Question

State the properties and uses of a Junction transistor.

Answer 1

A bipolar junction transistor consists of three regions of doped semiconductors. A small current in the center or base region can be used to control a larger current flowing between the end regions (emitter and collector).
The Junction Transistor can be used as:

1. Current amplifier: The larger collector current $I_C$ is proportional to the base current $I_B$ according to the relationship $I_C=\beta I_B$ , or more precisely it is proportional to the base-emitter voltage $V_{BE}$. The smaller base current controls the larger collector current, achieving current amplification.
2. Switch: For switching applications transistor is biased to operate in the saturation or cutoff region. Transistor in cutoff region will act as an open switching whereas in saturation will act as a closed switch.