Re: caps back to back


Mark wrote:
> the interesting question that we should get to is.....
>
> if you place two caps back to back.....+ to + or - to -
>
> is the value of the combination 1/2 each or not.....
>
>
> i.e. take 2 10 uF caps back to back, is it 10uF or 5 uF
>
> its not a simple question as it seems...
>
> Mark

There are a couple of ways of connecting up polarized caps to make a
bi-polar one:

1) Just put them in series back to back (doesn't matter which way).
Usually an electrolytic cap will have a higher leakage in the reverse
direction and act a bit like a diode (they used to have electrolytic
rectifiers that relied on this action). This will tend to give a DC
bias on the capacitor so both caps are biased in the correct direction.
The effective capacitance will be that of two caps in series i.e. 5uF
in your example.

2) As someone suggested you can augment the basic circuit with a couple
of diodes to ensure that the caps don't get reverse biased - the diodes
are not just put in series with the capacitors though, they are put
across each cap in the appropriate direction - this improves the
rectification to guarantee the bias on the capacitor. The effective
capacitance will be the same as above.

kevin

.

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