5150/5151 Video Card??

tony duell ard at p850ug1.demon.co.uk
Tue Aug 16 08:53:03 CDT 2016

> > Of course I was being ironic. The 'not joking' part refers to the
> > fact that it really is a switcher with a linear regulator.
> Which is not uncommon in multi-output switchers.  Not at all unusual to
> see the main (e.g. 5V) output directly regulated, but secondary outputs
> handled by 78xx/79xx linear regulators.

Of course. But the PSU in that Zenith monitor only has one output -- 
+12V. And there is no regulation feedback loop to the chopper stage.

On multi-output switchers often the main out has a much higher power
limit than the others. Perhaps 5V at 60A and +/-12V at a couple of amps
In which case it is not unreasonable to use linear regulators for the latter,
the power wasted is not that much.

As an aside, there is at least one DEC printer (LA324 I think) where the main
output from the SMPSU is the 36V one (that is the one that is sensed to regulate
the chopper), used for the motors, printhead, etc. The 5V rail (used for 
the logic, of course) comes off a linear regulator. One to watch for...

> That's not to say that the secondary outputs can't be switch-regulated.
> The "simple switcher" ICs are well-suited to that application.

You can of course do it with older technology too. The PDP11/44 PSU and
the HP9845 PSU spring to mind. A lot of ICs, chopper transistors, etc in there.


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