Capacitors Tutorial, Notes on Capacitors
Capacitor is a device that stores energy created between a pair of conductors.
An insulator (also called dielectric) of some kind is usually placed between
the plates. The conductors are plates / electrodes which store opposite charges
between them. The amount of charge a capacitor can hold can be found by multiplying
"capacitance" with the "potential difference" between the plates. Capacitance
is the amount of charge that can be stored on a capacitor plate. Generally,
Capacitance also varies with temperature. If a capacitor has "NPO"
written on it then it stands for "Negative-Positive-Zero" which means
the capacitance remains constant at all temperatures. The Electronic Industrial
Association also has some standard set of codes which indicate various tolerances.
If you are an average eletronic consumer then most of the common electrolytic
and general purpose ceramic capacitors and depending on the application, a more
temperature stable type like metal-film or polypropylene is what you are looking
If the capacitors are in series like then the capacitance is
Electrolytic Capacitor: As the name suggests
it is made up of electrolyte. Electrolyte is a salt mixed with solvent that
capable of conducting electricity. It is one of the popular capacitors since
it is cheap, readily available and has a good storage of charge. However it
is not very accurate and has leaking. When using these in circuits it is suggested
to choose one which is twice the amount of the voltage that is going to be used.
It will explode if the working voltage is exceeded or the polarity is reversed.
Tantalum Capacitor: Tantalum capacitors are
made of Tantalum with a symbol Ta, and atomic number 73. Tantalum can easily
form an oxide layer on the surface layer on the tantalum foil. The oxide layer
forms the dielectric and the electrolytic solution on the other side forms the
other plate needed for capacitor to work. Because the dielectric can be thin
a high capacitance can be achieved in a small space. They are mostly used in
pagers, personal computers, and automotive electronics. They are better than
electrolytic capacitor. Their capacitance doesnt change with temperature.
Super Capacitors - These capacitors use a molecule-thin
layer of electrolyte. Since energy is inversely proportional to the thickness
of dielectric layer these can carry enormous amount of energy. Usual capacitance
is about 0.47 Farad. The electrodes are made of activated carbon, which has
a high surface area per unit volume. A significant amount precaution must be
taken when using this kind of capacitor.
Polyester Film - Another cheap and readily available
capacitor is polyester film. It uses a thin polyester film as a dielectric.
Tolerance is around 5% to 10%. Although widely used it may not be suitable for
all electronic projects or media because of varying tolerance.
Polypropylene - This capacitor uses polypropylene
film as the dielectric. It has small tolerance of about 1% and so it is used
in places where more tolerance than polyester capacitor is needed. It can function
well under higher voltages and doesnt break down easily.
Ceramic - Ceramic capacitors are constructed with materials
such as titanium acid barium used as the dielectric. Their tolerance is below
10%. Their serial resistance and inductance is lower than that of tantalum capacitors.
Internally, these capacitors are not constructed as a coil, so they can be used
in high frequency applications. Typically, they are used in circuits which bypass
high frequency signals to ground. These capacitors have the shape of a disk.
Their capacitance is comparatively small. They are most widely available capacitor
and they can be identified by a black stripe on top.
Multilayer Ceramic - These capacitors are used
in applications to filter or bypass the high frequency to ground. These capacitors
are not polarized. That is, they have no polarity. Some of its characteristics
are small in size, very good temperature stability, excellent frequency stable
characteristics. The dielectric is made up of many layers.
Silver-Mica - This uses mica as a dielectric. Mica
capacitors have good stability because their temperature coefficient is small.
Because their frequency characteristic is excellent, they are used for resonance
circuits, and high frequency filters. Also, they have good insulation, and so
can be utilized in high voltage circuits. It was often used for vacuum tube
style radio transmitters, etc. Mica capacitors do not have high values of capacitance,
and they can be relatively expensive.
Variable Capacitors - They are also called
trimmer capacitors or adjustable capacitors. They usually have ceramic or plastic
as a dielectric. Most of them are color coded to easily recognize their tunable
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