I have been reading and watching TI's material on EMI input filter design, and I have a few questions.
My basic question is "How do you select the component values for your EMI input filter?" The specific application I am designing a filter for is a 24V, 120W flyback converter in the consumer electronics market.
Next, I will detail what I have learned.
The input EMI filter has 4 main components: Common-Mode choke, X-Cap, Y-Cap, and Filter Inductor.
The CM Choke and Y-Caps are in charge of attenuating the common-mode noise, while the Y-cap and Filter inductor are in charge of attenuating the differential-mode noise.
I believe that the common-mode choke is first selected based on its attenuation curve and what you think the the trouble frequencies will be. You then verify this choice experimentally.
I believe the X-Cap choice is based on power consumption and power factor (according to post linked below)?
I will admit that I am not sure how to calculate the power consumption of a capacitor in this context.
TI's application notes on the filter inductor put it in the context of a CLC filter, which is confusing because I thought we chose the input/smoothing capacitor value based on the input power and not the required attenuation.
My design (and the reference designs I am using) does not feature any Y-Caps because the line cord does not have an earth-ground connection prong.
Basically, I just need some help on how to initially determine the values for these components.