On 09/07/17 16:10, Cursitor Doom wrote:
Gentlemen,

The link below shows a scope trace of the output of a linear PSU (voltage
4.7VDC) with about 300mV of 100Hz ripple riding on it. This PSU is in-
circuit under load from the boards it supplies. Normally I would assume a
filter capacitor to be at fault here, but they all check out fine so
something else is causing this ripple. Note there is a characteristic
'knee' on the high peaks and I'm thinking this must be indicative of
*something* trouble is, I don't know what. If anyone recognises this
waveshape and knows what causes it, that'd be "awesome" - as our American
friends describe everything. Check it out:


https://www.flickr.com/photos/128859...in/dateposted-
public/

It took me 5 minutes to do a spice simulation
sufficient to generate such a picture.

The components were an ideal ac voltage source,
a diode, an ideal capacitor for smoothing, an
ideal resistor for the load, and an ideal resistor
in series with the smoothing capacitor representing
the smoothing cap's ESR.