Suntan Blog

An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. They are often referred to in electronics usage simply as "electrolytics". They are used in relatively high-current and low-frequency electrical circuits, particularly in power supply filters, where they store charge needed to moderate output voltage and current fluctuations in rectifier output. They are also widely used as coupling capacitors in circuits where AC should be conducted but DC should not. There are two types of electrolytics; aluminum and tantalum.

A common modeling circuit for an electrolytic capacitor has the following schematic:

Where Rleakage is the leakage resistance, RESR is the equivalent series resistance (ESR), LESL the equivalent series inductance (L being the conventional symbol for inductance).

RESR must be as small as possible since it determines the loss power when the capacitor is used to smooth voltage. Loss power scales quadratically with the ripple current flowing through and linearly with RESR. Low ESR capacitors are imperative for high efficiencies in power supplies. Low ESR capacitance can sometimes lead to destructive LC voltage spikes when exposed to voltage transients.

This is only a simple model and does not include dielectric absorption (soakage) and other non-ideal effects associated with real electrolytic capacitors.