output choke in negative rail improves EMI?

[rfdipper]

hi to all!

can anyone tell me why there are some designs that place the output choke on the ground side and not on the positive rail?

one more thing is the output rectifier is also placed at the ground side and not on the positive side?

i've heard that it improves the EMI performance of the circuit but i cannot find any technical write-up that prove this...

any ideas?

 

[brmadhukar]

Hi,
there seems to be a contradiction in what you are saying (is negative rail same as your ground?). There can be only one reason to provide a impedance between verious grounds and it is to improve the isolation between noisy and low signal circuits but for the effects of EMI i think it is not a solution. As more current flows thru' ground, it induces a higher voltage across the inductor and increases the radiation.
Hope this helps,
Madhukar

 

[rfdipper]

hello madhukar,

sorry to confuse you, it is the negative rail or common, I misused the term ground to refer to the common or negative connection.
because i have seen some designs in the internet that places the output choke in buck and buck-derived topology on the negative rail. I asked others and they said that this arrangement lowers EMI, maybe they are speaking out of experience, but I want to have a analytical understanding of what is really the effect and the reason why some designers prefer to place the choke on the negative rail.

regards,

rfdipper