BJT is introduced where the types of transistors and modes of operation is discussed.

1. UNIT-III
Bipolar Junction Transistor Biasing
& Amplifiers at low frequencies
ANIL NEERUKONDA INSTITUTE OF TECHNOLOGY & SCIENCES(A)
Department of Electronics and Communication Engineering

2. Why BJT?
• Applications of BJT are
Amplifier
Switch
Digital logic and memory circuits(ECL)
RF circuits for wireless systems
ANIL PRASAD DADI/ECE/ANITS

3. What is BJT?
• It is a three terminal device and has two
junctions
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JE JC JE JC

4. Modes of Operation
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Operating Region JE JC Application Property
Cutoff RB RB Switch Open Switch
Active FB RB Amplifier Amplification
Reverse Active RB FB Attenuator Attenuation
Saturation FB FB Switch Closed Switch

5. Symbols
• The arrow on the emitter lead specifies the
direction of emitter current flow when JE is
forward Biased.
• IE=IC+IB
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6. Transistor Configuration
• Transistor can be connected in a circuit in
following three ways
Common Base
Common Emitter
Common Collector
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7. Common Base Configuration
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Current amplification factor (α ) : The ratio of change in
collector current to the change in emitter current at
constant VCB is known as current amplification factor.

8. Common Emitter Configuration
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Current amplification factor (β ) : The ratio of change in
collector current to the change in base current .

9. Common Emitter Configuration
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10. Common Collector Configuration
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Current amplification factor (γ ) : The ratio of change in
emitter current to the change in base current is known
as current amplification factor.

11. BJT Configuration
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CB CE CC

12. Thank you
for listening