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What is MOSFETs: Types & How to MOSFET as a switch

MOSFET stands for metal-oxide-semiconductor-field-effect transistor. It is a special kind of field-effect transistor (FET).


The MOSFETs could be a voltage controlled device. The MOSFET has “gate“, “Drain” and “Source” terminals rather than a “base”, “collector”, and “emitter” terminals in a very bipolar transistor. By applying the voltage at the gate, it generates AN electrical field to control the current flow through the channel between drain and supply, and there's no current flow from the gate into the MOSFET.

The power MOSFETs are special to handle the high level of powers. The power MOSFETs is widely used in the n-channel enhancement mode, p-channel enhancement mode, and in the nature of n-channel depletion mode. Here we've got explained regarding the N-channel power MOSFET.


Basic Statures of Power MOSFET
There is three main basic status in the power MOSFETs.
·         On sate resistance
·         Breakdown voltage
·         Body diode

A MOSFET is also thought of as a variable resistor, wherever the Gate-Source voltage distinction will control the Drain-Source Resistance. When there is no applying voltage between the Gate-Source, the Drain-Source resistance is very high, which is almost like open circuit so no current may flow through the Drain-Source. When Gate-Source potential is applied, the Drain-Source resistance is reduced, and there'll be current flowing through Drain-Source, that is currently a loop.
In a nutshell, a FET is controlled by the Gate-Source voltage applied (which regulates the electrical field across a channel), like pinching or opening a straw and stopping or allowing current flow. Because of this property, FETs are nice for big current flow, and also the MOSFET is usually used as a switch.

How to use MOSFET as a switch?
To use a MOSFET as a switch, you've got to have its gate voltage (Vgs) on top of the source. If you connect the gate to the source (Vgs=0) it's turned off.
For example, we’ve IRFZ44N that is a “standard” MOSFET and only activates once Vgs=10V – 20V. But typically we strive to not push it too arduous thus 10V-15V is common for Vgs for this kind of MOSFET.
However, if you want to drive this from an Arduino that is running at 5V, you may like a “logic-level” MOSFET which will be turned on at 5V (Vgs = 5V). For example, the ST STP55NF06L. You should also have a resistor serial with the Arduino output to limit this since the gate is very capacitive and might draw a giant fast current when you try to turn it on. Around 220 ohms is a good value.
This page shows some detail clarification however a MOSFET works as a switch. This page shows some advanced usage of MOSFET.

Types of MOSFET
MOSFETs come in four different types. There are three main categories.
  • N-Channel (NMOS) or P-Channel (PMOS)
  • Enhancement or Depletion mode
  • Logic-Level or Normal MOSFET


N-Channel – For an N-Channel MOSFET, the supply is connected to ground. To turn the MOSFET on, we'd like to boost the voltage on the gate. To turn it off we want to attach the gate to ground.
P-Channel – The supply is connected to the ability of rail (Vcc). In order to allow current to flow the Gate has to be forced to the ground. To turn it off the gate must be forced to Vcc.
Depletion Mode – It requires the Gate-Source voltage (Vgs) applied to switch the device “OFF”.
Enhancement Mode – The transistor requires a Gate-Source voltage (Vgs) applied to switch the device “ON”.
Despite the variability, the most commonly used type is N-channel enhancement mode.

There are Logic-Level and normal MOSFETs, however, the only distinction is that the Gate-Source potential level needed to drive the MOSFET.
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