let's try to concentrate Spehro's good opinions... :)


On Tue, 17 Dec 2002, Jinx wrote:

> I'm using a 47uF cap to filter a 50mV signal on a PIC
> comparator pin.

Joe, if you dislike filtering using electrolytic capacitors then
integration using OA and not-polarised capacitors are just another
( expensive ) option.



Is 50mV enough to maintain the oxide
> layer or is this cap going to deteriorate. Web references
> to re-forming old or dead caps don't appear to give any
> clues as to what voltage is actually needed to keep the
> cap alive in the first place.


How many years do you offer guarantee for your products ? :)
With or without voltage, a good wet aluminium capacitor does not have a
life greater than 7...10 years at full capacity.


I recall a thread about using
> aluminium foil caps close to their rated voltage for best
> life. Would a Ta cap be better ?


Yes, only if you don't exceed the amount voltage drop ( in your case will
be ok ) The Ta have the avantage of filtering both low and high
frequencies noises, if you will use an inductive electrolytic capacitor then a small
non-inductive, non polarised one is also required ( usually 47...100nF )
connected in parallel with the first one.


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