DEC H744 +5 supply

[Noel Chiappa]

So there's something about the H744 I'm not sure I understand; hopefully those
with more analog-fu will set me straight if I'm confused.

This supply runs off 20-30V AC. It takes the input AC, rectifies it, and runs
it through a cap to filter out the ripple. What's next is that it's an early
switching supply; i.e. the electronics inside switches that newly-created main
DC off and on very quickly to keep the output voltage at around +5V.

However...

My understanding is that, without using a transformer (which creates an
independent circuit loop - more below), there's no way to increase the
_amperage_ out of circuit over what's fed into it: since amps are
electrons/second, the electrons/second out more or less have to equal
electrons/second in, since one can't easily 'create' electrons - at least, in
normal electonic gear! (Transformers, by creating a whole new circuit loop,
can 'create' more electrons/second in the new loop; since they tie the 'out'
of the new circuit back to its 'in', they can recirculate the 'extra'
electrons.)

And to the extent that the output is at lower voltage, the energy differential
has to be dumped; hence the huge heat sinks - a lot of the incoming power in
that 30V AC has to be thrown away, in producing +5V. Right?

My (possibly confused) understanding is that later switching supplies take the
incoming 60Hz wall AC, transform it to a higher frequency, run _that_ through
a transformer (which can be a lot smaller, since it's at a higher frequency,
and the higher the frequency, the smaller the transformer you can use - hence
the use of high frequency AC in airplanes, to allow use of smaller - and thus
lighter - transformers). That then turns out a massive amount of amps in the
output loop (since with a transformer, energy out is roughly energy in, modulo
resistive losses; and with constant power, if V goes down, I goes up).

So the losses are a lot lower - N amps at 110V in produce ~20N amps out at
+5V. (Well, depending on all the losses, ~20.) And the whole works is a lot
lighter, to boot.

Did this programmer get all that analog stuff correctly?

Thanks!

	Noel