Electrolytic Capacitors
Question:
What is the differences between dielectric capacitors and
electrolytic capacitors? Why does a electrolytic capacitor store
more charges under same voltage than dielectric capacitors?
Answer:
All capacitors involve a dielectric. Some are made up from a pair
of solid conductors separated by a very thin film of solid
dielectric material. Electrolytics was a "breakthrough"
in capacitor technology in the early 1900's. Instead of
placing a solid wedge of something (which can be quite thin), an
electrolyte solution is used. The electrolyte serves as the 2nd
electrode. The electrolyte is not the dielectric. The dielectric
is a very thin layer of oxide which is grown electro-chemically
in production. The thickness of this oxide layer is on the order
of .01um, much smaller than any piece of plastic or ceramic that
could be used as a separator. To contact the electrolyte, another
piece of foil is used, but it is the electrolyte that is truly
the plate.
The amount of charge a capacitor can hold at a certain
potential (its capacitance) depends on the ratio of surface area
to distance between the electrodes. In electrolytic capacators
the distance between electrodes is so small that the capacitance
can be quite high. With electrolytic capacitors care must be
taken that the voltage is never reversed in polarity. That
destroys the oxide layer.
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JDJ