Transistors are semiconductor devices that can amplify or switch electronic signals and electrical power. The transistor was invented in 1947 by American physicists John Bardeen, Walter Brattain, and William Shockley at Bell Labs. There are two main types of transistors: NPN and PNP. In an NPN transistor, electrons flow from the emitter to the collector, while in a PNP transistor, holes flow from the emitter to the collector. The base terminal controls the flow of current through the collector and emitter.

1. Transistor
By:
Md. Al Imran Bhuyan
Nazmul Hasan
Sabuj Mandal
Rukaiya Binte Farid
Nasif Hossain

2. What is a transistor?

3. Who invented
transistor?

4. P
P
P
N
N
N
Types of Transistor:
IB(µA) IB(µA)
Ic(mA)
IE(mA) IE(mA)
IC(mA)

5. N
P
NThe collector is lightly doped. C
The base is thin and
is lightly doped.
B
The emitter is heavily doped. E
NPN Transistor Structure

6. The C-B junction
is reverse biased.
N
P
N
NPN Transistor Bias
C
B
E
No current flows.

7. The B-E junction
is forward biased.
N
P
N
NPN Transistor Bias
C
B
E
Current flows.

8. When both junctions
are biased....
N
P
N
NPN Transistor Bias
C
B
E
Current flows
everywhere.
Note that IB is smaller
than IE or IC.
IC
IB
IE

9. N
P
N C
B
E
Although IB is smaller
it controls IE and IC.
IC
IB
IE
Note: when the
switch opens, all
currents go to zero.
Gain is something small
controlling something large
(IB is small).

10. N
P
C
B
E
IC = 99 mA
IB = 1 mA
IE = 100 mA
b =
IC
IB
The current gain from
base to collector
is called b.
99 mA
1 mA
= 99

11. N
P
C
B
E
IC = 99 mA
IB = 1 mA
IE = 100 mA
IE = IB + IC
99 mA= 1 mA +
= 100 mA
Kirchhoff’s
current law:

12. C
B
E
IC = 99 mA
IB = 1 mA
IE = 100 mA
In a PNP transistor,
holes flow from
emitter to collector.
Notice the PNP
bias voltages.

13. Emitter
Base
Collector
Memory aid: NPN
means Not Pointing iN.
EB
C
NPN Schematic Symbol

14. Collector
Base
Emitter
EB
C
PNP Schematic Symbol
Memory aid: NPN
means Pointing iN Properly.