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How to design EMI Filter?

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haimmuthu

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How to design EMI filter to avoid common mode noise.
I am working on DC-DC Converter with input voltage is 50 - 100VDC and output power is 200W.
Everybody is telling the overall architecture of EMI filter. https://obrazki.elektroda.pl/7778820600_1368074954.jpg.
But nobody is telling how to calculate these capacitor and common mode choke value.Can you please give any generic formula to calculate these components with respect to frequency?
 

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How to design EMI filter to avoid common mode noise.
I am working on DC-DC Converter with input voltage is 50 - 100VDC and output power is 200W.
Everybody is telling the overall architecture of EMI filter. https://obrazki.elektroda.pl/7778820600_1368074954.jpg.
But nobody is telling how to calculate these capacitor and common mode choke value.Can you please give any generic formula to calculate these components with respect to frequency?
Click to expand...
Hi haimmuthu
There are many of the application notes and text books which have been published to deal with EMI filter design . did you try to search for them ?
Have look here please :
https://www.emi-filter-design.com/
https://www.google.com/url?sa=t&rct...zaFyfkPRNH6t8X1QQA&bvm=bv.46340616,bs.1,d.ZWU

Best Wishes
Goldsmith
 
goldsmith said:
Hi haimmuthu
There are many of the application notes and text books which have been published to deal with EMI filter design . did you try to search for them ?
Have look here please :
https://www.emi-filter-design.com/
https://www.google.com/url?sa=t&rct...zaFyfkPRNH6t8X1QQA&bvm=bv.46340616,bs.1,d.ZWU
Click to expand...

I have went through your second link,
They are calculating Lc,Ld,Lcm,Ldm(177th page).Finally what value i should take for common mode chock and Differential mode chock in the attachment.Can you please fill inductor and capacitor values in the attachment.Because it is not matching with the final circuit which is there in next page.

Thanks in advance.
 

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  • EMI_inductor.JPG
    EMI_inductor.JPG
    17.9 KB · Views: 71

Switch Power Supply Handbook by Keith Billings has a great chapter on EMI filters. A design should start with the measurement of the EMI you're trying to block, and that measurement should be done only when the supply is mounted in its chassis and connected to its load, including all safety capacitors. Most of the common mode emi arises from parasitic capacitance between the circuitry and earth ground, so it's very important to do the measurement in a "real" scenario.
 

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