Capacitors Tutorial, Notes on Capacitors

Note 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, Q=C*V where:
Q= Charge in Coulomb,
C=Capacitance in Farads
V=Voltage in Volts.
Work is done when the charge in plates are transferred from the capacitor to elsewhere. The energy acquired by a charged capacitor is given by

, where V is the voltage across the capacitor and C is the capacitance.
Interpreting Capacitor Value:
If you are wondering how to interpret the capacitor value then don't worry. If the capacitor number is like 224 then you need to replace the third number with equal no. of zero. In this case the new number is 220000pf. The letters in the capacitor stands for tolerance which gives accuracy till which the given capacitance value is correct. The capacitance is in pico farad (pf = ). You can convert it to other value such as nano farad and micro farad using the If you have some product code written on the capacitor then all you need to do is enter them in our product search form. Else call 1-800-272-2737.

Letter Tolerance
D 0.5pF
F 1%
G 2%
H 3%
J 5%
K 10%
M 20%
P +100, -0%
Z +80, -20%

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 for.
The most commonly used capacitors are:

Electrolytic Capacitor
Tantalum Capacitor
Super Capacitors
Polyester Film Capacitors
                               Polypropylene Capacitors
                               Metalized Polyester Film Capacitors
                               Ceramic Capacitor
                               Multilayer Ceramic
                               Silver-Mica
                               Variable Capacitors

Many capacitors can be combined in a circuit to produce a certain capacitance value. To calculate capacitance first we need to identify whether the capacitors are in parallel or they are in series.

If the capacitors are in series like then the capacitance is
If the capacitors are in parallel like then the total 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.



Metalized Polyester Film - This is a good quality capacitor which is stable with temperature and has low drift. The dielectric is made of polyester or Mylar. It has good tolerance level too.



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 size.




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