physics-class-12-unit-14-chapter-08-transistor-as-an-amplifier-and-asa-switch-l-8-8-qc6vdurteu

Transistor as an Amplifier and as a Switch

Bipolar Junction Transistor

Bipolar Junction Transistor is made of back to back two p-n iunctions grown on the same semiconductor base.
The middle region is lightly doped and is very thin. This is called Base. One side is heavily doped and is called emitter. The other side is moderately doped and is called collector.

Transistor as an Amplifier and as a Switch

Bipolar Junction Transistor

Arrow is put on the emitter from $p$ to $n$ direction. It shows the direction ofthe current when the junction is forward biased.

Transistor as an Amplifier and as a Switch

Bipolar Junction Transistor

Two batteries are used for biasing two iunctions. If the batteries have a common terminal and that is connected to Emitter, it is called common emitter mode.
Similarly you can have common base or common collector modes.

Transistor as an Amplifier and as a Switch

Transistor

Emitter side is the Input side and Collector side is the Output Side
Working of a transistor:- Emitter emits large number of charge carriers in the base region. Most of these cross over the thin base region and make collector current. Some of the carriers injected make Base current.