Capacitors Capacitors A basic capacitor has two parallel A basic capacitor has two parallel plates separated by an insulating plates separated by an insulating material material A capacitor stores an electrical A capacitor stores an electrical charge between the two plates charge between the two plates The unit of capacitance is Farads The unit of capacitance is Farads (F) (F) Capacitance values are normally Capacitance values are normally smaller, such as smaller, such as µF, nF or pF µF, nF or pF
Transcript
CapacitorsCapacitors
A basic capacitor has two parallel A basic capacitor has two parallel plates separated by an insulating plates separated by an insulating materialmaterial
A capacitor stores an electrical A capacitor stores an electrical charge between the two platescharge between the two plates
The unit of capacitance is Farads (F)The unit of capacitance is Farads (F) Capacitance values are normally Capacitance values are normally
smaller, such as smaller, such as µF, nF or pFµF, nF or pF
CapacitorsCapacitors
Basic capacitor constructionBasic capacitor construction
Dielectric material
Plate 1
Plate 2The dielectric material is an insulator therefore no current flows through the capacitor
CapacitorsCapacitors
Storing a charge Storing a charge between the platesbetween the plates
Electrons on the left Electrons on the left plate are attracted plate are attracted toward the positive toward the positive terminal of the voltage terminal of the voltage sourcesource
This leaves an excess This leaves an excess of positively charged of positively charged holesholes
The electrons are The electrons are pushed toward the pushed toward the right plateright plate
are used in are used in communication communication equipment, radios, equipment, radios, televisions and VCRstelevisions and VCRs
They can be adjusted They can be adjusted by consumers by by consumers by tuning controlstuning controls
Trimmers are internal Trimmers are internal adjusted capacitors adjusted capacitors that a consumer that a consumer cannot adjustcannot adjust
CapacitorsCapacitors
These variable These variable capacitors would be capacitors would be difficult to squeeze difficult to squeeze into your mobile into your mobile phone and iPodphone and iPod
Current technology Current technology uses semi-uses semi-conductor variable conductor variable capacitors called capacitors called varactors (varicaps)varactors (varicaps)
CapacitorsCapacitors The capacitance in a The capacitance in a
varactor is created varactor is created when a purpose diode when a purpose diode is reversed biasedis reversed biased
Adjusting the reverse Adjusting the reverse bias alters the bias alters the capacitance valuecapacitance value
A simple radio A simple radio receiver using receiver using varactorvaractor
