Question

Explain the function of a transistor as a switch.

Answer 1

Hint: Transistor is a semiconductor device. Electronic signals and electrical power are amplified and switched using the transistors. The emitter, base, and collector are the three terminals of the transistor. There are two types that are transistors called NPN and PNP transistors.

Complete step by step answer:
(i)The name transistor is a combination of transfer and resistors. It means its resistance can be changed. It is made up of semiconductor materials germanium and silicon.
(ii)Transistors can be used as a switch in low voltage devices like LED.
(iii) The transistors can be used as switches when it is cut-off or saturated regions. A transistor can be operated in three modes. They are the active region, saturated region, and the cut-off region. Thus, the transistors can be used as an amplifier in the active region.
(iv)The operating conditions of the transistor are zero input base current ($I_B=0$), Zero collector current ($I_C=0$), and the maximum collector voltage (${V_{CE}}$=maximum) which results in the large depletion layer. There is no current flowing through the device. The transistor is switched to OFF. The transistor works as an OFF switch in the cut-off region.

(v) In the saturated region, the transistor will be biased so that the maximum amount of base current ($I_B=$maximum) is applied, resulting in maximum collector current($I_C=$ maximum) and then resulting in the minimum collector-emitter voltage (${V_{CE}} \approx 0$)drop. At this condition, the depletion layer will be small. Hence it allows maximum current to flow through it. Therefore, in the saturated regions, transistors are used as an ON switch.
(vi) In the transistor, unless the current flows in the base circuit, there is no current can flow in the collector circuit. This property allows the transistors to work as a switch.

Note:
Integrated circuits are made up of NPN type transistors. This is because
A) NPN construction is cheaper
B) Diffusion constant is reduced
C) NPN construction permits higher packing of elements
D) P-type base is preferred