Specifications
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Power Supplies
CONSTANT CURRENT SOURCE—A regulated power sup-
ply that delivers a constant current to a load, even when
the load resistance changes.
CONSTANT VOLTAGE SOURCE—A regulated power sup-
ply that delivers a constant voltage to a load even when
the load resistance changes.
CURRENT LIMITING—Ability to limit maximum current
output at a preset value. This feature helps protect the
load from overcurrent damage.
ISOLATION—Floating output, no reference to any voltage.
LINE REGULATION—How much the load voltage or cur-
rent changes when the power supply is operated at vary-
ing line voltages throughout a given range. Typically stat-
ed as a percentage of the total voltage or current available
from the supply. A rating of “0%” would mean perfect
regulation.
LOAD REGULATION—How much the load voltage or cur-
rent changes between operating the power supply at no-
load and full-load conditions. Typically stated as a per-
centage of the total voltage or current available from the
supply. A rating of “0%” would mean perfect regulation.
OVERLOAD PROTECTION—Means by which a power sup-
ply is protected from permanent damage due to short cir-
cuits, excessive loads, or reverse polarities connected
across the load terminals. Protection may be as simple as
a fuse (which can be economically replaced), or may be
electronic protection circuitry which automatically moni-
tors load conditions as well as power supply component
temperatures.
POWER CONSUMPTION—The input power that is
required by the power supply at a full load output condi-
tion.
POWER REQUIREMENTS—The line voltage that the
power supply requires to operate. High quality power
supplies have a selector switch that permits operation
from 110,120, 220 , and 240 VAC sources.
RECOVERY TIME—The time that it takes a power supply
t
o regulate its output after an abrupt change, such as
from full load to no load.
REGULATION—The ability to maintain a constant volt-
age or current at the load despite changes in line volt-
age or load resistance.
RIPPLE CURRENT— The portion of unfiltered AC current
at the output of a filtered power supply.
RIPPLE VOLTAGE—The portion of unfiltered AC voltage
and noise present at the output of a filtered power sup-
ply, operated at full load. Typically stated as rms and
peak-to-peak AC voltage (with zero ripple voltage would
represent a perfect power supply).
RMS VALUE (root mean square value)—The “effective”
value of an AC or periodic voltage or current. The
amount of work accomplished by a given rms value
equals the amount of work accomplished by an equal
DC value. The rms value can be obtained by first squar-
ing the ordinates of the wave, then finding the average
value of the squared wave, finally taking the square root
of the average found. The rms value of a pure sine
wave is 0.707 times the peak value (RMS = Vp x 0.707),
while the rms value of a square wave is 0.5 times the
peak value Vp = Peak Value = Vpp.
TRACKING—Two power supplies (within one case) that
are electrically coupled so that both can be varied by
using only one knob.
TEMPERATURE COEFFICIENT—The change in power
supply output voltage that is caused by temperature
change. It is usually expressed in millivolts per degree.
VA—Abbreviation for Volt-Ampere. Unit of input power
delivered to a load. For electronic equipment, the “VA”
load imposed on the isolation transformer or AC power
supply is simply the load voltage multiplied by the load
current, or the wattage rating of the load.
POWER SUPPLY TERMS