EMI filter in high frequency switching circuit

Hello everyone,

I have read about EMI filters used in power converters to reduce the noise produced by the high frequency switcher.
All articles agree that you have to measure the noise, its impedance in differential mode and common mode and then choose filter type and design it etc..

However, for example the simple SMPS online designer powersim.com or Power Integrations AC to DC converters online designer seems to design the EMI filter without needing any practical measurement. How comes that ? Is it because they already have conducted tests and suggest from their general collected data ?
Are there some standard EMI filters values depending upon the frequency and country regulations ?

See e.g. this example https://www.poweresim.com/index2.jsp?LoadRecommendSystem=2

Any comment is appreciated !

I should imagine they have standard filters at power.com.
But if you want you can go through it, and get a unfiltered conduction scan done...then you can see how many dB's down you need to be at whatever frequency, and then just design a filter with a transfer function that gives you that. Remember that you need to take the source (line) impedance as being 50 ohms cuzz thats what it will be when the LISN is in there.

Due to the nature of the EMC scan method, you cannot really very easily design the filter from pure theory straight away, because you have to consider the window size of the scan....and which frequencies get which window size by the spectrum analyser.

Ultimately, remember that although the regulations for EMC started out with good intent...the fact is that they (like many standards) become corrupted so that small newby competitors cannot easily come into the market and start competing with the big companies. The standards are often made deliberately opaque to keep the small co's out. Just my opinion.

There is a post on this forum which goes through the sizing of the inductance of the common mode choke.......there's no realistic way to exactly calculate exactly how much common mode inductance that you need....