Field Effect Transistor Working

In this article we learn about the Field effect transistor working and their application. We will also know that main construction of field effect transistor.

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Field Effect Transistor Working

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The field effect transistor (FET) is a three terminal uni polar semiconductor device in which current is controlled by an electric field. FETs are labeled as uni polar devices because it can carry either holes or electrons. FET are mainly used in logic circuits, in TV receivers and as an amplifier.  Hence it is the field effect transistor working, for knowing more about the Field effect transistor we need to know about construction of FET.

Construction of FET( field effect transistor).

For better understand about field effect transistor working we must know about the construction of FET. So here construction of FET given below.

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A FET can be fabricated with either N-channel or P-channel so the N-channel is preferred for fabricating N-channel FET. A narrow bar of n-type semiconductor is taken and two P-type junctions ate diffused on opposite sides of its middle part as shown in diagram. These two junctions form two p-n diode or gates and the area remains between the two gates is called channel. The two gates are connected internally and a single connecting lead is brought out of the device which is called the gate terminal. In this construction whole field effect transistor working depends.
Two leads are joined to the bar, one on each side and they are called source and drain. The p-type channel FET is similar in construction except that it uses p-type bar and two n-type junctions.
FET has three terminals by means of which the electrical connection is provided. Field effect transistor working depends on these three terminals.

1. Source

It is the terminal through which majority charge carriers enter the channel.

2. Drain

It is the terminal through which is formed by joining internally the two impurity reigns. It controls the travelling of majority carriers from source  drain.

3. Gate 

it is the terminal which is formed by joining internally the two impurity regions,. it constrols the travelling of majority carriers from source to drain.

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FET parameters

 It is more need to know about the FET parameter for know about field effect transistor working.
Some of the parameters of a FET when connected in common source configuration are as follows.

AC Drain Resistance

It is the ratio of change in drain source voltage to the change in drain current at constant gate source voltage.
Its unit is ohm. It is also known as dynamic drain resistance.
Amplification Factor
It is the ratio of change in drain source voltage to the change in gate source voltage at constant drain current.

Input Impedance

The Impedance available at the gate terminal is termed as input impedance. A FET has a high input impedance because the gate is reverse biased and gate current is negligible.
Output Impedance
The impedance available at the drain terminal of FET is termed as output impedance. A FET has low output impedance because the drain current has a high magnitude.

Application of FET( field effect transistor).

 After knowing about the field effect transistor working we also need to know about the application of FET.
Some of the important applications of FET are stated under.

1. Since, FET has high input impedance and low output impedance, it is widely used as buffer and in measuring in instruments and in receivers.

2. FETs are used in communication equipment’s for low noise level.

3. Since, FETs have low input capacitance; they are also used in cascade amplifiers used in measuring and testing instruments.

4. FET is a voltage controlled device so it is also used as a voltage variable resistor in op-amps.

5. FETs are used in mixer circuits in FM and TV receivers.

6. FETs are smaller in size in size as compared to BJT so they are mostly used in digital circuits and ICs.s

Hence it is the field effect transistor working and application if you will find any incorrect above please comment below in comment box.

For knowing more about the field effect transistor working and application you must watch this video.

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