●●●●
Every bench needs
a power supply to
fully complement
the rest of its test
equipment.
I consider this to be
just below the DMM
A TEST BENCH
POWER
SUPPLY
in essential test
equipment. The
question arises,
though, as to what
type of supply and
what features should
be incorporated so as
to make it as
universal as possible.
Ihave designed and built a dozen
different power supplies over the
years, but recently I built the one
presented in this article. It is the
culmination of many years on the
test bench, which I feel will cover
most situations without going to
ridiculous extremes.
When I started this design, I set
down certain parameters that I
thought were necessary and threw
out some that I felt were of too
limited use to warrant the extra
circuitry and expense. I based these
decisions on previous supplies I had
built. Some of my objectives were
the following: smallest physical size
possible so as to take up minimum
bench space; separate analog and
digital supplies with floating
grounds; at least two analog
supplies with easily variable voltage;
full metering on both these supplies;
and last but not least — good
regulation and stability.
The final design came out
something like this: dual 0-20V @
1A; 5V fixed @ 1A; no-load/full-load
regulation < 10 mV; RMS ripple < 0.5
mV; and simultaneous voltage and
current metering on both variable
supplies. This gave the capability for
design/repair of all low power control circuits, but still have enough
“oomph” for mid-power circuitry.
From previous experience, I
have found that dealing in high-power circuits (which doesn’t occur
that often), the requirements for that
power are all over the place. It
would be difficult and expensive to
design a supply to handle all these
situations. At present, I have only
one high-power supply — a 150
watt, 13.2V unit for standard mobile
use (auto, marine, etc.). For the
occasional circuits that I build under
the high-power heading, I construct
a supply just for that device and its
particular needs.
Since all outputs are floating
with respect to grounds, this can
be set up for ± supply voltages
(my preference) for analog circuitry
and still have a digital 5V source
40
March 2007
