[time-nuts] Power supply for time source concerns

[Achim Gratz]

Am 23.12.2019 um 16:03 schrieb jimlux:
> It is tough to build a "small" input filter that has good rejection at 
> low frequencies (<100kHz?)

Yes if you want a passive filter, but you can view an LDO as an active 
low-pass in some sense.  Again you need to take care that noise cannot 
bypass it, but most of it should be conducted noise in the LF case. 
Active filtering is also a good option if the power you need to deliver 
is low.

> Buck converter to 8V   (boost converters seem to have more noise)

That again depends on topology and control type.  The canned converters 
are almost always optimized to have the lowest number of switches and 
work with cheap magnetics (single coil) without easily entering 
problematic operation modes, noise is only a secondary concern. 
Producing less noise in the first place is possible if you change those 
constraints; i.e. allow more switches, more complicated energy storage 
(capacitors and magnetics) or employ control algorithms that are less 
robust and hence need to be tuned to the load to be stable.


-- 
Achim.

(on the road :-)