Star Tech Journal

March 1987 (13)
STAR*TECH Journal
~· inside Switching Power Supplies
(Part 1)
By James Beck
Greater southern Distributing Co.
Atlanta, Georgia
Well, I think we've covered just about
every aspect of the linear power supply.
Now let's make that quantum leap into the
realm of the switching regulator.
This month we'll skim over the history,
and some of the unique characteristics of
the "switcher".
As with most advances in technology, the
aerospace program brought the modem
switching power supply into existance.
They needed a conpact, highly efficient
neans of converting the power from a
sattelites solar panels into the tightly
regulated voltages that were required for
its operation.
Size is the most obvious feature of the
~switcher. They are extremely small
compared to their linear cousins. They
don't use bulky transformers, large filter
caps, or big heatsinks. What makes their
size even more remarkable is that there is
so much going on in that little box!
The "off the shelf" switching regulators
we run into everyday convert AC line
voltage into a filtered DC voltage, then
convert it into a pulsed DC voltage which
it applies to a transformer that changes
it into an AC output, and that in tum is
rectified, filtered, and regulated into an
output voltage or voltages. lots of
activity for such a little thing.
The main trick to all of this is the
frequency used. In the "old" 60Hz linear
systems, the power transformer had to be
large, and because of the frequency,
filter caps also had to be large. If you
up the operating frequency substantially,
you can d'lllrp the power transformer for a
much smaller pulse transformer, and the
~filter caps can be much smaller, also.
'Anyway, starting next nonth we'll begin
assenbly of a sinple switching regulator
and we will look at how each major section
operates. The ultimate goal of this series
is to give you the ability to recognize
and repair some of the nore co11100n
problems with these power supplies. Until
next month, have a good one!
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