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 ofcurrent carriers are electrons.
P-channel FET Similar to n-channel FET, p-channel FET is constucted using a bar of P-type material into which a pair of N-type regions are diffused. Fig-2 mentions circuit symbol of p-channel FET. Following are the features of P-channel Junction FET (JFET). SOT-23-3 P-Channel MOSFET are available at Mouser Electronics. Mouser offers inventory, pricing, & datasheets for SOT-23-3 P-Channel MOSFET.
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 source to drain) when no differencein 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 0V(VGS=0). However, if a voltage is applied to its gate lead, the drain-source channel becomesless resistive.
In this article, we will go over how both P-Channel enhancement-type and depletion-type MOSFETs are constructed and operate.
How P-Channel MOSFETs Are Constructed Internally
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 made up of N-type material.
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 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 positive voltage VS to the source of the MOSFET and apply a negative voltage to the gate terminal of the MOSFET (the gate must be sufficiently more negative than the threshold voltage across the drain-source region(VG
So with a sufficient positive voltage, VS, to the source and load, and sufficient negative voltage applied to the gate, the P-Channel Enhancement-type MOSFET is fully functional and is in the active 'ON' mode of operation.
How to Turn Off a P-Channel Enhancement Type MOSFET
To turn off a P-channel enhancement type MOSFET, there are 2 steps you can take. You can either cut off the bias positive voltage, VS, that powers the source. Or you can turn off the negative voltagegoing to the gate of the transistor.
P Channel Fet Circuits
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, for maximum operation, the gate voltage feeding the gate terminal should be 0V. With the gate voltage being 0V, the drain current is at is largest value and the transistor is in the active 'ON'region of conduction.
So, again, to turn on a P channel depletion-type MOSFET, positive voltage is applied to the source of the p-channel MOSFET. So we power the source terminal of the MOSFET with VS, a positive voltage supply. With a sufficient positive voltage, VS, 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 MOSFET, there are 2 steps you can take. You can either cut off the bias positivevoltage, VDD, that powers the drain. Or you can apply a negative voltage to the gate. When a negativevoltage is applied to the gate, the current is reduced. As the gate voltage, VG, becomes more negative, the current lessens until cutoff, which is when then MOSFET is in the 'OFF' condition. This stops a large source-drain current.
So ,again, as negative voltage is applied to the gate terminal of the P channel depletion-type MOSFET, the MOSFET conducts less and less current across the source-drain terminal. When the gate voltage reaches a certain negative voltage threshold, it shuts the transistor off. Negative voltage shuts the transistor off. This is for a depletion-type P-channel MOSFET.
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
How to Build a P-Channel MOSFET Switch Circuit
N-Channel MOSFET Basics
N Channel JFET Basics
P Channel JFET Basics
Types of Transistors
A P-Channel JFET is a JFET whose channel is composed primarily of holes as the charge carrier. This means that when the transistor is turned on, it is primarily the movement of holes which constitutesthe current flow.
This is in contrast to N-Channel JFETs, whose channel is composed primarily of electrons, which constitute the current flow.
A P-Channel JFET is composed of a gate, a source and a drain terminal.
It is made with an p-type silicon channel that contains 2 n-type silicon terminals placed on either side. The gate lead is connected to the N-type terminals, while the drain and source leads are connected to either ends of the P-type channel.
When no voltage is applied to the gate of a P-Channel JFET, current (holes) flows freely through the central P-channel. This is why JFETs are referred to as 'normally on' devices. Even without any voltage, they conduct current across from source to drain.
How a P-Channel JFET Works
This is a typical diagram you would see of voltage biasing of a P-channel JFET. This diagram also servesto show you all the parts of a P-channel JFET.
How to Turn on a P-Channel JFET
To turn on a P-channel JFET, apply a positive voltage VS to the source terminal of the transistor with no voltage applied to the gate terminal of thetransistor. This will allow a current to flow through the drain-source channel. If the gate voltage, VG, is 0V, the drain current is at its largest value for safe operation, and the JFET is in the ON active region.
So with a sufficient positive voltage to the source terminal of the transistor and no voltage (0V) applied to the base, the P-channel JFET is in maximum operation and has the largest current flow across the source-drain terminal.
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 positive voltage, VS, that powers the source terminal. Or you can apply a positive voltage to the gate. When a positivevoltage is applied to the gate, the source-drain current is reduced. As the gate voltage, VG, becomes more positive, the current lessens and lessens until it completes reaches cutoff, which is when then JFET is in the Off condition and no current conducts across from source to drain. This stops all drain-source current flow.
Characteristics Curve of a P-Channel JFET
The characteristics curve of a P Channel JFET transistor shown below is the the graph of the drain current, ID versusthe gate-source voltage, VGS.
This curve represents the transconductance, or simply the gain, of the transistor.
The transconductance of a transistor really means the gain of the transistor.
So this transconductance characteristics below shows the gain of the transistor, how much current the transistor outputs based on the voltage input into the gate terminal. Remember that gain is the the output over the input. The input is how much voltage is fed to the gate terminal. The output is how much current the transistor outputs.
You can see based on this P channel JFET transconductance curve that as the positive voltage to the gate increases, the gain decreases. You can see that the gain, the current ID output by the transistor, is highest when the voltage fed to the gate terminal is 0V. As we increase this voltage, again, as stated, the gain decreases.
This transconductance curve is important because it shows the operation of a P channel JFET.
You can also see that the transconductance curve, as for all semiconductor devices, is nonlinear, for most of the curve,meaning changes to VGSdo not directly (linearly) increase or decrease drain current, ID, even though this is a lesser issue.
The big point is that, a P-Channel JFET turns on by having a positive voltage applied to the source terminal of the transistor and ideally no voltage applied to the gate terminal. The transistor circuitshuts off by taking in a positive gate voltage, VGS, above about +4V or so. The transistor is in its fully conductive state and is in maximum operation when the voltage at the gate terminal is 0V. As we increase the amount of positive voltage the gate terminal receives, the transistor becomes less conductive. Once the positive voltage reachesa certain threshold, the P channel JFET circuit stops conducting altogether across the source-drain terminal.
Regions of the Characteristics Curve
The Regions that make this characteristic curve are the following:
Cutoff Region- This is the region where the JFET transistor is off, meaning no drain current, ID flows through the source-drain region.
Ohmic Region- This is the region where the JFET transistor begins to show some resistance to the drain current ID that is beginning to flow through the source-drain region. This is the only region in the curvewhere the response is linear.
Saturation Region- This is the region where the JFET transistor is fully operational and maximum current is flowing. During this region, the JFET is On and active.
Breakdown Region- This is the region where the voltage that is supplied to the source terminal of the transistor exceeds the necessary maximum. At this point, the JFET loses its ability to resist current because too much voltage is applied across its source-drain terminals. The transistor breaks down and current flowsfrom source to drain.
If you really want to make sense of all the technical details of the graph above, you have to really that a P-channel normally receives positive voltage to the source terminal of the JFET. So the source terminal receives positive voltage and the drain terminal is normally grounded. So the source terminal is positive relative to the drain terminal. Notice that the voltage on the horizontal of the graph represents the voltage, VDS. VDS is the voltage across the drain and the source, in that order. Since we, again, feed positive voltage to the source terminal and ground the drain terminal, the drain terminal is negative with respect to the source terminal. This is why you see negative voltages for VDS. A negative voltage for VDS just means that we're feeding positive voltage to the source terminal. So if you think of it that way, it makes a lot of sense. If you look all the way to the left of the curve at VDS being around 0V, no drain current can flow because the source terminal needs positive voltage. So if we increase positive voltage to the source terminal which means we're making the drain terminal more negative, we increase the output drain current. About +10V to the source is the midpoint of the graph (which is -10V VDS). And as we go above about +20V or so the source terminal, we reach the transistor's breakdown point.
P Fet Circuit
So this should help to understand a P Channel JFET characteristics curve better and thus a P channel JFET as a whole.
Related Resources
How to Build a P Channel JFET Switch Circuit
N-Channel JFET Basics
N-Channel MOSFET Basics
P-Channel MOSFET Basics
P Fet Reverse Protection