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EMI Filter Design For Synchronous Buck Converter

biswaIITH

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Currently Working on a 450 W(Vin=(40-60)Vdc & Vo=14V)....

I would like to know proper EMI filter design calculation for a sync buck converter.

Kindly, share your experience or any relevant application note
 

treez

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I used to work with the engineer who designed many of the power supplies for British military aircraft etc............on being asked about calculation of values of ferrite beads and common mode chokes and Y caps etc to fight common mode noise...this engineer said..."its like sprinkling currents into a cake".

At the time this engineer was working for a consultancy who was working on the same project as i was....but their bit was much bigger than mine.

Beware with diff mode L and C...if you use too big values, you may well get well below the line on the plot in places, but the common mode will be worse due to the parasticis of the big L and C
 

biswaIITH

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I used to work with the engineer who designed many of the power supplies for British military aircraft etc............on being asked about calculation of values of ferrite beads and common mode chokes and Y caps etc to fight common mode noise...this engineer said..."its like sprinkling currents into a cake".

At the time this engineer was working for a consultancy who was working on the same project as i was....but their bit was much bigger than mine.

Beware with diff mode L and C...if you use too big values, you may well get well below the line on the plot in places, but the common mode will be worse due to the parasticis of the big L and C
I see.. Thanks.. I have come across people who claims to pass CISPER 25 Class 4 Regulation with a Differential mode filter.

But is only a differential mode filter(In Pi Configuration) along with a good PCB Layout sufficient for fighting both type of EMI Noise??
 

Akanimo

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Hi,

Currently Working on a 450 W(Vin=(40-60)Vdc & Vo=14V)....

I would like to know proper EMI filter design calculation for a sync buck converter.

Kindly, share your experience or any relevant application note
See the text "Fundamentals of Power Electronics" by Robert Erickson and Dragan Maksimovic for input filter design considerations.
 

treez

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To be honest, passing Diff Mode is usually quite easy as long as you sufficiently damp out any LC filter oscillations. Its the common mode that is more challenging to get down low enough to pass.
 
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