Capacitors

The electronic components that are used to store the charge are called Capacitors. This capability of capacitors to store the energy (Charge) is called capacitance. Capacitance is measured in Farads (F). Farad is a very high unit of capacitance. Lower units are Micro Farad (µF) and Pico Farad (pF).

Capacitor consists of two conducting plates that are separated by an insulating material which is known as dielectric. Capacitor offers very low impedance to AC but it blocks DC. The reason behind this is that
X_C =1/2πfc and for AC frequency is 50-60 Hz but for DC frequency is 0 hence X_C= Infinite.

Capacitors are classified on the basis of die electric used between them. Some well known types of Capacitors are as Follows:

1) Mica Capacitors: These types of Capacitors are constructed with the help of two Aluminium foils separated by a mica sheet. These plates are connected to two electrodes. The entire unit is encapsulated in a plastic housing. These type of Capacitors are used for small capacitance values ranging from 5 pF to 10µF. These Capacitors can operate at up to 500V and has leakage current about 1000MΩ.


















2) Paper Capacitors: These types of capacitors are manufactured with the help of long spring of tin foil or Aluminum foil or copper foil that are separated by impregnated paper strips. This integration is done either with wax or oil. Such capacitors have capacity ranging from 500pF to 1000 µF with voltage rating ranging from 100V to 100kV. Their leakage resistance is about 100 MΩ.

3) Ceramic Capacitors: These types of capacitors are formed from dielectric that is made from earth fired under extreme heat. In this type of capacitor ceramic disc is coated on two sides with a metal such as copper or silver. Copper wires are attached to each coating which acts as electrodes. Ceramic capacitors are manufactured in various shapes and sizes hence they are enclosed in prospective housing and are marked with their capacitance value and voltage ratings. This is either done by printing values on them or by giving color codes or assigning numbers to them.

4) Electrolytic Capacitors: In these types of capacitors dielectric is used between two Aluminium electrodes. Electrolytic Capacitors are of Two Types:

i) Dry Type: In this type of capacitor Aluminium electrodes are separated by a paper soaked dry in viscous liquid or electrolytic paste. The capacitor is than encapsulated in hermetically sealed waxed cardboard tube.

ii) Wet Type: This type of capacitor consist of a metallic cylinder which is filled with an electrolyte such as ammonium borate. This also acts as cathode. Aluminium anode is also suspended co-axially inside the electrolyte. When current passes through the capacitor a thin film of Aluminium oxide is formed and acts like a dielectric and large capacitance is formed.