00190056| Datasheet

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Aluminum Electrolytic Capacitors General Technical Information General technical information
1 Basic construction of aluminum electrolytic capacitors Aluminum electrolytic capacitors, which will be abbreviated to "Al electrolytic capacitors" in the following, assume a special position among the various types of capacitors since their principle of operation relies, in part, on electrochemical processes. The advantages of Al electrolytic capacitors that have led to their wide application range are their high volumetric efficiency (i.e. capacitance per unit volume), which enables the production of capacitors with up to one Farad capacitance, and the fact that an Al electrolytic capacitor provides a high ripple current capability together with a high reliability and an excellent price/performance ratio. As is the case with all capacitors, an Al electrolytic capacitor comprises two electrically conductive material layers that are separated by a dielectric layer. One electrode (the anode) is formed by an aluminum foil with an enlarged surface area. The oxide layer (Al2O3) that is built up on this is used
as the dielectric. In contrast to other capacitors, the counter electrode (the cathode) of Al electrolytic capacitors is a conductive liquid, the operating electrolyte. A second aluminum foil, the so-called cathode foil, serves as a large-surfaced contact area for passing current to the operating electrolyte.
Dielectric (Al 2 O 3) Al anode foil Al cathode foil

Electrolyte and paper
KAL0001-S-E

Figure 1

Basic construction of an aluminum electrolytic capacitor

A C = 0 r --d

C 0 r A d

Capacitance Absolute permittivity Relative dielectric constant Capacitor electrode surface area Electrode spacing

F As/Vm (9,5 for Al2O3) m2 m

The anode of an Al electrolytic capacitor is an aluminum foil of extreme purity. The effective surface area of this foil is greatly enlarged (by a factor of up to 200) by electrochemical etching in order to achieve the maximum possible capacitance values. The type of etch pattern and the degree of etching is matched to the respective requirements by applying specific etching processes. Etched foils enable very compact Al electrolytic capacitor dimensions to be achieved and are the form used almost exclusively nowadays. The electrical characteristics of Al electrolytic capacitors 19 10/02