Specifications

To adequately specify the power
source for products that exhibit
pulsed and dynamic current load-
ing (such as digital cellular phones
and hard drives), you need to eval-
uate both the peak and dc aver-
ages current draws.
You could use an oscilloscope to
monitor a shunt or a current
probe, but this approach raises
issues with voltage drops, ground
loops, common mode noise, space,
and calibration.
As a simpler and cheaper alterna-
tive, use a power supply with built-
in measurement capabilities. The
HP 66312B and 66332B dynamic
measurement dc sources store up
to 4,096 data points at sample
intervals from 15.6 ms to 31,200 s.
Like an oscilloscope, they acquire
pre- and post-trigger buffer data by
crossing a user-set threshold.
These dynamic measurement
capabilities are illustrated in an
HP VEE program output panel
(Figure 1).
In Figure 2, note the SCPI com-
mands in the “Set Up Source,”
“Measure” and “Enter Array”
blocks. (You can use these com-
mands in other programming envi-
ronments as well.) Note that
“MEAS” can be used in place of
“FETC” to cause an immediate
trigger. Obtain subsequent mea-
surement parameters from the
same data by using “FETC.”
Use Your Power Supply to
Measure Pulsed Current
Tip
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Figure 1. An HP VEE program that makes para-
metric measurements and captures the pulse
current loading of a digital cellular phone.
Figure 2. Block flow diagram of the HP VEE program, showing program details.
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