> and feeding the secondary with 12VDC.
>
The switcher in a typical PC supply rectifies or in newer supplies
uses a power factor correcting boost converter to create 360V to 400V
DC. This high voltage DC is chopped to drive the secondary side
regulators. The waveform they get is pulsating DC. Usually this
pulsating DC is higher than the 12V that the PC needs for the disk
drive motors. You probably could drive the other regulators with a
lower pulsating DC and feed the disk drives from the 12V direct.
The complete 12V / 24V / 48V supplies are expensive because they are
in lower volume and still provide the isolation from the input
supply. That is to say, on a 12V input model one could potentially
feed it with +12 or -12 volts. The input supply ground is isolated
from the PC voltage supply ground. This is probably important to a
radio site user. Most radios have the radio negative supply rail
tied to ground. It can be a good thing to have the PC isolated from
the radio ground especially when lightning strikes the site's
antenna. Many people who use PC control at their radio site, have
opto isolationi in the control path and transformer isolation in the
audio paths. This isolation (from the AC mains and the
control/audio) permits the PC to float and ignore the possible
movement in ground potential between the AC neutral/safety ground,
the radio ground, etc. So one gets what they pay for.
Just as there is a difference in the quality of AC input power
supplies! I wouldn't use a "Sparkle" brand PC supply if yoou gave me
one.
just my three cents 73
Ed K3SWJ
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