TNY276 flyback do not pass EMC test

Could you PLS upload the schematc and layout? And looks lke you worry about EMi at high frequency.

regards

I am worry about EMI at high frequency and near 600 KHzJ 

See attachde files, please

Would you like to try RCD snubber for your primary side and RC snubber on the output diode? Make sure that the RCD snubber has a damping resistor and the damping effect is good.

Regards

Yes, I have tried RCD dumper and RC dumper:

R= 100K and C= 1000pF in parallel to P6KE200 - no effect (same EMI) 

R= 50K and C= 2200pF in parallel to P6KE200 - no effect (same EMI) 

R= 100K and C= 1000pF without a P6KE200 - no effect (same EMI) 

I will try RC snubber on the output diode. Our design do not use it now.

That is not the right way. Can you parallel a 4.7nF cap to the zenner and place a 100 ohm resistor between the snubber diode D4 and the 4.7nf snubber cap. the 100ohm works as a damper.

See attached file, please. We have tried all these variants. Output diode have snubber also. No effect. May be our design originally incorrect? May be isolated output should have C-L-C filter? Isolated output is 8V, 0.2A. On non isolated output 5V line after 7805 regulator connected tohether with input line? May be it is wrong, impossible?

 I found that very high voltage diode us1m are used as the output diodes, could you PLS use  schottky diode to replace it on the secodnary.  For the snubber, 160V TVS parallel with 10nF cap first, then series with a 100ohm resistor and connect to the RCD snubber didoe.

Can you check a design of our transformer? May be design is wrong? See attached file please.

If the EMI can pass, you do not have to change the transformer. If the EMI can not pass with schottky diode and good snubber, you can optimize the transformer and make ure the secondary winding 7-8 is close to the primary side main winding of 4-6. The leakage inductance can be reduced and thus it is very possible that the EMI could be improved.

Regards