piclist 2000\06\06\141627a >
Thread: Filter Capacitors
www.piclist.com/techref/logic/dsps.htm?key=filter
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face BY : David VanHorn email (remove spam text)



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At 10:53 AM 6/6/00 -0700, Peter Schultz wrote:
>What he is trying to say about a rule of thumb. Common practice is a few
>extra capacitor does not hurt.
>Most of the cases filtering is over done and try to compensate for bad
>layout, grounding systems....

Extra caps will not save a bad layout. It's like bigger engines on the
titanic.
Occasionally, accidentally, you may hit something that makes the problem
look better by shifting it somewhere else.

>Nice example is a high-end audio preamplifier, takes about 50 ma current
>from the power supply, which was filtered by 22000 uF capacitors....

Great example of bad bypassing.
If these large caps were perfect, then this would be a good idea.
It would be very interesting to sweep them, and see where they are really
acting as low impedance capacitors. I suspect they are very effective at
60-120 hz, (of course good regulation would do far more to eliminate PS hum
than large caps)  but up at 10-40kHz, they may not be any more effective
than maybe 100uF (not sure here, I haven't made the measurement on such
large caps, and it would be pretty specific to type)


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