[sdiy] emulating bi-polar capacitors

Danjel van Tijn / intellijel danjel at intellijel.com
Tue Feb 15 18:42:30 CET 2022

With high prices and scarcity of bi-polar caps I am trying to find the best
way to emulate them
using back-to-back polarized electrolytics.

The most common solution I have seen is to simply connect them in series
(negative terminal to negative terminal).   So if you needed 47u NP  you
would take two 100u in series.

However, I have concerns about longevity.

So another strategy I have seen is to put a diode in parallel with each
capacitor so that effectively only one capacitor is on at a time.  But I
have never found an example of this used in a pro audio circuit or in any
capacitor app note.   Also, there seems to be a debate on whether the
effective capacitance is that of just one capacitor or still both in series:

" I have seen people argue that each diode 'shorts out' its respective
capacitor on each half cycle, and that the capacitance is therefore the
value of just one capacitor. This is only true during the startup charging
phase when the diodes conduct, the effective capacitance will be that of
just one capacitor, 1uF. If the pair has been exposed to one AC voltage for
a while, so the centre node has charged to that voltage, and the voltage is
suddenly increased, there will be a further phase of charging, and a change
in effective capacitance while it charges."


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