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.

Working Operation
Types of MOSFET Devices
The MOSFET is classified into two types such as follows.
• Depletion mode MOSFET
• Enhancement mode MOSFET

Working Operation
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.

Working Operation
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.

Working Operation
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.

Working Operation
MOSFET Working Principle
 The deflection region populated by the bound negative charges which are
allied with the acceptor atoms.
Block Diagram

Working Operation
P- Channel MOSFET

Working Operation
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.

Working Operation
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.

Working Operation
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.

Working Operation
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)

Working Operation
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.

Working Operation
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.

Working Operation
Auto Intensity Control of Street Lights using
MOSFET
It 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.

Working Operation
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.

Working Operation
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.

Working Operation
Marx Generator Based High Voltage Using MOSFETs
 The output voltage can be measured with the help of the
Multimeter.

Working Operation
EEPROM based Preset Speed Control of BLDC Motor
 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.

Working Operation
 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.

Working Operation

Working Operation
LDR Based Power Saver for Intensity Controlled Street
Light

Working Operation
LDR Based Power Saver for Intensity Controlled Street
Light
 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.

Working Operation
SVPWM (Space Vector Pulse Width Modulation)

Working Operation
 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.

Working Operation
 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.

Working Operation
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.

Working Operation
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.

Working Operation
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.

Types of MOSFET Applications and Working Operation

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Types of MOSFET Applications and Working Operation