EMI filter design

[Peet19]

Hi all!

I want to design an EMI filter and I need some help. I need a formula that I can use to calculate the value of inductance and capacitors.
Unfortunately, I haven't found any help so far. Perhaps a drawing or an example calculation would help a lot.
Thank you in advance for your help!
I am planning a Buck converter and I want to put it on the input. The mains voltage is 230VAC. The frequency of the converter is 20kHz.

 

[ronsimpson]

I am planning a Buck converter

Is the supply isolated? Can you give us a schematic or even an approximant one.

 

[Peet19]

Yes, I disconnected the input.
I drew an EMI filter. I think the frequency transmission is pretty good, but I'm not sure.
It would be a forward converter.

The EMI in filter, capacitors C1, C2, C5 (x), C3, C4 (y). That's good?

 

[transconductance]

I have found this calculator useful for such filters. It's only set up for the differential mode, though.

 

[Peet19]

Thanks, I'll try.