Capacitors

1
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

2
Capacitors

• Basic capacitor construction

Dielectric material
The dielectric material is an insulator therefore
no current flows through the capacitor
Plate 2
Plate 1
3
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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4
Capacitors

• Types of capacitors
• The dielectric material determines the type of
  capacitor
• Common types of capacitors are
• Mica
• Ceramic
• Plastic film

5
Capacitors

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

6
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

7
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)

8
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

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