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Applications of FET (Field Effect Transistor)

FETs (Field Effect Transistors) are semiconductor devices that are widely used in various electronic applications due to their ability to amplify and control electrical signals. There are two main types of FETs viz. MOSFETs and JFETs.

FET has a very high input impedance in the order of 100 MΩ for JFET case and in the range from 10⁴ to 10⁹ MΩ for MOSFET case.

As it offers high input impedance, the drawbacks of ordinary transistor having low input impedance can be avoided with the use of FET device in the electronic circuit designs. Following are the FET uses in various electronic applications.

Amplification : FETs are often used as amplifiers in electronic circuits similar to BJT counterparts. They can amplify analog signals by controlling current flow between source and drain terminals based on voltage applied to the gate terminal.

Switching : They are widely used as electronic switches in digital circuits. MOSFETs are excellent for switching applications due to their low input current requirements, fast switching speeds and low power consumption.

Oscillators : They are used in oscillator circuits to generate continuous waveforms such as sine wave, square wave and triangular waves. They are used in signal generation and clock generation for digital systems.

Voltage regulators : They are used in voltage regulator circuits to stabilize and control the output voltage. They are used in linear voltage regulators to maintain steady output voltage despite input voltage fluctuations.

Mixers and Modulators : Used in frequency mixers and modulators for communication systems. These devices are essential for translating and modulating signals in various frequency bands.

VCOs (Voltage Controlled Oscillators) : Used to build VCOs which are essential components in PLLs, frequency synthesizers and RF signal generators/analyzers.

Voltage multipliers : Used in voltage multiplier circuits to generate high voltages from low input voltage. They find applications in CRT displays and high voltage power supplies.

Low Noise Amplifier (LNA) : Due to its low noise characteristics, FETs are used in sensitive applications like LNAs in communication systems and scientific instruments.

Sensor interface : They are employed as impedance converters in sensor interfaces to convert high impedance of certain sensors into low impedance suitable for measurement and signal processing.

Power electronics : Power MOSFETs are used in power electronics applications such as motor control, switching power supplies and inverters.

Other uses of FET

• Due to high impedance at input, they are widely used as input amplifiers in various test and measurement equipments such as voltmeters, oscilloscopes etc.
• As FET devices are voltage controlled devices, they are used in operational amplifiers as well as in tone controllers as VVRs(Voltage Variable Resistors).
• Due to lower intermodualtion distortions, FETs are used in RF mixer circuits employed in TV/FM receivers.
• They are used in amplifier section of FM tuners due to low noise level.
• Due to smaller size, FETs are employed in digital circuits namely memories, computers and LSI designs.
• They are used in low frequency amplifier modules of hearing aids as well as inductive transducers. This is due to addition of small coupling capacitors in the circuit where they have to be used.

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