The
electrolytic capacitor has a high
capacitance in
relation to its size. There are two
basic types, one
uses a
liquid electrolyte the other a dry.
The liquid electrolyte capacitor's
electrodes are mostly
made from
aluminium and dipped in an acidbath to make
its surface
porous. This increases the
surface area
of the electrode over 300 times. The electrodes are then
oxidized. This oxide layer forms the
dielectrum
A layer of
paper is put between the two electrodes.
This paper is moistened with an electrolyte
made from a mix of
boric acid,
glycol, salt and a solvent.
The electrolyte has a low
resistance and flows in to all the
small holes and crevices in the aluminium oxide. This creates
a good contact to the surface, and due to the large surface
area, the capacitor gets a high capacitance. These capacitors
are
polarized and should not be connected the other way as
they will explode (this is of course something students of
electronic engineering do for fun). These types of
capacitors have a capacitance of between 0.1uF to 0.5F and
are produced for
voltages up to 500V. The length this type of
capacitor's 'life' is highly dependant on temperature, its lifelength
is halved for each 10 degrees Celsius the temperature increases
The solid electrolyte capacitor (SAL, Solid Aluminium Electrolyte)
uses either
manganese dioxide or an
organic semiconductor
as the dielectric material.
They are made in a similar way to the liquid
electrolyte capacitor. But uses a fiberglass separator in stead of paper.
This is impregnated with the manganese dioxide or the semiconductor,
and put between the electrodes. The manganese dioxide
is available with values from 0.1uF to about 3000uF, and has
a higher
tolerance to temperature variation. But their lifetime
is more sensitive to the voltage than that of an liquid electrolyte
capacitor
The organic semiconductor type are manufactured with values
up to about 300uF. They have a higher
internal resistance
than the liquid electrolyte, but have a better temperature
tolerance.
The
tantalum capacitor is similar to a SAL but has
tantalum electrodes.