Bipolar Junction Transistor (BJT)CHAPTER 3Bipolar Junction Transistor (BJT) Notes | EduRev

: Bipolar Junction Transistor (BJT)CHAPTER 3Bipolar Junction Transistor (BJT) Notes | EduRev

 Page 1


Bipolar Junction Transistor 
(BJT)
CHAPTER 3
Page 2


Bipolar Junction Transistor 
(BJT)
CHAPTER 3
Introduction
• The basic of electronic system nowadays is
semiconductor device. 
• The famous and commonly use of this device 
is BJTs
(Bipolar Junction Transistors).
• It can be use as amplifier and logic switches.
• BJT consists of  three terminal:
? collector : C
? base : B
?emitter : E
• Two types of BJT : pnp and npn
Page 3


Bipolar Junction Transistor 
(BJT)
CHAPTER 3
Introduction
• The basic of electronic system nowadays is
semiconductor device. 
• The famous and commonly use of this device 
is BJTs
(Bipolar Junction Transistors).
• It can be use as amplifier and logic switches.
• BJT consists of  three terminal:
? collector : C
? base : B
?emitter : E
• Two types of BJT : pnp and npn
Transistor Construction
• 3 layer semiconductor device consisting:
• 2 n- and 1 p-type layers of material ? npn transistor
• 2 p- and 1 n-type layers of material ?pnp transistor
• The term bipolar reflects the fact that holes and 
electrons participate in the injection process into the 
oppositely polarized material
• A single pn junction has two different types of bias:
• forward bias
• reverse bias
• Thus, a two-pn-junction device has four types of bias.
Page 4


Bipolar Junction Transistor 
(BJT)
CHAPTER 3
Introduction
• The basic of electronic system nowadays is
semiconductor device. 
• The famous and commonly use of this device 
is BJTs
(Bipolar Junction Transistors).
• It can be use as amplifier and logic switches.
• BJT consists of  three terminal:
? collector : C
? base : B
?emitter : E
• Two types of BJT : pnp and npn
Transistor Construction
• 3 layer semiconductor device consisting:
• 2 n- and 1 p-type layers of material ? npn transistor
• 2 p- and 1 n-type layers of material ?pnp transistor
• The term bipolar reflects the fact that holes and 
electrons participate in the injection process into the 
oppositely polarized material
• A single pn junction has two different types of bias:
• forward bias
• reverse bias
• Thus, a two-pn-junction device has four types of bias.
Position of the terminals and symbol 
of BJT.
• Base is located at the middle 
and more thin from the level 
of collector and emitter
• The emitter and collector    
terminals are made of the 
same type of semiconductor 
material, while the base of the 
other type of material
Page 5


Bipolar Junction Transistor 
(BJT)
CHAPTER 3
Introduction
• The basic of electronic system nowadays is
semiconductor device. 
• The famous and commonly use of this device 
is BJTs
(Bipolar Junction Transistors).
• It can be use as amplifier and logic switches.
• BJT consists of  three terminal:
? collector : C
? base : B
?emitter : E
• Two types of BJT : pnp and npn
Transistor Construction
• 3 layer semiconductor device consisting:
• 2 n- and 1 p-type layers of material ? npn transistor
• 2 p- and 1 n-type layers of material ?pnp transistor
• The term bipolar reflects the fact that holes and 
electrons participate in the injection process into the 
oppositely polarized material
• A single pn junction has two different types of bias:
• forward bias
• reverse bias
• Thus, a two-pn-junction device has four types of bias.
Position of the terminals and symbol 
of BJT.
• Base is located at the middle 
and more thin from the level 
of collector and emitter
• The emitter and collector    
terminals are made of the 
same type of semiconductor 
material, while the base of the 
other type of material
Transistor currents 
-The arrow is always drawn
on the emitter
-The arrow always point 
toward the n-type
-The arrow indicates the 
direction of the emitter      
current:
pnp:E ? B
npn: B ? E
I
C
=the collector current
I
B
= the base current
I
E
= the emitter current
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