DEC H7822 power supply

Toby Thain toby at
Thu May 12 12:40:47 CDT 2022

On 2022-05-12 11:37 a.m., Peter Coghlan via cctalk wrote:
> Toby Thain via cctalk wrote:
>> On 2022-05-11 7:02 p.m., Peter Coghlan via cctalk wrote:
>>> Given the normal usage that has evolved for the terms DC and AC 
>>> rather than
>>> their dictionary definitions, I would suggest that the current that gets
>>> passed by a rectifier has both a DC component and an AC component.  When
>> It does not, due to unidirectionality.
> Consider the current through the rectifier as the sum of a "DC" current 
> plus
> an "AC" current.  The "DC" current has a steady positive value and the "AC"
> current varies above and below zero with a magnitude less than or equal to
> that of the "DC" current.
> When the two are summed, the result is a varying current which does not go
> below zero.  This is what I mean by it having a DC component and an AC
> component.

Sure, if you change the reference point, a DC signal under one reference 
("zero") potential becomes AC under a different potential. The 
definitions are relative to a reference, in order to define the current 

> This sort of analysis often used in electronic engineering to break down
> more complex entities into simpler ones which can be analysed separately
> with greater ease.  Didn't somebody have a theorem or an axiom or something
> that says this is a valid way to do it? I forget who.  It was a long time
> ago.  Kirchoff maybe? No, it wasn't him, maybe he was the one that said
> the sum of currents into and out of nodes is zero and stuff like that...
> It is a particularly suitable strategy for the case in hand because a
> transformer will not pass "DC" from primary to secondary so the effect of
> this component can be ignored (except that it could cause the transformer
> core to saturate which must be allowed for.  This is only relevant to the
> designer of the power supply but if I don't mention it, someone will
> surely tell me that I should have.)
> (I am starting to regret making the effort to accurately describe this
> unusual and confusing (to me anyway) circuit for the benefit of others who
> might find themselves struggling with this power supply as I was and might
> find some hints on how it operates to be helpful.)
> Regards,
> Peter Coghlan.

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