Placing electrolytic capacitors in an amplifier circuit.

[drummerguy198]

I am working various amplifiers in my labs. On nearly all of these amplifers (CC, CE, or CB), the input signal is capacative coupled. However, the cricuit schematic indicates the use of a polarized capacitor. The capacitors I am using are rated at a maximum voltage of 50V. Most of the voltage levels I am using never exceed 30Vrms. When the current reverses polarity, is it still possible that it could damage the capaictor? Why the use of electrolytics?

I have seen this on the power amplification portion of a superheterodyne AM/FM radio I built as well (That is, the use of electrolytic capacitors).

 

[skeptic2]

In most cases in applications like these, there will be a DC bias across the capacitor. The DC voltage is what should determine the direction the capacitor is connected. The peak voltage (not the RMS voltage) of the signal plus the DC bias is what should determine the voltage rating of the capacitor. Electrolytic capacitors are forgiving but I would still aim for a voltage rating at least 50% higher than the peak plus DC voltages. It won't matter if the polarity momentarily reverses.

If your electrolytic won't have a DC bias, there are non-polarized electrolytics available. I understand they are nothing more than two polarized electrolytics back-to-back. I have in fact used two electrolytics back-to-back in that kind of application without any problems.

Electrolytics provide high capacitance with low volume and cost.