Current (AC) Electrical current
that continuously reverses direction of flow, typically in a periodic fashion.
In the United States, standard AC power sources reverse direction sixty
times each second (called 60 cycles or 60 Hertz
AC). In Europe, the standard is 50 Hertz.
Air-cooled Design that disposes of excess heat without the use of fans or cooling liquids. Air cooled devices often rely on a heat sink to enhance heat dissipation.
Ampere or Amp Unit of measure of current flow. At a given point in a circuit, an Amp (1A) equals 1 coulomb of electrons passing in 1 second.
Ammeter A device that measures current flowing through an electrical circuit. An ammeter is typically connected in series.
Attenuation Decrease in signal strength as it passes through a system or medium. Measured in decibels.
American Wire Gauge (AWG) A standard used to measure the diameter of a wire conductor. The greater the number, the smaller the wire diameter. House wiring typically contains 12-gauge or 14-gauge solid wire. "Doorbell" wire is often 16-gauge stranded wire. Digital circuit boards are sometimes modified using small 22-gauge or 28-gauge wires.
Ball-bearing Fan A cooling fan with a center hub that glides on precision steel balls. Though more expensive, ball-bearing fans typically last longer than fans made with bushings.
Balun A transformer that presents high impedance to common-mode signals and low impedance to differential-mode signals. It is often used on the input of switching power supplies to suppress common-mode noise.
Blackout An abrupt, unanticipated loss of all electrical power.
Backup Power Supply (BPS) A second power source that activates if the primary power source fails.
Break An open (disconnected) circuit condition caused by a switch, damage to a conductor, etc.
Box A test device that can
be attached to a cable, making it easy to connect a wire to any conductor.
Some breakout boxes also feature LEDs to monitor signals on each line.
Breakdown Voltage The maximum AC or DC voltage that may be applied from input to output and/or chassis of a power supply.
A planned voltage
reduction by a utility company to counter excessive demand on their generation
and distribution system.
Burn-in Statistically, if an electrical device is going to fail, it will most often occur during its first hours of operation. Some suppliers first operate new electrical products at their factory for a predetermined period to weed out problems before shipment to customers. This process is known as burn-in. Sometimes, burn-in is conducted with the product under electrical or thermal load, to induce stress and make it easier to identify potential failures.
Bus A common electrical pathway between components or devices.
Standards Association (CSA) A
Canadian agency that establishes standards and tests products for public
Capacitor An electronic component that can store an electrical charge on conductive plates.
Capacitance Measured in farads, capacitance is an object's ability to store a charge.
Products sold in most parts of
Europe must be tested and certified to comply with CE standards. These
standards include limits on how much electromagnetic interference
(EMI) a device may emit, and its susceptibility to EMI induced problems.
Circuit A complete path for electrical flow from one terminal to the other of a power source such as a power supply or battery.
Circuit Board A sheet of plastic or other material bearing foil or wire conductors that make up an electrical circuit. Often, a photo etching process is used to mass-produce "printed circuit boards" (PCBs) for industry.
Clamp To divert excess voltage to ground.
Clamp Circuit Designed into surge protectors and suppression devices to clamp (shunt excess voltage to ground) in the event of a power surge.
Voltage The desirable, predetermined
level maintained by a clamp circuit.
Common-mode Noise The component of noise that is common to both the DC output and return lines with respect to input neutral.
Voltage The output
voltage range of of a constant current
Conductor A material that allows the flow of electricity.
Converter A device used to transform one DCvoltage to another.
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.
In a multiple output power
supply, the percent voltage change at one output caused by a load change
on another output.
Crowbar Circuit An overvoltage protection circuit that rapidly places a low resistance shunt across the power supply output terminals if a predetermined voltage is exceeded.
Current (I) The flow of electrons through a material. Current is measured in amperes.
Cycles The number of times an alternating current reverses in one second.
board that forms a subsystem of a larger main circuit
Decibel (dB) A logarithmic measure of signal power determined by comparing an initial reference level to a final measurement.
Derating A specified reduction in output power at elevated temperatures to improve reliability.
Differential Mode Noise The component of noise measured between DC output and output return.
Dirty Power An alternating current that includes spikes, surges or other unwanted fluctuations.
Multimeter (DMM) An electronic
device used to measure voltage, resistance,
and other circuit characteristics. Readings are
displayed on a digital LCD panel on the DMM.
Direct Current (DC) Electrical current that flows only in one direction, i.e., does not alternate.
Drift The change in power supply output over a specified period following a warm-up period, when all other characteristics such as line, load and ambient temperature are constant.
Industries Association (EIA) A
organization whose industry members establish standards for electrical
components and consumer electronics products. In 1988, the EIA created
a second group called the TIA to administer telecommunications and information
Electrostatic Type of force that exists between two electrically charged objects. Objects with a similar charge repel each other, and objects with dissimilar charges attract each other. No current flows in an electrostatic environment.
Electromagnetic Interference (EMI) An effect of undesirable energy. EMI is typically emitted by switching power supplies, and may be conducted or radiated.
Energy Star A U.S. government program to reduce unnecessary power consumption and waste. Energy Star certified computer systems use high efficiency power supplies and advanced power management techniques to help conserve electricity.
Efficiency The ratio of total power output to input power. Efficiency is typically measured at full load and nominal input voltage.
Series Resistance (ESR) The
amount of resistance in series with an ideal
that exactly duplicates the performance of a real capacitor.
In high frequency applications, low ESR is very important.
Farad Unit of capacitance. A capacitor has 1 farad of capacitance when it can store 1 coulomb of charge with a 1 volt potential across its plates.
Faraday Shield An electrostatic shield between the input and output windings of a transformer, designed to reduce output common mode noise.
Fault-mode Input Current The input current to a power supply or DC-DC converter, with the output short-circuited.
Federal Communications Commission (FCC) United States regulatory agency that oversees telecommunications and radio frequency communications.
FCC Class A United States federal regulations that define permissible levels of electromagnetic emissions from an electronic device operated in a commercial environment.
FCC Class B United States federal regulations that define permissible levels of electromagnetic emissions from an electronic device operated in a residential environment.
Feed forward A control technique in which line regulation of a power supply is improved by directly sensing the input voltage.
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.
Flyback Converter Power supply switching circuit that 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 in which the output current decreases with increasing overload, reaching a maximum at short-circuit.
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.
Full Bridge Converter A power switching circuit that has four transistors connected in a bridge configuration to drive a transformer primary.
Gain An increase in signal power, typically the result of amplification.
Giga (G) Metric prefix meaning one billion, or 1,000,000,000.
Slang for a device that complies
with Energy Star program qualifications.
Ground A voltagereference level in a circuit, typically connected to earth ground at some point.
Ground Fault Circuit Interrupter (GFCI) A power receptacle that reduces the hazards of ground fault currents that can cause injury or death. Upon detecting a ground fault current in a protected circuit, a GFCI will trip, resulting in the removal of power.
Loop An unwanted feedback
condition caused by two or more circuits sharing
a common electrical ground.
Heat Sink A milled piece of aluminum or other material bearing fins or fingers to increase surface area, and thus dissipate unwanted heat into the air more rapidly than a device with no heat sink attached.
Hertz (Hz) Repetitions per second.
Hi-pot Short for "High potential" test. A test to determine if the breakdown voltage of a power supply or transformer exceeds the minimum requirement. A hi-pot test is conducted by applying high voltage between two isolated test points.
Hold-up Time The period during which a power supply's output voltage remains within specifications following a loss of input power.
To remove and replace a system
component while power is on and the system is functional (without first
shutting the system down).
Impedance Apparent resistance to the flow of current in an ACcircuit, directly related to the circuit's true resistance to the flow of direct current.
Inductance The ability of a coil to oppose changes in current flowing through it.
Inductor A coil of wire wrapped a specific number of turns around a core material, used to produce inductance in a circuit.
Line Filter A band-reject
or low-pass filter on a power supply's input
designed to reduce the level of line noise being
introduced to the supply.
Inrush Current The peak instantaneous input current drawn by a power supply when it is powered on.
Inrush Current Limiting A circuit design that limits inrush current to an acceptable level.
Insertion Loss Decrease in power resulting from the insertion of a component or splice in a circuit.
Institute of Electrical and Electronic Engineers (IEEE) An organization of scientists, engineers and others that creates standards for the electronics industry.
Electrotechnical Commission (IEC) A
Geneva-based organization that sets international electronics standards.
Inverter A device that converts DC input power into AC output power.
Isolation The electrical separation between input and output of a power supply by means of the power transformer. Isolationresistance (normally in megohms) and isolationcapacitance (normally in picofarads) are generally specified and are a function of materials and spacings employed throughout the power supply.
Isolation Voltage The maximum AC or DC voltage that may be continuously applied from the input to the output or chassis of a power supply.
The outermost layer of an electrical
cable. Typically made of plastic, rubber or similar non-conductive materials,
the jacket encases inner conductors and helps
protect against short-circuits, electrical shocks,
mechanical damage and environmental hazards.
Kilo (k or K) Metric prefix meaning 1000.
Layer Winding A method of winding a transformer whereby the primary and secondary are wound in layers over one another, separated by an insulating layer.
or DC current flowing from the
input to the output or chassis of an isolatedpower
supply at a specified voltage.
Line Regulation The change in output voltage in percent as the input voltage is varied over its specified limits, with load and temperature constant.
Linear Regulator A popular stabilization circuit in which a control device is placed in series or parallel with the load to deliver a constant voltage across the load. The control device is always conducting, and the difference between input and output power is dissipated by the control device.
Load Regulation The percent change in output voltage as the load is changed from minimum to maximum, at constant line and constant temperature. The load change may be specified for other than no load to full load, e.g., 30% to full load
Sensing Using the power
supply output voltage terminals as the
sense points to provide feedback to the voltage
Magic Packet A standard for remotely waking a personal computer from sleep mode or a power off condition. Originated by AMD(tm) and Hewlett-Packard(tm), this technique is implemented by sending a special Ethernet or Token Ring message known as a "Magic Packet." The wake-up signal is intercepted by a network interface that remains functional due to power from the PC's standby voltage source.
Time Between Failure (MTBF) A
reliability term that expresses a component's average failure rate in hours.
Mega (M) Metric prefix meaning one million, or 1,000,000.
Micro (?) Metric prefix meaning one millionth or 1/1,000,000.
Milli (m) Metric prefix meaning one thousandth or 1/1000.
Mirrored Replicated by a functional, exact duplicate to provide a real-time backup system.
The main circuit
board in a computer system or other digital electronic device.
Nano (n) Metric prefix meaning one billionth or 1/1,000,000,000.
Noise Signal interference generated by electrical components or external sources that can disrupt or corrupt data transmissions.
Power Supply A power
supply that operates directly off the AC line, without
using a power transformer prior to rectification
Ohm Unit of resistance to the flow of electrical current.
Law Physical law that defines
electrical voltage in relation to current
and resistance. Voltage
(E in volts) is equal to Current
(I in amps) multiplied by Resistance
(R in ohms), or E = IR, or R = E/I, or I = E/R, etc.
Output Current Limiting An output protection feature that limits the output current to a predetermined value in order to prevent damage to the power supply or the load under overload conditions. The supply is automatically restored to normal operation following the removal of the overload.
Impedance The ratio of change
in output voltage to the change in load current.
Output Voltage The nominal value of the DC voltage at the output terminals of a power supply.
Output Voltage Accuracy For a fixed output supply, the tolerance in percent of the output voltage with respect to its nominal value under all minimum or maximum conditions.
Overload Protection An output protection feature that limits the output current of a power supply under overload conditions so it will not be damaged.
A transient change in output
voltage, in excess of specified output accuracy
limits, that can occur when a power supply
is turned on or off, or when there is a step change
in line or load.
Overvoltage Protection A power supply feature that shuts down the supply, or crowbars or clamps the output, when its voltage exceeds a preset level.
Parallel Operation The connection of the outputs of two or more power supplies of the same output voltage to obtain a higher output current than from either supply alone. This technique requires power supplies specifically designed to share a load.
and Random Deviation (PARD) A
term used to describe the sum of all ripple
and noise components measured over a specified bandwidth and stated
in either peak-to-peak or RMS values.
Pico (p) Metric prefix meaning one thousand-billionth (in U.S. and France, called one trillionth) or 1/1,000,000,000,000.
Filter A filter commonly
used on the input of a switching supply or
DC-DC converter to reduce the reflected ripplecurrent.
The filter usually consists of two parallel
and a series inductance and is generally built
into the power supply.
Polarity Electrical condition in which there are two opposing voltage levels or charges, i.e., positive and negative poles.
Post Regulation A linear regulator used on the output of a switching power supply to improve line and load regulation and reduce output ripple voltage.
Power Fail Detection An optional power supply feature that causes the supply to send a logical output signal in the event of the loss of line input voltage.
Foldback A power
supply feature that causes the input power to be reduced under output
Power Supply An electrical device that provides a known potential difference in place of a battery. A power supply is typically plugged into a wall outlet, and can be a standalone device, or a fundamental component of a larger electrical product.
Preregulation Regulation at the front end of a power supply, typically by a type of switching regulator. This is followed by output regulation, usually by a linear regulator.
Programmable Power Supply A power supply that has its output controlled by an external resistor or a digital code.
Pulse-width Modulation Method of voltage regulation used in switching supplies whereby the output is controlled by varying the width, but not the height, of a train of pulses which drive a power switch.
Push-Pull Converter A power switching circuit that uses a center-tapped transformer and two switches that are alternately driven on and off.
Mount Variety of device whose
special design enables it to be mounted in a standard cabinet, often in
a 19" wide opening.
Rated Output Current The maximum load current that a supply is designed to provide at a specified ambient temperature.
Redundant Array of Inexpensive Disks (RAID) A technique for storing data on multiple hard disk drives, to provide higher reliability and faster data access.
Power Supply A power
supply made by duplicating identical components to provide greater
reliability. In the event the primary supply
should fail, a secondary supply is activated
(or it assumes the entire load instead of merely half the load).
Reference Stable voltage, generally from a Zenar diode, from which the output voltage of a regulated supply is controlled.
Ripple Current The AC current
generated at the input of a power supply or DC-DC converter by the switching
operation of the converter, stated as peak-to-peak or RMS.
Regulated Voltage Power supply output voltage that is held constant despite fluctuating current drain.
Relay A remote switch activated by an electromagnetic coil.
Sensing Technique of regulating
the output voltage of a power
supply at the load by means of sensing leads which extend from the
load to the regulator. This method compensates for voltage
drops in the load leads.
Resistance (R) Opposition to current flow, measured in ohms.
Resistor (R) An electrical device that inserts a predetermined level of resistance into a circuit.
In an adjustable power
supply, the smallest change in output voltage
that can be realized by the adjustment.
Return Name for the common output terminal of a power supply, the "return" carries the return current for the outputs.
Voltage Protection Feature
that protects a power supply against reverse
applied to input or output terminals.
Ripple and Noise The magnitude of ACvoltage on the output of a power supply, at a specified bandwidth, expressed in RMS or millivolts peak-to-peak. This is the result of feed through of the rectified line frequency, internal switching transients and other random noise.
Series Regulation The most popular method of linear regulation in which the control device is in series with the raw DC and the load, to achieve constant voltage across the load.
Short-Circuit An abnormal path of little or no resistance across the terminals of a circuit, resulting in an excessive flow of current.
Short-Circuit Protection A feature that limits the output current of a power supply under short-circuit conditions so the supply will not be damaged.
Shunt Regulation A method of linear regulation in which the control device is in parallel with the load to achieve constant voltage across the load.
Start A feature that limits
the start up switching currents of a switching power
supply, causing the output voltage to
rise gradually to its specified level.
Spike A burst of undesirable high voltage on a power line, typically lasting only a fraction of a second.
Bobbin Winding Means of winding
a transformer in which the primary and secondary
are wound side-by-side on a bobbin, with an insulator between the two windings.
Standby Voltage (SB) Special output from a power supply in shut-down mode, used to provide enough power to restart a personal computer, or enable a network or modem connection.
Step Change A instantaneous change in a quality from one value to another.
Relief A plastic collar or
similar contrivance added to a cable at the point it enters a case, designed
to help protect the cable from mechanical damage caused by flexing or pulling.
Surge A sudden increase in line voltage of short duration that can sometimes cause damage to electrical devices.
Swell An undesirable condition in which actual voltage lingers above the normal voltage level.
Switching Frequency The rate at which DCvoltage is switched in a switching power supply or DC-DC converter.
Switching Regulator A high-efficiency switching circuit that uses a closed-loop system to regulate output voltage, typically be means of a pulse-width modulator.
Temperature Coefficient The average percent change in output voltage per degree Centigrade change in ambient temperature over a specified temperature range.
Thermal Protection Internal safeguard circuit in a power supply that shuts the unit down in the event of excess internal temperature.
Tracking A characteristic of dual or multiple output power supplies in which one or more outputs follow another output with changes in line, load or temperature, such that each maintains the same proportional output voltage with respect to common.
Recovery Time Time required
for the output voltage to settle within specified
output accuracy limits following a step change in output load current or
Transformer A device that uses principals of electromagnetic induction to "step-up" (increase) or "step-down" (decrease) voltage from an AC source.
Technischer Uberwachungs-Verein (TUV) A German organization similar to U.L. that tests and certifies products for safety.
Undershoot A transient change in output voltage, below output accuracy limits, that can occur when a power supply is turned on or off, or when there is a step change in line or load.
Underwriters Laboratories (UL) A independent, U.S.-based non-profit organization that tests and certifies components and products for safety.
Uninterruptible Power Supply (UPS) A power supply that continues to provide electricity despite the loss of AC input power. This is made possible by means of a backup battery and a DC-AC inverter or DC-DC converter.
Deutscher Electrotechniker (VDE) German
national standards and test agency.
Volt (V or E) Electrical unit of voltage or potential difference. One volt is the force necessary to move the sufficient number of electrons through one ohm of resistance to create one ampere of current.
Voltage A measure of electromotive push on an electron.
Balance The difference in
magnitude, in percentage, between two output
voltages of a dual output power supply
where the voltages have equal nominal values with
Voltage Drop A change in available voltage between two points in a circuit, due to current flowing through resistance. Also known as an IR drop.
Voltmeter An electrical device used to measure the voltage between two points in a circuit.
Wake-on-LAN (WOL) Another name for Magic Packet technology.
Drift The initial change
in output voltage of a power
supply from power-on until it reaches thermal equilibrium at nominal
line, full load, 25¢XC ambient temperature.
Warm-up Period The time required, following initial power-on, for a power supply to meet its performance specifications.
Watt (W) A unit of power. Equal to 1 joule per second, power in Watts can be calculated by multiplying voltage times current.
Document de Quantum Power Labs, Inc.