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Different types of transistors | applications of transistor types

This article covers different types of transistors and mentions applications of these transistor types. It describes different types of transistors viz. BJT, FET, MOSFET, UJT etc.

What is Transistor?

Introduction:
• Transistors are manufactured as discrete components as well as incorporated in ICs. ICs contain several thousands of transistors on a tiny slice of silicon.
• 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.

Transistor biasing

• They are three terminal devices.
• They are active components unlike passive ones (e.g. resistors, capacitors, inductors, diodes).
• 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.

It uses same identification codes as used for diodes but american system uses letters "2N" followed by serial number. Conventional system two letters followed by serial number. The first letter indicates semiconductor material (A=germanium, B=silicon) and second letter indicates its use (C=Audio frequency amplifier, F = radio frequency amplifier, S = switching transistor).
➤Example: BC108 is a Silicon Audio Frequency Amplifier.

Transistor Types | Types of transistors with their applications

Let us understand different types of transistors with their applications. Common transistor applications are as follows.
➤It can be used as amplification device to amplify current or voltage.
➤It can be used as switching device in analog or digital circuits.
➤It is used as regulator for voltage or current or power.
➤It is used as building blocks of ICs.
➤It is used as buffer or impedance matching purpose between mismatched circuits.

BJT Transistor

• BJT stands for Bipolar Junction Transistor.
• Its operation depends on flow of both majority and minority carriers.
• It consists of two p-n junctions in the same crystal.
• A very thin slice of lightly doped p-type or n-type semiconductor (known as base-B) is sandwiched between two thicker and heavily doped materials of opposite type (known as collector-C and emitter-E).
• There are two possible configurations of BJT transistor viz. NPN and PNP.
• As shown in NPN current flows from "B" to "E" terminal. In PNP current flows from "E" to "B" terminal.

BJT transistor

Applications: BJT transistor is used as oscillator, switch and amplifier. It is also used in logic circuits. It is found in mobile phones, TV, radio transmitters, industrial control etc.

FET Transistor

• FET stands for Field Effect Transistor.
• The current is due to majority carriers only (either electrons or holes).
• Unlike BJT which is a current controlled amplifying device, FET is voltage controlled device. In FET, output current is controlled by an input voltage.
• In FET transistor, narrow channel of doped semiconductor connects two metal contacts called as drain (D) and source (S). Voltage applied to the third terminal is known as gate (G) which is located between "S" and "D". This gate voltage determines current which flows from "S" to "D".
• Refer BJT vs FET >> for more information.

FET transistor

Applications: FET transistor has very high input impedance. It is widely used as input amplifiers in oscilloscopes, as voltmeters and used in other test and measurement equipments. It is used as voltage variable resistors in Op-amplifiers. It is used as tone controls in FM receiver and TV receiver circuits. It is used in digital switching logic circuits. The other FET transistor applications include low noise amplifier, buffer amplifier, cascode amplifier, analog switch, chopper, multiplexer, current limiter, phase shift oscillators etc.

MOSFET Transistor

• In MOSFET, both positive and negative voltages can be applied to the gate terminal. This is not possible in JUGFET. When gate voltage is made positive in JUGFET, it is forward biased due to which input resistance falles to few tens of ohms and consecutively very large current flows which will damage the device JUGFET.
• There are two modes in which MOSFET works viz. depletion and enhancement.
• Refer Depletion and enhancement MOSFET >> and JUGFET vs MOSFET >> for more information.

MOSFET structure

Applications: It is used for switching and amplifier circuits. It is used as inverter, It is also used in digital circuit. It is used as high frequency amplifier.

UJT Transistor

• Figure-7 depicts structure and symbol of UJT.
• As shown it is n-type silicon bar with connections on both ends.
• The leads are referred as "B1" and "B2". Along the bar between the two bases , PN junction is constructed between P-type Emitter and N-type Bar. This lead is referred as "Emitter Lead-E".
• It is the short form of Unijunction Transistor.
• It is 3 terminal switching device made of semiconductor materials.
• Refer UJT vs SCR vs Diac vs Triac >> for more information.

UJT structure and symbol

Applications: It is used as triggering device for SCR/Triac devices. UJT transistor applications include sawtooth generators, oscillators, phase control circuit and timing circuit.



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