C E F G
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P R S
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FAILURE. An artificially induced failure of a
component, usually as a result of "abnormals" testing for regulatory agency
safety compliance. For instance manually shorting components to see the effect
on the safety of the power supply.
(Alternating Current) An electrical current that
periodically reverses direction.
TEMPERATURE. The temperature of the environment in
the proximity of the power supply.
AMP Ampere, quantitative unit of
measurement of electrical current equal to 1 coulomb of charge per second.
BLACKOUT A total loss of electrical power,
as opposed to brownout.
BANDWIDTH. A range of frequencies over
which a certain phenomenon is to be considered, for example noise bandwidth.
CONVERTER. A DC to DC converter topology
(configuration) employing four active switching components in a bridge
configuration across a power transformer. This has lower losses than a bridge
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.
COUPLING. Coupling of a signal between tow circuits,
due to discrete or parasitic capacitance between the circuits. For example, the
windings of a transformer are not only magnetically coupled, but also
capacitively coupled due to their close proximity. .
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
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.
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
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
LIFE. The expected lifetime of a power supply during
which it will operate to its published specifications.
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
DIP A short term voltage decrease. EMI -
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
EFFICIENCY. The ratio of total output
power to input power expressed as a percentage. Normally specified at full load
and nominal input voltage.
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.
(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.
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.
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.
Abbreviation for High Potential, and generally
refers to the high voltages used to test dielectric withstand capability for
regulatory agency electrical safety requirements.
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.
NOISE. Noise generated in a circuit by a varying
magnetic field produced by another circuit.
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.
VOLTAGE. The maximum AC or DC voltage which maybe
continuously applied from input to output and/or chassis of a power
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).
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.
REGULATION. The change in output voltage when the
load on the output is changed.
AMPLIFIER. Sometimes abbreviated "Mag Amp," a
saturating inductor which is placed in series with a power supply output for
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.
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.
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.
IMPEDANCE. The ratio of change in output voltage to
change in load current.
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.
PROTECTION. A circuit which either shuts down the
power supply or crowbars the output in the event of an overvoltage
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.
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
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.
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.
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.
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
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.
CURRENT. The input current drawn by a power supply
when shut down by a control input (remote inhibit) or under no load.
FREQUENCY. The rate at which the DC voltage is
switched on and off during the pulse width modulation process in a switching
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.
PROTECTION. A power supply protection circuit which
shuts the power supply down in the event of unacceptably high internal
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
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
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.
BALANCE. The difference in magnitudes, in percent,
of two output voltages that have equal nominal voltage magnitudes but opposite
WARM-UP TIME. The time
required after initial turn on for a power supply to achieve compliance to its