1. Bipolar Junction Transistor (BJT) Construction
Emitter
Base
Collector C E B
It is three layer semiconductor device, consisting of either two n- and one p-type layers of material or two p- and one n-type layers.

2. Bipolar Junction Transistor (BJT) Construction
Since three layers are involved in this device, therefore it will have three terminals. These terminals are known as:-
Emitter.
2. Base.
3. Collector.

3. Emitter layer is heavily doped. Base layer is lightly doped.
Bipolar Junction Transistor (BJT) Construction
Emitter layer is heavily doped.
Base layer is lightly doped.
Collector is very lightly doped.
The base layer is very thin as compared to other two, normally in the range of 150:1.

4. Bipolar Junction Transistor (BJT) Construction
The designated terminology for three terminals is as follows:-
Emitter: This layer emits electrons.
Base: It helps minority carriers to transfer rapidly from emitter to collector. Electric field is created in base by non-uniform doping, so that minority carriers are accelerated from emitter to collector.
Collector: This layer collects the emitted electrons.

5. These types are in equation to constructional arrangement of layers.
Bipolar Junction Transistor Construction
Two basic types of BJTs
These types are in equation to constructional arrangement of layers.
The arrangement shown in the figure is called NPN Transistor.

6. N N P C E (Collector) (Emitter) B (Base)
Bipolar Junction Transistor Construction N N P C
(Collector) E
(Emitter) B
(Base)

7. Bipolar Junction Transistor The Symbol for NPN Transistor
The arrow shows direction of flow of conventional current.

8. The arrangement is known as PNP transistor.
Bipolar Junction Transistor Construction
The arrangement is known as PNP transistor. P N E B C

9. Bipolar Junction Transistor The Symbol for NPN Transistor
The arrow shows direction of flow of conventional current.

10. P N E B C VEE + - Bipolar Junction Transistor Operation
Depletion region P N E B C
Majority Carriers
VEE + -

11. C E P N B VCC + - Bipolar Junction Transistor Operation
Depletion region
VCC
Minority Carriers

12. C E P N IC IE IB B VCC + - Bipolar Junction Transistor Operation
Depletion region P N E B C + -
VCC
Minority Carriers IE IC IB

13. OPERATING CONFIGURATIONS OF BJT
There are three basic configurations under which transistor may be operated, these configurations depend upon the situation and requirements. These configurations are called
Common Base Configuration.
Common Emitter Configuration.
Common Collector Configuration.

14. OPERATING CONFIGURATIONS OF BJT
Common Base Configuration N P E B C + -
VCC IE IC IB
VEE

15. OPERATING CONFIGURATIONS OF BJT+ - IE IC IB
VCC
VBB
Common Emitter Configuration +

16. OPERATING CONFIGURATIONS OF BJT
Common Collector Configuration + N P E B C IE IC
+ - -
VEE IB
VBB

17. Directions of Currents in BJT

18. MODES OF OPERATION OF BJT
There are three modes of operation for BJT
Cut Off
Active
Saturation

19. Graphical Presentation of BJT
Input or driving point characteristics
Ic=IsevBE/VT

20. Graphical Presentation of BJT OutPut or Collector Characteristic for Common Base Configuration.

21. MODES OF OPERATION OF BJT
EBJ CBJ
Cut Off Reverse Reverse
Active Forward Reverse
Saturation Forward Forward

22. MODES OF OPERATION OF BJT
For the transistors shown, state mode of operation.

23. MODES OF OPERATION OF BJT

24. MODES OF OPERATION OF BJT