A
plastic film capacitor uses a
plastic film as the
dielectric material. The
electrodes are either made of
a
metal film or by metallizing. One
capacitor can have one
or more layers. The
plastic film capacitor has a low
electrode resistance. The most used plastic films are
polyester,
polycarbonate,
polypropylene,
polystyrene
and
polyenylenesulphide
The
polyester film is cheap and easy to
metallize, but
has low
stability. Used in circuits where
stability is not
critical
The
polycarbonate film is
relatively easy to
metallize
and better
stability than
polyester.
It has lower
dielectric constant than
polyester makes
a
polycarbonate capacitor larger and more
expensive.
This
capacitor is used in
applications where the high
stability
is needed.
Polypropylene is hard to
metallize and to make thin, but
is
stable, has a low loss
factor and has a low
dielectric
absorption (A low
dielectric absorption means that the
capacitor
won't 'self recharge'). The low
absorption makes this
capacitor
ideal in
sample and
hold circuits and
audio equipment.
Polystyrene is hard to
metallize and has a low
voltage
tolerance but has high
stability and low
dielectric absorption.
This
capacitor is most used in
filters.
The polyenylene
sulphide has high
temperature tolerance,
good
stability and a very low voltage
loss, but
it has a low
voltage tolerance.
Plastic film capacitors are
available with
values from about 12pF up to 100uF.