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off the shelf SMPS ground noise

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Colon

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Hi everyone,

I work for a company making sensitive RF receiver equipment and need to find a suitably quiet 24V 80W+ supply. I could go with a linear supply but my main stumbling blocks there are fitting it in our chassis (82mm high) and having end-user selectable input AC voltage (110/220V is needed). A SMPS would be preferred if I can make it quiet in my band of interest, which is 10kHz to 1.5MHz.

I can deal with radiated noise through our own screening. I can also deal with DC rail conducted noise if I throw enough CM and DM filtering at it. The problem I have found this week is noise getting through onto my chassis through the earth, presumably through mains filter Y caps. I see this at the switching frequency and also much lower, around 10-15kHz, which I assume is pulse skipping.

Does anyone have any ideas on how to deal with this, or a quiet supply I can try, or even what to look for in the specs. So far I've tried an Emerson LPS100-M, TDK NV175 and Traco TXL, which we had lying around. Emersons was worst despite being medically rated with a low leakage current. Traco was best.

Also, an earth choke doesn't help I've discovered...

Thanks
James
 

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