Jose Da Silva wrote:

>> In circuits I sometimes see capacitors over each of the fout diodes
>> in a diode bridge. What is the prurpose and effect of these
>> capacitors? 
> 
> You didn't mention how-big the caps were, but guessing 100nF, then the 
> "resistance" of the capacitors could be seen as:
> 
> X = 1 / ( 2 * pi * f * C)

> possible electric motor noise
> X = 1/(2*3.141*5000hz*100nF)=318ohms (low impedance to hi-freq)
> 
> possible fluorescent ballasts
> X = 1/(2*3.141*50000hz*100nF)=32ohms (very low resistance)

This doesn't explain why they need to be parallel to individual diodes and
why there need to be four of them, does it? If you want to filter high
frequencies (in or out), a low pass either on the AC supply lines that go
to the diode bridge or on the DC supply lines that come out of it would be
just as good, I suppose. 

Gerhard

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