I have a linear (non-switched) power supply that states in the specs a ripple of 10 mV p-p

Measuring it with the oscilloscope, as you can see in the image it measures Vpp = 30mV.

The oscilloscope is measuring 30 mV on those strong, high spikes, but what is the actual power supply ripple, those high spikes, or the thick line that is about 10 mV?

What can be those high peaks that are seen in the image? Maybe some interference generated by some c.i. regulator?

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I have connected the oscilloscope probe to the source crocodiles

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Power Supply Specifications

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  • \$\begingroup\$ You should describe your test method clearly, preferably with a circuit diagram \$\endgroup\$
    – armcc
    Commented Aug 9, 2023 at 6:23
  • \$\begingroup\$ I'll try, but it's just connecting the oscilloscope probe to the output pins of the power supply, no components involved \$\endgroup\$
    – Mario
    Commented Aug 9, 2023 at 6:26
  • 1
    \$\begingroup\$ Please link to the datasheet for said power supply and include a photo of your measurement setup. \$\endgroup\$
    – winny
    Commented Aug 9, 2023 at 6:46
  • \$\begingroup\$ What is scope bandwidth set as? What is your probing setup? (Note mere connections don't matter: wire position, length, etc. all matter at these frequencies!) \$\endgroup\$ Commented Aug 9, 2023 at 6:51
  • \$\begingroup\$ Linear regulator will not have ripple like those spikes. There must either be a switch mode supply before it, or nearby it. Also commonly the noise is measured with 20 MHz band limit, which the scope settings shows to be off. \$\endgroup\$
    – Justme
    Commented Aug 9, 2023 at 7:17

1 Answer 1


As said by @Tim Williams and @Justme, be careful when making oscilloscope measurements with low resolution. In some cases, voltage peaks don't exist, they're artifacts.

Here's a naive measurement (yellow probe):

enter image description here

The same measurement with a ground spring tip (green probe). The green probe is above the yellow probe:

enter image description here

enter image description here

And the result. The voltage peaks don't exist, they're artifacts. Artifacts arise from mutual inductance coupling between the probe loop, formed by the probe and its ground, and the environment.

enter image description here

Make sure you measure with a ground spring tip and in AC coupling.

  • \$\begingroup\$ This is good advice and the likely explanation for the "background noise" in the picture, but I don't think it explains the spikes. \$\endgroup\$
    – Lundin
    Commented Aug 9, 2023 at 7:38
  • 1
    \$\begingroup\$ Thanks... right now I'm without the oscilloscope but when I get it back here I'll try your advice \$\endgroup\$
    – Mario
    Commented Aug 9, 2023 at 16:30

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