The issue

I was making a project in which I had to use a 2.2uF electrolytic capacitor in series with a microphone and weirdly, the circuit works even if I toggle the polarity of the capacitor, that is the capacitor can be inserted in either polarity to make the circuit work.
Why does this happen? What are the criteria for doing so intentionally? Additionally, if I am to substitute a ceramic capacitor with an electrolytic capacitor, in what polarity should the capacitor be inserted?


Bluetooth Audio Adapter

This schematic is based on the manufacturer's schematic, in which also, a ceramic capacitor of 2.2uF is used.

This question is referring to the MIC portion of the schematic only.

  • 2
    \$\begingroup\$ What was the original capacitor type? Also, there is no DC bias in that part of the circuit. \$\endgroup\$ – DKNguyen Mar 8 '19 at 3:09
  • 1
    \$\begingroup\$ That is likely a ceramic capacitor. Unless noted otherwise you can assume all aluminum and tantalum capacitors ARE polarized. If you install them backwards across power supply rails (or they have an internal short, much less common in recent decades) they tend to go BANG with some violence, possibly charring the PCB. A ceramic capacitor is not polarized unless it has a black band or polarity mark at one end. \$\endgroup\$ – user105652 Mar 8 '19 at 3:55
  • \$\begingroup\$ At millivolt level and and a small reverse bias a polarized capacitor doesn't care, at least for a short time. Over time it might die much earlier than you expect. Don't try it again. \$\endgroup\$ – Ale..chenski Mar 8 '19 at 4:07
  • \$\begingroup\$ @Toor What do you mean by the original capacitor type? \$\endgroup\$ – Utkarsh Verma Mar 8 '19 at 4:15
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    \$\begingroup\$ You only mention the capacitor that you first used was 2.2uF and that it worked in both polarities. However, you never mentioned what type of capacitor it actually was. 2.2uF makes it likely that it was a bipolar type and if it was, of course it would have worked in both directions. \$\endgroup\$ – DKNguyen Mar 8 '19 at 5:47

An aluminum electrolytic will handle a reverse polarity of about 1 volt or so. The cap probably never sees anything near that.

This appnote from Nichicon shows that under 1V the capacitors don't have much of leakage and seems fully functional, see Fig.2-2, with little degradation (see Fig.2-3).

  • \$\begingroup\$ Would you suggest its use in a circuit meant to be used for long terms? \$\endgroup\$ – Utkarsh Verma Mar 8 '19 at 4:21
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    \$\begingroup\$ @UtkarshVerma, please read the Nichicon article and make your own determination. The article mentions " progressing formation of an oxide layer on the cathode electrode", so the cap might not last longer than 200-300 hours. \$\endgroup\$ – Ale..chenski Mar 8 '19 at 4:25
  • \$\begingroup\$ @Ale..chenski Thanks for the document. I'll read it and post what I'll conclude over here. \$\endgroup\$ – Utkarsh Verma Mar 8 '19 at 4:35
  • \$\begingroup\$ It depends on the voltage rating. At one time we safely used -10% \$\endgroup\$ – Tony Stewart EE75 Mar 8 '19 at 7:00

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