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Thread: How measure ripple/noise of psu

  1. #21
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    Quote Originally Posted by Stefan Payne View Post
    No, you need 20MHz.
    The plots above seem to show variations at the scale of just a few kHz (Time 10.0ms), and that circuit is from 1973 so I imagine components are better these days (45 years on)
    Last edited by ashiekh; 03-07-2018 at 08:57 PM.

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    Quote Originally Posted by Per Hansson View Post
    Holy thread batman revival time!
    Just a small question on this theme: what sort of setup for the capacitors do you folks use?
    I have always neglected to do it: but when testing to rebuild this Seasonic PSU discussed here I found out the hard way that it really matters!
    Not satisfied with the result after recapping it with LOW esr caps (actually motherboard grade) I bought some general purpose caps like the originals seems to be.
    But the result was worse, but then I put on a 10µF electrolytic cap and a 100nF film cap and most of the ripple I thought was there was gone, meaning it was mostly HF noise...
    But holding those caps + probes and cables in close proximity made me feel there might be a prettier solution to this
    I think that most testers (Sunmoon) used by the big sites contain the bypass caps inside the testing equipment right behind the BNC output jacks.
    Anyway the Intel design guidelines are a bit wierd, the text reads:
    Ripple and noise are defined as periodic or random signals over a frequency band of 10 Hz
    to 20 MHz. Measurements shall be made with an oscilloscope with 20 MHz bandwidth.
    Outputs should be bypassed at the connector with a 0.1 µF ceramic disk capacitor and a
    10 µF electrolytic capacitor to simulate system loading. See Figure 5.
    Yet they then suggest these as candidates:
    Filter Note:
    0.1uf - Kemet, C1206C104K5RAC or equivalent
    10uf - Vishay 293D106X0025D2T or equivalent

    The latter of course being a Tantalum capacitor and not an electrolytic!
    I think I'm just going to make a small board with alligator clips with these caps on it, and then put some shrink wrap over it all.
    That will do fine for my uses
    "The one who says it cannot be done should never interrupt the one who is doing it."

  3. #23
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    Quote Originally Posted by Per Hansson View Post
    I think that most testers (Sunmoon) used by the big sites contain the bypass caps inside the testing equipment right behind the BNC output jacks.
    Not from factory, they don't. I had to install them on both SM-268s and the FastAuto. IIRC Tazz had to do the same thing on the SM-5500.

    It does make a difference on some but not all units tested with them.

  4. The Following User Says Thank You to Oklahoma Wolf For This Useful Post:

    Per Hansson (03-12-2018)

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