Basic introductory presentation of bipolar junction transistor (BJTs).

1. BIPOLAR
JUNCTION
TRANSISTORS
(BJTS)
Muhammad Abrar​

2. AGENDA
Description
Construction
​Operation
Configuration
​Summary​

3. INTRODUCTION
 Bipolar junction transistor or BJT was invented in 1948 at Bell Telephone
Laboratories, New Jersey, USA.
 BJTs are also simply known as bipolar transistors.
 BJTs are still preferred in this era for specific high-frequency and analog
applications due to their:
 High Speed: Ideal for fast signal processing.
 Low Noise: Ensures clean signal amplification.
 High Output Power: Essential in applications like cell phone
amplifier circuits.

4. CONSTRUCTION
 The term "bipolar" signifies the utilization of both holes and electrons as
current carriers within the transistor structure.
 The BJT is constructed with three doped semiconductor regions separated
by two pn junctions, which are responsible for its operation.
 These three regions are named the emitter, base, and collector as shown
in figure, each playing a critical role in the transistor's functionality.
Bipolar Junction Transistors (BJTs) 4

5. TYPES
 There are two types of bipolar junction transistor.
 Symbolic representation.
Bipolar Junction Transistors (BJTs) 5

6. OPERATION
NPN Transistor Operation
 The BJT is forward-biased at the base-emitter (BE)
junction, and reversed-biased at the base-collector
(BC) junction.
 The base region contains a low density of majority
carrier holes, represented by white circles.
 Electrons that enter the base region undergo one of
two processes:
 Some electrons recombine with holes, transforming
into valence electrons. They contribute to the hole
current (minority current), or into the base lead where
they revert to free electrons and flow as external base
current.
 Alternatively, most of the electrons may enter the
collector region due to the thinness of the base and the
attractive force of the positive collector supply voltage,
which exists because the BC junction is reverse-
biased.
 The current from base and collector flows back to the
emitter. So,
𝐼𝐸 = 𝐼𝐵 + 𝐼𝐶
Bipolar Junction Transistors (BJTs) 6

7. MODES OF OPERATION
MODES
EMITTER-
BASE
JUNCTION
COLLECTOR-
BASE
JUNCTION
APPLICATIONS
Cut-off Reverse biased
Reverse
biased
As a Switch
Saturation Forward biased Forward biased
Active Forward biased
Reverse
biased
Amplifier
Reverse
Active
Reverse biased
Forward biased
Performance
Degradation
Bipolar Junction Transistors (BJTs) 7

8. MODES OF OPERATION
Bipolar Junction Transistors (BJTs) 8
Collector Characteristic Curves

9. THANK YOU