How to combine elecrolytic capacitors into one big bipolar one

Question

I want to make capacitor with large capacity which can hold both positive and negative charges. Is it possible to combine elecrolytic capacitors somehow to achieve this?

Answer 1

Yes. There are two ways to do this. The rough way, and the nice way.

^{simulate this circuit – Schematic created using CircuitLab}

The rough way is to omit the positive bias and R1. Diodes D1 and D2 will conduct when required to rectify the input signal and 'pump up' the middle node to keep the capacitors from becoming more than one diode drop reverse biassed, which is usually OK for aluminium electrolytics. While the initial charging is happening, the overall capacitor will appear to have a value of C1 or C2, with a diode drop in series. Once the middle node is charged, the capacitor will behave as C1 in series with C2, capacity = C1*C2/(C1+C2).

The nice way is to use a positive bias to pre-charge the middle node to more than the expected signal swing. This will keep both capacitors correctly biassed throughout. The diodes are still required for safety.

Usually, you'll make C1 equal to C2, though there's no requirement to.