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.
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.
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.
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.
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
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
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
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
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
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.
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
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.
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
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.
(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
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.