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AC/DC 500W Supply EMC Issue's

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fordj06:
Hi guys

I'm a EE student on placement and I've just taken over an existing power supply design that was never EMC tested. We are now wanting to put the design into a system that needs to be certified for EMC class A (EN 55032 CISPR 32). I took the system to the EMC test house the other day for some pre-compliance testing and it failed, miserably.

We determined that it was the AC/DC power supply that was the source because the system was still failing with just the power supply in the test rack.

We are using a PFE500SA-48 from TDK-Lambda as the main power module and have used the same supporting passives as they used for there in house verification. (See attached schematic).

Some notes from the pre-compliance:

- It failed both emission and immunity
- When we increased the size of the earthed chassis the results were worse
- It was failing at around 30MHz (Ive attached some results)
- It was broadband interference


Any experience would be appreciated.

Thanks 

moffy:
Have you tried a suitable ferrite  in series with the mains cable to attenuate the 30MHz etc?

poorchava:
Am I missing something or you don't ahve a capacitor between primary and secondary ground? Ie a way for interferences to close the loop. you could try adding a small (eg 4.7n y1 type) capacitor between grounds.

T3sl4co1l:
Probably do this.

L1 probably isn't doing much.

What's conducted look like?

Tim

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