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Meer Zafarullah (KF16ES-33)

Kaleemullah Magsi (KF16ES-57)

Introduction

Mehran University Of Engineering and Technology Shaheed Z.A Bhutto Campus Khairpur Mir’s Sindh.

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Topic

FET Transistor and it’s types

Field Effect Transistor

In a Field Effect (FET) the output characteristics are controlled by

input voltage (Electric filed) and not by input current. This is the

main difference between BJT and FET. There are two basic types

of field effect transistors.

Junction Field effect transistor (JFET).

Metal Oxide Semiconductor field effect transistor (MOSFET).

Junction field effect transistor is a three terminal semiconductor

device in which current conduction is by one type carrier, i.e,

electrons and holes.4

Field Effect Transistor

The JFET was developed about the same time as the

transistor but it came into general use only in the late 1960s.

In JFET the current conduction is either by electrons or holes

and is controlled by means of electric field between the gate

electrode and the conducting channel of the device.

Because of one type of charge carriers JFET transistors are

called Unipolar transistors.

JFET has high input impedance and low noise level

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Junction Field Effect Transistor

Construction of JFET

• A JFET consists of a p type or n type silicon bar containing

two PN junctions at the sides.

• It has three terminals called as Gate, Source and Drain.

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It has very high input impedance (of order of 100M

Ohm). This permits high degree of isolation between

the input and output.

JFET has negative temperature coefficient of

resistance, this avoids thermal runaway.

It has very high power gain.

It has smaller size and longer life and high efficiency.

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Advantages of JFET

Salient Features of JFET

• JFET is a three terminal voltage controlled semiconductordevice.

• JFET is always operated with gate-source PN junction reversebiased.

• JFET has gate current zero.• It does not runaway by increasing temperature.

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Schematic Symbol

Applications

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As a Buffer Amplifier.

Phase Shift Oscillators.

As RF Amplifier (in communication Electronic).

Applications

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MOSFET

Metal Oxide Silicon Field Effect Transistor

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1. MOSFET is a special type of fet transistor2. We can vary the width of a channel along which

charge carriers ( electron s or hole s) flow.3. The wider the channel, the better the device

conducts. The charge carriers enter the channel atthe source , and exit via the drain . The width of thechannel is controlled by the voltage on an electrodecalled the gate , which is located physically betweenthe source and the drain.

Introduction

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Curve for Zener diode

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1. The main advantage of a MOSFET is that it requiresalmost no input current to control the load current,when compared with bipolar transistors.

Introduction

Construction

• The MOSFET is a four terminal device with source(S), gate(G), drain (D) and body (B) terminals.

• The body of the MOSFET is frequently connected to thesource terminal so making it a three terminal device like fieldeffect transistor.

• It is a special type of field-effect transistor ( FET )

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1. Depletion Mode:When there is no voltage on the gate, the channelshows its maximum conductance. As the voltage on thegate is either positive or negative, the channelconductivity decreases.

The MOSFET can function in two ways

2. Enhancement mode:• When there is no voltage on the gate the device does

not conduct. More is the voltage on the gate, the betterthe device can conduct.

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Working Principle of MOSFET:

• The aim of the MOSTFET is to be able to control the voltageand current flow between the source and drain. It worksalmost as a switch.

• Now, if a voltage is applied between the drain and source, thecurrent flows freely between the source and drain and thegate voltage controls the electrons in the channel.

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• Zener Diode as Peak Clipper.

• Meter Protection.

• Zener Diode Shunt Regulator.

• Switching Operation.

Applications

Varactor diode

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• The MOSFET transistor is a semiconductor device.• Used for1. Switching2. Amplifying electronic signals in the electronic

devices.

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USES

The MOSFET has certain advantages over the FET, or JFET.

1. The gate is insulated electrically from the channel, nocurrent flows between the gate and the channel,

2. Thus, the MOSFET has practically infinite impendance.3. This makes MOSFETs useful for power amplifiers.4. The devices are also well suited to high-speed

switching applications.5. Some integrated circuits ( IC s) contain tiny MOSFETs

and are used in computers.15/08/2017

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• Auto Intensity Control of Street Lights using MOSFET

• MOSFET Used as a Switch• Amplifiers

MOSFET Applications

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