Types of MOSFET, Applications, Working, And Operation

Types of MOSFET ApplicationsAnd Working Operation

INTRODUCTION

MOSFET (metal-oxide semiconductor field-effect transistor, pronounced MAWS-feht) is a special type of field-effect transistor (FET) that works by electronically varying the width of a channel along which charge carriers (electrons or holes) flow. The wider the channel, the better the device conducts. The charge carriers enter the channel at the source, and exit via the drain. The width of the channel is controlled by the voltage on an electrode called the gate, which is located physically between the source and the drain and is insulated from the channel by an extremely thin layer of metal oxide.

Types of MOSFET Devices

The MOSFET is classified into two types such as follows.

·         Depletion mode MOSFET

·         Enhancement mode MOSFET

Depletion Mode MOSFET

·        When there is zero voltage on the gate terminal, the channel shows its maximum conductance.

·        As the voltage on the gate is negative or positive, then decreases the

Channel conductivity.

Enhancement Mode MOSFET

·         When there is no voltage on the gate terminal the device does not conduct.

·         When more voltage applied on the gate terminal, the device hasgood

·         conductivity.

MOSFET Working Principle

·         The working of MOSFET depends upon the metal oxide capacitor (MOS).

·         It is the main part of the MOSFET.

·         The oxide layer presents among the source and drain terminal.

·         It can be set from p-type to n-type by applying positive or negative gate voltages respectively.

·         When apply the positive gate voltage the holes present under the oxide layer with a repulsive force and holes are pushed downward through the substrate.

·         The deflection region populated by the bound negative charges which are allied with the acceptor atoms.

                                                                   Block Diagram

P-Channel MOSFET

P-Channel MOSFET

·         The P-Channel MOSFET consist negative ions so it works with negative voltages.

·         When we apply the negative voltage to gate, the electrons present under the oxide layer through pushed downward into the substrate with a repulsive force.

·         The deflection region populates by the bound positive charges which are allied with the donor atoms.

·         The negative voltage also attracts holes from p+ source and drain region into the channel region.

N-Channel MOSFET

·         When we apply the positive gate voltage the holes present under the oxide layer pushed downward into the substrate with a repulsive force.

N-Channel MOSFET

·         The deflection region is populated by the bound negative charges which are allied with the acceptor atoms.

·         The positive voltage also attracts electrons from the n+ source and drain regions into the channel.

·         If a voltage is applied among the drain and source the current flows freely between the source and drain and the gate voltage controls the electrons in the channel.

·         In place of positive voltage if we apply a negative voltage (hole)channel will be formed under the oxide layer.

MOSFET Applications

·         The applications of the MOSFET used in various electrical and electronic projects which are designed by using various electrical and electronic components.

·         MOSFET Used as a Switch

·         Auto Intensity Control of Street Lights using MOSFET

·         Marx Generator Based High Voltage Using MOSFETs

·         EEPROM based Preset Speed Control of BLDC Motor

·         LDR Based Power Saver for Intensity Controlled Street Light

·         SVPWM (Space Vector Pulse Width Modulation)

Advantage

·         Mosfet are small compare to BJT so it fabricated easily and space saving scheme on the IC's

·         Mosfets input impedance are very high so they do not load the circuits. loading effect doesn't arise.

·         Operating frequency is very high so may be used at higher frequencies.

·         Used in digital circuits for it's reliability.

·         Effect of noise is less than BJT . so high signal to noise ratio.

·         Mosfets are unipolar devices so reverse saturation current doesn'texist.

·         7-it consume less D.C power rather than BJT.

Disadvantage

·         Handling is not easy.

·         Mosfet is very sensitive to electrostatic charge so it may bedestroy when you touch the pins of a mosfet devices by hand.

·         Trans conductance is low than BJT.