Re: one more try at my input filter question

In article <6-OdnY8LdY9J6MbZnZ2dnUVZ_u-dnZ2d@xxxxxxxxxxxx>,
John Popelish <jpopelish@xxxxxxxx> wrote:
David Collier wrote:
[...]
All the PSU chips which run at fixed frequencies say "this makes the
noise easier to filter" - Hmmm. how exactly?

Beats me.

To the degree that you work at only one running frequency figuring out the
filter is easier.

If the PWM chip had a frequency that varied all over the place, the same
marketing person would find a way to say "spread spectrum" in the data
***.

[...]

a cut-off frequency well below 500KHz. But I have a PCB artwork already,
and PCBS built, and that would require making new PCBs. I'd like a
retrofit mod if I can work one out.

If this is a big complex PCB with lots of other stuff on it, I suggest you
consider this:

If you can identify the footprint of some part that you can use more or
less as a connector, you can make a small sub-assembly that plugs on there
to carry the better filter.

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