[sdiy] DC wallwart +/- on-board V Reg ?

[ASSI]

On Friday 06 March 2015, 11:02:12, Andre Majorel wrote:
> About 10 years ago, I read something to the effect that getting
> rid of the noise of a switch-mode power supply by following it
> with a linear voltage regulator does not work. Not as well as
> people think it should, anyway.

You'll have to look at the power spectral density of the noise and the 
frequency dependent PSRR of the linear regulator.  Generally it will drop 
towards higher frequencies, often to very low values already in the kHz 
range.  Once you've done that you will realize that you'll need a fair 
amount of passive filtering before the added linear regulation (which only 
really cleans up low-frequency noise) starts to have any benefit on the 
total noise.  Another concern is that high-frequency noise can find lots of 
ways past the linear regulator if you aren't extra careful.  The closer you 
filter towards the source of such noise, the better the chances you can 
actually contain it.


Regards,
Achim.
-- 
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