EMC issue 50 - 150 MHz

Posted by: dl7atr on 12/02/2010

We have designed a 20W power supply with TNY377PN. Conducted emission from 150kHz to 30 MHz no problem. Radiated emission we have an issue between 50MHz and 150MHz. Peak at app. 94 MHz. Detection with near field probe identifies power supply as source of emission.

Any suggestion/idea ?

Regards
Hans-Juergen

Comments

A very common problem for radiated emissions is the output diodes. Do you have any kind of R-C snubber across the diode? Also could you provide a schematic of the design so I can better help you?

-Wesley

Hello Wesley,

yes we have R-C snubber across the diodes. I have attached the schematic.

Best regards
Hans-Juergen

I don't see a schematic attached anywhere.

Please try again.

Hello Wesley,

second try with the schematic. I have also attached the power supply PCB.

Best Regards
Hans-Jürgen

We have designed a 37W SMPS and I seee some radiated emissions like yours? at the same frequencies?

How did you fix the problem, can you help,

Best regards

Another common solution is a high frequency common mode choke on the output cable if you have a long one. Many cellphone, laptop, and other chargers have a choke on the output cable ("lump in cord").