How Do Capacitors Filter AC and DC Signals?

[jeff1evesque]

Statement
Capacitors can be used to store energy or to filter signals. Example, filtering out AC is used to reduce the "ripple" of a DC power supply. Also Filtering out DC: Only time-varying signal will pass through a capacitor. The circuit on either side of the capacitor can be at different DC voltages.

Question
Can someone explain to me in general term [or in detailed], what filtering out AC or DC means?

Thanks,

Jeff

 

[vk6kro]

The output of a rectifier in a power supply is pulses of voltage shaped like a half of a sinewave.

These pulses are unsuitable for many applications because they are not a constant voltage and this may be heard in the output of an amplifier, for example.

If these pulses are put into a capacitor it will charge up to the peak value of the pulses.

In between the pulses, the capacitor will try to discharge into the load ( which is the resistance of the thing which is being powered ). The more current is being used by the load, the more the voltage will drop before the next rectifier pulse arrives to charge up the capacitor again.

This is called filtering. The output ends up more smooth than it would be without the capacitor, but the size of the ecapacitor has to be suitable for the load the power supply is supplying power to.