Something I never really thought about until just now. When electrolytics are used for AC coupling in (say) audio circuits I assume they survive because AC isn't polarising?
If there's a DC bias (and there often is) you wire them in that way.
True, but the voltage swings both ways even with bias.
Should still be OK. They won't explode on a slight negative for less than
50% of the time. But it would be better to bias them into the correct setting.
I was just casually wondering whether modern electrolytics are fairly immune to AC, since I have seen some AC electrolytics advertised.
The electrolytics survive because the DC voltage impressed across the capacitor is much greater than the peak-to-peak levels of the AC being impressed. If you have a capacitor between a 20 VDC source and a 5 VDC source, the DC voltage seen by the capacitor is 15 VDC. Now, suppose the AC signal is 1VAC. the capacitor never becomes reverse biased, therefore, it stays polarized in the manner it was designed to be. If, however, the AC signal voltage is greater than the DC voltage across the capacitor, then you need to use a non-polarized unit, or a non-electrolytic unit.
"Dirk Bruere at NeoPax"
** Obviously, AC current is not polarising.The electro cap value needs to be large enough so very little SIGNAL voltage appears across it - maybe 100mV rms at the lowest operating frequency.
........ Phil
"DaveM"
** It will "survive" and function fine long as any reverse polarity imposed is limited to a low voltage - ie under 1 volt.Be even more careful with tantalum electros - as reverse current flow permanently damages them. If this is a possibility, then parallel any with a diode for protection.
** Better get this clear - in a correctly designed circuit, the AC voltage ACROSS a polarised electro is normally FAR less than the AC signal voltage it couples to the load.IOW do not use a polarised electro to create a low frequency roll off in a circuit with no polarising voltage for the cap.
...... Phil
Usually, an "AC electrolytic" is a non-polarized electrolytic, or it was derated by 50% to 75% on voltage.
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