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Application Guide, Aluminum Electrolytic Capacitors
Aluminum Electrolytic Capacitor Overview
This Application Guide
Except for a few surface-mount technology (SMT) alu-
minum electrolytic capacitor types with solid elec-
trolyte systems an aluminum electrolytic capacitor con-
sists of a wound capacitor element, impregnated with
liquid electrolyte, connected to terminals and sealed in
a can. The element is comprised of an anode foil,
paper separators saturated with electrolyte and a cath-
ode foil. The foils are high-purity aluminum and are
etched with billions of microscopic tunnels to increase
the surface area in contact with the electrolyte.
While it may appear that the capacitance is between
the two foils, actually the capacitance is between the
anode foil and the electrolyte. The positive plate is the
anode foil; the dielectric is the insulating aluminum
oxide on the anode foil; the true negative plate is the
conductive, liquid electrolyte, and the cathode foil
merely connects to the electrolyte.
This construction delivers colossal capacitance
because etching the foils can increase surface area
more than 100 times and the aluminum-oxide dielec-
tric is less than a micrometer thick. Thus the resulting
capacitor has very large plate area and the plates are
awfully close together.
These capacitors routinely offer capacitance values
from 0.1 µF to 3 F and voltage ratings from 5 V to 500
V. They are polar devices, having distinct positive and
negative terminals, and are offered in an enormous
variety of styles which include molded and
can-style SMT devices, axial- and radial-leaded can
styles, snap-in terminals styles and large-can, screw-
terminal styles. Representative capacitance-voltage
combinations include
330 µF at 100 V and 6800 µF at 10 V for SMT
devices,
100 µF at 450 V, 6,800 µF at 50 V and 10,0