Measuring ripple from ATX PSU

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fredrik.jacobsson
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Joined: Thu Sep 23, 2010 11:26 am

Measuring ripple from ATX PSU

Post by fredrik.jacobsson » Thu Sep 23, 2010 11:59 am

Hi!

I'm trying to figure out how to mesure the ripple/noise from a ATX psu. For my setup now is a ATX PSU connected to a constant load and my picoscope 3206 connected to it.
My problem is that the values are inconsistent.

http://img46.imageshack.us/img46/1362/pico1.png
http://img40.imageshack.us/img40/6356/pico2.png

and with slower sample time:
http://img714.imageshack.us/img714/1818/pico3.png

I've added 3 mesurements, AC RMS, True RMS and Peak to Peak, what value should I use?

// Fredrik

gruntman
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Joined: Thu Sep 28, 2006 3:50 pm

Re: Measuring ripple from ATX PSU

Post by gruntman » Mon Oct 04, 2010 7:59 pm

Fredrik,

Going by the three images that you posted, I wouldn't necessarily state that the values are inconsistent - You are comparing a zoomed out capture to one that is basically zoomed in x200. The short window that you are looking at you are going to see the values change drastically as the burst come and go.

Since the ATX specifications is as follows:
Voltage Rail Tolerance
+5VDC ± 5 %
-5VDC (if used) ± 10 %
+12VDC ± 5 %
-12VDC ± 10 %
+3.3VDC ± 5 %
+5VSB ± 5 %

*ATX Specification Version 2.2 2004 Intel Corporation

I would probably set up a min and max parameter and note if the waveform goes over those two values. PicoScope's mask testing functionality would make this testing a breeze.

Regards,

Richard Boyd
Crag Technologies, Inc
http://www.pc-oscilloscopes.com

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