Homebrew_PCBs

On Mon, 11 Jul 2005 17:12:24 +0200, Roy J. Tellason
<rtellason@...> wrote:

> An
>> electro-magnetic interference coil, supposed to remove common waveforms
>> across all signals. I read somewhere it is a good idea to place these
>> when
>> cables enter a PCB, to remove interference they pick up.
> I've seen those used that way, and also in the transformer primary
> circuit,
> but if you do that make sure you select a part rated for that use. Often
> capacitors (also specially rated and often called "safety" capacitors)
> are
> placed across the line at each end of the coil. This can also have some
> effect on interference getting out into the line from the equipment, as
> well.

You can get mains filters as complete module, really cheap, sometime
combined with the power plug.
Also, they can often be found in various equipment like PC supplies and
other stuff.

I don't think they are needed for a transformer supply however.

ST