DEC H7822 power supply
cc at informatik.uni-stuttgart.de
Fri May 13 02:36:08 CDT 2022
On Thu, 12 May 2022, Peter Coghlan wrote:
> Can we agree that there is such a thing as an "AC current" and there
> is such a thing as a "DC current" and the two of them can be added
Ouch... an alternating current current and direct current current ;-)
And you usually add the voltages, not the currents.
> A variac does not provide isolation. If it is not wired correctly, it is
Good "variacs" provide galvanic isolation from the mains, i.e. they are
> I just wanted to describe the obscure (to me) circuit I found in a DEC H7821
> power supply in case anyone else needs to know how it seems to work.
That indeed is really interesting. The only reason that I can imagine why
they used the ripple voltage to generate the transceiver voltage is that
they "forgot" to implement an extra secondary winding on the transformer
(or they reused the transformer from another design).
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