[time-nuts] Low noise power supplies - dont' use Electrolytics

Attila Kinali attila at kinali.ch
Mon Nov 28 17:22:34 EST 2011

On Mon, 28 Nov 2011 16:16:58 -0500 (EST)
SAIDJACK at aol.com wrote:

> Use foil caps to avoid vibration-microphonics. Very expensive, but hey you  
> get what you pay for. Use Tantalum caps if bulk bypassing is needed, using  
> multiple 100uF units if necessary. The design is not right if you need more 
> than  say 470uF anyways unless you are switching tens of amps as in an 
> Audio power  amp..

I can agree on that, though i also had a design where i used 5*100uF
and it was barely enough (a system that usually used just a couple of
mA, but occasionaly could draw up to 2A for half a second. Of course,
the power supply could only deliver about 500mA)
> Use ceramic caps where vibration is not an issue. Use high frequency  
> (>2MHz) switchers wherever efficiency is required, otherwise use linear  
> regulators.

Not really. If you want to have good efficiency, then you want to stay
below 1MHz, otherwise switching loses get too high. But the disadvantage
is that you have big and bulky capacitors and inductors. 

Staying somewhere between 1MHz and 1.5 is usually a good compromise if
you can tolerate PFM (aka pulse skip) for low load conditions. Going up
to 2MHz (and beyond) is only recomended if you are severly space limited.

			Attila Kinali

Why does it take years to find the answers to
the questions one should have asked long ago?

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