Hi all,

I am getting myself a bit confused with how to best approach filtering the following scenario.

I have a SMPS which generates 4 voltage rails all sharing the same tap (ground) on the secondary, before I receive it. General knowledge tells me, I should worry about common mode noise since it is a switched mode supply.

There already exists a block filter as shown in the attached image. V1 already is filtered as such so I am hesitant to change it, however I want to filter adequately V2, V3 and V4. I was thinking of just differential filtering them through a largish ferrite and Y cap to DC-GND.

Do block filters like this have much in the way of common mode attenuation? The two input inductors don't appear to be coupled, so it just appears to me mostly differential.

Any insight would be much obliged.

Cheers,

James

 

I'm surprised to see L2 in the ground line. Are you sure it's connected like that?

Pi filters are very commonly used, and work pretty well.
http://en.wikipedia.org/wiki/Capacitor-input_filter

 

I'm surprised to see L2 in the ground line. Are you sure it's connected like that?

Pi filters are very commonly used, and work pretty well.
http://en.wikipedia.org/wiki/Capacitor-input_filter

I was to to be honest. Attached is the datasheet. Maybe I'll just scratch it and go with a more standard approach as otherwise I'm concerned of how I'll share all of the grounds appropriately.