Help! high power supply ripple?

[Ryanfawcett]

I have a Manson EP-613 linear power supply, output ripple should be 5mV pk-pk according to data sheet, however I am getting 400mV pk-pk as seen from photos regardless of load.

I’m sure I measured it when I bought it and it was within spec, have I damaged it somehow?

Cheers,
Ryan

[jsantoro]

Change the scope to AC coupling.

[Kean]

And turn on 20MHz BW limit

[Kean]

Aha, the PSU is off in second photo!
You likely have an external noise source being picked up by the probe.  New LED lighting maybe?

Dave has talked about similar PSU ripple measurement issues in a recent video.

[Kosmic]

Also the ground lead of the probe is too long. It's better to use a probe<->BNC adapter, then BNC to Banana to the power supply.

[tautech]

I have a Manson EP-613 linear power supply, output ripple should be 5mV pk-pk according to data sheet, however I am getting 400mV pk-pk as seen from photos regardless of load.

I’m sure I measured it when I bought it and it was within spec, have I damaged it somehow?

Cheers,
Ryan

Welcome to the forum.

There are a few traps for the unwary in accurately measuring low levels of PSU ripple especially the background noise. LED lighting is particularly bad. Adding a resistive load to the PSU and measuring ripple at it terminals also helps suppress external noise.
Some tips for you in the screenshots in this thread:
https://www.eevblog.com/forum/testgear/a-good-scope-for-measuring-low-levels-of-noise-(e-g-linear-ps-noise)/

[David Hess]

Use a differential or isolated probe to remove common mode noise.