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AC Brownout: The condition that exists when the ac line voltage drops below some specified value.

AC Line Filter: A circuit filter placed in the ac line to condition or smooth out variations that are higher in frequency than the line frequency.

Alternating Current (ac): A periodic current the average value of which 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.

Ambient Temperature: The average temperature of the environment immediately surrounding the power supply. For forced air-cooled units, the ambient temperature is measured at the air intake.

Ampere (A): Electron or current flow representing the flow of one coulomb per second past a given point in a circuit.

Apparent Power: Power value obtained in an ac circuit as the product of RMS current times RMS voltage.

Attenuation: Decrease in amplitude or intensity of a signal.

Auxillary Supply: A power source supplying power other than load power as required for the proper functioning of a device.

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Balun: A transformer which represents 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.

Bandwidth: Based on the assumption that a power supply can be modeled as an amplifier, the bandwidth is that frequency at which the voltage gain has fallen off by 3dB. Bandwidth is an important determinant of transient response and output impedance.

Baseplate: Mounting platform for power supply components.

Baseplate Temperature: The temperature at the hottest spot on the mounting platform of the supply.

Battery Back-up: Battery support to maintain function of selected components or devices.

Battery Charger: Electrical equipment designed to restore capacity to secondary batteries.

Bead: A small ferrite normally used as a high frequency inductor core.

Bleed: A low current drain from a power source.

Boost Regulator: One of several basic families of switching power supply topologies. Energy is stored in an inductor during the pulse, then released after the pulse.

Breakdown Voltage: The maximum AC or DC voltage which may be applied from input to output and/or chassis of a power supply.

Bridge Circuit: Circuit with series-parallel groups of components.

Bridge Rectifier: Full-wave rectifier circuit employing two or more rectifiers in a bridge configuration.

Brownout: A planned voltage reduction by a utility company to counter excessive demand on their generation and distribution system.

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.

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 end of a regulator.

Bulk Voltage: The voltage across a bulk capacitor.

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.

Bus: The common primary conductor of power from a power source to two or more separate circuits.

Bysyn: Trade name for a symmetrical bipolar transistor designed for synchronous rectification.

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Canadian Standards Association (CSA): An organization chartered to test and evaluate products and to set applicable safety standards in Canada.

Capacitance: Inherent property of an electric circuit or device that opposes change in voltage. Property of circuit whereby energy may be stored in an electrostatic field.

Capacitor: A device that stores a charge. A simple capacitor consists of two conductors separated by a dielectric.

Capacitor Input Filter: Filter employing capacitor as its input.

Capacity: The ability of a component, battery or other device to store and discharge a given quantity or current (A) or power (W) over a specified period of time (Ah or Wh)

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.

Cell: The basic electrochemical unit used to generate or store electrical energy.

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 Voltage: The voltage applied to a cell during charge.

Chassis: The structure supporting or enclosing the power supply.

Chassis Ground: The voltage potential of the chassis.

Circuit Input Filter: A filter employing an inductor (L) or an inductor/capacitor (L/C) as its input.

Clamp Circuit: A circuit that biases a voltage waveform to a different voltage level.

Clamp Diode: A diode in either a clipper or clamp circuit.

Closed-Circuit Voltage (CCV): The potential or voltage at the terminals of an electrical device when current is flowing.

Closed Loop Buck Converter: A circuit where energy is pulsed to an averaging L/C filter and delivered to a load.

Common-Mode Noise: The component of noise which is common to both the DC output and return lines with respect to input neutral.

Common-Mode Output: The electrical output supplied to an impedance connected between the terminals of the ungrounded floating output of a power supply and the ground point to which the source power is returned.

Common Return: A return conductor common to two or more circuits.

Compliance Range: Range of voltage needed to sustain a given constant current throughout a range of load resistance.

Compliance Voltage: The output dc voltage range of a constant current power supply.

Conformal Coating: An insulating layer often applied by spraying or dipping that covers and protects the components on a circuit board.

Conformance: Manufacturer's commitment that product meets specified standards.

Connector: A mechanical device used to link conductors.

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 for changes in line, 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.

Continuous Wave (CW): Uninterrupted sinusoidal rf wave radiated into space, with all wave peaks equal in amplitude and evenly spaced along time axis.

Control Circuit: The circuit that carries the electric signals directing the performance of a control device, but does not carry the power which the device controls.

Control Loop: A feedback circuit used to control an output signal.

Clamp Circuit: A circuit that biases a voltage waveform to a different voltage level.

Clamp Diode: A diode in either a clipper or clamp circuit.

Closed-Circuit Voltage (CCV): The potential or voltage at the terminals of an electrical device when current is flowing.

Convection: The transfer of thermal energy in a gas or liquid by currents resulting from unequal temperatures.

Convection-Cooled Power Supply: A power supply cooled exclusively from the natural motion of a gas or liquid over the surfaces of heat dissipating elements.

Converter: A device that changes the value of a signal or quantity.

Cooling: The process of removing heat dissipated by a power supply during transformation and regulation.

Core: Magnetic material serving as a path for magnetic flux.

Coulomb: The quantity of electricity when one ampere flows for one second, representing 6.24 x 1018 electrons.

Coupling: The characteristic of isolated circuit elements to interact with one another.

Creepage: The movement of electrolyte onto surfaces of electrodes or other components of a cell with which it is not normally in contact.

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

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.

Crowbar: A overvoltage protection circuit which rapidly places a low resistance shunt across the power supply output terminals if a predetermined voltage is exceeded.

Current (I): The rate of transfer of electrical energy measured in amperes.

Current Limiting: An electronic overload protection circuit which limits the maximum output current to a circuit.

Current Mode: The functioning of a power supply so as to produce a stabilized output current.

Current Sensing Resistor: A resistor placed in series with the load to develop a voltage proportional to load current.

Cycle Life: The number of cycles under specified conditions before a device fails to meet specified performance criteria.

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Density: 1) The ratio of mass of material to its own volume. 2) Number per unit.

Derating: The specified reduction in an operating parameter to improve reliability. Generally for power supplies, it is the reduction in output power at elevated temperatures.

Dielectric: An insulating material between conductors.

Differential Mode Noise: The component of noise measured between the dc output and output return.

Diode: A two-element device containing a cathode and an anode that permits flow in one direction and blocks flow from the other.

Direct Current (DC): Flow of electrons in one direction. In text, use lower case: dc.

Discharge: The conversion of the chemical energy of a cell or battery into electrical energy and withdrawal of the electrical energy into a load.

Drift: A change in output over a period of time independent of input, environment or load.

Droop: The decrease in amplitude of a flat top square pulse; a form of square pulse distortion.

Duration: The time interval between the first and last instants at which the instantaneous amplitude reaches a stated fraction of the peak pulse amplitude.

Duty Cycle: 1) The ratio of time on to time off in a recurring event. 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.

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.

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EMI Filter: A circuit composed of reactive and resistive components for the attenuation of radio frequency components being emitted from a power supply.

Effective Value: The value of a waveform that has the equivalent heating effect of a direct current. For sine waves, the value is .707 x Peak Value; for non-sinusoidal waveforms, the Effective Value = RMS (Root Mean Square) Value.

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

Electricity: Property of fundamental particles of matter that have a force field associated with them to gain or lose electrons.

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 electromechanical action.

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 a close enough proximity to discharge.

Electrostatic Shield: A conductive screen that shunts induced electrical energy to ground.

Enclosure: A housing for an electronic device designed to separate and protect both the internal componentary and the outside environment.

Energy: Power output capability in a closed circuit as a function of time.

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 which exactly duplicates the performance of a real capacitor.

Equivalent Series Resistance (ESR): The amount of resistance in series with an ideal capacitor which 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.

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Failure Mode: The way in which a device has ceased to meet specified minimum requirements.

Fan Cooled: A method of forced-air cooling used to maintain design temperatures.

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: C = Q/E

Faraday Shield: An electrostatic shield between input and output windings of a transformer. This can be used to reduce coupling capacitance which in turn reduces output common mode noise.

Fault Mode Input Current: Input current drawn by a power supply with the output short circuited.

Fault Tolerant: A high level of redundancy to provide continued operation following specified failures.

Federal Communications Commission (FCC): A board of commissioners appointed by the President, having the power to regulate all interstate and foreign electrical communications systems and emissions originating in the United States.

Feedback: The process of returning part of the output signal of a system to its input.

Feed Forward: A control technique whereby the line regulation of a power supply is improved by directly sensing the input voltage.

Feed Through: A plated-through hole in a printed circuit board which electrically connects a trace on top of the board with a trace on the bottom side.

Ferroresonance: The property of a transformer design in which the transformer contains two separate magnetic paths with limited coupling between them. The output contains a resonating tank circuit and draws power from the primary to replace power delivered to the load.

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.

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.

Floating Output: Ungrounded output of a power supply where either output terminal may be referenced to another specified voltage.

Flyback Converter: A power supply switching circuit which normally uses a single transistor. During the first half of the switching period the transistor is on and energy is stored in a transformer primary; during the second half period this energy is transferred to the transformer secondary and the load.

Foldback Current Limiting: A power supply output protection circuit whereby the output current decreases with increasing overload, reaching a minimum at short circuit. This minimizes internal power dissipation under overload conditions. Foldback current limiting is normally used with linear regulators and is unnecessary with switching regulators.

Forced Discharge: Discharging a cell or battery, with external battery or power source, below zero volts into voltage reversal.

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.

Frequency: Number of cycles per second measured in hertz.

Frequency Response: Rating of a device indicating its ability to operate over a specified range of frequencies, e.g. gain-frequency characteristics of an amplifier.

Full Bridge Converter: A power switching circuit in which four (4) transistors are connected in a bridge configuration to drive a transformer primary.

Full-Bridge Rectifier: A rectifier circuit that employs four diodes per phase.

Full-Wave Rectifier: Rectifier circuit that produces a dc output for each half cycle of applied alternating current.

Fuse: Safety protective device that permanently opens an electric circuit when overloaded.

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Gate: 1) A device or element that has the ability to block or pass a signal. 2) A device having one output channel and two or more input channels that perform a logic function. 3) A control electrode in a semiconductor device such as a triac, or FET.

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 Bus: A bus to which individual grounds in a system are attached and that in turn is grounded at one or more points.

Ground Loop: A condition that causes undesirable voltage levels when two or more circuits share a common electrical return or ground lines.

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Harmonic Distortion: The distortion of a sinusoidal wave characterized by the presence of harmonics of the fundamental frequency.

Heat Sink: The medium through which thermal energy is dissipated.

Hertz (Hz): The SI unit of measurement for frequency, name in honor of Heinrich Hertz who discovered radio waves. One hertz equals one cycle per second.

Hi-Pot Test (High Potential Test): A test performed by applying a high voltage for a specified time to two isolated points in a device to determine adequacy of insulating materials.

Hiccup: A transient condition that momentarily confuses a control loop.

Holdup 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 Pluggable/Swappable: The ability to add or remove an element from a system while energy is being supplied or dissipated by the element.

Hybrid: The combination of different component technologies on a single substrate.

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Impedance (Z): Total resistance to flow of an alternating current as a result of resistance and reactance.

Inductance (L): The inherent reactive property, measured in henrys, of an electric circuit or circuit element that opposes a change in current flow. Hence, inductance causes changes to lag behind voltage changes.

Inductor: A coil or component with the properties of inductance.

Input Impedance: The impedance of the input terminals of a circuit or device, with the input disconnected.

Input Line Filter: A low-pass or band-reject filter at the input of a power supply which reduces line noise fed to the supply. This filter may be external to the power supply.

Input Voltage Range: The range of input voltage for which a power supply or device operates within specified limits.

Inrush Current: The peak instantaneous input current drawn by a power supply at turn on.

Inrush Current Limiting: The characteristic of a circuit that limits inrush current when a power supply is turned on.

Insulation: Nonconductive materials used to separate electric circuits.

Integrated Circuit (IC): A combination of active and passive circuit elements contained on a single semiconductor substrate.

International Electrotechnical Commission (IEC): Headquartered in Geneva, Switzerland, writes and distributes recommended standards on electrical products and components. The recommendations include references to safety and performance. The IEC does not perform any testing; this function is left to the national testing agencies. National standards are frequently based on IEC publications.

Inverter: A device that changes dc power into ac power.

Isolation: The electrical separation between two circuits, or circuit elements.

Isolation Voltage: The maximum ac or dc specified voltage that may be continuously applied between isolated circuits.

ISO 9000: ISO 9000 is a set of standards created by the 91-nation International Standards Organization (ISO) to define the basics of a quality system for manufacturing, including documentation, controls and worker training.

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L-C Filter: A low pass filter that consists of an inductance (L) and capacitance (C). Also known as an averaging filter.

Leakage Current: 1) The ac or dc current flowing from input to output and/or chassis of an isolated device at a specified voltage. 2) The reverse current in semiconductor junctions.

Leakage Flux: Magnetic lines that go beyond their intended path and do not serve their intended purpose.

Light-Emitting Diode (LED): A semiconductor device that radiates in the visible spectrum when energized by an electric current.

Life Test: A test in which a device is subjected to actual or accelerated use to obtain an estimate of life expectancy.

Line Conditioner: A circuit or device designed to improve the quality of an ac line.

Line Regulation: The percentage change in output due to the input voltage varying over its specified limits, at specified load values, with all other factors constant.

Line Regulator: Power conversion equipment that regulates and/or changes the voltage of incoming power.

Linear Regulation: A regulation technique wherein the control device, such as 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.

Linear Supply: An electronic power supply employing linear regulation techniques.

Line Transient: A perturbation outside the specified operating range of an input or supply voltage.

Load: Capacitance, resistance, inductance or any combination thereof, which, when connected across a circuit determines current flow and power used.

Load Decoupling: The practice of placing filter components at the load to attenuate noise.

Load Impedance: The complex resistance to the flow of current posed by a load that exhibits both the reactive and resistive characteristics.

Load Regulation: 1) Static: The change in output voltage as the load is changed from the specified minimum to maximum and maximum to minimum, 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 dynamic regulation is expressed as a ± percent for a worst case peak-to-peak deviation for dc supplies, and worst case rms deviation for ac supplies.

Logic ground: Common return or reference point for logic signals.

Logic Inhibit/Enable: A referenced or isolated signal that turns a power supply output off or on.

Loop: The path used to circulate a signal.

Loop Response: The speed with which a loop corrects for specified changes in line or load.

Low Line: Lowest specified input operating voltage.

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Master/Slave Operation: Interconnection of two or more regulated supplies in which one (master) controls the others (slaves).

Maximum Load: 1) The highest allowable output rating specified for any or all outputs of a power supply under specified conditions including duty cycle, period and amplitude. 2) The highest specified output power rating of a power supply specified under worst case conditions.

Maximum Power Transfer: Condition that exists when resistance of load equals internal resistance of source.

Mean Time Between Failure (MTBF): The average length of time between system failures, exclusive of infant mortality and rated end-of-life.

Migration: The transportation of ionic species in the electrolyte due to the presence of an electric field.

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 the power supply will turn on and operate safely.

Minus (-): Negative terminal or junction of a circuit, circuit element or power supply.

Modular: 1) A physically descriptive term used to describe a power supply made up of a number of separate subsections, such as an input module, power module or filter module. 2) An individual power unit 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 switching power supply.

Multiple Output Power Supply: A power supply with two or more outputs.

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N+1 Redundancy: The ability to have one extra element in a system act as an on-line replacement for an element that fails.

Negative Regulator: A voltage regulator whose output voltage is negative compared to the voltage at the return.

Negative Temperature Coefficient: A decreasing function with increasing temperature. The function may be resistance, capacitance, voltage, etc.

Network: Two or more components connected in series, parallel or a combination thereof.

Neutral: The ac return somewhere connected to ground, but which should not be used for ground because it is a current-carrying path.

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: The aperiodic random component on the power source output which is unrelated to source and switching frequency. Noise is typically expressed in peak-to-peak units over a specified bandwidth.

Nominal Value: The stated or objective value of a quantity or component, which may not be the actual value measured.

Nominal Voltage: The stated or objective value of a given voltage, which may not be the actual voltage measured.

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Off-Line Power Supply: A power supply switched into service upon line loss to provide power to the load without significant interruption.

Ohm's Law: The fundamental mathematical relationship between current (I), voltage (E) and resistance (R) discovered by George Simon Ohm. E.G. P(Power expressed in watts)=E*I(expressed in amps)

Open-Circuit Voltage (OCV): The difference in potential between the terminals of a cell or voltage when the circuit is open (no-load condition).

Open-Frame Construction: A construction technique where the power supply is not provided with an enclosure.

Open Loop: A signal path without feedback.

Open Loop Gain: Ratio of output signal to input signal without feedback.

Operating Temperature Range: The range of ambient, baseplate or case temperature through which a power supply is specified to operate safely and to perform within specified limits.

Output: The energy or information delivered from or through a circuit or device.

Output Choke: The inductor in the LC filter of the output.

Output Current Limiting: A protective feature that keeps the output current of a power supply within predetermined limits during overload to prevent damage to the supply or the load.

Output Filter: One or more discrete components used to attenuate output ripple and noise.

Output Range: The specified range over which the value of a stabilized output quantity (voltage or current) can be adjusted.

Output Rectifier: A diode(s) used to convert ac to dc in the secondary of the transformer.

Output Voltage: The voltage measured at the output terminals of a power supply.

Overload Protection: A feature that senses and responds to current of 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 Protection (OVP): A feature that senses and responds to a high voltage condition.

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Parallel: The interconnection of power sources in which like terminals are connected such that the combined currents are delivered to a single load.

Parallel Operation: The connection of two or more power sources of the same output voltage to obtain a higher output current.

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 Inverse Voltage (PIV): Maximum value of voltage applied in a reverse direction.

Peak Output Current: The maximum current value delivered to a load under specified pulsed 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 band width and stated, unless otherwise specified, in peak-to-peak values.

Phase Shift: The difference between corresponding points on input and output signal wave forms expressed as degrees lead or lag.

Pi Filter: A filter consisting of two line-to-line capacitors and series inductance in a Pi configuration used to attenuate noise and ripple.

Pin Out: The pin assignment of a device.

Plated Through Hole: A conductive material deposited on the walls of a hole in a printed circuited board.

Plus (+): Positive terminal of a circuit, circuit element or power source.

Polarity: Property of device or circuit to have poles such as north and south, or positive and negative.

Post Regulation: Refers to the use of a secondary regulator on a power supply output to improve line/load regulation and to attenuate ripple and noise.

Pot: Abbreviation for potentiometer.

Potting: An insulating material for encapsulating one or more circuit elements.

Power (P): Measured in watts, P = EI.

Power Density: The ratio of the power available from a power source to its volume, e.g., watts/inch.

Power Factor: The ratio of true to apparent power expressed as a decimal, frequently specified as lead or lag of the current relative voltage.

Power Factor Correction: Technique of forcing current draw to approach being in-phase with the voltage in an ac circuit.

Power Failure Signal: A logic signal from a power supply that provides advance notice that the output voltage is about to fall out of specifications due to loss of line.

Power Rating: Power available at the output terminals of a power source based on the manufacturers specifications.

Power Supply Cord: An assembly of a suitable length of flexible cord provided with an attachment plug at one end.

Primary Circuit: A circuit electrically connected to the input or source of power to the device.

Programmable Power Supply: A power supply with an output controlled by an applied voltage, current, resistance or digital code.

Pulse: A step rise, a level, and a step fall of voltage or current. Characteristics of a pulse are: rise time, duration and fall time.

Pulse Loading: A pulse load imposed on top of the normal output current from a power supply.

Pulse-Width Modulation (PWM): A method of regulating the output voltage of a switching power supply by varying the duration, but not the frequency, of a train of pulses that drives a power switch.

Push-Pull Converter: A power switching circuit that uses two or more power switches driven alternately on and off.

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Radio Frequency Interference (RFI): An undesired radiated or conducted signal in the radio frequency spectrum.

Rail: Either conductor of the output of a supply.

Rated Capacity: The number of ampere-hours a cell or battery can deliver under specific conditions (rate of discharge, end voltage, temperature); usually the manufacturer's rating.

Rated Output Current: The maximum continuous load current a power supply is designed to provide under specified operating conditions.

Recovery Time: The time required for the measured characteristic to return to within specified limits following an abnormal event.

Rectification: The process of changing an alternating current to a unidirectional current.

Rectifier: A component that passes current in one direction, e.g., a diode.

Reference Ground: Defined point in a circuit or system from which potential measurements shall be made.

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: The process of holding constant selected parameters, the extent of which is expressed as a percent.

Regulator: The power supply circuit that controls or stabilizes the output parameter at a specified value.

Relay: A magnetic component or solid state device that opens or closes an isolated switch(es) when a voltage is applied to the control terminals.

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. Remote sensing compensates for specified maximum voltage drops in the load leads.

Resistance (R): Property of a material that opposes the flow of current.

Resonance: The state in which the natural response frequency of a circuit coincides with the frequency of an applied signal, or vice versa, yielding intensified response.

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; it carries the return current for the outputs.

Reverse Polarity: A connection that is opposite to that which is specified or intended.

Reverse Voltage Protection: A circuit or circuit element that protects a power supply from damage caused by a voltage of reverse polarity applied at the input or output terminals.

Ripple: The periodic ac component at the power source output harmonically related to source or switching frequencies. It is typically expressed in peak-to-peak units over a specified band width.

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: For a sine wave, .707 x Peak Value.

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Safety Ground: A conductive path from a chassis, panel or case to earth to help prevent injury or damage to personnel or equipment.

Secondary Output: An output of a switching power supply that is not sensed by the control loop.

Sense Line: The conductor which routes output voltage to the control loop.

Sequencing: The process that forces the order of turn on and turn off of individual outputs of a multiple output power supply.

Series: The interconnection of two or more power sources such that alternate polarity terminals are connected so their voltages sum at a load.

Setting Time: The time for a power supply to stabilize within specifications after an excursion outside the input/output design parameters.

Shelf Life: The duration of storage under specified conditions at the end of which a component or device retains the ability to give a specified performance.

Shield: Partition or enclosure around components in a circuit to minimize the effects of stray magnetic and radio frequency fields.

Short-Circuit: A direct connection that provides a virtually zero resistance path for current.

Short-Circuit Protection: A protective feature that limits the output current of a power supply to prevent damage.

Shunt: A parallel conducting path in a circuit.

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.

Signal Ground: The common return or reference point for analog signals.

Sine Wave: A wave form of a single frequency alternating current whose displacement is the sine of an angle proportional to time or distance.

Slave: A power supply which uses the reference in another power supply, the master, as its reference.

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.

Snubber: An RC network used to reduce the rate of rise of voltage in switching applications.

Soft Start: Controlled turn on to reduce inrush currents.

Source: Origin of the input power, e.g., generator, utility lines, mains, batteries, etc.

Source Voltage Effect: The change in stabilized output produced by a specified primary source voltage change.

Standby Current: The input current drawn by a power supply under no load conditions.

Standoff: A mechanical support used to connect and support a wire or device away from the mounting surface.

Start-Up Delay: The time delay between either applying ac or a remote "on" and the time at which the outputs are in regulation.

Start-Up Sequence: The order of events that occur in a power supply during start-up.

Static Load: A load that remains constant over a given time period.

Status Signals: Logic signals that indicate normal or abnormal conditions of operation, including:
ac lowac okdc lowdc ok

Step Change: An abrupt and sustained change in one of the influence or control quantities of a power supply.

Step-Down Transformer: A transformer with a turns ratio more than one. The output voltage is less than the input voltage.

Storage Temperature: The range of ambient temperatures through which an inoperative power supply 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 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.

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Technischer Uberwachungs-Verein (TUV): Laboratories licensed by the West German government for testing electronic products to DIN, IEC and VDE standards.

Temperature Coefficient: The average percent change in output voltage per degree Centigrade change in ambient temperature over a specified temperature range.

Temperature Derating: The amount by which power source or component ratings are decreased to permit operation at elevated temperatures.

Thermal Protection: A protective feature that shuts down a power supply if its internal temperature exceeds a predetermined limit.

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.

Tolerance: Measured or specified percentage variation from nominal.

Toroid: A round magnetic core with a hole in the middle. A doughnut shaped core.

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.

Transformer: Device which transfers energy from one circuit to another by electromagnetic induction.

Transient: An excursion in a given parameter, typically associated with input voltage or output loading.

Transient Recovery Time: The time required for the output voltage of a power supply to settle within specified output accuracy limits following a transient.

Transient Response Time: The interval between the time a transient is introduced and the time it returns and remains with a specified amplitude range.

Two-Step Charge: A charge which starts at one current and at a predetermined point, continues at a lower current.

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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 Incorporated (UL): American association chartered to test and evaluate products, including power sources. The group has four locations so an applicant can interact with the office closest in the country to his/her own location.

Uninterruptible Power Supply (UPS): A type of power supply designed to support the load for specified periods when the line varies outside specified limits. (CPI does not offer)

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Verband Deutscher Elektrotechniker (VDE): West German organization charged to test and evaluate products, including power sources.

Volt (V): Unit of measurement of electromotive force or potential difference.

Voltage: A derivative electrical quantity, E, measured in the unit Volts and defined in terms of the independently obtained Ampere, I, and unit of resistance, Ohm (R) by Ohm's Law E = IR.

Voltage Drop: Difference in potential between two points in a passive component or circuit.

Voltage Limit: Maximum or minimum value in a voltage range.

Voltage Multiplier: Rectifier circuits that produce an output voltage at a given multiple greater than input voltage, usually doubling, tripling or quadrupling.

Voltage Regulation: The process of holding voltage constant between selected parameters, the extent of which is expressed as a percent.

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Warmup Drift: The change in output voltage of a power source from turn on until it reaches thermal equilibrium at specified operating conditions.

Warmup Time: The time required after a power supply is initially turned on before it operates according to specified performance limits.

Watt (W): Unit of measurement of power equal to 1 joule/sec. (W = EI). Power (W) = DC Volts(E) X Amps(I). Ex. 5V X 3A = 15 Watts

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.

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