What is Capacitor ?

A Capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. It is also known as condenser. Capacitors store energy by holding apart pairs of opposite charges. The simplest design for a capacitor is a parallel plate, which consists of two metal plates with a gap between them. The unit of electrical capacitance is the farad (abbreviated F).

A capacitor stores electrical energy when charged by a DC source. It can pass alternating current (AC), but blocks direct current (DC) except for a very short charging current, called transient current.

The amount of charge a capacitor can hold (capacitance) is measured in Farads. In practice, one farad is a very large amount of capacitance, making the most common term used micro-farad or one millionth of a farad. There are three factors that determine the capacitance that exist between two conductive plates: 

1. The bigger the plates are (Surface Area), the higher the capacitance. Capacitance (C) is directly proportional to Area (A). 

2. The larger the distance is between the two plates, the smaller the amount of capacitance. Capacitance (C) is indirectly proportional to distance (d). 

3. The larger the value of the dielectric constant, the more capacitance (Dielectric constant is equivalent to softness of the rubber in our pipe analogy). The capacitance (C) is directly proportional to the Dielectric Constant (K) of the insulating material. From the above factors, the formula for capacitance in Farads becomes: 

C = 0.244K A(N-1)/d Picofarads * 

C = Capacitance in Picofarads (Farad x 10-12) 

K = Dielectric Constant 

A = Area of one Plate in square inches 

N = Number of Plates 

d = Distance between plates in inches

The older styles of capacitors were marked with colored dots or rings similar to resistors. In recent years, the advances in technology has made it easier to print the value, working voltage, tolerance, and temperature characteristics on the body of the capacitors. Certain capacitors use a dielectric that requires markings to insure one lead is always kept at a higher voltage than the other lead. 


Typical capacitors

Types of Capacitors :

There are many different types of capacitors used in electronics. Each type is made from different materials and with different methods. Capacitors are also made to handle different amounts of electrical pressure or voltage. Each capacitor is marked to show the maximum voltage that it can withstand without breaking down. All capacitors contain the same fundamental parts, which consist of two or more conductive plates separated by a nonconductive material. The insulating material between the plates is called the dielectric.

1) Ceramic capacitors

2) Film capacitors

3) Power film capacitors

4) Electrolytic capacitors

5) Variable capacitors

6) Miscellaneous capacitors