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Advantages of Transistor | disadvantages of Transistor

This page covers advantages and disadvantages of Transistor. It mentions Transistor advantages or benefits and Transistor disadvantages or drawbacks. BJT transistor type is used for discussion on working operation, applications etc.

What is Transistor?

• The transistor is a solid state equivalent of a triode valve which was used in radio and early computers.
• It is made of three layer semiconductor materials. Common semiconductor materials in transistor construction are silicon and germanium.
• It act as an insulator and a conductor.
• The 3 layered transistor is also known as BJT (Bipolar Junction Transistor). The name has been derived from the term "bipolar" due to use of both electrons and holes as charge carriers in the structure of the transistor. BJT transistor is categorized into NPN and PNP types.
• Transistor has three regions viz. emitter, base and collector. Emitter is heavily doped, base part is lightly doped and collector part is moderately doped.
• Basic planar structure of BJT transistor is shown in the figure-1.

BJT planar structure

• The symbols of transistor of NPN and PNP types are shown in the figure-2.
• There are difference types of transistor viz. BJT, FET and MOSFET etc.
• BJT is a current controlled device which provides amplification or gain to the input signal. FET is a voltage controlled device with terminals source, gate and drain.

BJT FET

• For transistor to be operational, BE (Base-Emitter) junction is forward biased and BC (Base-Collector) junction is reverse biased. As a result of this connection, current flows where, IE = IB + IC. This is shown in the figure below.
• There are three operating regions of a BJT transistor viz. cutoff, linear and saturation. This can be resembled to different conditions of a water tap viz. OFF, ON and full ON respectively.

Transistor biasing

• Transistor can be used as switch >> and also as an amplifier. As a switch it operates in either cutoff or saturation region. As an amplifier, Due to small changes in the base current, collector current will mimic input base signal with higher amplitude.

Refer PNP vs NPN transistor >> , BJT vs FET >>, MOSFET vs BJT >> and UJT >> for more information.

Benefits or advantages of Transistor

Following are the benefits or advantages of Transistor:
➨Input impedance is highest and output impedance is lowest for common collector BJT amplifier. Darlington pair is used where very high impedance is needed. Darlington pair offers very high current gain.
➨It is used as current controlled current source.
➨It is used for fast switching applications.
➨It is available at very low cost.
➨It is very smaller in size.
➨It has longer life.
➨It uses low voltage for its operation. Hence it offers more safey.
➨There is no power consumption by cathode heater.

Drawbacks or disadvantages of Transistor

Following are the drawbacks or disadvantages of Transistor:
➨Due to its small size, it is difficult to trace out faulty ones due to failure. Moreover it is very difficult to unsolder and replace new ones.
➨Manufacturing techniques are very complex and requires clean room environment.
➨Transistor has non zero ON resistance. Hence when it is ON, voltage across transistor is never zero. Moreover during OFF state also, there is flow of small leakage current. Hence it does not work as efficiently as mechanical switch or electrical switch or relay.



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