bipolar junction transistors (bjts)
Post on 26-Jan-2016
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Bipolar Junction Transistors (BJTs)
Types of BJTs
NPNPNP
NPN-BJT Structure
n-type p-type n-type
NPN BJT Symbol
E
B
C
PNP-BJT Structure
p-type n-type p-type
PNP BJT Symbol
Emitter is reversed
E
B
C
Current Flow Convention
EEmitter (n-type)
Base (p-type)
Collector (n-type)
B
C
IE
IB
IC
WORKING
BJT structure
note: this is a current of electrons (npn case) and so theconventional current flows from collector to emitter.
Transistor Connections
Common Base Connection Common Collector Connection Common Emitter Conncetion
Common Base Connection
Current Amplification Factor α =IC / IE ( constant VCB)
• The value of α is lies b/w 0.9 to 0.999
• Total collector current • IC=αIE+Ileakage
Common Collector Connection
Current Amplification Factor
• γ = IE/IB
• Expression for collector current.
• IC= IB /1-α + ICBO /1-α
Common Emitter Conncetion
Base Current Amplification Factor
• β= IC / IB
• The range of β is 20 to 500.
• Expression for collector current.• IC = βIB + ICEO
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