulation	The initial regulation circuit in a device containing at least two cascade regulation loops.
primary cell or battery	A cell or battery which is not intended to be recharged and is discarded when the cell or battery has delivered all its electrical energy.
primary circuit	A circuit electrically connected to the input or source of power to the device.
primary side control	A name for an off-line switch mode power converter with the pulse-width modulator in the primary circuit.
primary winding	The transformer winding to which the input is connected.
programmable coefficient	The required range in control resistance to produce a one volt change in output voltage. Expressed in ohms per volt. The ratio of change in a control parameter to induce a unit change in an output, e.g. 100 ohms/volt, or 100 ohms/ampere.
programmable overcurrent shutdown	A method of providing load circuit protection where the overcurrent threshold can be adjusted in accordance with the expected load.
programmable power supply	A power supply with an output controlled by an applied voltage, current, resistance or digital code.
programming	The control of a power supply parameter, such as output voltage, by means of a control element (usually a resistor) or signal (analog voltage or current, or digital code).
programming speed	Programming speed is a measure of a power supply's ability to respond to a varying command to change its output setting from one level to another. Programming speed can be measured in terms of a programming time constant and a slewing rate.
programming time	Elapsed time between the initiation of a programmed event and arrival within a specified range of the final value. In the absence of a specified range, 95% of the desired change shall be used.
PROM	Programmable read only memory.
propagation delay	The time required for a signal to pass through a signal path.
proportional base drive	A scheme for providing a base drive current proportional to the transistor switching (emitter) current so the switch is driven into soft saturation to maintain rapid switching times.
proportional load	Distribution of the load drawn on a multi-output power supply such that each output is delivering the same percentage of its own maximum, continuous power rating, and the total load is equal to the maximum continuous power rating of the power supply.
protection coordination	Properly localizing a fault condition so that only the protective device nearest to the fault operates while others closer to the source continue to supply loads.
psi	1. Pounds per square inch. 2. The 23rd letter of the Greek alphabet.
Pt	A measure of the energy content of short duration pulses used in the selection and rating of semiconductor devices, fuses and other elements subjected to current surges.
pulse	A step rise, a level, and a step fall, of voltage or current. Characteristics of a pulse are: amplitude, rise time, duration and fall time.
pulse discharge	A discontinuous discharge.
pulse droop	A distortion in the flat top of a rectangular pulse, where the amplitude of the flat top declines over time.
pulse duration	The time between a specified reference point on the first transition of a pulse waveform and a similarly specified point on the last transition.
pulse loading	A pulse load imposed in addition to the normal steady-state output current of a power supply.
pulse modulation	Modulation of one or more characteristics of a pulse carrier.
pulse train	A continuous or discontinuous series of pulses.
pulse transformers	1. Signal: Provide isolation for logic "event" information. Voltages are typically a few volts, usually unipolar, but may be bipolar for two distinct "events." Pulse durations are often in the 10-100 ns range. 2. Drive: Provide isolated drive to FETs or BJTs, essentially of a unipolar pulse nature, which may range from ns to µs in duration (voltage pulses for FETs, current pulses for BJTs). 3. Current: Similar to ac current transformers, with output diodes to allow core resetting between unipolar or bipolar current pulses.
pulse-width modulation (PWM)	A method of regulating the output voltage of a switch mode power converter by varying the duration or duty ratio, not the frequency, of a train of pulses.
pulse-width modulator (PWM)	A circuit that modulates the duty ratio of a constant frequency pulse train.
push-pull converter	A power switching circuit that uses two or more power switches driven alternately on and off.
PWM	Variously, pulse-width modulation or pulse-width modulator.
Q	The energy-storing characteristic of an electric circuit, system or device, equal to reactance divided by resistance. Q determines rate of decay of stored energy; the higher the Q, the longer it takes for the energy to be released or dissipated.
quiescent	At rest, inactive.
quiet ground	A low noise analog or logic ground.
R	Symbol for resistance.
r	Variously, the symbol for radius or radio.
race condition	An undesired state that exists when two inputs to a logic or control circuit are both changing, so as to produce an unpredictable output.
radio frequency (RF)	The frequency in the portion of the electromagnetic spectrum that is between the audio-frequency portion and the infrared portion.
radio frequency choke (RFC)	Coil with specified impedance to radio frequency currents.
radio frequency interference (RFI)	An undesired radiated or conducted signal in the radio frequency spectrum.
rail	Either conductor of the output of a supply.
RAM	Random access memory.
rated capacity	The number of ampere-hours a cell or battery can deliver under specific conditions such as rate of discharge, end voltage, and temperature.
rated output current	The maximum continuous load current a power supply is designed to provide under specified operating conditions.
rating drain	The specified current withdrawn from a cell or battery to determine its rated capacity.
RC	Resistance-capacitance, as in a filter.
reactance (X)	Opposition to alternating current as result of inductance or capacitance.
reactor	A component that exhibits the property of either capacitance or inductance.
recharge	To charge after discharge.
rechargeable	Capable of being recharged.
recombination	The mechanism whereby oxygen reacts with the negative active materials to prevent loss of water from the system.
recovery time	The time required for a measured characteristic to be within specified limits following an abnormal event.
rectification	The process of changing an alternating current to a unidirectional current.
rectifier	1. A component or circuit that passes current only in one direction, e.g., a diode. 2. A device for converting ac voltage to dc voltage; often refers to an ac-input power supply with a single dc output.
redox cell (reduction- oxidation cell)	A secondary cell in which two reactant fluids, separated by a membrane, form the active materials.
redundancy	Use of multiple devices or modules to provide continued operation following a failure of one such device or module.
reference electrode	A specially chosen electrode having a reproducible potential against which other electrode potentials may be referred.
reference ground	A specific point in a circuit or system from which potential measurements shall be made.
reference voltage	The defined or specified voltage to which other voltages are compared.
reflected ripple current	The peak-to-peak or rms ac current generated at the input of a power supply by the switching operation of the converter.
regulated power supply	A device that maintains within specified limits a constant output voltage or current for specified changes in line, load, temperature or time.
regulation	1. The process of holding constant selected parameters, the extent of which is usually expressed as a percent. 2. In power supplies, the maximum amount that the output will change as a result of the specified change in line voltage, output load, temperature, or time.
regulation band	The total error band allowable for an output voltage. This includes the effects of all of the types of regulation line, load, and cross.
regulator	The power supply circuit that controls or stabilizes the output parameter.
reinforced insulation	As defined by Underwriters Laboratories, Inc., an improved basic insulation with such mechanical and electrical qualities that it, in itself, provides the same degree of protection against electrical shock as double insulation.
relay	An electromechanical or electronic device that opens or closes an isolated circuit when a voltage is applied to its control terminals.
reliability	The ability of a unit to perform a required function for a stated period of time.
reluctance	The ratio of the magnetomotive force to the magnetic flux through any cross section of a magnetic circuit.
remote enable/disable	A logic signal applied to a power supply to turn the unit on or off.
remote sensing	A technique for regulating the output voltage of a power supply at the load by connecting the regulator error-sensing leads directly to the load.
repeatability	The ability to duplicate results under identical operating conditions.
required headroom	The minimum voltage across a series pass element in a series regulator, at which the regulator can provide the specified output.
reset current	A current injected into the winding of a magnetic component to restore the magnetic flux to the desired operating point for subsequent operation.
reset signal	A signal used to return a circuit to a desired state.
residual flux	The flux that exists in a magnetic core after the field strength is returned to zero.
resistance (R)	Property of a material that opposes the flow of current.
resolution	The smallest increment of change in output that can be obtained by an adjustment.
resonance	The state in which the natural frequency of a circuit coincides with the frequency of an applied signal, or vice versa, yielding intensified response.
resonant circuit	A circuit in which inductive and capacitive elements are in resonance at an operating frequency.
resonant converter	A class of converters that uses a resonant circuit as part of the regulation loop.
resonant inductor	An inductor used with a capacitor to form a tuned resonant circuit. Current is largely or exclusively ac. High circulating (reactive) power is the basic requirement, and core air gap(s)are usually required. Winding dc and ac resistances are both important, and core flux is usually limited by core losses. Fringe flux near discrete air gaps can significantly raise the ac resistance of the winding.
resonant frequency	The natural frequency at which a circuit oscillates or a device vibrates. In an L-C circuit, inductive and capacitive reactances are equal in magnitude at the resonant frequency.
resonant transition switching	A process in a high-frequency power supply using at least one switch that is controlled to conduct periodically, and arranging the circuit, usually using circuit parasitic inductance and/or capacitance, to cause the voltage across the switch to fall to zero before the switch is closed, or its current to fall to zero before the switch is opened. Either process eliminates an element of loss in the circuit associated with high-frequency switching, and increases its operating efficiency. Zero-voltage switching (ZVS) is one method of producing a resonant switching transition.
response time	The time required for the output of a power supply or circuit to reach a specified fraction of its new value after a step change or disturbance.
return	The name for the common terminal of the output of a power supply that carries the return current for the outputs.
return loss	A measure of the undesirable signal reflections from an imperfectly terminated transmission line.
reversal	The changing of the normal polarity of a cell or battery.
reverse current	Current that flows upon application of reverse voltage.
reverse energy	The product of reverse voltage times reverse current in a diode, integrated over a specified time.
reverse polarity	A connection that is opposite to that which is specified or intended.
reverse recovery time (diode)	The time required to remove charge carriers from the junction of a rectifier when reverse voltage is applied.
reverse voltage protection	A circuit or circuit element that protects a power supply from damage caused by a voltage or reverse polarity applied at the input or output terminals.
RF	Radio frequency.
RFC	Radio frequency choke.
RFI	Radio frequency interference.
RI	Resistance, internal.
ripple	The alternating-current component in the output of a direct- current power supply arising from sources within the power supply.
ripple voltage	The periodic ac component superimposed upon the dc output of a power supply.
rise time	The time required for a pulse to rise, typically from 10 percent to 90 percent, of its maximum amplitude.
rms	Root mean square.
RoHS	Reduction Of Hazardous Substances, which refers to various governmentally required programs to reduce to eliminate the use of substances presumed to be hazardous in products.
root mean square	The square root of the average of the squares of all the instantaneous values of current or voltage during one-half cycle of an alternating current. For a sine wave, the rms value is approximately equal to 0.707 times the peak value of the waveform.
rpm	Revolutions per minute
s	Second (unit of time).
S	Variously, the symbol for source, secondary winding, or siemens.
safety extra low voltage (SELV)	Obsolete. See separated extra low voltage (SELV).
safe operating area (SOA)	A manufacturer-specified power/time or voltage/current locus relationship that must be observed to prevent damage to power semiconductors.
safety circuit	Any circuit that is relied upon to reduce risks of electrical shock or fire (an interlock circuit, for example).
safety classes	Grouping of products by various safety agencies to conform to their unique standards.
safety compliance	Certification listing, licensing, recognition or approval by safety agencies.
safety ground	A conductive path from a chassis, panel or case to earth to help prevent injury or damage to personnel and equipment.
saturable reactor	A magnetic component that provides output voltage control by varying the saturation of its magnetic core and, thus, its reactance.
saturation	1. In a bipolar transistor, the condition whereby an increase in base current will not produce an appreciable change in collector-emitter voltage. 2. In a magnetic material, the condition whereby an increase in field strength will not produce an appreciable increase in flux density.
sawtooth waveform	A waveform containing a ramp and a return to initial value, the two portions usually of unequal duration.
SCC	Short-circuit current.
Schottky diode	A diode device that exhibits a low forward voltage drop and fast recovery time in comparison to a standard silicon diode.
SCR	Silicon-controlled rectifier.
secondary breakdown	A failure mode that occurs when a bipolar transistor is operated outside its safe operating area.
secondary cell	A galvanic cell which, after discharge, may be restored to the fully charged state by the passage of an electric current through the cell in the opposite direction to that of discharge.
secondary circuit	A circuit electrically isolated from the input or source of power to the device.
secondary circuit protection	Overcurrent protection located in the secondary circuit.
secondary output	An output of a power supply that is not sensed by the main control loop.
secondary winding	A transformer winding that receives energy from the primary winding by mutual induction and delivers energy to the load.
self-terminating	A switching configuration which automatically terminates a signal path when it is not connected to any other signal path.
self-discharge	The loss of useful capacity of a cell or battery on storage due to internal chemical action (local action).
self-discharge rate	The rate at which a cell or battery loses rated capacity when standing idle.
self-inductance	Property of a magnetic coil that produces an induced voltage at its terminals as the result of a change in current flow through the winding.
SELV	See separated extra low voltage.
semiregulated output	A subjective term indicating partial regulation.
sense line	The conductor which routes output voltage to the control loop.
sense line return	The conductor that routes the voltage on the output return to the control loop.
separated extra low voltage (SELV)	A secondary circuit which is so designed and protected that under normal operating conditions and single fault conditions, its voltages do not exceed a safe value, usually 42.4 V peak, or 60 V dc. Previously called “safety extra low voltage.”
separator	An ionic, permeable electronically nonconductive spacer which prevents electronic contact between electrodes of opposite polarity in the same cell.
sequencing	The process that forces the order of turn on and turn off of individual outputs of a multiple output power supply or of multiple power supplies.
serial port	A port that transfers data one bit at a time.
series	The interconnection of two or more power sources such that alternate polarity terminals are connected so their voltages sum at a load.
series inductance transformer	A transformer where the leakage inductance is significantly in creased with a large space between the windings, placing the windings on separate legs of a core, or incorporating a low permeability (or air gapped) magnetic "flux shunt" between the windings, in order of increasing effectiveness. The equivalent circuit is that of an inductor in series with a transformer winding. A sufficiently high series inductance can limit currents to acceptable levels even with a short circuit on a winding, a technique used for generations in neon sign, oil furnace ignition and arc welding transformers. The high leakage inductance can also be a useful component in some resonant converter topologies.
series-shunt inductance transformer	Although not common, the series and shunt inductance can both be enhanced. A specialized application would be in coupled resonant (tuned) circuits where a single two winding magnetic structure contains all inductances. Furthermore, the two resonant inductances and the coupling coefficient can be independently controlled.
shunt inductance transformer	This transformer structure reduces the magnetizing inductance such that significant energy is stored in the magnetic field, usually achieved with an air gapped high permeability core or a low permeability distributed gap core. The equivalent circuit is that of an ideal transformer with a shunt inductance in parallel with a winding. The most common example is the flyback converter transformer, where energy stored in the magnetic field when the primary switch is closed is delivered to the output when the switch is opened. The approach can also be used in some resonant converter topologies, where the shunt inductance is used in a resonant tank circuit.
series pass	A controlled active element in series with a load that is used to regulate voltage.
series regulator	A regulator in which the active control element is in series with the dc source and the load.
service life	The period of useful life of a device before a predetermined end- point condition is reached.
service maintenance	The percent of rated capacity remaining after a specified period of time.
set point accuracy	The ratio of actual to specified output voltage.
setting range	The range over which the value of the stabilized output quantity may be adjusted.
settling time	The time for a circuit or device to stabilize within specifications after a perturbation to the input or output.
shape change	Change in the shape of an electrode due to migration of active material during charge/discharge cycling.
shelf life	The duration of storage under specified conditions at the end of which a component or device retains the ability to achieve a specified performance.
shield	Partition or enclosure around components of a circuit to minimize the effects of stray magnetic and radio frequency fields.
shielding	A metal enclosure or gasket for a circuit, or a metal shield surrounding wire conductors (as in coaxial or triaxial cable) to lessen interference, interaction, or current leakage. The shield is usually grounded.
shock hazard	A potentially dangerous electrical condition that may be further defined by various industry or agency specifications.
short-circuit	The initial value of the current obtained from a power source in a circuit of negligible resistance.
short-circuit protection	Any automatic current-limiting system that enables a power supply to continue operating at a limited current, and without damage, into any output overload including a short circuit. The output voltage must be restored to normal when the overload is removed, as distinguished from a fuse or circuit breaker system that opens at overload and must be closed to restore power.
short-circuit test	A test in which the output is shorted to ensure that the short circuit current is within its specified limits.
shunt	1. A parallel conducting path in a circuit. 2. A low value precision resistor used to monitor current.
shunt regulator	A linear regulator in which the control element is in parallel with the load, and in series with an impedance, to achieve constant voltage across the load or constant current through the load.
shutdown	A fault condition or external stimulus that reduces the output power of a power supply to zero or near-zero.
SI	System International D'unites.
siemens (S)	Sl unit of conductance (replacing the cgs unit, mho) in which a current of one ampere is produced by an electric potential difference of one volt.
signal ground	The common return or reference point for analog signals.
silicon-controlled rectifier (SCR)	A unidirectional, four-layer (pnpn) junction device in which conduction is initiated by the application of a gate current. Conduction will continue until the device current is reduced to some minimum value.
sine wave	A waveform of a single frequency alternating current whose amplitude over time is a sinusoid.
single-ended input	A circuit that responds to the voltage between one input terminal and ground.
single-point ground	The one point in a system that connects multiple grounds and returns, also known as star ground.
sintered electrode	An electrode construction in which active materials are deposited in the interstices of a porous metal matrix made by sintering metal powder.
sinusoidal frequency response	The maximum sinusoidal frequency to which a fast- programmable power supply will respond with specified distortion in the output waveform.
SIP	Single inline package
slave	A power supply that uses the reference in another power supply, the master, as its reference.
slewing rate	The rate of change of the output of a power supply in response to a change in its control (programming) input.
SLI battery	A Starting, lighting and ignition battery designed to start internal combustion engines and to power the electrical systems in automobiles when the engine is not running.
slow start	A feature that ensures the smooth, controlled rise of the output voltage, and protects the switching transistors from transients when the power supply is turned on.
SMD	Surface mounted device.
SMPS	Switched mode power supply.
SMT	Surface mount technology.
snubber	A network used to reduce the rate of rise of transient voltage or current.
SOA	Safe operating area.
SOC	State-of-charge.
soft line	A condition where considerable impedance is present in the ac mains feeding input to a power supply, causing the input voltage to drop significantly with increasing load.
soft start	Controlled turn-on to limit inrush current or control the rate of rise of output voltage.
solar cell	Synonym for photovoltaic cell.
soldered	Connection of metal surfaces by fusion of a metal alloy.
solid state relay	A relay, controlled by an isolated control input that switches electric current by use of semiconductor elements without moving contacts.
solid-state switch	A semiconductor switching device.
source	1. Origin of input power, e.g., generator utility lines, mains, batteries, etc. 2. In a field-effect transistor, the source terminal is that from which the carriers (electrons or electron holes) flow to the drain.
source frequency effect	The effect on an output of a change in source frequency.
source voltage effect	The effect on an output of a change in source voltage.
spacing	The clearance distance between conductors.
specific gravity	The ratio of the weight of a solution to the weight of an equal volume of water at a specified temperature.
spiral wound	The shape of the internal roll in a cylindrical device made by winding electrodes or conductors and separators or insulators into a multi-turn, spiral wound (jelly-roll-like) construction.
split bobbin winding	The method of winding a transformer whereby the primary and secondary are wound side-by-side on a bobbin with an insulation barrier between the two windings.
SRAM	Static random access memory.
stability	1. An aspect of system behavior wherein bounded input perturbations result in bounded output perturbations. 2. The change in output parameter as a function of time, with all other factors constant, following a specified warm-up period. Usually stated as a percentage of nominal.
standard electrode potential	The equilibrium value of an electrode potential when all the constituents taking part in the electrode reaction are in the standard state.
standby battery	A battery designed for emergency use in the event of a main power failure.
standby current	The input current drawn by a power supply under no load or quiescent conditions.
standby power supply (SPS)	A power source designed to furnish power in periods of line loss.
standoff	A mechanical support, which may be an insulator, used to connect and support a wire or device away from a mounting surface.
star ground	Synonym for Single Point Ground.
start-up sequence	The order of events that occur in a power supply during start up.
starved electrolyte cell	A cell containing little or no free fluid electrolyte. This enables gases to reach electrode surfaces during charging and facilitates gas recombination.
state-of-charge (SOC)	The remaining capacity in a cell or battery, expressed as a percentage of rated capacity.
static load	A load that remains constant.
static transfer switch	A solid-state switch used in standby power supply (SPS) and uninterruptible power supply (UPS) systems for transferring the load between the ac power line and inverter output.
stationary battery	A battery designed for use in a fixed location.
status signals	Logic signals that indicate normal or abnormal conditions of operation, such as ac low, over-temperature, and over-current.
step change	An essentially instantaneous change of a variable from one value to another.
step-down transformer	A transformer whose output voltage is less than the input voltage.
step-up transformer	A transformer whose output voltage is greater than the input voltage.
stiff line	A condition where no significant impedance is present in the ac mains feeding input to a power supply. The input voltage does not change appreciable with the load.
storage battery	A battery comprised of one or more rechargeable cells of the lead-acid, nickel-cadmium, or other rechargeable electrochemical types.
storage life	The nonoperating time interval under specified conditions, after which a device will still exhibit a specified operating life and performance.
storage temperature	The range of ambient temperatures through which an inoperative power supply or other device can remain in storage without degrading its subsequent operation.
STRIFE testing	A short form of STRess and lIFE, a form of accelerated stress testing. See HALT.
sulfation	The formation of lead sulfate on the electrodes of a lead-acid battery. The term is usually applied to large crystals or crusts of insoluble lead sulfate which form after inappropriate or abusive use.
summing point	The point at which two or more signals are added algebraically.
supplementary insulation	As defined by Underwriters Laboratories, Inc., an independent insulation provided, in addition to the basic insulation, to protect against electric shock in case of mechanical rupture or electrical breakdown of the basic insulation. An enclosure of insulating material may form a part of the whole of the supplementary insulation.
surface mounted devices (SMD)	A family of components intended to be mounted directly upon the surface of a substrate or circuit board.
surge	An abnormally high transient voltage, current, or power
swinging choke (inductor)	A filter inductor designed to have a relatively high inductance at low dc currents, with a significant decrease in inductance as current approaches the design maximum. Used to improve load regulation over a wide range of currents with a "choke input" filter, by preventing the inductor current from going to zero at low currents (which raises the output voltage). Although "distributed gap" cores show some decrease in inductance with high dc flux, the effect may be enhanced by adding a parallel magnetic path of a high permeability but easily saturated material such as ferrite. When silicon steel, ferrite or similar cores are used with a discrete air gap, the gap is wedge- or step-shaped to provide early saturation of part of the core.
switched current	The maximum current level that can be reliably handled while opening and closing contacts.
switching frequency	The rate at which the input dc voltage is switched in a converter or power supply.
switching regulator	A switching circuit that operates in a closed loop system to regulate the power supply output.
sync	Abbreviation for synchronizing.
synchronous rectification	A rectification scheme in a power supply in which a transistor is substituted for the rectifier diode to improve efficiency.
Systeme International D’unites (SI)	The system of measurements based on meters, kilograms and seconds, as basic units.
t	Variously, the symbol for time, transformer, temperature, or tesla.
t filter	1. (Low pass) A filter consisting of two series inductors and a shunt capacitor connected between the inductor connection point and the other rail to attenuate noise and ripple. 2. (High pass) A filter consisting of two series capacitors and a shunt inductor connected between the capacitor connection point and the other rail to attenuate low-frequency signals and provide dc isolation.
tank circuit	A parallel resonant circuit.
tape core	A toroidal magnetic core formed by concentric wraps of an iron or amorphous alloy with thin insulated film between layers.
taper charge	A charge regime delivering moderately high rate charging current when the battery is at a low state of charge and tapering the charging current to lower rates as the battery is charged.
Technischer Uberwachungs – Verein (TUV)	A German organization that is approved for testing products to standards set by VDE.
Telcordia	Formerly Bell Communications Research, Inc. or Bellcore, Telcordia is a telecommunications research and development (R&D) company based in the United States and created on January 1, 1984 as part of the 1982 Modification of Final Judgment that broke up the Bell System. Bellcore was a consortium established by the Regional Bell Operating Companies upon their separation from AT&T. Since AT&T retained Bell Laboratories, the operating companies wanted to have their own R&D facility. Bellcore provided joint R&D, standards setting, and centralized government point-of-contact functions for its co-owners, the seven Regional Holding Companies that were themselves divested from AT&T as holding companies for the 22 local Bell Operating Companies.
temperature coefficient	The average percent change in output voltage per degree change in ambient temperature over a specified temperature range.
temperature derating	The amount by which power source or component ratings are decreased for operation at elevated temperatures.
temperature range, operating	See operating temperature range.
temperature range, storage	See storage temperature range.
temperature range	The operating temperature range is the specified ambient temperature range over which it is safe to operate a power supply. The storage temperature range is the specified ambient temperature range over which the power supply can be stored without risk of damage.
tertiary winding	A third winding on a transformer.
tesla (t)	The Sl unit of magnetic flux density (magnetic induction) expressed as 1 weber/square meter.
thermal equilibrium	The point at which the temperature of a component or device becomes stable.
thermal protection	A protective feature that shuts down a power supply if its internal temperature exceeds a predetermined limit.
thermal runaway	A condition in a power source or component where an increase in temperature increases power dissipation causing a further increase in temperature, a spiraling effect that can lead to failure.
thermistor	An electronic device that makes use of the change of resistivity of semiconductor with a change in temperature. In power supplies, negative temperature coefficient thermistors frequently are used as inrush current limiting devices.
three terminal regulator	A power integrated circuit in a 3-terminal standard transistor package.
three-phase current	Combination of three alternating currents having their voltages displaced by 120 degrees, or one-third cycle.
thyristor	A bistable semiconductor device comprising three or more junctions that can be switched from the OFF state to the ON state or vice-versa, such switching occurring within at least one quadrant of the principal voltage-current characteristic.
time constant	The time period required for an exponential variable to increase to 63.2 percent of its steady-state or final value, or decrease to 36.8 percent of its initial value.
tolerance	The measured or specified percentage variation from nominal.
toroid	A round (doughnut-shaped) magnetic core with a hole in the middle.
total effect	The change in a stabilized output produced by concurrent worst- case changes in all influence quantities within their rated range.
total regulation band	The change in regulation due to all variations such as input voltage, output load, temperature, drift, etc.
trace	A conducting path on a printed circuit board.
tracking	A characteristic of a multiple-output power supply that describes the changes in the voltage of one output with respect to changes in the voltage or load of another.
tracking regulator	A power supply in which changes in one output are duplicated in the other(s).
train lighting battery	A battery used in trains to maintain essential services such as lighting and air conditioning.
transfer time	The amount of time it takes an uninterruptible power supply to sense a power interruption and switch to inverter output to the load.
transformer	A device which transfers energy from one circuit to another by electromagnetic induction. Transformers usually contain two or more windings, on a ferromagnetic core to reduce magnetizing currents and confine the magnetic field. Principal functions are to transform electrical impedance (V/I) and/or to provide isolation between two circuits. Winding voltage is proportional to the number of turns, and current is inversely proportional to the number of turns.
transient	A rapid and short-term deviation from a steady-state condition.
transient recovery time	The time required for the output voltage of a power supply to settle within specified output accuracy limits following a step change in output load current or a step change in input voltage.
transient response	Response of a circuit to a sudden change in an input or output quantity.
transient response time	The interval between the time a transient is introduced to a circuit or device, and the time the circuit or device returns to the steady- state condition.
transition time	The time of an electrode process from the initiation of the process at constant current to the moment an abrupt change in potential occurs signifying that a new electrode process is controlling the electrode potential.
transport number	The fraction of the total cell current carried by the cation or anion of an electrolyte solution. The fraction for cations is called the "cation transport number." Similarly, the fraction of the total current carried by the anion is referred to as the "anion transport number."
triac	A bi-directional silicon-controlled switch.
triaxial cable	A cable with three conductors, with one conductor surrounded by an inner shield, and all conductors surrounded by an isolated outer shield.
trickle charge	A charge at low rate, balancing losses through local action and/or periodic discharge, to maintain a cell or battery in a fully charged condition.
trifilar winding	A winding which uses three bundled conductors.
trigger	An external stimulus that initiates one or more instrument functions.
triport	A magnetic structure with two isolated input windings, and an output winding, arranged so that either input can supply power to the output.
true power	Actual power generated or dissipated a circuit, with reactive effects excluded, thus the heating value.
TTL	Transistor-transistor logic.
TUV	Technischer Uberwachungs – Verein. A European standards organization
tubular plate	A battery plate in which an assembly of perforated metal or polymer tubes holds the active materials
tuned circuit	Circuit containing capacitance, inductance and (optionally) resistance, connected in series or parallel such that, when energized at a specific frequency known as its resonant frequency, an interchange of energy occurs between the coil and the capacitor.
Turn-on delay time	The time from the application of input power or assertion of an on/off control signal until the output voltage starts to increase (usually measured at the point where the voltage is at 10% of its final value).
Turn-on time	The time from the application of input power or assertion of an on/off control signal until the output voltage is in regulation and meet specification.
turns ratio	Ratio of the number of turns on the primary winding of a transformer to the number of turns on the secondary winding.
twin cell	Two cells in a container, connected in series.
two-step charge	A charge cycle that starts at a higher current and, at a predetermined point, continues at a lower current.
UL	See Underwriters Laboratories.
UL Listed	A form of approval granted by Underwriters Laboratories to equipment that will be user installed or operated and that is found to meet the safety requirements of the applicable UL standards.
UL Recognized	A form of formal approval granted by Underwriters Laboratories to devices that are not used as free standing equipment on their own, but are to be installed into some other system by a manufacturer, electrician, or possibly by an end-user.
unbalanced	A transmission circuit referenced to ground, also referred to as a single-ended transmission line.
unactivated cell	A cell which may be stored in an inactive state and made ready for use by adding electrolyte (or other cell component) or, in the case of a thermal battery, melting a solidified electrolyte.
unactivated shelf life	The period of time, under specified conditions, that an unactivated cell or battery can be stored before deteriorating below a specified capacity.
undershoot	A transient change in output voltage in excess of specified output regulation limits.
undervoltage protection	A circuit that inhibits the power supply when output voltage falls below a specified minimum.
Underwriters Laboratories	An independent organization that writes specifications for and provides testing services related to product safety.
uninterruptible power supply (UPS)	A power supply that continues to supply ac power during a loss of ac input by means of a backup battery or other standby energy source and a dc/ac inverter.
unity coupling	The theoretical positioning of two coils so all lines of magnetic flux of one coil cut across all turns of a second coil.
unity gain bandwidth	The upper frequency limit at which the open-loop gain becomes unity.
UPS	Uninterruptible power supply.
utilization	The percent of rated capacity which can be obtained from a cell or battery during discharge under specified conditions.
UUT	Unit under test.
UV	Undervoltage.
UVP	Undervoltage protection.
V	Abbreviation (SI unit symbol) for volt.
VA	Symbol for volt-ampere.
vacuum impregnation	The process of using a vacuum to remove gaseous materials from a potting, conformal coating, or varnish compound prior to curing.
valve regulated cell	A cell that is sealed under normal conditions, but allows the escape of gas if the internal pressure exceeds a critical value.
VAR	The unit of measurement of reactive power. It is derived from volt- ampere reactive.
varistor	A two-electrode semiconductor device having a voltage- dependent nonlinear resistance.
varnish dip	The process of dipping a transformer or coil in varnish to bind or protect materials.
varnish impregnation	A varnishing and baking process used to bind together the turns on a magnetic component and protect the component against moisture,
VDE	Verband Deuttscher Elektrotechniker.
vent	A normally sealed mechanism that allows for the controlled escape of gases from within a cell or capacitor.
vented cell	A cell design in which a vent mechanism operates to expel gases that are generated during the operation of the cell.
Verband Deuttscher Elektrotechniker (VDE)	An independent organization that sets standards for product safety and noise emission in the German marketplace.
via	See plated through hole.
volt (V)	Unit of measurement of electromotive force or potential difference.
volt-microsecond clamp	A circuit that limits the flux in a magnetic component to a predetermined value by limiting the volt-microsecond product applied to it.
voltage	A derivative electrical quantity, E, measured in the unit volts and defined in terms of the independently obtained ampere, I, and the unit of resistance, ohm (R) by Ohm's Law E = lR.
voltage balance	The difference in magnitude, in percent, between differential tracking output voltages of a power supply where the voltages have equal nominal values with opposite polarities.
voltage clamp	A circuit that limits the peak voltage across a semiconductor device.
voltage clamping	The circuitry necessary to protect relay or solid state switching elements from excessive voltage, possibly caused by switching current into inductive loads.
voltage delay (batteries)	Time delay for a cell or battery to deliver the required operating voltage after it is placed under load.
voltage dip	A momentary (few cycles) reduction in ac voltage usually caused by a surge in load current.
voltage divider	A network consisting of impedance elements connected in series, to which a voltage is applied, and from which one or more voltages can be obtained across any portion of the network.
voltage doubler	A circuit that separately rectifies each half cycle of the applied alternating voltage and adds the two rectified voltages to produce a direct voltage whose amplitude is approximately twice the peak amplitude of the applied alternating voltage. Half-Wave Voltage Doubler Full-Wave Voltage Doubler
voltage drop	Difference in potential between two points in a component or circuit.
voltage efficiency (batteries)	The ratio of average voltage during discharge to average voltage during recharge under specified conditions of charge and discharge.
voltage limit	Maximum or minimum value of voltage.
voltage limiter	Circuit used to set specified maximum or minimum voltage levels.
voltage mode	The functioning of a power supply so as to produce a stabilized output voltage.
voltage monitor	A circuit or device that determines whether or not a voltage is within some specified limits.
voltage multiplier	A rectifying circuit that produces a direct voltage whose amplitude is approximately equal to an integral multiple of the peak amplitude of the applied alternating voltage. The circuit below is attributed to Cockroft and Walton, and is often called a Cockroft- Walton voltage multiplier. C C 2C 2C (n-2)C 2 n Vpeak (n-1)C (n-1)C nC Vpeak nC 0 -Vpeak Voltage Multiplier
voltage regulation	The process of holding voltage constant between selected parameters the extent of which is expressed as a percent.
voltage sag	A short-term drop in ac voltage.
voltage source	A power source that tends to deliver constant voltage.
voltage stabilization	The use of a circuit or device to hold an output voltage constant within given limits.
voltage transformer	A magnetic device that transforms voltage to a more convenient level for sensing or measurement, and/or provides isolation. Voltage transformation accuracy is often important.
voltaic cell	Cell producing a potential difference by chemical action.
volt-ampere (VA)	The unit of apparent power in the International System of Units (SI).
vpc	Volts per cell.
VRD	Voltage regulator down, a dc-dc converter that is manufactured using individual components on the same circuit board as the load it is powering
VRM	Voltage regulator module, an assembled dc-dc converter product used to provide conversion and collage regulation. Most often associated with dc-dc converters providing dedicated power to higher performance microprocessors.
VSWR	Voltage standing wave ratio, the loss due to the mismatch of load and source impedances.
W	SI unit symbol for watt.
watt (W)	Unit of power, equal to 1 joule/sec.
wattage	Actual delivered energy. In an ac power system, wattage is voltage multiplied by current multiplied by power factor.
watt-hour (Wh)	Unit of energy, equal to one watt for one hour (3600 joules).
watt-hour capacity	The total electrical energy delivered by a cell or battery under specified conditions.
watt-hour efficiency	The ratio of the watt-hours delivered on discharge of a battery to the watt-hours needed to restore it to its original state under specified conditions of charge and discharge.
walk-in	A feature in large battery plants that slowly increases the output current of the battery chargers when ac power is applied. Used to limit load surges on the power source.
warm-up	Process of approaching thermal equilibrium after turn on.
warm-up drift	The change in output voltage or current of a power source from turn on until it reaches thermal equilibrium, under specified operating conditions.
warm-up time	The time from initial turn on for a power supply to achieve compliance with performance specifications.
wb	Abbreviation for weber.
weber (wb)	The SI unit of magnetic flux (equal to 108 maxwells). One weber is the amount of flux that, when reduced to zero at a constant rate over a period of one second, will induce 1 volt/turn of wire in a loop perpendicular to the flux.
WEEE	Waste Electrical and Electronic Equipment Directive (WEEE Directive), the European Community directive 2002/96/EC on waste electrical and electronic equipment which, together with the RoHS Directive 2002/95/EC, became European Law in February 2003, setting collection, recycling and recovery targets for all types of electrical goods
Wh	SI symbol for watt-hour.
wideband	An adjective describing the characteristics of a communications circuit or channel that can carry a large quantity of information at a high rate.
winding	A conductor wrapped onto a magnetic core or core form, e.g., a transformer primary or secondary.
winding area	The cross-sectional area of a bobbin or magnetic core that can be filled with a winding.
winding length	The allowable length on a core form or bobbin that can be occupied by a single layer winding. One dimension of the core window.
winding machine	A machine designed to put wire onto a bobbin or core form, or onto a toroid.
window	The specified range of given values.
wire style number	The categorization by regulatory and testing agencies of appliance wiring material with respect to insulation type, thickness, number of conductors and use.
wire table	A listing of wire gauges that includes the diameter, cross- sectional area, insulation and resistance of each wire gauge size.
withstand voltage	The maximum voltage that can be applied between separate circuits without causing failure.
working voltage	The specified operating voltage, or range of voltages, of a component, device or cell.
worst case condition	A set of conditions where the combined influences on a system or device are most detrimental.
XC	Symbol for capacitive reactance.
X	Symbol for reactance.
X capacitors	EMI filter capacitors across the ac line that meet the requirements of certain regulatory agencies.
XL	Symbol for inductive reactance.
Y	Symbol for admittance (the reciprocal of impedance).
Z	Variously, a symbol for impedance, or atomic number.
ZCS	Zero-current switching
ZVS	Zero-voltage switching
Z match	Abbreviation for impedance matching.
Zener break frequency	A frequency on a Bode plot at which the tangent to the gain increases.
Zener diode	A diode that makes use of the reverse breakdown properties of a PN junction.
Zener voltage	The reverse voltage at which breakdown occurs in a Zener diode..
zero-current switching	A control method that turns a switch off when there is no current flowing through it. This eliminates an element of loss in the circuit associated with high-frequency switching, and increases its maximum feasible operating efficiency.
zero-voltage switching	A control method that turns a switch on when there is no voltage across its main terminals. This eliminates an element of loss in the circuit associated with high-frequency switching, and increases its maximum feasible operating efficiency.

Some common (and less common) terms that are used in the Power Conversion industry.

Term

Definition