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Load Effect (Load Regulation)
Load Effect or Load Regulation is a static perform-
ance measurement which defines the ability of a
power supply under test to remain within specified
output limits for a predetermined load change (see
Figure 3). In a CV power supply, the influenced
quantity of interest is the steady-state output cur-
rent. In a CC power supply, the influenced quantity
is the steady-state output voltage. For single output
CV power supplies, voltage load effect is given for a
load current change equal to the current rating of
the supply. A typical specification would be stated
in millivolts, or as a % of the rated output voltage.
For multiple output CV power supplies, cross
load effect is determined. This is an extension of
the load effect test for a single output power sup-
ply, and determines the ability of all outputs of a
CV power supply to remain within their specified
voltage rating for a load current change on one
output. Conversely, the ability of one output to
withstand the effects of changes on all other out-
puts can be specified.
Test Overview/ Procedures
For a CV power supply, measurement of the output
voltage and input voltage should be made after the
load is varied from the minimum to the full current
rating of the power supply under test (Figure 4).
Measurement of the AC input voltage is necessary
to ensure that the output voltage change is a result
of only the load change, and not from a change in
the AC input. To decrease the test time when test
throughput is a concern, a regulated AC source
providing a predetermined AC input level and fre-
quency can be utilized. This will eliminate the need
for the AC input voltage measurement.
The output voltage should be allowed the specified
settling time before measurements are taken. An
electronic load selected for this test must be capa-
ble of operating in CC or CR mode, and must have
input ratings (voltage, current, and power) suffi-
cient to accommodate the maximum ratings of the
power supply under test.
Figure 3. Load Effect
For a load current change equal to the full current rating of a CV
power supply, the resulting change in V
OUT
should not exceed the
predetermined load effect band. Typical specifications for load
effect range from 0.005 to 0.5% of the maximum output voltage.
Figure 4. Load Effect Testing Configuration
A regulated AC source is used in this load effect testing configuration to maintain the AC input at a predetermined
value. This will ensure that the test results reflect changes in V
OUT
only with respect to load current changes.