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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.

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Presentation Transcript
capacitors
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
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Capacitors
  • Basic capacitor construction

Dielectric material

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

Plate 2

Plate 1

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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

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Capacitors

Types of capacitors

  • The dielectric material determines the type of capacitor
  • Common types of capacitors are:
    • Mica
    • Ceramic
    • Plastic film
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Capacitors
  • Some capacitors are polarised, they can only be connected one way around
  • Electrolytic capacitors are polarised
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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
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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)
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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

http://www.microst.it