Power Supply Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

ABSOLUTE MAXIMUM RATINGS – Specifications that, if exceeded could cause permanent damage to the power supply or converter. These are not continuous ratings and proper operation is not implied.

ADAPTOR – An external power supply desktop, regulated or unregulated, desktop or wall plug-in.

AGING – Operating a converter under controlled conditions for a predetermined time in order to screen out failures. Also see “Burn-In”

ALTERNATING CURRENT - (AC) A periodically varying current whose average value over a period is zero. Unless distinctly specified otherwise, the terms refers to a current that reverses at regularly recurring intervals of time and that has alternately positive and negative values.

AMBIENT TEMPERATURE - The still air temperature in the immediate vicinity of a power supply, measured in a minimum of 4 inches (1OOmm) from the supply.

AMPERE (A) - The basic unit of electric current in a circuit. A charge of one coulomb passing a point in one second.

APPARENT POWER - Power value obtained in an AC circuit as the product of RMS current times RMS voltage.

AUTO-PARALLEL OPERATION – A parallel connection of outputs of two or more supplies used for obtaining a current output greater than that obtainable from one supply.

AUTO-SERIES OPERATION – A series connection of the output of two or more power supplies used for obtaining a voltage power greater than that obtainable from one supply.

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.

BALUN – a transformer that presents a high impedance to common-mode signals and low impedance to differential mode signals. It is commonly used on the input of switching power supplies to suppress common-mode noise.

BATTERY BACKUP – A subsystem for electronic equipment that provides power in the event of a input power loss.

BIPOLAR TRANSISTOR - A junction transistor having both majority and minority charge carriers.

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.

BREAKDOWN VOLTAGE - The maximum AC or DC voltage that may be applied from input to output and/or chassis of a power supply.

BROWN-OUT - The condition created during peak usage periods when electric utility companies intentionally reduce their line voltage by approximately 10 to 15 percent to counter excessive demand.

BUCK REGULATOR - One of several switching power supply topologies where a series of pulses are applied by a switching device to an averaging L-C filter and then applied to a load. Output voltage is less than the input voltage.

BURN-IN - The operation of a newly fabricated device or system prior to application with the intent to stabilize the device, detect defects, and expose infant mortality.

CANADIAN STANDARDS ASSOCIATION (CSA) - A Canadian organization concerned with testing for public safety.

CASE TEMPERATURE – The temperature of the case when a power supply and surrounding system are operating normally. Often used as a specification for power supplies with extended temperature ranges.

COMMON – Conductive path used as a return for two or more circuits. Common is used interchangeably with ground, which is not technically correct unless it is connected to earth.

COMMON RETURN - A return conductor common to two or more circuits.

COMMON-MODE NOISE - The component of noise voltage that appears equally and in phase on conductors relative to a common reference.

COMPLIANCE - Agency certification that a product meets its standards. See Safety Compliance.

COMPLIANCE VOLTAGE – The output voltage range of a constant current power supply.

CONDUCTED EMI – Also called radio frequency interference (RFI), EMI is unwanted high-frequency energy causes by the power transformer rectifiers, in a adaptors. That portion that is present on the input and output lines is known as Conducted EMI. Most Conducted EMI measurements are between 150KHz and 30MHz.

CONDUCTION COOLED – Cooling a power supply via a solid material, such as a heat sink or thermal conductive enclosure.

CONSTANT CURRENT POWER SUPPLY - A power supply that regulates its output current, within specified limits, against charges in line voltage, load ambient temperature and time.

CONSTANT VOLTAGE POWER SUPPLY - A power supply that regulates its output voltage for changes in line, load, ambient temperature_ and time.

CONVECTION-COOLED - A power supply cooled exclusively from the natural motion of a gas or a liquid over the surfaces of heat dissipating elements.

COULOMB- A unit of electrical charge equal to 6.26 x 10 to the 18th degree electrons.

CROSS-REGULATION - In a multiple output power supply, the percent voltage change at one output caused by the load change on another output.

CROWBAR - An overvoltage protection circuit that rapidly places a low resistance shunt across the power supply output terminals if a predetermined voltage is exceeded.

CUBIC FEET PER MINUTE (CFM) – The measure of the volume of air flowing in a system.

CURRENT - 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 LIMITING - An overload protection circuit that limits the maximum output current to a present value.

CURRENT LIMIT KNEE – On a plot of output voltage versus current, the point at which current begins to limit (or foldback).

DERATING - 1) Practice of applying components or devices at a lower stress level than specified capabilities in order to reduce the occurrence of stress-related failures. 2) Reduction in rated power output as a function of elevated ambient temperature.

DIELECTRIC – Material used to prevent two points in an electrical circuit from becoming conductively connected. Sometimes called Dielectric Barrier.

DIELECTRIC WITHSTAND VOLTAGE – The maximum voltage an insulating material can withstand before breaking down (suffering punch-through or arcing).

DIFFERENTIAL MODE NOISE - The component of noise measured between the DC output and output return. See "Ripple and Noise".

DRIFT – The change in output voltage of a power supply over a specified period of time, following a warm-up period, with all other operating parameters such as line, load, and ambient temperature held constant.

DYNAMIC LOAD REGULATION - 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 RESPONSE – The ratio of total output to input power expressed as a percentage. Efficiency is normally measured at full rated output power and normal input line conditions.

EFFICIENCY - 1) The ratio of total output power to total input power, expressed as a percentage, under specified conditions. 2) The ratio of a secondary cell or battery on discharge to the input required to restore it to the initial state of charge under specified conditions.

ELECTROMAGNETIC INTERFERENCE (EMI) - Unwanted energy, generally emitted from switching power supplies, which may be conducted or radiated.

ELECTROSTATIC DISCHARGE (ESD) – Current produced by two objects having a static charge when they are brought close enough to produce an arc or discharge.

EMI FILTER – A filter placed at the input of a power supply to minimize the effects of EMI on the power supply and associated system.

ENCLOSURE – The case or container used to package a power supply or system.

EQUIVALENT SERIES RESISTANCE (ESR) - The amount of resistance in series with an ideal capacitor that exactly duplicates the performance of a real capacitor. In high frequency applica­tions low ESR is very important.

FARADY SHIELD - An electrostatic shield between input and output windings of a transformer. This can be used to reduce primary-secondary coupling capacitance, which in turn reduces output common-mode noise.

FAULT-MODE INPUT CURRENT – The input current to a power supply or DC/DC converter, with the output short circuited.

FEED FORWARD - A control technique whereby the line regulation of a power supply is improved by directly sensing the input voltage.

FEEDBACK - The process of returning part of the output signal of a system to its input.

FERRORESONANT POWER SUPPLY – An open-loop voltage stabilized power supply in which a portion of the transformer core is driven into saturation by a resonant tank circuit. The output is derived from the saturated portion of the transformer and is relatively independent of input voltage.

FLOATING OUTPUT – Power supply output that is ungrounded and not reference to another output. Typically, floating outputs are fully isolated and may be referenced positively or negatively by the user. Outputs that are not floating share a common return and as such are referenced to one another.

FLYBACK CONVERTER - A switching power supply circuit that normally uses a single transistor. During the first part of the cycle the transistor is on and energy is stored in a transformer primary; during the second part of the cycle this energy is transferred to the transformer secondary and the load.

FOLDBACK CURRENT LIMITING – a power supply output protection circuit whereby the output current decreased with increased overload, reaching a minimum at short circuit. This minimizes dissipation under overload conditions. Fold back current limiting is normally used with linear regulators and is unnecessary with switching regulators.

FORCED CONVECTION COOLING - Heat transfer from dissipative elements by movement of cooling fluid by means of a fan or pump.

FORWARD CONVERTER - A power supply switching circuit in which energy is transferred to the transformer secondary when the switching transistor is on. In this circuit minimal energy is stored in the transformer.

FREE CONVECTION – Operating environments where the natural movement of air (assisted by fans or blowers) maintains the power supply within its operating limits. Also called natural convection.

FREQUENCY (Hz) - Number of periods per unit time measured in hertz.

FRONT END – A particular type of AC/DC converter (usually high power) used in Distributed Power Architecture (DPA) systems that provide the DC voltage that is bussed around the system. The bussed voltage is usually 24VDC or 48VDC.

FULL BRIDGE CONVERTER - A power switching circuit in which four power switching devices are connected in a bridge configuration to drive the load.

FULL LOAD – The maximum value of output load specified for a power supply under continuous operating conditions.

GROUND - A conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to earth, or to some conducting body that serves in place of earth.

GROUND LOOP - A condition that causes undesirable voltage levels and current Row when two or more circuits share a common electrical return or ground line.

HALF BRIDGE CONVERTER - A power switching circuit similar to the full bridge converter except that only two transistors are used, with the other two replaced by capacitors.

HARMONIC DISTORTION - The distortion of a sinusoidal wave characterized by the presence of harmonics of the fundamental frequency. Percent Harmonic Distortion is an appropriate figure of merit and is defined as the ratio (in percent) of the square root of the sum of the squares of all RMS harmonic voltages (or currents) to the fundamental.

HEAT SINK – The metal plate, extrusion, case, etc. used to transfer heat away from sensitive components and/or circuits.

HI-POT TEST - 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.

HOLDOVER TIME - See "Hold-Up time".

HOLD-UP TIME - The time under worst case conditions during which a power supply's output voltage remains within specified limits following the loss or removal of input power.

HOT PLUG-IN – A common requirement in distributed power systems wherein the power board must be capable of being connected or disconnected from the power bus without damage. Power board components must be protected against the resultant high inrush currents.

INPUT CURRENT – The current drawn from the input power source by a power supply when operating under normal conditions.

INPUT LINE FILTER - A low-pass or band-reject filter at the input of a power supply that reduces line noise fed to the supply. This filter may be external to the power supply.

INPUT PI FILTER - See "Pi Filter".

INPUT TRANSIENT – A spike or step change in the input to a power supply

INPUT VOLTAGE RANGE - The high and low input voltage limits within which a power supply or DC/DC converter meets its specifications.

INRUSH CURRENT - The peak instantaneous input current drawn by a power supply at turn-on.

INRUSH CURRENT LIMITING - A circuit that limits the inrush current during turn-on of a power supply.

INSULATION – Non-conductive material used to protect and separate electrical components and circuits.

INSULATION RESISTANCE – The resistance offered by an insulating material to current flow.

INTERNAL POWER DISSIPATION – Power dissipated (as heat) within the power supply during normal operations. This is primarily a function of the power handling capability and efficiency of the power supply. Internal power dissipation is normally given as a maximum specification that cannot be exceeded without risking damage.

INVERTER - A power converter that changes DC input power into AC output power.

ISOLATION - The electrical separation between input and output of a power supply by means of the power trans­former. The isolation resistance (normally in megohms) and the isolation capacitance (normally in picofarads) are generally specified and are a function of materials and spacings employed throughout the power supply.

ISOLATION VOLTAGE - The minimum AC or DC voltage that may be continuously applied from input to output and/or chassis of a power supply.

LAYER WINDING – The method of winding a transformer whereby the primary and secondary are wound in layers over one another, separated by an insulation layer.

LEAKAGE CURRENT - The AC or DC current flowing from input to output and/or chassis of an isolated power supply at a specified voltage.

LIFE TEST – A reliability test in which a power supply is operated over some period of time to approximate its life expectancy.

LINE - 1) Medium transmission of electricity between circuits or devices. 2) The voltage across a power transmission line.

LINE REGULATION - The change in output voltage in percent as the input voltage is varied over its specified limits, with load and temperature constant.

LINEAR REGULATOR - A popular stabilization circuit in which a control device is placed in series (or parallel) with the load to give a constant voltage across the load. The control device is always conducting, and the difference between input and output power is dissipated by the control device.

LOAD DECOUPLING – Placement of filter components (typically capacitors) at the power terminals in order to reduce noise.

LOAD REGULATION - The percent change in output voltage as the load is changed from minimum to maximum, at constant line and constant temperature. The load change may be specified for other than no load to full load, such as 20% load to full load.

LOCAL SENSING - Using the power supply output voltage terminals as the sense points to provide feedback to the voltage regulator.

LONG TERM STABILITY - 1) The percent change in output parameter as a function of time, with all other factors constant, following a specified warm-up period. 2) The ability to stay on a given frequency or in a given state without undesired variation.

LOW LINE – The minimum value of input line voltage specified for normal power supply operation.

MAXIMUM LOAD – The highest amount of output load under the continuous operating specifications of a power supply.

MAXIMUM OPERATING TEMPERATURE - The highest operating temperature at which the power supply will continuously operate safely and within specifications.

MEAN TIME BETWEEN FAILURE (MTBF) - The failure rate of a power supply, expressed in hours, established by the actual operation or calculation from a known standard such as MIL-HDBK-217.

METAL OXIDE VARISTOR (MOV) - a device of nonlinear resistance used as a surge protective device or voltage limiter.

MINIMUM LOAD – The minimum amount of output load required on a power supply in order to maintain normal continuous operating specifications.

MINIMUM OPERATING TEMPERATURE - The lowest ambient temperature at which a power supply or other device will continuously operate safely and within specifica­tions.

MOSFET - Abbreviation for Metal Oxide Semiconductor Field Effect Transistor.

NEUTRAL - The AC return that is connected at some point to ground, but should not be used for safety ground because it is a current carrying path.

NO LOAD VOLTAGE – Voltage level present at the output pins of a power supply when zero load is applied.

NOMINAL VALUE - The stated or objective value for a quantity, such as output voltage, which may not be the actual value measured.

OFF-LINE POWER SUPPLY – A power supply that operates off the AC line directly, without using a power transformer prior to rectification and filtering. OHM (W) - Unit of measure resistance.

OPEN FRAME – A type of power supply that is not encased in a metal or plastic shell or frame and subsequently is not covered with a potting compound.

OPERATING TEMPERATURE RANGE - The range of ambient, base plate 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 with a high open loop gain regulator that acts like an operational amplifier and can be programmed with passive components.

OPTOCOUPLER - A package that contains a light emitter and a photoreceptor used to transmit signals between electri­cally isolated circuits.

OUTPUT CURRENT LIMITING – An output protection feature that limits the output current to a predetermined value in order to prevent damage to the power supply or the load under overload conditions. The supply is automatically restored to normal operation following removal of the overload.

OUTPUT IMPEDANCE - The impedance presented by the output terminals of a power supply to a load.

OUTPUT VOLTAGE – The nominal value of DC voltage at the output terminals of a power supply.

OUTPUT VOLTAGE ACCURACY – For a fixed output supply, the tolerance in percent of the output voltage with respect to its nominal value under all minimum or maximum conditions.

OVERLOAD PROTECTION – An output protection feature that limits the output current of a power supply under overload conditions so that it will not be damaged.

OVERSHOOT - A transient change in output voltage, in excess of specified output accuracy 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 CROWBAR – An overvoltage protection circuit that rapidly places a low resistance shunt across the power supply output terminals if a predetermined voltage is exceeded.

OVERVOLTAGE PROTECTION (OVP) – A power supply feature that shuts down the supply, or crowbars or clamps the output, when its voltage exceeds a preset level.

PARALLEL OPERATION - The connection of two or more power sources of the same output voltage that are designed for this type of operation to obtain a higher output current.

PARALLELING DIODE - A diode connected between the output of a power supply and a load bus energized by paralleled power supplies to isolate the load bus from internal supply faults - also called 0 ring diode because it provides a logical or function.

PEAK OUTPUT CURRENT - The maximum current value delivered to a load under specified pulsed conditions.

PERIODIC AND RANDOM DEVIATION (PARD) - A term used for the sum of all ripple and noise components measured over a specified band width and stated in either peak-to-peak or RMS values.

PI FILTER - A filter consisting of two line-to-line capacitors and a series inductance used to attenuate noise and ripple. The elements are connected together to resemble the Greek letter pi (p).

POLARITY - The ability of a power supply to provide an output that is positive or negative referenced to ground.

POST REGULATION – A linear regulator used on the output of a switching power supply to improve line and load regulation and reduce ripple voltage.

POWER DENSITY – The ratio of power supply output power to power supply volume.

POWER FACTOR CORRECTION – A technique usually applied to the input of a power supply to improve the power supply’s power factor and to minimize harmonies generated by the power supply onto the AC power line.

POWER FAIL DETECTION – A power supply option which monitors the input voltage and provides an isolated logic output signal when there is a loss of line voltage.

POWER FOLDBACK – A power supply feature whereby the input power is reduced to a low value under output overload conditions.

POWER GOOD SIGNAL - A logic signal from a power supply indicating that outputs are within predetermined specifications.

PREREGULATION – The regulation at the front-end of a power supply, generally by a type of switching regulator; this is followed by output regulation, usually by a linear type regulator.

PRIMARY CIRCUIT – The input side of an isolated power supply.

PROGRAMMABLE POWER SUPPLY – A power supply with an output controlled by an external resistor, voltage or digital code.

PULSE-WIDTH MODULATOR – A method of voltage regulation used in switching supplies whereby the output is controlled by varying the width, but not the height, of a train of pulses which drive a power switch.

PUSH-PULL CONVERTER – A power switching circuit that uses a center-tapped transformer and two power switches that are driven on and off alternatively. This circuit does not provide regulation by itself.

RADIATED EMI – Also called RFI, Radiated EMI is unwanted high frequency noise generated by a power supply. That portion that is radiated through space is called Radiated EMI. Typical Radiated EMI measurements are done between 30MHz and 300MHz

RATED OUTPUT CURRENT – The maximum load current that a power supply was designed to provide at a specified ambient temperature.

REDUNDANT OPERATION – The parallel configuration of power supplies used in a distributed power system to increase system reliability.

REFERENCE – The stable voltage, generally a Zener diode, from which the output voltage of a regulated power supply is controlled.

REGULATION – The ability of a power supply to maintain an output voltage within specified limits under varying conditions of input line and output load.

REFLECTED RIPPLE CURRENT – The AC current generated at the input of a power supply or DC/DC converter by the switching operation of the converter, stated as peak-to-peak or RMS.

REMOTE PROGRAMMING – A feature of many power supplies that permit control of the regulated output current or voltage by means of a remotely varied resistance or voltage.

REMOTE SENSING – A technique for regulating the output voltage of a power supply at the load by means of sensing leads which go from the load back to the regulator. This compensates for voltage drops in the load leads.

RESOLUTION – For an adjustable supply, the smallest change in output voltage that can be realized by the adjustment.

RETURN – The name for the common terminal of the output of a power supply; it carries the return currents for the outputs.

REVERSE VOLTAGE PROTECTION – A feature that protects a power supply against a reverse voltage applied at the input or output terminals.

RIPPLE AND NOISE – The magnitude of AC voltage on the output of a power supply, expressed in millivolts peak-to-peak or RMS, at a specified bandwidth. This is the result of feed through of the rectified line frequency, internal switching transients and other random noise.

RISE TIME - The time required for a pulse to rise from 10 percent to 90 percent of its maximum amplitude.

ROOT MEAN SQUARE (RMS) VALUE - The square root of the average of the square of the value of the function taken throughout one period. For a sine wave, .707 x Peak Value.

SAFETY COMPLIANCE - Certification, listing, licensing, or recognition by safety agencies such Underwriters laboratories Inc. (ULI U.S.A.) Canadian Standards Association (CSA), or other registered testing laboratories.

SAFETY EXTRA LOW VOLTAGE (SELV) - International safety standards as described in IEC 950 and VDE 0805.

SECONDARY CIRCUIT - A circuit electrically isolated from the input or source of power to the device.

SEMI-REGULATED OUTPUT - A subjective term indicating partial regulation.

SERIES REGULATION - A regulation technique wherein the control device, such as a transistor, is placed in series or parallel with the load. Output is regulated by varying the effective resistance of the control device to dissipate unused power.

SHORT-CIRCUIT PROTECTION - A protective feature that limits the output current of a power supply to prevent damage.

SHUNT REGULATION - 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.

SINE WAVE - A wave form of a single frequency alternating current whose displacement is the sine of a linear function of time.

SOFT START – A feature that limits the start-up switching currents of a switching supply and causes the output voltage to rise gradually to its final value.

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.

STABILITY, LONG TERM - 1) The percent change in output parameter as a function of time, with all other factors constant, following a specified warm-up period. 2) The ability to stay on a given frequency or in a given state without undesired variation.

STANDBY CURRENT – The input current drawn by a power supply under no load or when shut down by a control input.

STANDBY POWER SUPPLY (SPS) - A power source designed to furnish power in periods of line loss.

STEP CHANGE - An instantaneous change in a quantity from one value to another.

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.

SURFACE MOUNTED DEVICES (SMD) - A family of components intended to be mounted directly upon the surface of a substrate or circuit board.

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.

TEMPERATURE COEFFICIENT - The average percent change in output voltage per degree Centigrade change in ambient temperature over a specified period of temperature range.

TEMPERATURE RANGE, OPERATING - The range of ambient, base plate or case temperatures through which a power supply is specified to operate safely and to perform within specified limits.

TEMPERATURE RANGE, STORAGE - The range of ambient temperatures through which an inoperative power supply or other device can remain in storage without degrading its subsequent operation.

THERMAL CONDUCTIVITY – A given material’s ability to conduct heat, which is the time rate for heat transfer (via conduction) across a unit material thickness of 1 meter and when the temperature differential of the two opposite faces is 1 degree Kelvin.

THERMAL GASKET – A flexible pad or wafer with a very low thermal resistance that is put between a power module base plate and heat sink to ensure the high thermal conductivity across the junction.

THERMAL JOINT COMPOUND – A fluid or paste spread between the mating surfaces of a power device base plate and a heat sink or system chassis.

THERMAL PROTECTION - A protective feature that shuts down a power supply if its internal temperature exceeds a predetermined limit.

THERMAL RESISTANCE – The measure of a given material’s opposition to the flow of heat.

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.

TOPOLOGY – The way in which the power handling part of a power supply is configured. Choice of topology influences many of the basic characteristics of a power supply.

TOTAL REGULATION BAND - The range of combined regulation tolerances such as the effects of input voltage variation, output load variation, temperature variation, drift and other specified variables. It is expressed as a plus/ minus percent from nominal. Also known as accuracy limits.

TRACKING – A characteristic or a dual or other multiple output power supply whereby one or more outputs follow another with changes in line, load and temperature, so that each maintains the same proportional output voltage, within specified tracking tolerance, with respect to common.

TRANSIENT – A spike or step change in a power supply parameter, typically a step change in output load current or a step change in input voltage..

TRANSIENT RECOVERY TIME - The time required for the output voltage of a power supply to settle with in specified output accuracy limits following a step change in output load current or a step change in input voltage.

TRUE POWER - Actual power generated or dissipated a circuit.

U.L. - Underwriters Laboratories Inc. - An independent, non­profit U.S. organization that tests products for safety.

UNDERSHOOT - A transient change in output voltage in excess of specified output regulation limits.

UPS - UNINTERRUPTIBLE POWER SUPPLY - 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.

VDE - VERBAND DEUTSCHEER ELEKTROTECHNIKER - A German organization that tests equipment for public safety and emitted noise.

VOLTAGE - A derivative electrical quantity (EI 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=IR.

VOLTAGE BALANCE – The difference in magnitude, in percent, between the two output voltages of a dual output power supply where the voltages have equal nominal values with opposite polarities.

VOLTAGE DROP - Difference in potential between two points in a passive component or circuit.

WARM-UP DRIFT - The change in output voltage or current of a power source from turn on until it reaches thermal equilibrium at specified operating conditions.

WARM-UP TIME - The time required, after initial turn-on for a power supply to meet its performance specifications.