Another Unrelated PSU Question

Brent Hilpert bhilpert at
Sat Apr 18 12:57:31 CDT 2020

On 2020-Apr-18, at 10:03 AM, Rob Jarratt via cctalk wrote:
> I have another PSU I have been meaning to look at for a long time. This one
> has fairly high output ripple and some of the voltages do not appear to be
> where they should be. I have checked all the capacitors for ESR and they
> appear to be OK, with the exception of the two big smoothing capacitors on
> the primary side. One of them appears to be slightly bulging, but has
> low-ish ESR, the other has a much higher ESR. Is it possible that these
> capacitors could be the cause of the out-of-spec outputs?

What frequency is the ripple - mains frequency (50/60Hz) or switching frequency?

If the ripple is at mains frequency then, yes, the problem could be the mains/primary filtering. (Primary supply drooping far enough across mains cycles that the switcher is affected and unable to maintain drive.)

Either way, you could scope the primary supply under operation (some load), to see what the ripple there looks like.

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