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Mechanism of Capacitor

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MD.SUMON SARDER 161-15-953

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Capacitors

A basic capacitor has two parallel plates separated by an insulating material

A capacitor stores an electrical charge between the two plates

The unit of capacitance is Farads (F) Capacitance values are normally smaller, such as µF,

nF or pF

Capacitors

Basic capacitor construction

Dielectric material

Plate 1

Plate 2The dielectric material is an insulator therefore no current flows through the capacitor

Capacitors

Storing a charge between the plates

Electrons on the left plate are attracted toward the positive terminal of the voltage source

This leaves an excess of positively charged holes

The electrons are pushed toward the right plate

Excess electrons leave a negative charge

+ -

+_

+ _

Capacitors

Types of capacitors The dielectric material

determines the type of capacitor

Common types of capacitors are: Mica Ceramic Plastic film

Capacitors

Some capacitors are polarised, they can only be connected one way around

Electrolytic capacitors are polarised

Capacitors

Variable capacitors are used in communication equipment, radios, televisions and VCRs

They can be adjusted by consumers by tuning controls

Trimmers are internal adjusted capacitors that a consumer cannot adjust

Capacitors

These variable capacitors would be difficult to squeeze into your mobile phone and iPod

Current technology uses semi-conductor variable capacitors called varactors (varicaps)

Capacitors

The capacitance in a varactor is created when a purpose diode is reversed biased

Adjusting the reverse bias alters the capacitance value

A simple radio receiver using varactor