Beaten by VT100 PSU.

js at js at
Wed Aug 17 13:30:59 CDT 2016

On 8/17/2016 1:19 PM, tony duell wrote:
>>> More load _reduces_ the ripple? That's very unusual.
>> Perhaps a parasitic oscillation that's defeated by more load
>> because now the loop gain is below 1?
> But loading the +5V output also reduces the ripple on the +12V
> output. Loading the +5V output would, I think, vary the mark-space
> ratio of the drive to the main chopper and thus the drive signal to
> the 555 in the +12V regulator. Not that I can see how that would
> affect things.
> -tony

And yet, I've had several times where more load smoothed out a whining SMPS.

The most simple explanation is a cap problem somewhere causing an instability.

Mattis, have you checked ALL the electrolytic caps in your power supply, and beyond just simple ESR testing?   Have you properly reformed all these caps?

- John

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