[ericj]

I understand how a common mode choke works. Two chokes right on top of each-other on an AC line -- if noise on the AC is common -- present on both wires -- it will cancel itself out when it hits the common mode choke.

They always seem to be hooked up directly to mains power, which makes sense.

The question i have is, if i have an AC power brick, with no room in it for a choke, does it make any sense at all for me to use a common mode choke on the stepped-down AC voltage after it gets into the box with the rest of the power supply?

Seems like the lower voltage swing would probably make a common-mode choke less effective, but maybe there is still some value in using one? I mean, as long as i've got a bunch of them, and room on the power supply board.

 

[tangent]

I'm certain I've seen line filters on the secondary side before.

 

[Garbz]

Correct me if I am wrong but common mode noise can't actually travel through a transformer.

 

[tangent]

Depends on how the transformer is wound.