Electrolytic capacitor
An electrolytic capacitor is a type of capacitor that has a larger capacitance than other types of capacitors. In electrical circuits they are used like tiny rechargeable batteries for example to smooth out pulsed DC voltage from a rectifier.Electrolytic capacitors are constructed from two conducting aluminium foils, one of which is coated with an insulating oxide layer, and a paper spacer soaked in electrolyte. The foil insulated by the oxide layer is the anode while the liquid electrolyte and the second foil acts as cathode. This stack is then rolled up, fitted with pin connectors and placed in a cylindrical aluminium casing.
A schematic replacement circuit for a real electrolytic capacitor looks like this:
R_inside
_______
o-----|_______|-----o
| |
| |
(+) | || | _______ (-)
0-----o--------||---------o-----|_______|-----oOoOoOo-----0
|| R_ESR L_ESL
C
R_ESR is the Electric Series Resistance, L_ESL is an inductivity.R-ESR must be as small as possible since it defines the loss power when the capacitor is used to smooth voltage. Loss power scales linearly with the ripple current flowing through and quadratically with R-ESR. Low ESR capacitors are imperative for high efficiencies in power supplies.
Since the electrolytes evaporate, design life is most often rated in hours at a set temperature. For example, typically as 2000 hours at 105 degrees centigrade (which is the highest working temperature). Design life doubles for each 10 degrees lower, reaching 15 years at 45 degrees.
Electrolytic capacitors may explode (have weak link safety valve) when charged up with wrong polarity.
