Knowledge Base


View Glossary Terms:

A Symbol for Ampere
Abnormal Failure The failure of a component resulting from an induced condition that causes a malfunction of the device.
Absolute Accuracy The correctness of the indicated value in terms of its deviation from the true or absolute value.
AC In text, use lower case: ac. Abbreviation for Alternating Current
AC Line The set of conductors that route ac voltage from one point to another.
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.
Ah Abbreviation for Ampere-Hour
Alive (Live) Electrically connected to a source of voltage difference or electrically charged so as to have a voltage different from that of earth; the term may be used in place of 'current-carrying' where the intent is clear, to avoid repetition of the longer term.
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 that 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. See also Operating Temperature, Storage Temperature, Temperature Coefficient
Ampere (A) Electron or current flow representing the flow of one coulomb per second past a given point in a circuit.
Ampere-Hour (Ah) A measurement of quantity of electricity computed as the product of current (in amperes) and time (in hours).
Ampere-Hour Capacity The quantity of electricity measured in ampere-hours (Ah) which may be delivered by a cell or battery under specified conditions.
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.
Amplifier A circuit or element that provides gain.
Amplifier, DC A direct coupled amplifier that can provide gain for zero-frequency signals.
Amplifier, Differential An amplifier which has available both an inverting and a non-inverting input, and which amplifies the difference between the two inputs.
Amplifier, Inverting An amplifier whose output is 180 degrees out of phase with its input. Such an amplifier can be used with degenerative feedback for stabilization purposes.
Amplifier, Non-inverting An amplifier whose output is in phase with its input.
Amplifier, Operational A dc amplifier whose gain is sufficiently large that its characteristics and behavior are substantially determined by its input and feedback elements. Operational amplifiers are widely used for signal processing and computational work.
Apparent Power Power value obtained in an ac circuit as the product of current times voltage. See VA.
Attenuation Decrease in amplitude or intensity of a signal.
Authorized Person A qualified person who, by nature of his duties or occupation, is obliged to approach or handle electrical equipment or, a person who, having been warned of the hazards involved, has been instructed or authorized to do so by someone in authority.
Auto-ranging Input An input voltage sensing circuit in the power supply that automatically switches to the appropriate input voltage range (90-132 VAC or 180-264 VAC). Sometimes known as Auto-select input. See also Universal Input.
Auxiliary Supply A power source supplying power other than load power as required for the proper functioning of a device.
Available Capacity The total capacity, Ah or Wh, that will be obtained from a cell or battery at defined discharge rates and other specified discharge or operating conditions.
AWG Abbreviation for American Wire Gauge
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.
Baseplate Mounting platform for power supply components.
Baseplate Temperature The temperature at the hottest spot on the mounting platform of the supply.
Basic Insulation The insulation applied to live parts to provide basic protection against electric shock.
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 Back-up Battery support to maintain function of selected components or devices.
Battery Charger Electrical equipment designed to restore capacity to secondary batteries.
Battery Voltage The total voltage between the positive and negative terminals of the battery. See also Nominal Voltage, Voltage, Working Voltage
Bead A small ferrite normally used as a high frequency inductor core.
Bench Power Supply A power source fitted with output controls, meters, terminals and displays for experimental bench-top use in a laboratory.
Bipolar Transistor A junction transistor having both majority and minority charge carriers.
Bit A binary unit of digital information having a value of "0" or "1". See also Byte
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.
Bobbin A non-conductive material used to support windings.
Boost Charge A charge, generally at high-rate, far a limited period to restore capacity in all cells of a battery.
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 1) The voltage level which causes insulation failure. 2) The reverse voltage at which a semiconductor device changes its conductance characteristics.
Bridge Circuit Circuit with series-parallel groups of components.
Bridge Rectifier Full-wave rectifier circuit employing two or more rectifiers in a bridge configuration.
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.
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. In power supplies, a period during which a supply is energized and loaded to peak output, with the intent of finding potentially weak components. Typical burn-in tests can include temperature cycling, input cycling, and/or load cycling
Byte A sequence of binary digits, frequently comprised of eight (8) bits, addressed as a unit. See also Bit
C Variously, the abbreviation for capacitance, capacitor, Celsius, centigrade and coulomb.
C/10 rate = 500 Ah/10 = 50 A ?
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.
Capacitance, Distributed The capacitance in a circuit resulting from adjacent turns on coils, parallel leads and connections.
Capacitive Coupling Coupling resulting from the capacitive effect between circuit elements.
Capacitive Effect Leakage Current The current flow between segregated conductive metal parts; voltage and frequency dependent.
Capacitive Reactance (XC) Opposition to ac as a result of capacitance.
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 of current (A) or power (W) over a specified period of time (Ah or Wh).
Carry-Over See Holdup Time
Catch Diode See Free Wheel Diode
CCV Abbreviation for Closed-Circuit Voltage
CE A mark applied to an end-use product certifying that the product meets "applicable directives" and can be sold in Europe. "Certified Europe" is the result of the "harmonization" or unification of European safety and other standards. Each type of end-use equipment has "applicable directives" which must be met in order to display the CE mark. Power supplies intended for use within an end-use system are not required to have a CE mark. However, many power supply manufacturers offer CE-certified power supplies which have been tested to the applicable directives which the power supply manufacturer believes will be necessary for the anticipated end-use equipment.
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 Voltage The dc voltage potential between the individual positive and negative terminals of a cell in a battery. See also Nominal Voltage, Voltage, Working Voltage
Centimeter Gram-Second Unit (CGS Unit)-An absolute unit based on the centimeter, gram and second as fundamental units.
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 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 expressed as:
Charge Voltage The voltage applied to a cell during charge.
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
Chassis The structure supporting or enclosing the power supply.
Chassis Ground The voltage potential of the chassis.
Choke Coil An Inductor
Choke, RF A choke coil with a high impedance at radio frequencies.
Circuit Input Filter A filter employing an inductor (L) or an inductor/capacitor (LIC) 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.
Clearance Distance The shortest path separating two conductors or two circuit components.
Clock An oscillator producing timing pulses to synchronize various elements of a system. In switching mode power supplies, a clock is used to produce the power pulses that are modulated to control power transfer. In digital interfaces that communicate on a bus (such as the IEEE-488) a clock is used to synchronize the data transfer and commands.
Closed Loop Buck Converter A circuit where energy is pulsed to an averaging LIC filter and delivered to a load.
Closed Loop Gain In a feedback control circuit, the increase in value of an output signal due to the effects on it of various other components or signals in the circuit. See also Gain
Closed-Circuit Voltage (CCV) The potential or voltage at the terminals of an electrical device when current is flowing.
Collector 1) Electronic connection between the electrochemical cell electrode and the external circuit. 2) In a transistor, the semiconductor section which collects the majority carriers.
Common Choke See Integrated Magnetics
Common Point With respect to operationally programmable power supplies one output/sense terminal is designated "common to which load, reference and external programming signal all return.
Common-Mode Noise The component of noise voltage that appears equally and in phase on conductors relative to a common reference.
Communications Port A standard communications interface, such as an IEEE 488 or RS-232, that provides information flow from a processor to a peripheral device, such as a power supply.
Comparison Amplifier A dc amplifier which compares one signal to a stable reference, and amplifies the difference to regulate the power supply power-control elements.
Compensation The addition of circuit elements to assist in stabilization of a control loop.
Compliance Agency certification that a product meets its standards. See also Safety Compliance
Compliance Range Range of voltage needed to sustain a given constant current throughout a range of load resistance.
Compliance Voltage The maximum dc output voltage of a constant current supply.
Component An element in an electrical circuit.
Conductance (G) The ability to conduct current. It is equal to amperes per volt, or the reciprocal of resistance, and is measured in siemens (metric) or mhos (English). G = 1/R
Conductor Material which permits free motion of large number of electrons.
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 Charge A charge during which the current is maintained at a steady state value.
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, load, ambient temperature and time. Constant current supplies are sometimes used to drive certain types of loads (such as large incandescent lamps) or in certain applications where very long output leads can result in significant induced noise and resistive losses (such as industrial environments).
Constant Voltage Charge A charge during which the voltage across the battery terminals is maintained at a steady state.
Constant Voltage Power Supply A power supply that regulates its output voltage within specified limits, against changes in line, load, ambient temperature and time.
Constant Voltage Transformer Maintains approximately constant voltage ratio over the range from zero to rated output.
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 a liquid over the surfaces of heat dissipating elements.
Converter A device that changes the value of a signal or quantity. Examples: DC-DC; a device that delivers dc power when energized from a dc source. Fly-Back; a type of switching power supply circuit. See also Flyback Converter. Forward; A type of switching supply circuit. See also Forward Converter
Cooling The process of removing heat dissipated by a power supply during transformation and regulation.
Cooling: Forced air Forced air cooling ratings may be specified in either linear feet per minute (LFM), cubic feet per minute (CFM), or pound mass per minute (lb/mm). Linear feet per minute ratings are a more valid measure of the air flow because they specify exactly where the air flows and directly relate to heat transfer. However, CFM values are usually specified. Flow measured in lb/mm is most useful when dealing with varying air densities or high altitude, and is calculated by CFM and density (lb/w). This application note explains the relationship between forced air specifications in linear feet per minute and in cubic feet per minute. This application note applies to all Astec power supplies requiring forced air cooling. To Convert from CFM to LFM and LFM to CFM given the cross sectional area: To convert from CFM to LFM and vice-versa, we need the cross section area of the power supply. This would be the actual area that the air is being blown through. The formula is CFM LFM x cross sectional area. A popular selection is 2.5" x 5.0". This corresponds to 0.0868 square feet. For any fixed cross sectional area, the relationship is linear and can be shown with a graph.
Cord Set An assembly of a suitable length of flexible cord provided with an attachment plug at one end and a second 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 molecules in an iron core to orient in one direction due to the application of direct current.
Coulomb The quantity of electricity when one ampere flows for one second, representing 6.24 x 1018 electrons. See also Current, Faraday
Coupled Choke See Integrated Magnetics
Coupling The characteristic of isolated circuit elements to interact with one another. See also Coefficient of Coupling
Creepage The movement of electrolyte onto surfaces of electrodes or other components of a cell with which it is not normally in contact.
Creepage Distance The shortest distance separating two conductors as measured along a surface touching both conductors.
Crowbar An overvoltage protection circuit which rapidly places a low resistance shunt across the power supply output terminals if a predetermined voltage is exceeded.
Cuk Converter A variation of the buck/boost topologies.
Current (l) The rate of transfer of electrical energy 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 Control See Current Stabilization
Current Density The current per unit active area of the surface of an electrode.
Current Fed Supply A buck regulator with a choke in the primary.
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, or limit.
Current Limiting An electronic overload protection circuit which limits the maximum output current to a preset value. See also Output Current Limiting
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.
Current Source A power source that tends to deliver constant current.
Current Stabilization The process of controlling an output current.
Current Transformer 1) Instrument Transformer: Intended to have its primary winding connected in series with the conductor carrying the current to be measured or controlled. 2) Metering: Designed for use in the measurement or control of current. Its primary winding may be single turn or bus bar, and is connected in series with the load. 3) Power and Distribution Transformer: Intended to have its primary winding connected in series with the conductor carrying the current to be measured or controlled. (In window-type 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 terminated. The cutoff voltage is specified by the cell manufacturer and is generally a function of discharge rate.
CW Abbreviation for Continuous Wave
Cycle A period of time in which recurring events are completed.
Cycle Life The number of cycles under specified conditions before a device tails to meet specified performance criteria.
D Variously, the symbol for diameter, drain and deuterium.
DB Abbreviation for Decibel
DC In text, use lower case: dc, Abbreviation for Direct Current
DC Component The dc value of an ac wave that has an axis other than zero.
DC/DC Converter A circuit or device that changes a dc input signal value to a different dc output signal value.
Debug The process of detecting and correcting errors.
Decay Time See Fall Time
Decibel The numerical expression of the relative loudness of two signals, such as sound. The difference in decibels between two signals is ten times the common logarithm of the ratio of their powers.
Dedicated Set aside for a special purpose.
Density 1) The ratio of mass of material to its own volume. 2) Number per unit.
Destructive Testing A test to determine the point at which a device catastrophically fails.
Differential Mode Noise The component of noise, excluding common-mode noise, that is measured between two lines with respect to a common reference point. The value is the difference of the noise components on the two lines.
Differential Voltage The difference in voltages at two points as measured with respect to a common reference.
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.
Direct Plug-In A device that engages a receptacle without a cord.
Double-Layer Capacitance The capacitance of the double layer.
Drift A change in output over a period of time independent of input, environment or load. For power supplies, the change in DC output as a function of time at constant line voltage, load, and ambient temperature. Normally specified for an eight hour period after a half hour warm-up.
Driver A current amplifier used for control of another device or circuit.
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 a 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.
Earth An electrical connection to the earth frequently using a grid or rod(s). See also Ground
Eddy Current Loss Energy loss resulting from eddy currents circulating in a magnetic material.
Eddy Currents A circulating current induced in a conducting material by a varying magnetic field.
Efficiency 1) The ratio of total output power to total input power, expressed as a percentage, under specified conditions. For power supplies efficiency is generally measured at full load with nominal line conditions. 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
Electrical Double Layer See Double Layer
Electricity Property of fundamental particles of matter that have a force field associated with them to gain or lose electrons.
Electrolytic Capacitor A device that contains two electrodes separated by an electrolyte.
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. For power supplies, unwanted energy, generally emitted from switching power supplies, which may be conducted or radiated.
Electron(e?) Negatively charged particle.
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.
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.
EMI Abbreviation for Electromagnetic Interference
EMI Filter A circuit composed of reactive and resistive components for the attenuation of radio frequency components being emitted from a power supply. See also EMI
EMI Filtering Process or network of circuit elements to reduce electromagnetic interference emitted from or received by an electronic device. See also EMI
Enclosure A housing for an electronic device designed to separate and protect both the internal componentry and the outside environment.
Equivalent Circuit An electrical circuit that models the fundamental properties of a device or circuit.
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.
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 Abbreviation for Electrostatic Discharge
ESL Abbreviation for Equivalent Series Inductance
ESR Abbreviation for Equivalent Series Resistance
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 = QIE
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
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 failure
Fe Symbol for iron.
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.
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 a top of the beard with a trace on the bottom side.
Feedback The process of returning part of the output signal of a system to its input.
Ferrite A ceramic material that exhibits low loss at high frequencies, and which contains iron oxide mixed (with oxides or carbonates of one or more metals such as manganese, zinc, nickel or magnesium.
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 Transformer An AC regulator designed to operate at a given input frequency and which uses a resonant circuit to achieve regulation. Although the regulation is imprecise, the device itself is simple, very rugged and reliable. Typically operating at 50Hz or 60Hz, these "iron-core" (actually laminated silicon steel) transformers incorporate a capacitor in one of the secondaries that resonates with the inductance of the transformer. An excessively high input AC voltage which would otherwise result in excessive secondary voltage will cause the resonant circuit voltage to ring high enough to locally saturate the transformer core. Once saturated, the primary winding magnetic flux no longer links the secondary winding and the secondary voltage is limited.
FET Abbreviation for 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. See also Junction Field Effect Transistor, Metal Oxide, Semiconductor Field Effect Transistor
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 which 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.
Flash Current See Short-Circuit Current
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 for retaining a charged battery in a fully charged condition. This is also known as float charging.
Floating Output ungrounded output of a power supply where either output terminal may be referenced to another specified voltage.
Flooded Cell A cell design which incorporates an excess amount of electrolyte.
Flux Total number of lines of magnetic force.
Flux Density (B) Number of lines of flux per cross-sectional area of a magnetic circuit expressed in Gauss.
Flyback Converter A power supply switching circuit which normally uses a single transistor. During the first half of the switching cycle the transistor is on and energy is stored in a transformer primary; during the second half of the switching 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 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 not necessary to protect switching regulators. However, many switchers incorporate foldback to protect the load form excessive current.
Forward Converter A power supply switching circuit that transfers energy to the transformer secondary when the switching transistor is on
Free Wheel Diode A diode in a pulse-width modulated switching power supply that provides a conduction path for the counter electromotive force of an output choke.
Full-Bridge Converter A power switching circuit in which four power switching devices 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. See also Over-current Device, Overcurrent Protective Device
G Variously, the symbol for gram conductance
Gain Ratio of an output signal to an input signal. See also Closed Loop Gain, Gain Margin, Open Loop Gain
Gain Margin The gain of a control loop at the frequency for which there is 360 degrees of phase shift around the control loop.
Gap A non-magnetic segment in the magnetic path in a transformer or choke.
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 performs a logic function. 3) A control electrode in a semiconductor device such as a triac, or FET.
Gauss Measure of flux density in Maxwells per square centimeter of cross- sectional area. One gauss is iC-4 Tesla.
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. (National Electric Code)
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 ampacity to carry any fault current liable to be imposed on it, and of a sufficiently low impedance to limit the voltage rise above ground.
h Variously the abbreviation for height, hour
H Variously, the symbol for Henry, Magnetic Field Strength, or Magnetomotive Force.
Half-Bridge Converter A switching power supply design in which two power switching devices are used to drive the transformer primary. See also Bridge Rectifier
Half-Wave Rectifier A circuit element, such as a diode, that rectifies only one-half the input ac wave to produce a pulsating dc output.
Heat Sink The medium through which thermal energy is dissipated.
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.
High Line Highest specified input operating voltage.
High Voltage Power Supply A power supply with an output voltage of 100V or more. High Voltage power supplies often use air as the primary dielectric medium, avoiding the weight and serviceability problems associated with other dielectrics. Most high voltage supplies are of two types. The first type is simply a step-up power transformer with rectified and filtered (but otherwise unregulated) high voltage secondary. This is the most straightforward, efficient, and lowest cost power supply because of its simplicity. The second basic type is essentially a switcher with a string of voltage doublers that provide the high voltage output. As a switcher, the second type enjoys heat, weight and size advantages over the first type. By employing pulse width modulation, the switcher's output can be regulated. On the negative side, the switcher includes an input energy storage cap that sustains the high voltage output even if the AC power is cut off. This can result in a safety hazard. Product selection requires extra attention to the design features and construction techniques that contribute to safety and protection against failures. Pulse-width modulation and full-wave/symmetrical cascade high voltage multipliers, with surge limiting resistors, contribute to high efficiency and reliability.
Hipot 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. For power supplies, it is often a test to determine if the breakdown voltage of a transformer or power supply exceeds the minimum requirement.
Hysteresis 1) The property of a magnetic substance that causes magnetization to lag behind the 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 in a cyclically magnetized material: one when the magnetizing force is increasing, the other when it is decreasing.
Hysteresis Loss Energy dissipated due to molecular friction as domains move through cycles of magnetization.
Hz Abbreviation for Hertz
I Symbol for electric Current
I2R Loss See Copper Loss
IC Abbreviation for Integrated Circuit
Impedance (Z) Total resistance to flow of an alternating current as a result of resistance and reactance. Also the ratio of voltage to current in AC circuits, containing both resistance and reactance terms, usually expressed as ohms.
Impedance Matching (Z Match) The connection across a source impedance of a matching impedance to allow optimum undistorted energy transfer.
Induced Current Current that flows as a result of an Induced EMF (Electromotive Force).
Inductance (L) inherent reactive property, measured in henrys, of an electric circuit or circuit element that opposes a change in current flow. Hence, inductance causes current changes to lag behind voltage changes. See also Henry
Inductive Circuit Circuit in which an EMF is produced by a changing current.
Inductive Reactance (XL) Opposition to a changing current as a result of inductance:
Inductor A coil or component with the properties of inductance.
Input AC The sinewave input voltage normally specified in volts RMS. An input waveform that is not sinusoidal, such as a square wave or distorted sinewave wave (from a UPS) can affect power supply operation and must be defined. Contact Professor Power for information on derating of standard catalog power supplies for voltage, frequency, and wave shape variations beyond those specified in the catalog.
Input DC The DC level normally specified in volts. Lower DC voltages can cause heating and limit output power. Contact Professor Power for information on derating at low input voltage.
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 or fed onto the input power lines. This filter may be external to the power supply.
Input Pi Filter See Pi Filter
Input Reflected Ripple Current (DC/DC converters) The AC ripple current measured at the input and generated by the switching action of the converter. Low ESR (Effective Series Resistance) input capacitors are used to reduce the input ripple voltage caused by the ripple current.
Input Surge See Inrush Current
Input Voltage Range The range of input voltage values for which a power supply or device operates within specified limits.
Inrush Current The peak instantaneous input current drawn at turn on by a power supply.
Inrush Current Limiting The characteristic of a circuit that limits inrush current when a power supply is turned on.
Insulation Non-conductive materials used to separate electric circuits.
Insulation Resistance The resistance of an insulating material to the flow of current resulting from an impressed dc voltage. Usually measured in megohms.
Integrated Circuit (IC) A combination of active and passive circuit elements contained on a single semiconductor substrate.
Integrated Magnetics A magnetic component in which separate circuit elements share a common core segment.
Interleaved Transformer Windings The segmentation of portions of the same winding by another to improve or control inductive coupling.
Internal Impedance The impedance exhibited by a circuit element or component.
Internal Resistance 1) The resistance exhibited by a circuit element or component. 2) The opposition or resistance 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.
Inverter 1) A device that changes dc power into ac power. 2) A circuit, circuit element or device that inverts the input signal.
IR Drop See Voltage Drop
Iron Core A general class of cores that contain iron. Sometimes used to refer to cores made only from steel laminations. See also Core, Ferrite, Powdered Iron Core
ISO9000 The International Standards Organization quality assurance system is gaining popularity around the world. ISO9000 is the overall standard. ISO9001 is the most stringent standard, which requires a complete quality system including engineering and design, resource planning, documentation, installation and service. ISO9002 contains quality requirements for product production and installation. ISO9003 pertains only to inspection and testing. ISO9004 gives detailed directions for implementing each of the ISO9000 standards.
Isolation The electrical separation between input and output of a power supply by means of the power transformer. The isolation resistance (normally in megaohms) and the isolation capacitance (normally in picofarads) are generally specified and are a function of materials and spacings employed throughout the power supply.
Isolation Transformer A transformer with a one-to-one turns ratio. See also Step-Down Transformer, Step-Up Transformer, Transformer
Isolation Voltage The maximum ac or dc specified voltage that may be continuously applied between isolated circuits.
J Symbol for Joule
JFET Abbreviation for Junction Field Effect Transistor. See also 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, and Kelvin.
Kelvin (K) 1) Unit of temperature in the International System of Units (SI) equal to the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The Kelvin temperature scale uses Celsius degrees with the scale shifted so 0 K is at absolute zero. Add 273.16 to any Celsius value to obtain the corresponding value in Kelvins. 2) A technique using 4 terminals to isolate current carrying leads from voltage measuring leads.
kW Symbol for kilowatt
kWh Symbol for kilowatt-hour.
L Variously, the symbol for Inductance and length, and the abbreviation for liter.
L-C Filter A low pass filter that consists of an inductance (L) and a capacitance (C). Also known as an averaging filter/
Layer Winding The method of winding a transformer or choke whereby conductors are layered one top of another, commonly separated by an insulating layer.
Lead Resistance DC resistance in the leads of a circuit element or device.
Lead-Acid Cell Secondary cell which uses lead peroxide and sponge lead for plates, and sulfuric acid water for electrolyte.
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 of force that go beyond their intended path and do not serve their intended purpose.
Leakage Inductance Self inductance in a transformer caused by leakage flux.
LED Symbol for Light-Emitting Diode
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 sulphide emits light in the 555 nanometer (green) range, the area of peak sensitivity of the human eye.
Line 1) Medium for transmission of electricity between circuits or devices. 2) The voltage across a power transmission line. See also High Line, Low Line
Line Conditioner A circuit or device designed to improve the quality of an ac line.
Line Effect See Line Regulation
Line Frequency Regulation The percentage change in output for a specified change in the line frequency at specified load values, with all other factors constant.
Line Power Supply 1) A power supply 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. See also Uninterruptible Power Supply
Line Regulation The change in value of DC output voltage resulting from a change in AC input voltage over a specified range, or from low line to high line or from high line to low line. Normally specified as the + or
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 1) In a straight line. 2) A mathematical relationship in which quantities vary in direct proportion to one another, the result of which, when plotted, forms a straight line.
Linear Power Supply An electronic power supply employing linear regulation techniques. "Linears" can provide fast transient response, very precise output regulation, very low output PARD (noise), and excellent isolation from the source voltage. They are also larger (about 10X) heavier (about 10X) and generate more heat (about 5X) compared to an equivalent switcher. Linear supplies typically utilize a 50Hz - 60Hz transformer to provide an isolated lower unregulated secondary voltage that is then regulated with a "linear pass device". The pass device is usually a transistor controlled with a local feedback loop.
Linear Regulation A regulation technique wherein the control device, such as a transistor, is placed in series or parallel with the load. The output voltage is regulated by varying the effective resistance of the control device to dissipate the power resulting from the difference between input and output voltage time the current. See also Linear Power Supply
Linear Regulator A power transistor or device connected in series with the load of a constant voltage power supply in such a way that the feedback to the series regulator changes its voltage drop as required to maintain a constant dc output.
Linearity 1) The ideal property wherein the change in the value of one quantity is directly proportional to the change in the value of another quantity, the result of which, when plotted on graph, forms a straight line. 2) Commonly used in reference to Linearity Error
Linearity Error The deviation of the output quantity from a specified reference line.
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 attentuate noise.
Load Effect See Load Regulation
Load Impedance The complex resistance to the flow of current posed by a load that exhibits both the reactive and resistive characteristics.
Load Line Shaper See Snubber
Load Regulation 1) Static: The change in output voltage as the load is changed from 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 rate of change shall be expressed as current/unit of time, e.g., 20 amperes A/u second. 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.
Load Transient Overshoot See Overshoot
Load Transient Response Time See Transient Recovery Time
Local Control Control over the stabilized output signal by means located within or on the power supply. May or may not be calibrated.
Local Sensing Using the power supply output voltage terminals as the error-sensing points to provide feedback to the voltage regulator.
Logic Ground Common return or reference point for logic signals.
Logic High A voltage representing a logic value of one (1) in positive logic.
Logic Inhibit/Enable A referenced or isolated logic signal that turns a power supply output off or on.
Logic Low A voltage representing a logic value of zero (0) in positive logic.
Long-term Stability The output voltage change of a power supply, in percent, due to time only, with all other factors held constant. Long-term stability is a function of component aging.
Low Line Lowest specified input operating voltage.
M Symbol tar Mutual Inductance
Magnetic Amplifier Transformer type device employing a control circuit to vary the magnetic core saturation, thus varying the output voltage of the amplifier.
Magnetic Field Strength (H) See Magnetomotive Force
Magnetic Flux Total number of lines of magnetic force. See also Flux
Magnetic Flux Density The number of lines of flux per cross-sectional area of a magnetic circuit expressed in Gauss or Tesla. Sometimes referred to as Magnetic Induction.
Magnetic Gap See Air Gap
Magnetic Induction The use of a magnetic field to generate currents or voltages in a conductor sometimes referred to as Magnetic Flux Density.
Magnetizing Current The no-load current in the transformer primary winding that is required to magnetize the core. Sometimes called exciting or excitation current.
Margining The ability to temporarily shift output voltage by a specified amount (often +/- 5%) for system testing.
Master/Slave Operation Interconnection of two or more regulated supplies in which one (the master) controls the others (the 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 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. An established method of calculating MTBF is described in Mil Handbook 217.
Mean Time to Repair (MTTR) The average time required to repair a product.
Metal Oxide Semiconductor Field Effect Transistor (MOSFET) See Field Effect Transistor
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 continuously operate safely and within specifications.
Minimum Starting Temperature The lowest ambient temperature at which a power supply will turn on and operate safely.
Mismatch Incorrect matching of load and source impedance.
MOSFET Abbreviation for Metal Oxide Semiconductor Field Effect Transistor
MTBF Abbreviation for Mean Time Between Failure
MTTR Abbreviation for Mean Time to Repair
Multimeter A meter capable of measuring current, voltage and resistance.
Multiple Output Power Supply A power supply with two or more outputs.
Mutual Inductance (M) A measure of the amount of inductive coupling between two coils.
Mylar A registered trade mark of El Dupont De Nemours & Co. for polyethylene terephathalate. The polyester film is a common insulating material used in transformers, capacitors, etc.
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. See Off-Load, Open Circuit Voltage
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. Unless specified otherwise, noise is 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 measured.
O Symbol for oxygen
OCV Abbreviation for Open-Circuit Voltage
OEM original equipment manufactuter
Off-Load Voltage See Open-Circuit Voltage
Offset Current The direct current that appears as an error at either input terminal of a dc amplifier when the input current 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 (O) Unit of measure of Resistance.
Ohm's Law The fundamental mathematical relationship between current (I), voltage (E) and resistance (~ discovered by George Simon Ohm. The passage of one Ampere through one Ohm produces one Volt.
On-Line Power Supply A power supply that continuously provides output power to the load without any interruption. See also Uninterruptible Power Supply
On-Load Voltage The difference in potential between the terminals of a cell or battery when it is discharging.
OP-AMP Abbreviation for Operational Amplifier
Open-Circuit Voltage (OCV) The difference in potential between the terminals of a cell or voltage when the circuit is open (no-load condition). See No Load Voltage
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. See also Ambient Temperature, Storage Temperature
Operational Amplifier (OP-AMP) A high gain differential input device that increases the magnitude of the applied signal to produce an error voltage.
Operational Power Supply A power supply with a high open loop gain regulator which acts like an operational amplifier and can be programmed with passive components.
Opto-Coupler A package that contains a light emitter and a photoreceptor used to transmit signals between electrically isolated circuits.
Opto-Isolator See Opto-Coupler
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. Also see Current Limiting
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 Impedance The impedance that a power supply appears to present to its output terminals.
Output Inductor See Output Choke
Output LC Filter The low pass filter in the secondary of a switching power supply that smooths the rectified output to its average value. Also called an averaging filter.
Output Range The specified range over which the output voltage or current can be adjusted.
Output Rectifier A diode(s) used to convert ac to dc in the secondary of the transformer.
Output Ripple and Noise Output ripple is the periodic AC component imposed on the output voltage of a converter. Output noise refers to unwanted variations in the converter output that are unrelated to the switching frequency. Ripple and noise are typically specified together as a peak-to-peak value over a specified bandwidth. Ripple and noise is sometimes referred to as Periodic And Random Deviation (PARD). Care must be taken when measuring output noise and ripple not to induce errors in the test instrumentation. Attach a twisted wire pair (about 1 foot in length) with three twists per/inch between the converter outputs and an appropriate load. Connect a 33 uF electrolytic capacitor across the load. Using an oscilloscope with a minimum bandwidth of 20 MHz and a probe with the ground clip disconnected, measure the ripple at the connection of the load and twisted pair wires. This method eliminates the 'common mode noise" that interferes with measurements made directly at the converter output pins. Also see Periodic and Random Deviation
Output Voltage The voltage measured at the output terminals of a power supply.
Output Voltage Accuracy the maximum allowable deviation of the DC output from its ideal or nominal value. Output voltage accuracy is sometimes called "output voltage tolerance" or "output voltage setpoint" and is commonly given as a percentage of output voltage.
Overcurrent Device A device capable of automatically opening an electric circuit, both under predetermined overload and short-circuit conditions, either by fusing of metal or by electro-mechanical means.
Overcurrent Protection See Output Current Limiting
Overload Protection Power supply protection based on power supply input power. Many low cost switching power supplies have no method to control or limit output current. The easiest and least expensive protection method is sensing input power. If input power becomes excessive, you assume that one power supply output must have an excessive load. Some overload circuits permanently shut down the power supply; others will automatically recover when the fault is removed. Also see Output Current Limiting
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 1) The potential difference between the equilibrium of an electrode and that of the electrode under an imposed polarization current. 2) A voltage that exceeds specified limits.
Overvoltage Protection (OVP) A power supply feature which shuts down the supply usually by firing a crowbar or clamping the output when an output voltage exceeds a preset level. See also Overvoltage, Crowbar
OVP Abbreviation for Overvoltage Protection
P Variously, the abbreviation for Power, 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.
Paralleling Connecting the output of two or more supplies together, either for the purpose of delivering additional current or creating redundancy. The reliability of a power system is critical to overall system performance. Indeed, the requirements for power systems are generally higher than those for the system overall. A cost effective way to provide very high levels of reliability is to connect a number of independent power supply units in parallel, such that if one power supply fails, the remaining power supplies will continue delivering sufficient current to supply the maximum system load without any interruption. This architecture is often referred to as an (n+x) redundant power supply. If any one of several paralleled supplies can fail without causing the entire system to fail, the power system is said to be (n+1) redundant. If any two of several paralleled supplies can fail without causing the entire system to fail, the power system is said to be (n+2) redundan. By allowing the live removal or insertion of power supply boards to and from the system power bus, a "hot pluggable" redundant power supply system provides a practical way to achieve the zero down time required in critical applications such as mainframe computer systems and telecommunications systems. In practice, (n+x) redundancy can be difficult to achieve. Connecting power supplies in parallel and ensuring that the failure of one parallel supply unit does not affect the remainder presents particular difficulties, ruling out paralleling schemes such as master-slave configurations entirely.
Pb Symbol for lead.
Peak Maximum value of a waveform reached during a particular cycle or operating time.
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 bandwidth and stated, unless otherwise specified, in peak-to-peak values. See Output Ripple and Noise
Phase Angle The angle that a voltage waveform leads or lags the current waveform.
Phase Shift The difference between corresponding points on input and output signal wave forms (not affected by magnitude) expressed as degrees lead or lag.
Pi Filter A filter consisting of two line-to-line capacitors and a series inductance in all configuration used to attenuate noise and ripple.
Polarity Property of device or circuit to have poles such as north and south or positive and negative.
Pot Abbreviation for potentiometer. Also, name of plant grown in Mendicino County, California.
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. See also Core, Ferrite, Iron Core
Power (P) 1) Measured in watts, P=EI, 12R or E2/R: 1 watt = 1 joule/second, 1 joule = 1 watt-second 2) In a resistive circuit, power is the product of the in-phase components voltage and current (volt-amperes). See also Apparent Power, True Power
Power Factor The ratio of true to apparent power expressed as a decimal. It has been frequently specified as lead or lag of the current relative to voltage. However, switching power supplies have almost no phase shift but a significant difference between true and apparent power. Thus a switcher's power factor is measured with special equipment. Also see VA.
Power Factor Correction 1) Technique of forcing ac current draw to either approach being in-phase with the voltage waveform or approach a pure sinewave 2) Addition of capacitors to an inductive circuit to offset the reactance and subsequent phase shift. Also see VA.
Power FET Specialized field effect transistor designed for high current or high power applications.
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, cell, battery, power pack, power supply, solar 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. Typical application of power supplies include to convert raw input power to a controlled or stabilized voltage and/or current for the operation of electronic equipment.
Power Supply Cord An assembly of a suitable length of flexible cord provided with an attachment plug at one end. See also Cord Set
Pre-regulation The initial regulation circuit in a system containing at least two cascade regulation loops.
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 switching power supply with the pulse-width modulator in the primary.
Primary Winding A driven coil in a transformer
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 or signal.
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-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.
Pulse-Width Modulator (PWM) An integrated discrete circuit used in switching-type power supplies, to control the conduction time of pulses produced by the clock.
Push-Pull Converter A power switching circuit that uses two or more power switches driven alternately on and off.
PWM variously, the abbreviation for Pulse-Width Modulation, Pulse-Width Modulator
Q The energy-storing characteristic of an electronic circuit, system or device, equal to reactance divided by resistance. Q determines rate of decay of stored energy; the higher the 0, the longer it takes for the energy to be released.
r Variously, the symbol for radius, radio.
R Symbol for Resistance
R1 Abbreviation for Internal Resistance
Radio Frequency Choke (RFC) Coil with specified impedance to of currents.
Radio Frequency Interference An undesired radiated or conducted signal in the radio frequency spectrum.
Rated Output Current The maximum continuous load current a power supply is designed to provide under specified operating conditions.
RC Symbol for resistance-capacitance.
Reactance (X) Opposition to alternating current as result of inductance or capacitance.
Reactive A component that exhibits the property of either capacitance or inductance.
Real Power the actual power consumed by a circuit irrespective of power factor, See VA.
Recharge See Charge
Rechargeable Capable of being recharged; refers to secondary cells or batteries.
Recovery Time The time required for the measured characteristic to return to within specified limits follow mg an abnormal event.
Rectification The process of changing an alternating current to a unidirectional current. See Full-Wave Rectifier, Half-Wave Rectifier
Rectifier A component that passes current only in one direction, e.g., a diode.
Redundancy Power supplies connected in parallel operation so that if one fails, the others will continue delivering enough current to supply the maximum load. This method is used in applications where power supply failure cannot be tolerated. See Paralleling.
Reference Ground Defined 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.
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
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. It may consist of one or more layers of insulating material. It is acceptable in place of double insulation.
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.
Reluctance Resistance to flow of magnetic lines of force. Unit of measurement is the REL.
Remote Programming See Programming
Remote Sensing A technique for regulating the output voltage of a power supply at the load by connecting the error-sensing leads to the load. Remote sensing compensates for voltage drops in cables and connectors between the power supply and the load. Since the remote sense leads usually directly control the power supply's internal feedback loop, the system should not be operated with the remote sense leads disconnected. Also, when connecting remote sense leads, make sure the + lead goes to the + end of the load. A very common mistake is to reverse the leads, which can damage the system.
Remote Voltage Adjustment Adjustments of the output voltage made remotely over a limited range by a variable resistor. This type of control is often found on high density DC/DC converters.
Reset Current A current injected into the winding of a magnetic component to reset the core.
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 H field is returned to zero.
Resistance (R) Property of a material that opposes the flow of current.
Resonance 1) 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. 2) The state in which the vibration frequency of a body coincides with an applied vibration force, or vice versa, yielding rein-forced vibration of the body.
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 Frequency The natural frequency at which a circuit oscillates or a device vibrates. In an L circuit, inductive and capacitive reactances are equal at the resonant frequency.
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 currents for the outputs.
Reverse Current See Leakage Current
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 rectifier when reverse voltage is applied.
Reverse Voltage Protection A circuit or circuit element that protects a power supply from damage by a voltage of reverse polarity applied at the input or output terminals.
RF Abbreviation for radio frequency.
RFC In text, use lower case: rfc. Abbreviation for Radio Frequency Choke
RFI Abbreviation for Radio Frequency Interference
Ripple The periodic ac component at the power source output harmonically related to source or switching frequencies. Unless specified otherwise, it is expressed in peak-to-peak units over a specified bandwidth.
Ripple and Noise See Periodic and Random Deviation (PARD)
Ripple Voltage The periodic ac component of the dc output of a power supply.
Rise Time The time required for a pulse to rise from 10 percent to 90 percent of its maximum amplitude
RMS Value In text, use lower case: rms. Abbreviation for Root Mean Square Value
Root Mean Square (RMS) Value The equivalent DC voltage that produces exactly the same amount of heating as the AC waveform in a simple (non-inductive) resistor. The RMS value of a sine wave is 0.707 x Peak Value.
s Abbreviation for second.
Safe Extra Low Voltage (SELV) International safety standards as described in IEC 380 and VDE 0806.
Safety Classes Grouping of products by various safety agencies to conform to their unique standards.
Safety Compliance Certification, recognition or approval by safety agencies such as Underwriters Laboratories Inc. (UL/USA), Canadian Standards Association (CSA), etc.
Safety Ground A conductive path from a chassis, panel or case to earth to help prevent injury or damage to personnel and equipment.
Saturation (Bipolar Transistor) A condition when an increase in base current will not produce an appreciable change in the collector-emitter voltage.
Saturation (Magnetic) A condition in a magnetic material in which an increase in (B) will no longer produce an appreciable increase in (H).
SCC Abbreviation for Short-Circuit Current
Schottky Diode A diode device that exhibits a low forward voltage drop and fast recovery time relative to a standard silicon diode.
SCR Abbreviation for Silicon-Controlled Rectifier
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 switching power supply that is not sensed by the control loop.
Secondary Protection See Overload Device
Secondary Winding A coil that receives energy from the primary winding by mutual induction and delivers energy to the load is the secondary winding.
Self-Inductance Inductance that produces an induced voltage in itself as the result of a change in current flow.
SELV Abbreviation for Safe Extra Low Voltage
Semiregulated Output A subjective term indicating partial regulation.
Sense Line The conductor which routes output voltage to the control loop. See also Remote Sensing
Sense Line Return The conductor which routes the voltage on the output return to the control loop. See also Remote Sensing
Separator An ionic, permeable, electronically nonconductive spacer which prevents electronic contact between electrodes of opposite polarity in the same cell.
Series 1) The interconnection of two or more power sources such that alternate polarity terminals are connected so their voltages sum at a load. 2) The connection of circuit components end to end to form a single current path.
Series Pass A controlled active element, such as a transistor, in series with a load that is used to regulate voltage.
Series Regulation See Linear Regulation
Series Regulator A regulator in which the active control element is in series with the dc source and the load.
Service Maintenance The percent of rated capacity remaining after a specified period of time.
Setting Range The range over which the value of the stabilized output quantity may be adjusted.
Settling Time The time for a power supply to stabilize within specifications after an excursion outside the input/output design parameters. Related topic: Transient Response
Short-Circuit A direct connection that provides a virtually zero resistance path for current.
Short-Circuit Current (SCC) The initial value of the current obtained from a power source in a circuit of negligible resistance.
Short-Circuit Protection A protective feature that limits the output current of a power supply to prevent damage.
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.
Signal Ground The common return or reference point for analog signals.
Silicon-Controlled Rectifier (SCR) A uni-directional, four-layer (PNPN) junction device in which conduction is initiated by the application of a gate current. Conduction will continue until the current is reduced to some minimum value.
Sine Wave A wave form of a single frequency alternating current whose displacement is the sine of an angle proportional to time or distance.
Single Point Ground The one point in a system that connects multiple grounds and returns. Also known as star ground, or holy point ground.
Slave A power supply which uses the reference in another power supply, the master, as its reference.
Slewing Rate The maximum rate of change a power supply output can produce when subjected to a large step response or specified step change.
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 Abbreviation for Surface Mounted Device
SMPS Abbreviation for Switched Mode Power Supply
Snubber An RC network used to reduce the rate of rise of voltage in switching applications.
Snubber Network A circuit that uses a RC network and a diode in unipolar switching applications.
SOC Abbreviation for State-of-Charge
Solidstate Switch A switch that uses no moving parts.
Source Origin of the input power, e.g., generator, utility lines, mains, batteries, etc.
Spacings See Clearance Distance, Creepage Distance Specific Energy-See Energy Density
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.
SPS Abbreviation for Standby Power Supply
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.
Standby Current The input current drawn by a power supply under no load conditions.
Star Ground See Single Point Ground
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 low, dc low, ac ok, dc ok, overtemperature, overvoltage, undertemperature, overcurrent.
Step-Down Transformer A transformer with a turns ratio more than one. The output voltage is less than the input voltage. See also, Isolation Transformer, Step-up Transformer, Transformer
Storage Temperature The range of ambient temperatures through which an inoperative power supply can remain in storage without degrading its subsequent operation. See also Ambient Temperature, Operating Temperature
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.
Switching Frequency The rate at which the dc voltage is switched in a converter or power supply.
Switching Power Supply "Switchers" are typically smaller (by about 10X), lighter (by about 10X) and generate less heat (by about 5X) compared to an equivalent linear supply. At output power ratings above about 25W they are usually less expensive. However, their transient response is slower, output regulation less precise, and have higher PARD (noise). These latter issues aren't usually a problem for most digital circuits, but must be considered when powering sensitive analog circuits.
Switching Regulator A switching circuit that operates in a closed loop system to regulate the power supply output.
Synchronous Rectification A rectification scheme in a switching power supply in which a FET or bipolar transistor is substituted for the rectifier diode to improve efficiency.
t Symbol for temperature in 0C.
T Variously, the symbol for transformer, absolute temperature. The abbreviation for Tesla
Temperature Coefficient The average percent change in output voltage per degree Centigrade change in ambient temperature over a specified temperature range. See also Ambient Temperature
Temperature Range, Operating The range of ambient or case temperatures within which a power supply may be safely operated and meet its specifications. See Operating Temperature Range
Temperature Range, Storage The range of ambient temperatures within which a power supply may be safely stored, non-operating, with no degradation in its subsequent operation. See Storage Temperature Range
Tertiary Winding A third winding on a transformer.
Tesla (T) SI unit of magnetic flux density (magnetic induction) expressed as 1 weber/square meter.
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.
Three Terminal Regulator A power integrated circuit in a 3-terminal standard transistor package. It can be either a series or shunt regulator IC.
Thyristor A solid state device that has bistable electrical characteristics. Three common thyristor devices are diacs, silicon-controlled-rectifiers (SCRs) and triacs.
Time Constant Time period required for the voltage of a capacitor in an RC circuit to increase to 63.2 percent of maximum value or decrease to 36.7 percent of maximum value.
Tolerance Measured or specified percentage variation from nominal.
Toroid A round magnetic core with a hole in the middle. A doughnut shaped core.
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 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 called accuracy limits.
Transformer Device which transfers energy from one circuit to another by electromagnetic induction. See Isolation Transformer, Step-Down Transformer, Step-up Transformer
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 Ability of a power supply to recover a constant voltage following a step change in output current.
Transient Response Time The interval between the time a transient is introduced and the time it returns and remains within a specified amplitude range.
Triac A bi-directional silicon-controlled switch.
True Power Actual power generated or consumed in a circuit.
TTL Abbreviation for transistor-transistor logic.
Turns Ratio Ratio of the number of turns on the primary winding of a transformer to the number of turns on the secondary winding.
Two-Step Charge A charge which starts at one current and, at a predetermined point, continues at a lower current.
Undershoot A transient change in output voltage in excess of specified output regulation limits. See Overshoot
Undervoltage Protection A circuit that inhibits the power supply when output voltage falls below a specified minimum.
Uninterruptible Power Supply (UPS) A type of power supply designed to support the load for specified periods when the line varies outside specified limits. UPS systems generally filter the AC line voltage and provide battery-backup power in the event that the main AC power fails. UPS systems are separated into two major categories, standby and continuous operation systems. Within each of these categories are square, quasi-square and sinewave output systems. The simplest and least expensive UPS is a standby UPS with square wave output. In a standby UPS, input power flows through the UPS (usually through a triac) to the output. If there is no filtering, the output will include noise or transients present at the input. When the input AC voltage falls below a minimum value, the input is turned off, battery power is inverted to AC and delivered to the output. The transition or switching time (from mains power to battery power) must be shorter than the power supply's holdup time or the power supply will momentarily fail. In a continuous UPS, the DC/AC inverter is continuously supplying power to the load and the AC power serves to maintain battery charge. Of the three different types of waveforms, generating a square waveform is the easiest, least expensive and least desirable waveform. Not only does a square wave include a rich compliment of undesirable harmonics, it also charges the input energy storage capacitor of a conventional switcher (which is usually the UPS load) to a lower-than-normal peak voltage, increasing switching current, switch transistor temperature and reducing component lifetime. On the other hand, generating a sinewave output is far more difficult, expensive but more electrically desirable.
Universal Input Power supply's ability to accept a wide input voltage range (90VAC to 264VAC) without the selection of input range, either manually or electronically. As opposed to autoranging or auto-select input. See Autoranging Input
UPS Abbreviation for Uninterruptible Power Supply
V Abbreviation for Volt
VA Abbreviation for Volt-Ampere. This term is used when the AC voltage and AC current waveforms can be or are out of phase, and the product of their RMS values does NOT equal the real power. Whenever a power supply output is AC (alternating current), the potential exists for the voltage and current waveforms to be out-of-phase or non-sinusiodal. In these cases, the VA product can be much larger than the real power delivered. In an extreme case, the voltage and current sine waveforms may be 90 degrees out-of-phase. The power supply providing this output is delivering no output power but could be well over its maximum voltage or current output rating.
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.
Volt (V) Unit of measurement of electromotive force or potential difference. Symbol E, in electricity; symbol V in semiconductor circuits.
Volt-Ampere (VA) Measurement unit of apparent power. VA implies the product of volts rms times amps rms. Whenever a power supply output is AC (alternating current), the potential exists for the voltage and current waveforms to be out-of-phase or non-sinusiodal. In these cases, the VA product can be much larger than the real power delivered. In an extreme case, the voltage and current sine waveforms may be 90 degrees out-of-phase. The power supply providing this output is delivering no real output power but could be well over its maximum voltage or current output rating.
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 = IR.
Voltage Clamp See Clamp Circuit, Clipper Circuit
Voltage Divider Tapped or series resistance or impedance across a source voltage to produce multiple voltages.
Voltage Drop Difference in potential between two points in a passive component or circuit.
Voltage Efficiency 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 in a voltage range.
Voltage Limiting Bounding 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 an output voltage is within some specified limits.
Voltage Regulation The process of holding voltage constant between selected parameters, the extent of which is expressed as a percent. See also Regulation
Voltage Source A power source that tends to deliver constant voltage.
Voltage Stabilization The use of a circuit or device to hold constant an output voltage within given limits.
W Abbreviation for Watt
Watt (W) Unit of measurement of power equal to 1 joule/sec. (W=[l).
Watt-Hour (Wh) Unit of energy measurement, equal to one watt per hour (3600 joules).
Wh Abbreviation for Watt-Hour
Winding A conductor wrapped onto a magnetic core or core form, e.g., a transformer primary or secondary. Change from the nominal DC output voltage.
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.
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.
X Symbol for Reactance
X Capacitors EMI filter capacitors across the line that meet the requirements of certain regulatory agencies.
Xc Symbol for Capacitive Reactance
XL Symbol for Inductive Reactance
XL= 2(fL
Y Capacitors EMI filter capacitors between line and ground that meet the requirements of certain regulatory agencies.
Z Variously, symbol for Impedance, atomic number.
Zener Diode 1) A diode that makes use of the breakdown properties of a PN junction. If a reverse voltage across the diode is progressively increased, a point will be reached when the current will greatly increase beyond t normal cut-off value to maintain a relatively constant voltage. Either voltage point is called the Zener voltage. 2) The breakdown may be either the lower voltage Zener effect or the higher voltage avalanche effect.
Zener Voltage The reverse voltage at which breakdown occurs in a zener diode.