How To Design A Line Filter?

hello everyone
what is relation between line filter cutoff frequency and power supply frequency?
i have a flyback converter with 100KHz switching frequency,how can i design a LC input line filter for it?
thank in advance.

Hi,

You need to be low impedance at mains frequency and you need to be high impedance at high frequency.

I'd start with a filter frequency of sqrt(mains_frequency x 100kHz)
About 2kHz... 3kHz.
With a first order filter you may attenuate (theoretically) the 100kHz to about 1/40.

You may increase filter order and adjust filter frequency to improve performance.

Klaus