types of mosfet applications and working operation

Types of MOSFET Applications and

Working Operation

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Introduction

Types of MOSFET Applications And Working Operation

The MOSFET is an important element in embedded system design which is used to control the loads as per the requirement. Many of electronic projects developed using MOSFET such as light intensity control, motor control and max generator applications. The MOSFET is a high voltage controlling device provides some key features for circuit designers in terms of their overall performance. This article provides information about different types of MOSFET applications.

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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 has good 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.







MOSFET Working Principle 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)







MOSFET Used As a Switch In this circuit, a N-channel MOSFET is being used to switch the lamp for ON

and OFF.

The positive voltage is applied at the gate of the MOSFET and the lamp is ON (VGS =+v).

At the zero voltage level the device turns off (VGS=0).

If the resistive load of the lamp was to be replaced by an inductive load and connected to the relay or diode to protect the load.

When using MOSFET to switch either inductive load or capacitive load protection is required to contain the MOSFET applications.







MOSFET Used As a Switch If we are not giving the protection, then the MOSFET will be damaged.

For the MOSFET to operate as an analog switching device

Needs to be switched between its cut off region where VGS =0 and saturation region where VGS =+v.







Auto Intensity Control of Street Lights using MOSFETIt is to control the lights automatically on the highways using microprocessor by variants of the clock pulses.

MOSFET plays major role that is used to switch the lamps as per the requirement.

The proposed system using a Raspberry Pi board, consist a processor to control it.

Here we can replace the LEDs in place of HID lamps.

Which are connected to the processor with the help of the MOSFET.

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Auto Intensity Control of Street Lights using MOSFET The microcontroller release the respective duty cycles, then switch the

MOSFET to illuminate the light with bright intensity.







Marx Generator Based High Voltage Using MOSFETs

The concept is to delivers the output approximately triple to that of the input voltage by Marx generator principle.

If the input voltage applied is around 12v volts DC, then the output voltage is around 36 volts DC.

It uses 555 timer in Astable mode, which delivers the clock pulses to charge the parallel capacitors during on time.

The capacitors are brought in a series during the off time through MOSFET switches.

It develops a voltage approximately triple to the input voltage but little less.







Marx Generator Based High Voltage Using MOSFETs The output voltage can be measured with the help of the

Multimeter.








It is to control the speed of the BLDC motor by varying the duty cycle.

The main intention is to operate a BLDC motor at a particular speed with a predefined voltage .

The motor remains in an operational state or restarted to operate at the same speed as before by using stored data from an EEPROM.

The speed control of the DC motor is achieved by varying the duty cycles (PWM Pulses) from the microcontroller as per the program.








The microcontroller receives the percentage of duty cycles stored in the EEPROM from inbuilt switch commands.

It delivers the desired output to switch the driver IC in order to control the speed of the DC motor.

If the power supply is interrupted, the EEPROM retains that information to operate the motor at the same speed as before while the power supply was available.








In HID Lamp, intensity cannot be controlled according to the requirement.

so there is a need to switch to an alternative method of lighting system, i.e., by using LEDs.

Its intensity that can be controlled according to requirement during non-peak hours.

The microcontroller contains programmable instructions that controls the intensity of lights based on the PWM (Pulse width modulation) signals generated.







SVPWM (Space Vector Pulse Width Modulation)







SVPWM (Space Vector Pulse Width Modulation) The Space Vector PWM is a sophisticated technique for controlling AC

motors by generating a fundamental sine wave that provides a pure voltage to the motor with lower total harmonic distortion.

In this system, DC supply is produced from the single-phase AC after rectification.

It is fed to the 3-phase inverter with 6 numbers of MOSFETs.

For each phase, a pair of MOSFET are used.

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SVPWM (Space Vector Pulse Width Modulation) Therefore, three pairs of MOSFETs are switched at certain intervals of

time for producing three-phase supply to control the speed of the motor.

This circuit also gives light indication of any fault that occurs in the control circuit.







Advantage Mosfet are small compare to BJT so it fabricated easily and space saving

scheme on the ic's

Mosfet's 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't exist.

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 be destroy when you touch the pins of a mosfet devices by hand.

Trans conductance is low than BJT.







Conclusion

The MOSFET requires high voltage whereas transistor requires low voltage and current. As compared to a BJT, the driving requirement for the MOSFET is much better.

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types of mosfet applications and working operation

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