Re: one more try at my input filter question

In article <memo.20060505141516.3084C@xxxxxxxxxxxxxxxxx>,
David Collier <from_usenet_sci_elec_des@xxxxxxxxxxx> wrote:
[....]
That causes noise on the wire going back to the supply. That stops me
getting CE approval for the box ;-(

Is it noise raditation from the wire or conducted noise on the wire that
you are concerned with. In the past, I have gone so fars as to run power
supply lines as shielded wire or even coax to reduce radiation.

[....]
Now, back when I did exams, I seem to remember circuits which would
exhibit a high impedance at a single frequency. usually consisting of a
cap and inductor.

Parallel tuned circuits in the filter are seldom a good idea. The AC
current in the inductor is large so you need a big core. If you've got a
big core, you could make a larger inductor at a lower ripple current.

Can you place an inductor right at the power entry to the PCB? Some types
of inductors, such as "pot cores" are easy to mount to the *** metal.
If you've got the room, this may help.

They make PCB mounting coil formers for pot cores and a few otehr types.
You could use one of these to hold a small PCB onto the POT core and
chassis. This will give you room for more capacitors.


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