DEC H744 +5 supply

Noel Chiappa jnc at
Fri Sep 21 17:20:35 CDT 2018

    > From: Mattis Lind

    > The H744 is a buck converter. You can read about buck converters here:

Wow, that was incredibly hard to read; no clear and simple explanation of the
basic concept of how it works, before getting into the details!

If I understand it correctly, it stores part of the incoming energy of a block
of current in the field around the inductor; later, switches change state to
create a loop that includes the inductor, and it uses the stored energy to
cause electrons to flow around the new (temporary, because of the switch)
circuit. Is that about right?

The H744 manual doesn't really talk much about that aspect of the circuit's
operation (at least in terms of 'we use this trick to get all the energy out
of the incoming current flow'); it just describes the stuff around the coil as
"an LC filter". It says "This type circuit is basically only an averaging
device", which I wouldn't say is really on point - that would describe my
(incorrect) prior description as well as the correct one.

And just to make it even more confusing, it says "most of the input voltage is
absorbed across the emitter-collector of Q5", but I looked, and Q5 is tiny,
and I eventually figured out that that only applies to the +15V needed to run
the voltage regulator.


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