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EMI filter design, values of cap and ind.

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hi all,

I have to design EMI filter for a device, unfortunately ı am new at this issue. I decide to design CLC pi filter, but ı cant documents about this subject.

My problem is ı design smps having 132 kHz switching frequency and having about 10w power , it is successful electrically. Provides 2A 5V continuously, but fail EMI test. I use C-L filter but according to some document ı have to use C-L-C filter but this documents haven't got any info about this C-L-C values for any design. So ı want to learn design design.

Is there any friend help me?

thanks replies.
 
Is this for the input of the smps?

In some cases the input EMI can be significantly reduced by a common-mode filter. Suggest you look at those also.
 
How about sending a schematic. At least of the filter.
Do you have the data on the EMI failure? What frequencies and by how much? What type of EMI?

If you fail at 132khz the answer is different than failing at 100mhz.
Radiated or conducted, Common mode or differential mode?
 
Assuming that the EMI test you failed was for conducted emissions, the classic filter is a balanced pi network optimized for common mode inductance, with additional common mode capacitors to earth ground. Look at the online catalogs and datasheets for Corcom, Schurter, Filter Concepts, etc. Their internal schematics and attenuation tables will show you how the big boys do it. For low power switchers, Power Integrations datasheets, design kits, and app notes have filter design.

You don't say the frequencies at which the tests failed, or which standards your device was being tested to (this planet has over 100 of them).

Note - radiated and conducted emissions are very dependent on component placement and pc board layout techniques. Also, even though the switching frequency is not very high, there could be parasitic oscillations in the hundreds of megahertz caused by such things and the particular type of output rectifier diode. Without detailed test results, everything is guesswork.

ak
 
Guys, this is an ancient thread reactivated by a drive-by poster.
JimB
 
.............................:sorry:...mutter mutter..............................:sorry:..mutter mutter.......................................:sorry:
 
there is a reasonable filter CAD and design package you can download
LG, be aware that the type of filter being discussed in this thread is not an active filter using an opamp.
JimB
 
LG, be aware that the type of filter being discussed in this thread is not an active filter using an opamp.
JimB
I have answered the wrong post anyway!! It couldnt get worse (well it could), I didnt check the date either!! I HATE it when I get caught by the drive by's!! I wonder if they sit and watch :D. Yeah I reread and noticed the noob mistake on filter type!! ONE of THOSE days clearly!
 
shame the thread died it would have been a good discussion once I got on the correct page :D
 
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