Author Topic: Help! high power supply ripple?  (Read 424 times)

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Offline Ryanfawcett

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Help! high power supply ripple?
« on: September 11, 2020, 02:37:09 pm »
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

 

Offline jsantoro

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Re: Help! high power supply ripple?
« Reply #1 on: September 11, 2020, 02:41:24 pm »
Change the scope to AC coupling.
 

Offline Kean

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Re: Help! high power supply ripple?
« Reply #2 on: September 11, 2020, 02:44:17 pm »
And turn on 20MHz BW limit
 

Offline Kean

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Re: Help! high power supply ripple?
« Reply #3 on: September 11, 2020, 03:49:47 pm »
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.
 

Offline Kosmic

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Re: Help! high power supply ripple?
« Reply #4 on: September 11, 2020, 04:02:28 pm »
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.



« Last Edit: September 11, 2020, 04:04:44 pm by Kosmic »
 

Offline tautech

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Re: Help! high power supply ripple?
« Reply #5 on: September 11, 2020, 08:25:44 pm »
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)/
Avid Rabid Hobbyist
 

Offline David Hess

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Re: Help! high power supply ripple?
« Reply #6 on: September 12, 2020, 01:05:25 pm »
Use a differential or isolated probe to remove common mode noise.
 


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