Re: Question about Oxley RFI suppression filters FLTM/P/5000

On Fri, 31 Jan 2025 20:17:55 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

Jeroen Belleman <jeroen@nospam.please> wrote:

On 1/31/25 15:40, Jean-Pierre Coulon wrote:

On Thu, 30 Jan 2025, john larkin wrote:
 

EMI filters only filter high frequency stuff, AM band and up. If your
problem is AC-line frequency ripple or low frequency switcher noise, a
typical EMI filter won'[t help.
 
What does the contamination look/sound like?

 
At 10 MHz the ripple of my power supplies contaminates my output signal
at a level much higher than the documented inserson loss.
 
So I suspect some 10 MHz makes its way through a magnetic field and
perhaps a filter with only a simple annular capacitor would be?
effective.
 
 

 
It looks like your circuit has gain from power-in to output. That's
bad.

>

Anyway, it's poor practice to expect a feedthrough filter to clean
switcher noise off your power lines.
 

>
Common in single-ended circuits, though. I do a lot of discrete amps and
(for my sins) photoreceivers, which use two-transistor, four-pole cap
multipliers with >>100 dB rejection at SMPS frequencies.
>
Cheers
>
Phil Hobbs
>

 

HF noise coupling paths may not all be visible on the schematic. I
could tell horror stories.

Some switchers are really nasty.

Jean-Pierre, what switcher are you using?