Alessandro Queri wrote:
> It seems you have not red all the message. I'm wondering if there's a
> way of achieve that BELOW the 50KHz switching freq.

You can certainly make a buck switcher that runs at less then 50KHz
switching frequency, but that's not what you asked.  You wanted *no noise*
in the 50KHz "band".  Switching power supplies have substantial harmonics,
so switching frequencies well below 50KHz can still have significant noise
at 50KHz.  No matter what your switching frequency, there will always be
*some* noise above 50KHz.  Requiring no noise at all makes the problem
impossible.  Noise in a certain band can be arbirarily attenuated given
enough resources.  It can't, however, ever be totally eliminated (infinitely
attenuated).

Since all schemes will generate some noise above 50KHz, you need to specify
how much you can tolerate.  "None" is a useless and impossible
specification.


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