Specifications

Objective
Characterize the time it takes
for a power supply to stabilize
its output voltage after a step
change in the load.
Approach
Connect a DC load (B&K
Precision 8500 DC load) to a
power supply. Use the DC
load's transient mode to apply
a step change in load to the
power supply.
Setup
A B&K Precision 9130 power
supply was set to 5 V output
with the current limit set to 3
A. A B&K Precision 2542
digital oscilloscope was used
to view the power supply's
output voltage. The scope
was AC coupled and set to
trigger on a negative slope.
DC Load Setup
The DC load was set to
transient mode from 1.5 A to
3 A. Pulse triggering mode
was selected for the DC load,
which means a trigger signal
causes the load to go from 1.5
A to 3 A, then back to 1.5 A.
Results
Looking at Figure 2, the load
transient response is observed
during the rise time in the load
with a step change from 1.5 A
to 3 A. The output voltage
dropped by approximately 1.6
mV.
Load Regulation
Load regulation is another
important element when
testing a power supply. It is a
performance measurement
that requires setting the power
supply to its rated voltage. To
be specific, the test for
measuring this element is
based on measuring the
output voltage levels of the
supply when a load connected
to it changes from zero
current to rated current, which
differs depending on the
model used under testing.
The purpose for this test is to
ensure the accuracy and
capability for a power supply
to maintain its voltage output
level under rated load current
changes. Before testing,
verify that the load used for
the test supports the
maximum rated current and
voltage of the power supply.
Objective
Measure the change in output
voltage from no current load
to the rated current load of
the power supply.
Approach
Use a DC voltmeter to
measure the voltage change
when the DC load is used to
step the power supply from 0
current to rated current.
Setup
The measurement is
conceptually simple, but it is
critical that the voltmeter
used to measure the voltage
change is connected to the
output terminals of the power
supply independently of the
leads used to connect to the
DC load. Failure to do this will
measure the contact
resistance of the power leads,
overestimating the load
regulation and output
resistance of the power
supply. Connect the voltmeter
and DC load in parallel to the
power supply's terminals (See
Figure 3 for setup diagram).
DC Load Setup
Press the I-set button (for B&K
Precision 8500) to change the
DC load to constant current
mode (you may have to press
the button twice). Set the
current to the rated current of
the power supply.
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Figure 3. Load Regulation Test Setup
Voltmeter
+ -
Power Supply
Settings: Rated output V
Current: Max. limit
+ -
DC Load
Mode: CC mode
Current: Rated current of
pow er supply
+ -