Transcript Bipolar Junction Transistors (BJTs)

Bipolar Junction Transistors
(BJTs)
Types of BJTs
 NPN
PNP
NPN-BJT Structure
n-type
p-type
n-type
NPN BJT Symbol
C
B
E
PNP-BJT Structure
p-type
n-type
p-type
PNP BJT Symbol
Emitter is reversed
C
B
E
Current Flow Convention
E
Emitter
(n-type)
Base
Collector
(p-type) (n-type)
IE
C
IC
IB
B
 WORKING
BJT structure
note: this is a current of electrons (npn case)
and so the
conventional current flows from collector to
emitter.
Transistor Connections
 Common Base Connection
 Common Collector Connection
 Common Emitter Conncetion
Common Base Connection

Current Amplification Factor
α =I / I
C
E
( constant VCB)
• The value of α is lies b/w 0.9
to 0.999
• Total collector current
• I =αI +I
C
E
leakage
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