Question

Describe with diagram the working method of p-n-p and n-p-n transistors.

Hint:

The transistor acts as a current amplifier: small base current controls larger collector current.

Answer 1

Step 1: In a Bipolar Junction Transistor (BJT), the emitter-base junction is forward biased to allow the majority charge carriers (electrons in an NPN transistor or holes in a PNP transistor) to flow from the emitter into the base region. This forward bias reduces the barrier potential, enabling carrier injection.
Step 2: The base-collector junction is reverse biased, creating a strong electric field that sweeps the injected carriers from the base into the collector region. Because the base is thin and lightly doped, most carriers pass through it without recombining.
Step 3: The small base current controls the large collector current, resulting in the amplification property of the transistor. This allows the transistor to act as a current amplifier, where a small input current at the base controls a much larger current flowing from emitter to collector.