The document discusses the history and development of transistors. The vacuum tube triode was invented in 1906 by Lee De Forest and was used in early radios and computers. John Bardeen and Walter Brattain invented the first transistor in 1947 called the "point contact" transistor. A transistor is an electronic device made of semiconductor material that can act as an insulator or conductor, consisting of three layers known as a bipolar junction transistor. The transistor functions by using both holes and electrons as charge carriers and can operate in different regions including cutoff, linear, and saturation.

2. History of transistors
In 1906, an American inventor and physicist,
Lee De Forest, made the vacuum tube
triode or audion as he called it.
 Used in radios
 Used in early computers

3. The first transistor
In 1947, John
Bardeen and
Walter Brattain
deviced - the first
"point contact"
transistor.

4. Transistor Definition
Transistor is an electronic device
made of three layers of semiconductor
material that can act as an insulator
and a conductor.
The three layered transistor is also
known as the bipolar junction
transistor.

5. Bipolar Junction Transistors (BJT’s)
The term bipolar refers to the use of both
holes and electrons as charge carriers in the
transistor structure
 There are two types of BJTs, the NPN and
PNP

6. Basic construction

7. Regions of a transistor
A transistor has three regions namely,
Emitter- heavily doped
Base- lightly doped
Collector- moderately doped

8. Transistor symbols

9. Transistor biasing
 The base-emitter (BE) junction is forward biased
The base-collector (BC) junction is reverse biased.

10. Operating regions of BJT
Cut off region
Linear region
Saturation region

11. Types of transistor
BJT - Bipolar Junction Transistor
UJT- Unipolar Junction Transistor
FET - Field Effect Transistor
MOS - Metal Oxide Semiconductor