OVERVIEW OF CAPACITORS - What is capacitor? - Classification of capacitors

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Capacitor is a device which is used to store energy in electrostatic fields. In practical capacitor, the device consists of two parallel metallic plates separated by an insulating material called the dielectric. The metal plates can be made of any conducting material like copper. The dielectric material may be ceramic, mica, etc.

Classification of capacitors

The capacitors can be classified into two major types :

Fixed capacitors
Variable capacitors

Fixed capacitors

The fixed capacitors can be classified in accordance with physical construction, dielectric usage, voltage rating, and polarization. Fixed capacitors are those whose capacitance value cannot be varied mechanically. The fixed capacitors classified depending upon its dielectric materials.

Paper capacitors

Paper capacitors make use of tissue or cellulose paper called Kraft paper. They are usually high voltage capacitors and mechanically very strong. The capacitance value of paper capacitors is usually between 0.002 µF and 0.05µF. Paper capacitors are very cheap but they have poor high frequency characteristics.

Ceramic capacitors

Ceramic capacitors make use of ceramic as the dielectric material. Basic ceramic materials are formed from titanium dioxide. Some of the dielectric materials used are barium titanate, and sirconium titanate. The range of ceramic capacitance between pF and nF. The ceramic capacitors are light in weight and they are suitable for use in hybrid integrated circuits. But very high voltage ceramic capacitors are not available. They are used hybrid ICs and coupling capacitors in low voltage circuits.

Mica capacitors 
Mica is complex silicate of aluminum with K, Mg, and Fe etc. Mica capacitor have good mechanical strength, they can be operate to temperatures as high as 9000C. But mica capacitors are silver migration occurs high DC voltages, high temperatures, and high humidity.

Plastic capacitors

The plastic capacitors are made by polycarbonate, polyethylene and polyvinyl chloride. Plastic capacitors have high dielectric strength and large permittivity. They can withstand temperature up to 2500C. Plastic capacitors have high capacitance in small volume. Plastic capacitors have comparatively high capacity with good high voltage and low leakage properties. They have low leakage but capacitance of more than a few micro-farads are not available at present.

Electrolytic capacitors

Due to electrolysis chemical reaction, a thin oxide film is formed around one of the electrodes, and it is this film that act as the dielectric material for electrolytic capacitor. These types of capacitors are available with 1µF to thousands of micro-farads.

Variable capacitors

For some application, we need the capacitance used in the circuit be variable. For instance radio and television tuning set. We also have air cored and plastic cored capacitors. Air cored capacitors were used in olden days. Plastic capacitors are widely used. Plastic cored capacitors made by polyvinyl chloride. Most of the modern radios using transistors and ICs; we use the PVC type of variable capacitors.

OVERVIEW OF CAPACITORS - What is capacitor? - Classification of capacitors OVERVIEW OF CAPACITORS -  What is capacitor? - Classification of capacitors  Reviewed by knowledge people creators on January 17, 2019 Rating: 5
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