MOSFET is a metal oxide semiconductor that is under the category of the field-effect transistor (FET). These transistors are widely used under the varieties of the applications relating to the amplification and the switching of the devices. Because of its fabrication MOSFET’s are available in smaller sizes. It consists of a source, drain, gate and the substrate of the transistor as its terminals. For the circuitry of analog or it be digital this one is the widely preferred transistor. Based on the variation at the depletion region width and the flow of the majority concentration of the carriers the working of the MOSFET is classified as depletion type and enhancement type.
- Unipolar means single polarity. There are basically two types of polarities which are positive (hole) polarity or negative (electron) polarity. MOSFET is a type of field-effect transistor (FET) in which there is only one type of charge that is either electron or hole. That is why MOSFET is considered as unipolar.
- The first type of transistor is BJT (Bipolar Junction Transistor) and MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is another type of transistor introduced later. For a better understanding of this concept, here this article gives the main difference between BJT and MOSFET.
Mar 23, 2020 Classification of MOSFET The MOSFET is Classified into two types based on the type of operations, namely Enhancement mode MOSFET (E-MOSFET) and Depletion mode MOSFET (D-MOSFET), these MOSFETs are further classified based on the material used for construction as n-channel and p-channel. So, in general, there are 4 different types of MOSFETs. Wolfsberger ac 1920 kitsempty spaces the blog.
What is MOSFET?
A FET that is designed with the gate terminal being insulted from the substrate which is either the p-type or n-type material is called as Metal Oxide Semiconductor Field Effect Transistor. The Gate terminal which is a metal piece is insulated by material like silicon dioxide(Si02). The working of these MOSFETs depends upon the conduction of the charges through the channels based on the gate-source voltage.
Types of MOSFETs
Firstly based on the types of the channel it is classified as p-channel or n-channel MOSFETs. The presence of the channel in the transistor makes the MOSFET to operate into two different modes. If the channel exists and once the biasing is provided it starts to conduct then it is referred to as Depletion mode. Due to the biasing if the channel is created and then the conduction began then it is this referred to as Enhancement mode.
(1) Enhancement Mode
The application of the voltage makes the device to turn into ON mode known as Enhancement Mode. Generally, it is known for the characteristics similar to that of an open switch.
(2) Depletion Mode
In this mode, the application of the voltage makes the device turn into OFF mode. Hence these mode characteristics are equivalent to the closed switch.
MOSFET Symbol
The symbol of the MOSFET consists of the terminals and the representation of the channels based on the condition of the biasing and the way channel reacts to it make the device to conduct the flow of the charge carriers. The direction of the arrow in the below symbols represents the direction of the flow of charge carriers. In N- channel type it flows outward towards the gate and in P- channel type it flows inward away from the gate terminal.
Symbols for N-channel Depletion and Enhancement Types
Structure of MOSFET
The structure of the MOSFET is highly dependent on the influence of the majority of the charge carriers. Hence it makes the designing of this type of structure as the quite difficult one in comparison with the structure of the JFET. The formations of the electric field in this MOSFET either enhancement or depletion is completely dependent on the voltage applied at the terminal gate which in turn depends on the channel . If it is p-channel the majority of the concentration of the carriers will be holes and for n-type the majority of the concentration of the carriers are electrons.
Based on the biasing applied at the terminal gate the transistor conducts. If there is no conducting voltage provided then, in that case, it will remain in non-conducting mode. So these are generally preferred in switching the devices because it makes the device to turn ON or OFF based on the biasing.
Threshold Voltage
The voltage that is applied between the gate and the source terminal upon which the device turns on or off is called threshold voltage and it is also referred to as the gate voltage.
MOSFET Working
MOSFET working is highly dependent on the channel present in between the terminals. The presence of a p-type channel makes the transistor conduction possible due to its majority charge carriers referred to as holes. In the n-type channel, the transistor conductivity is based on their majority charge concentrations that are known as electrons.
(1) P-Channel
In this type of MOSFET, the source and drain are highly doped with a p-type material and they have very lightly doped n-type substrate. When the space between the drain and source are doped with a p-type impurities which becomes a channel between the source and the drain then it is a P-type depletion mode MOSFET and if the channel is formed between drain and source by the application of the gate voltage then it is P-type enhancement mode MOSFET.
P-Channel Enhancement Mode Working
Here the device starts conducting when a negative voltage is applied to the Gate terminal. When a negative voltage is applied to all the holes which are minority carriers in the n-type moves toward the gate terminal. But on its way, some of them combine with the some of the electrons which are minority carriers in the p-type drain and source. But at a particular voltage known as the threshold voltage, the holes will be able to overcome the recombination resulting in the formation of the channel between the drain and the source. Under this condition when a negative voltage is applied to the drain terminal the device starts conducting. Since the channel formed here is of holes it is called as P-channel Enhancement MOSFET.
P-Channel Depletion Mode Working
In this Mode when the gate voltage is zero and when a negative voltage is applied between the drain and the source then the holes start moving towards the drain because of the negative voltage and the device starts conducting. When a positive voltage is applied to the Gate terminal then the holes in the p channel get pushed toward the N-type substrate and start the recombine with the electrons in the N-type substrate. As the voltage increase, the number of recombination increases and this results in the depletion of the charge carriers(holes) which results in the reduction of the drain current. At a particular positive voltage of the gate terminal, the device stops conducting this voltage is called the Pinch-off voltage. When a negative voltage is applied to the Gate terminal then the holes which are the minority carriers in the n-type substrate moves directly towards the channel, as a result, the Drain current starts increasing. Epos 4 excel version 1.2 releasedepos 4 excel. As the negative voltage of the Gate terminal increases the Drain current also increases. This region is called the Enhancement region.
P-Channel Depletion MOSFET
The variation in the width of the regions impacts the conductivity of the transistor. This is the reason it is known as the depletion type of p-channel MOSFET.
(2) N-Channel
In an N-type MOSFET, the source and the drain have a highly doped N-type material and lightly doped P-type substrate. Based on the way the channel is formed these are also classified as enhancement and the depletion type of MOSFETs.
N-Channel Enhancement Mode Working
The positive polarity of the voltage is considered here because n-channel consists of the majority of the carriers as electrons. The operation is similar to p-type MOSFET except that the device starts conducting when a positive voltage applied to the gate terminal. As the positive voltage in the gate terminal is increased at a particular threshold voltage and a channel gets formed drain and source. Under this condition, if a positive voltage is applied between the drain and source the device starts conducting.
N-Channel Depletion Mode Working
This mode of operation is similar to the P-type depletion-mode except that the drain to source terminal should be forward biased and a positive voltage should be applied to the Gate terminal for the current to flow from the drain to source. When a negative voltage is applied the major charge carriers get repelled towards the substrate and combines with the electrons resulting in the depletion of the major charge carriers in the channel and so then there will be a reduction in the drain current. At a particular negative voltage, the drain current becomes zero. This voltage is called a pinch-off voltage. Hence this type of MOSFET is known as the N-channel Depletion mode MOSFET.
N-Channel Depletion MOSFET
The enhancement mode is known for its characteristics based on the applied voltage whereas depletion is based on the variation of its width of the depletion region.
MOSFET Characteristics
The characteristics of the MOSFET are also dependent on the depletion and the enhancement modes.
Enhancement Mode Characteristics
The most preferred transistor in MOSFET is of enhancement type. In this type, there is no conduction seen if the voltage at the gate and the source terminals are zero. As the voltage reaches the threshold the conductivity tends to increase.
Depletion Mode Characteristics
In this mode, the width of this depletion region is dependent on the applied voltage at the terminal gate. If it is increased in terms of the positive polarity considered then this increment can be seen in the width of the depletion region. This mode of a transistor is very rarely preferred during the design of the electronic circuitry.
MOSFET Applications
The applications of the MOSFET are vast in terms of the electronics
(1) The switching consequence of the devices based on the threshold value makes the MOSFET to work as a switch. Based on the channels the polarity of the biasing voltage may vary.
(2) By the application of the pulse-width modulation technique (PWM) the movement of the motors like DC, Stepper, etc… can get controlled.
(3) The amplifiers designed from these devices are used in the systems of the sounds as well as the radio frequency systems.
(4) The operation of the switching leads to the exploitation of the circuits of the chopper. In this, the value of the DC voltages is converted into the AC voltage by maintaining the same levels for the amplitudes.
(5) If the depletion region of the MOSFET is made in the configuration of the source follower then these circuits are utilized as the voltage regulators in the linear mode.
(6) As the sources that provide the constant value of the current these transistors are utilized.
(7) In order to drive the current or the value of the voltage at a high level, these are preferred in the circuits of oscillators or the mixers.
(8) These are the transistors with the impedance at the high level and possess the switching speed to be at a high level. Because of these characteristics, these are preferred for digital electronics.
(9) It is preferred in various types of systems of sound in the automobiles and the reinforced systems of the sound.
(10) These are preferred in the designing of the calculators.
Hence the above are some of the various applications of the MOSFET.
In this way, the types of MOSFETs are discussed. Though it has a complex design than JFET it is more preferred in analog and digital electronics. This has the features that are responsible for its tremendous growth in technology. Now based on the description can you anyone give an example of an application that used JFET but later replaced with the MOSFET?
MOSFET
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.
MOSFET and Its Applications
The MOSFET (Metal Oxide Semiconductor Field Effect Transistor) transistor is a semiconductor device which is widely used for switching and amplifying electronic signals in the electronic devices.The MOSFET is a three terminal device such as source, gate, and drain. The MOSFET is very far the most common transistor and can be used in both analog and digital ckt.
The MOSFET works by varying the width of a channel along which charge carriers flow (holes and electrons). The charge carriers enter the channel from the source and exits through the drain. The channel width is controlled by the voltage on an electrode is called gate which is located between the source and drain. It is insulated from the channel near an extremely thin layer of metal oxide. There is a different type of MOSFET applications which is used as per the requirement.
Types of MOSFET Devices
The MOSFET is classified into two types such as;
- Depletion mode MOSFET
- Enhancement mode MOSFET
Depletion Mode: 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.
Depletion Mode MOSFET
Enhancement Mode
When there is no voltage on the gate terminal the device does not conduct. More voltage applied on the gate terminal, the device has good conductivity.
Enhance Mode MOSFET
MOSFET Working Principle
The working of MOSFET depends upon the metal oxide capacitor (MOS) that 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.
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.
P-Channel MOSFET
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. 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. Now, 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 Transistor Operation
N-Channel MOSFET
MOSFET Applications
The applications of the MOSFET used in various electrical and electronic projects which are designed by using various electrical and electronic components. For better understanding of this concept, here we have explained some projects.
MOSFET Used as a Switch
In this circuit, using enhanced mode, 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) or 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. In the above circuit, it is a very simple circuit for switching a resistive load such as LEDs or lamp. But when using MOSFET to switch either inductive load or capacitive load protection is required to contain the MOSFET applications. If we are not giving the protection, then the MOSFET will be damaged. For the MOSFET to operate as an analog switching device, that needs to be switched between its cutoff region where VGS =0 and saturation region where VGS =+v.
Auto Intensity Control of Street Lights using MOSFET
Now-a-days most of lights placed on the highways are done through High Intensity Discharge lamps (HID), whose energy consumption is high. Its intensity cannot be controlled according to the requirement, so there is a need to switch on to an alternative method of lighting system, i.e., to use LEDs. This system is built to overcome the present day drawbacks of HID lamps.
Auto Intensity Control of Street Lights using MOSFET
This project is designed to control the lights automatically on the highways using microprocessor by variants of the clock pulses. In this project, MOSFET plays major role that is used to switch the lamps as per the requirement. The proposed system using a Raspberry Pi board that is a new development 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. 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 main concept of this project is to develop a circuit that delivers the output approximately triple to that of the input voltage by Marx generator principle. It is designed to generate high-voltage pulses using a number of capacitors in parallel to charge during the on time, and then connected in series to develop a higher voltage during the off period. If the input voltage applied is around 12v volts DC, then the output voltage is around 36 volts DC.
This system utilizes a 555 timer in astable mode, which delivers the clock pulses to charge the parallel capacitors during on time and the capacitors are brought in a series during the off time through MOSFET switches; and thus, develops a voltage approximately triple to the input voltage but little less, instead of exact 36v due to the voltage drop in the circuit. The output voltage can be measured with the help of the multimeter.
EEPROM based Preset Speed Control of BLDC Motor
The speed control of the BLDC motor is very essential in industries as it is important for many applications such as drilling, spinning and elevator systems. This project is enhanced to control the speed of the BLDC motor by varying the duty cycle.
EEPROM based Preset Speed Control of BLDC Motor
The main intention of this project is to operate a BLDC motor at a particular speed with a predefined voltage . Therefore, 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 and 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.
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LDR Based Power Saver for Intensity Controlled Street Light
In the present system, mostly the lightning-up of highways is done through High Intensity Discharge lamps (HID), whose energy consumption is high and there is no specialized mechanism to turn on the Highway light in the evening and switch off in the morning.
LDR Based Power Saver for Intensity Controlled Street Light
Its 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. This system is built to overcome the present day, drawback of HID lamps.
This system demonstrates the usage of LEDs (light emitting diodes) as light source and its variable intensity control, according to the requirement. LEDs consume less power and its life is more, as compared to conventional HID lamps.
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The most important and interesting feature is its intensity that can be controlled according to requirement during non-peak hours, which is not feasible in HID lamps. A light sensing device LDR (Light Dependent Resistance) is used to sense the light. Its resistance reduces drastically according to the daylight, which forms as an input signal to the controller .
A cluster of LEDs is used to form a street light. The microcontroller contains programmable instructions that controls the intensity of lights based on the PWM (Pulse width modulation) signals generated.
The intensity of light is kept high during the peak hours, and as the traffic on the roads tend to decrease in late nights; the intensity also decreases progressively till morning. Finally the lights get completely shut down at morning 6 am, to resume again at 6pm in the evening. The process thus repeats.
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. This method overcomes the old technique SPWM to control an AC motor that has high-harmonic distortion due to the asymmetrical nature of the PWM switching characteristics.
In this system, DC supply is produced from the single-phase AC after rectification, and then is fed to the 3-phase inverter with 6 numbers of MOSFETs. For each phase, a pair of MOSFETare used, and, 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
Therefore, this is all about types of MOSFET applications, Finally, we will conclude that, 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.Furthermore, any queries regarding this article you can comment us by commenting in the comment section below.