How MOSFET Transistor Works | What It Can do

 How MOSFET Transistor Works | What It Can do

I show how MOSFETs work in real life, and explain where they can be used and how to check them. With this simple circuit the transistor works as a switch.

In the video I use IRF540N MOSFET with N-channel, it has three terminals: Gate, Drain, and Source. MOSFET transistor requires very little current to turn on while it can deliver a much higher current to a load, so it works as an amplifier.

MOSFET transistors are used to amplify and switch electronic signals.

What is MOSFET? Its Working, Types, Operation, Advantages, Disadvantages & Applications

Transistors are the basic building blocks in electronics and logic circuits where they are used for switching and amplification. MOSFET is a type of FET (Field Effect Transistor) whose gate is electrically isolated by using an insulating layer. Therefore, it is also known as IGFET (Insulated Gate Field Effect Transistor).

What is a MOSFET?

MOSFET or Metal Oxide Semiconductor Field Effect Transistor is a type of FET having four terminals namely Drain, Gate, Source and Body/Substrate. The body terminal is shorted with the source terminal leaving a total of three working terminals just like any other transistor.

The MOSFET conducts current between its source and drain through a path called a channel. The width of this channel is controlled by the voltage at the gate terminal.

MOSFET is a voltage-controlled device whose output depends on the gate voltage. The metal oxide gate is electrically isolated from the channel using a thin layer of silicon dioxide. It increases its input impedance significantly in the range of Megaohms “= 106 MΩ”. Therefore, MOSFET does not have any input current.

The D-MOSFET is also known as “normally ON” MOSFET because they have a built-in channel is during manufacturing. Applying gate voltage reduces the channel width, switching the MOSFET OFF. While the E-MOSFET is also known as “Normally OFF” MOSFET because there is no channel during fabrication but it is induced by applying voltage.

Therefore the D-MOSFET symbol has a continuous line to represent a channel between the drain and source that allows the current flow at zero gate-source voltage. While the broken line in E-MOSFET represents a broken path or absence of channel for current flow at zero gate-source voltage. The arrow pointing inward shows N-channel while the arrow pointing outward shows P-channel MOSFET.

MOSFET Regions of Operation

Transistors act like an insulator or a conductor based on a very small signal. The MOSFET just like any other transistor also operates in three regions.

Cutoff Region: In this region, the MOSFET remains turned off and there is no drain current ID. When MOSFET is used as a switch, it utilizes this region as OFF-state or opened-state of a switch.

Saturation Region: In the saturation region, the MOSFET allows a constant current between source and drain. It acts as the ON-state or closed-state of a switch. The MOSFET is fully on allowing maximum drain current ID through it.

Linear or Ohmic Region: In this region, the MOSFET offers constant resistance that is controlled by the voltage level VGS. The drain current ID increases with the level of the voltage VGS. Therefore, this region is used for amplification.

Deletion MOSFET

The Depletion type MOSFET or D-MOSFET is a type of MOSFET that has a channel constructed during the process of fabrication. In other words, it has a channel even when there is no voltage applied to it. Therefore, it can conduct current between source and drain when the gate-source voltage VGS = 0 volts. Due to this reason, it is also known as “Normally ON” MOSFET.

Connecting the gate-source terminal in reverse bias will deplete the channel of the charge carrier thus the name depletion MOSFET. It reduces the width of the channel until it disappears completely. At this point, the D-MOSFET stops conduction and this VGS voltage is known as VTH threshold voltage.

If Gate and source are connected in forward bias and the VGS is increased, more majority carriers will get induced in the channel and its width will increase. It will result in increasing the current flow between drain and source. This is why the D-MOSFET can work in both depletion and enhancement mode.

The D-MOSFET can be ‘N-channel D-MOSFET’ or ‘P-channel D-MOSFET’ depending on the channel being used. The type of channel also affects its biasing as well as its speed and current capacities.

Related Post: Thyristor & Silicon Controlled Rectifier (SCR)

N-Channel D-MOSFET

In N-channel D-MOSFET, the source and drains electrode is placed on small N-type layers. While the gate electrode is placed on top of an insulating metal oxide layer that electrically insulates it from the channel beneath it. The channel made for N-type material is fabricated on top of a P-type substrate.

 How MOSFET Transistor Works | What It Can do

I show how MOSFETs work in real life, and explain where they can be used and how to check them. With this simple circuit the transistor works as a switch.

In the video I use IRF540N MOSFET with N-channel, it has three terminals: Gate, Drain, and Source. MOSFET transistor requires very little current to turn on while it can deliver a much higher current to a load, so it works as an amplifier.

MOSFET transistors are used to amplify and switch electronic signals.

What is MOSFET? Its Working, Types, Operation, Advantages, Disadvantages & Applications

Transistors are the basic building blocks in electronics and logic circuits where they are used for switching and amplification. MOSFET is a type of FET (Field Effect Transistor) whose gate is electrically isolated by using an insulating layer. Therefore, it is also known as IGFET (Insulated Gate Field Effect Transistor).

What is a MOSFET?

MOSFET or Metal Oxide Semiconductor Field Effect Transistor is a type of FET having four terminals namely Drain, Gate, Source and Body/Substrate. The body terminal is shorted with the source terminal leaving a total of three working terminals just like any other transistor.

The MOSFET conducts current between its source and drain through a path called a channel. The width of this channel is controlled by the voltage at the gate terminal.

MOSFET is a voltage-controlled device whose output depends on the gate voltage. The metal oxide gate is electrically isolated from the channel using a thin layer of silicon dioxide. It increases its input impedance significantly in the range of Megaohms “= 106 MΩ”. Therefore, MOSFET does not have any input current.

The D-MOSFET is also known as “normally ON” MOSFET because they have a built-in channel is during manufacturing. Applying gate voltage reduces the channel width, switching the MOSFET OFF. While the E-MOSFET is also known as “Normally OFF” MOSFET because there is no channel during fabrication but it is induced by applying voltage.

Therefore the D-MOSFET symbol has a continuous line to represent a channel between the drain and source that allows the current flow at zero gate-source voltage. While the broken line in E-MOSFET represents a broken path or absence of channel for current flow at zero gate-source voltage. The arrow pointing inward shows N-channel while the arrow pointing outward shows P-channel MOSFET.

MOSFET Regions of Operation

Transistors act like an insulator or a conductor based on a very small signal. The MOSFET just like any other transistor also operates in three regions.

Cutoff Region: In this region, the MOSFET remains turned off and there is no drain current ID. When MOSFET is used as a switch, it utilizes this region as OFF-state or opened-state of a switch.

Saturation Region: In the saturation region, the MOSFET allows a constant current between source and drain. It acts as the ON-state or closed-state of a switch. The MOSFET is fully on allowing maximum drain current ID through it.

Linear or Ohmic Region: In this region, the MOSFET offers constant resistance that is controlled by the voltage level VGS. The drain current ID increases with the level of the voltage VGS. Therefore, this region is used for amplification.

Deletion MOSFET

The Depletion type MOSFET or D-MOSFET is a type of MOSFET that has a channel constructed during the process of fabrication. In other words, it has a channel even when there is no voltage applied to it. Therefore, it can conduct current between source and drain when the gate-source voltage VGS = 0 volts. Due to this reason, it is also known as “Normally ON” MOSFET.

Connecting the gate-source terminal in reverse bias will deplete the channel of the charge carrier thus the name depletion MOSFET. It reduces the width of the channel until it disappears completely. At this point, the D-MOSFET stops conduction and this VGS voltage is known as VTH threshold voltage.

If Gate and source are connected in forward bias and the VGS is increased, more majority carriers will get induced in the channel and its width will increase. It will result in increasing the current flow between drain and source. This is why the D-MOSFET can work in both depletion and enhancement mode.

The D-MOSFET can be ‘N-channel D-MOSFET’ or ‘P-channel D-MOSFET’ depending on the channel being used. The type of channel also affects its biasing as well as its speed and current capacities.

Related Post: Thyristor & Silicon Controlled Rectifier (SCR)

N-Channel D-MOSFET

In N-channel D-MOSFET, the source and drains electrode is placed on small N-type layers. While the gate electrode is placed on top of an insulating metal oxide layer that electrically insulates it from the channel beneath it. The channel made for N-type material is fabricated on top of a P-type substrate.