30 Mar
2022
30 Mar
'22
12:07 p.m.
You were right, it is switching noise. As you said, I was zoomed in too far, I hadn't
paid proper attention! The actual ripple is about 50mV peak to peak.
https://rjarratt.files.wordpress.com/2022/03/pin-1-5v-averaged-ripple.jpg
Regards
Rob
-----Original Message-----
From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Matt Burke via
cctalk
Sent: 29 March 2022 01:31
To: cctalk at classiccmp.org
Subject: Re: PDP 11/24 - A Step Backwards
On 28/03/2022 23:22, Rob Jarratt via cctalk wrote:
Its 600mV, but it is more of a spike than a
ripple. Here is a trace:
https://rjarratt.files.wordpress.com/2022/03/pin-1-5v-ripple.jpg
I think that's just switching noise. You appear to be zoomed in on the point
where the main switching transistor is turning back on. Here is a trace from
an H7100 power supply (connected to a 70A dummy load) for
comparison:
http://www.9track.net/posts/h7100_trace.png
If you turn on averaging mode on the oscilloscope (acquire menu) then that
should filter our some of the noise and you will be able to see the actual
ripple a bit better. It should be noted though that a differential probe is
required for accurate ripple and noise measurements.
Regards,
Matt 
