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ABNORMAL FAILURE. An artificially induced failure of a component, usually as a result of "abnormals" testing for regulatory agency
safety compliance.
AC
(Alternating Current) An electrical current that continually reverses direction.
AMBIENT TEMPERATURE. The temperature of the environment in the proximity of the power supply.
AMP
Quantitative unit of measurement of electrical current
BLACKOUT A
total loss of electrical power.
BANDWIDTH. A
range of frequencies over which a certain phenomenon is to be considered.
BRIDGE CONVERTER. A DC to DC converter topology (configuration) employing four active switching components in a bridge configuration
across a power transformer.
BROWNOUT. A
reduction of the AC mains' distribution voltage, usually caused deliberately by the utility company to reduce power consumption
when demand exceeds generation or distribution capacity.
BURN-IN.
Operating a newly manufactured power supply, usually at rated load, for a period of time in order to force component infant
mortality failures or other latent defects before the unit is delivered to a customer.
CAPACITIVE COUPLING. Coupling of a signal between tow circuits, due to discrete or parasitic capacitance between the circuits.
CONVERTER.
An electrical circuit which accepts a DC input and generates a DC output of a different voltage, usually achieved by high
frequency switching action employing inductive and capacitive filter elements.
CREST FACTOR.
In an AC circuit, Crest Factor is the mathematical ratio of the peak to RMS values of a waveform. Crest factor is sometimes
used for describing the current stress in AC mains supply wires, since for a given amount of power transferred, the RMS value,
and hence the losses, become greater with increasing peak values. Crest Factor gives essentially the same information as Power
Factor, and is being replaced by Power Factor in power supply technology.
CURRENT The
flow of electricity expressed in amperes. Current refers to the quantity or intensity of electricity flow, whereas voltage
refers to the pressure or force causing the electrical flow.
CURRENT MONITOR. An analog power supply signal which is linearly proportional to output current flow. Usually only feasible for
single output power supplies.
DC - DIRECT CURRENTElectrical current
which flows in one direction.
DERATING. A
reduction in an operating specification to improve reliability. For power supplies it is usually a specified reduction in
output power to facilitate operation at higher temperatures.
DESIGN LIFE.
The expected lifetime of a power supply during which it will operate to its published specifications.
DIFFERENTIAL MODE NOISE. Noise that is measured between two lines with respect to a common reference point excluding common-mode noise. The
resultant measurement is the difference of the noise components of the two lines. The noise between the DC output and DC return
is usually measured in power supplies.
DIP A short
term voltage decrease. EMI - Electro-Magnetic Interference
DRIFT. The
change in an output voltage, after a warm-up period, as a function of time when all other variables such a line, load, and
operating temperature are held constant.
DROPOUT. The
lower limit of the AC input voltage where the power supply just begins to experience insufficient input to maintain regulation.
The dropout voltage for linears is quite load dependent. For most switchers it is largely design dependent, and to a smaller
degree load dependent.
EFFICIENCY.
The ratio of total output power to input power expressed as a percentage. Normally specified at full load and nominal input
voltage.
ELECTRONIC LOAD. An electronic device designed to provide a load to the outputs of a power supply, usually capable of dynamic
loading, and frequently programmable or computer controlled.
EMI (Electromagnetic Interference)Unwanted noise during the operation of a power supply or other electrical or electronic
equipment.
ESR.
Equivalent Series Resistance. The value of resistance in series with an ideal capacitor which duplicates the performance
characteristics of a real capacitor.
FAULT MODE INPUT CURRENT. The input current to a power supply with a short circuit on the output.
FERRORESONANT POWER SUPPLY. Power supply used at higher power levels in fixed applications, since they are very
heavy. Can only be used effectively when the line frequency is very stable as they are sensitive to variations of input AC
frequencies.
Filter An
electronic device that allows only certain frequencies to pass.
GROUND. An
electrical connection to earth or some other conductor that is connected to earth. Sometimes the term "ground" is used in place
of "common," but such usage is not correct unless the connection is also connected to earth.
GROUND LOOP.
An unintentionally induced feedback loop caused by two or more circuits sharing a common electrical ground.
HAVERSINE. A
waveform that is sinusoidal in nature, but consists of a portion of a sine wave superimposed on another waveform. The input
current waveform to a typical off-line power supply has the form of a haversine.
HEADROOM.
Used in conjunction with series pass regulators, and is the difference between the input and output voltages.
HIPOT.
Abbreviation for High Potential, and generally refers to the high voltages used to test dielectric withstand capability for
regulatory agency electrical safety requirements.
HOLD-UP TIME.
The length of time a power supply can operate in regulation after failure of the AC input. Linears have very short hold-up
times due to the CV squared energy storage product of their low voltage secondary side output capacitors. Switchers have longer
times due to their higher voltage primary side energy storage capacitors.
INDUCED NOISE. Noise generated in a circuit by a varying magnetic field produced by another circuit.
INPUT LINE FILTER. An internally or externally mounted low-pass or band-reject filter at the power supply
input which reduces the noise fed into the power supply.
INVERTER. A
power supply which produces an AC output, usually from a DC input.
ISOLATION.
Two circuits that are completely electrically separated with respect to DC potentials, and almost always also AC potentials. In
power supplies, it is defined as the electrical separation of the input and output via the transformer.
ISOLATION VOLTAGE. The maximum AC or DC voltage which maybe continuously applied from input to output and/or chassis of a power
supply.
LEAKAGE CURRENT. A term relating to current flowing between the AC supply wires and earth ground. The term does not necessarily
denote a fault condition. In power supplies, leakage current usually refers to the 60 Hertz current which flows through the EMI
filter capacitors which are connected between the AC lines and ground (Y caps).
LINE REGULATION. The change in output voltage when the AC input voltage is changed from minimum to maximum specified. It is usually a
small value, and may be near zero with current mode control.
LOAD REGULATION. The change in output voltage when the load on the output is changed.
MAGNETIC AMPLIFIER. Sometimes abbreviated "Mag Amp," a saturating inductor which is placed in series with a power supply output for
regulation purposes.
MARGINING.
Adjusting a power supply output voltage up or down from its minimal setting in order to verify system performance margin with
respect to supply voltage. This is usually done electrically by a system-generated control signal.
MINIMUM LOAD.
The minimum load current/power that must be drawn from the power supply in order for the supply to meet its performance
specifications. Less frequently, a minimum load is required to prevent the power from failing.
NOISE An undesirable signal that is
irregular and is riding on top of the desired signal.
OFF LINE. A
power supply which receives its input power from the AC line, without using a 50/60 Hz power transformer prior to rectification
and filtering, hence the term "off line" power supply.
OPTOISOLATOR.
An electro-optical device which transmits a signal across a DC isolation boundary.
OUTPUT IMPEDANCE. The ratio of change in output voltage to change in load current.
OUTPUT NOISE. The AC component that may be present on the DC output of a power supply. Switch-mode power supply output noise has
two components: a lower frequency component at the switching frequency of the converter and a high frequency component due to
fast edges of the converter switching transitions. Noise should always be measured directly at the output terminals with a
scope probe having an extremely short grounding lead.
OVERVOLTAGE PROTECTION. A circuit which either shuts down the power supply or crowbars the output in the event of an overvoltage
condition.
PEAK POWER.
The absolute maximum output power that a power supply can produce without immediate damage. Peak power capability is typically
well beyond the continuous reliable output power capability and should only be used infrequently.
POWER FACTOR.
The ratio of true power to apparent power in an AC circuit. In power conversion technology, power factor is used in conjunction
with describing the AC input current to the power supply.
PRIMARY. The
input section of an isolated power supply which is connected to the AC mains and hence has dangerous voltage levels
present.
RATED OUTPUT CURRENT. The maximum load current that a power supply can provide at a specified ambient temperature.
REGULATION.
The ability of a power supply to maintain an output voltage within a specified tolerance as referenced to changing conditions
of input voltage and/or load.
REGULATION BAND. The total error band allowable for an output voltage. This includes the effects of all of the types of regulation:
line, load, and cross.
REVERSE VOLTAGE PROTECTION. A protection circuit that prevents the power supply from being damaged in the event that
a reverse voltage is applied at the input or output terminals.
RFI. An
abbreviation for Radio Frequency Interference, which is undesirable noise produced by a power supply or other electrical or
electronic device during its operation. In power supply technology, RFI is usually taken to mean the same thing as EMI.
RIPPLE AND NOISE. The amplitude of the AC component on the DC output of a power supply usually expressed in millivolts peak-to-peak or
RMS. For a linear power supply it is usually the frequency of the AC mains. For a switching power supply, it is usually the
switching frequency of the converter stage.
SAFETY GROUND. A conductive path to earth that is designed to protect persons from electrical shock by shunting away any dangerous
currents that might occur due to malfunction or accident.
SECONDARY.
The output section of an isolated power supply which is isolated from the AC mains and specially designed for safety of
personnel who might be working with power on the system.
SEQUENCING.
The technique of establishing a desired order of activating the outputs of a multiple output power supply.
SURGE An
abnormally high voltage lasting for a short period of time.
STANDBY CURRENT. The input current drawn by a power supply when shut down by a control input (remote inhibit) or under no load.
SWITCHING FREQUENCY. The rate at which the DC voltage is switched on and off during the pulse width modulation process in a switching
power supply.
TEMPERATURE COEFFICIENT. The average output voltage change expressed as a percent per degree centigrade of ambient
temperature change. This is usually specified for a pre-determined temperature range.
THERMAL PROTECTION. A power supply protection circuit which shuts the power supply down in the event of unacceptably high internal
temperatures.
TRACKING. A
characteristic in a multiple output power supply where any changes in the output voltage of one output caused by line, load,
and/or temperature are proportional to similar changes in accompanying outputs.
TRANSFER TIME The amount of time it takes a stand-by or off-line type UPS to sense a power interruption and switch from utility
output to inverter output. Normally expressed in milliseconds. See also Switching Time. Transformer
TRUE POWER.
In an AC circuit, true power is the actual power consumed. It is distinguished from apparent power by eliminating the reactive
power component that may be present.
UPS
(Uninterruptible Power Supply). A power supply which continues to supply power during a loss of input power. Two types are the
stand-alone UPS, which is located external to the equipment being powered, and the battery back-up power supply, which is
embedded in the equipment being powered, such as a POWER-ONE SPM series high power product with a G5 battery back-up
module.
VOLTAGE BALANCE. The difference in magnitudes, in percent, of two output voltages that have equal nominal voltage magnitudes but
opposite polarities.
WARM-UP TIME. The time required after
initial turn on for a power supply to achieve compliance to its performance specifications.
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