P-Channel MOSFET Basics


P-Channel MOSFET


A P-Channel MOSFET is a type of MOSFET in which the channel of the MOSFET is composed of a majority of holes as current carriers. When the MOSFET is activated and is on, the majority of the current flowing are holes moving through the channels.

This is in contrast to the other type of MOSFET, which are N-Channel MOSFETs in which the majority of current carriers are electrons.

Before, we go over the construction of P-Channel MOSFETs, we must go over the 2 types that exist. There are 2 types of P-Channel MOSFETs, enhancement-type MOSFETs and depletion-type MOSFETs.

A depletion-type MOSFET is normally on (maximum current flows from drain to source) when no difference in voltage exists between the gate and source terminals. However, if a voltage is applied to its gate lead, the drain-source channel becomes more resistive, until the gate voltage is so high, the transistor completely shuts off. An enhancement-type MOSFET is the opposite. It is normally off when the gate-source voltage is 0 (VGS=0). However, if a voltage is applied to its gate lead, the drain-source channel becomes less resistive.

In this article, we will go over how both P-Channel enhancement-type and depletion-type are constructed and operate.

How P-Channel MOSFETs Are Constructed Internally


P-Channel MOSFET

An P-Channel MOSFET is made up of a P channel, which is a channel composed of a majority of hole current carriers. The gate terminals are N-channels. Depending on the voltage quantity and type (negative or positive) determines how the transistor operates and whether it turns on or off.

How a P-Channel Depletion-type MOSFET Works

How to Turn on a P-Channel Depletion-Type MOSFET

To turn on a P-Channel Depletion-Type MOSFET, apply a negative voltage VDD to the drain of the transistor with respect to the source (the source must be sufficiently more negative than the drain (Vs>VD). This will allow a current to flow through the drain-source channel. If the gate voltage, VGG, is 0V, the drain current is at its largest value for safe operation, and the transistor is in the 'On' condition.

So with a sufficient negative voltage, VDD, and no voltage (0V) applied to the base, the P-channel Depletion-type MOSFET is in maximum operation and has the largest current.

How to Turn Off a P-Channel Depletion-type MOSFET

To turn off a P-channel JFET, there are 2 steps you can take. You can either cut off the bias negative voltage, VDD, that powers the drain. Or you can apply a positive voltage to the gate (relative to the source (S)). When a positive voltage is applied to the gate, the drain current is reduced. As the gate voltage, VGG, becomes more positive, the current lessens until cutoff, which is when then MOSFET is in the 'Off' condition. This stops a large drain-source current.



How a P-Channel Enhancement-type MOSFET Works




How to Turn on a P-Channel Enhancement-type MOSFET

To turn on a P-Channel Enhancement-type MOSFET, apply a negative voltage VDD to the drain of the transistor with respect to the source (the gate must be sufficiently more negative than the drain (VDS). Then apply a small negative voltage at its gate- relative to its source, so that VG>VS. This will allow a current to flow through the drain-source channel.

So with a sufficient negative voltage, VDD, and sufficient negative voltage applied to the gate, the P-Channel Enhancement-type MOSFET is fully functional in the 'on' operation.

How to Turn Off a P-Channel JFET

To turn off a P-channel JFET, there are 2 steps you can take. You can either cut off the bias negative voltage, VDD, that powers the drain. Or you can turn off the negative voltage going to the gate of the transistor.


MOSFET transistors are used for both switching and amplifying applications. MOSFETs are perhaps the most popular transistors used today. Their high input impedance makes them draw very little input current, they are easy to make, can be made very small, and consume very little power.


Related Resources

Types of Transistors

N-Channel MOSFETs



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