ANPEC APM4015PU MOSFET. APM4015PUP-Channel Enhancement Mode MOSFETFeatures.-40V/-45A, RDS (ON)= 13mΩ (typ.) @ VGS=-10V R. TO-92-3 P-Channel MOSFET are available at Mouser Electronics. Mouser offers inventory, pricing, & datasheets for TO-92-3 P-Channel MOSFET.
In this project, we will go over how to connect an P-Channel MOSFET to a circuit for it to function as an electronic switch.
The type of P-Channel MOSFET we will use is the enhancement-type MOSFET, the most commonly used type of MOSFET.
MOSFETs, like BJTs, can function as electronic switches. Although unlike BJTs, MOSFETs are turned on, not by current, but by voltage.
2N6845, datasheet for 2N6845 - POWER MOSFET P-CHANNEL (BVdss=-100V, Rds (on)=0.60ohm, Id=-4.0A) provided by International Rectifier. 2N6845 pdf documentation and 2N6845 application notes, selection. The trouble with using a high side P channel MOSFET driven from a signal that doesn't get close (less than 0.5 volts) to the high side voltage is that there is a decent probability that it will appear to be still active when you believe you have it turned off. Let us fix the problem for you. We will do our best to get back to you as soon as possible. We feel that finding the parts you need should not be a major task. We will work hard to fix any problems.
MOSFETs are voltage-controlled devices. This means that a voltage applied to the gate controls whether the transistor switches on or off. When aP-channel (enhancement-type) MOSFET has no voltage at its gate, it is OFF and no current conducts across from source to drain; thus, the load connected to the MOSFET will not turn on.When there is sufficient voltage at the gate (about -3V), the MOSFET is on and current conducts across from the source to the drain to power on the load.
Know the distinction between a voltage-controlled device and a current-controlled device. MOSFETs are voltage-controlled. This means that only voltage hasto be applied to the gate for it turn on. It does not need current. Therefore, when we are wiring up the P-channel MOSFET, we simply connect the voltage source to the gate terminal. No resistor is necessary, as would be the case for a bipolar junction transistor, which is current-controlled. We simply connect a negative voltage to the gate terminal without an external resistor. Therefore, with a MOSFET, biasing the circuit is actually a little simpler than with BJTs.
Components Needed
- IRF9640 MOSFET
- DC Motor or Buzzer
- 6 'AA' batteries or Dual DC Power Supply
In our circuit, we are going to use the IRF9640 P-channel MOSFET.
The IRF9640 is an enhancement-type MOSFET, meaning as more negative voltage is fed to the gate, the current from the drain to the source increases. This is in contrast to depletion-type MOSFETs, in which increasing negative voltage to the base blocks the flow of current from the drain to the source, while placing no voltage at the gate makes the MOSFET fully on.
Know that an P-channel MOSFET, like all MOSFETS, have 3 pins, the drain, the gate, and the source.
If you look at the back view of the transistor, as shown above, the leftmost pin will be the source, the middle pin is the drain, and the rightmost pin is the gate. This is a very different pinout than the N-Channel MOSFET, so make sure you observe this for your connection setup.
The gate terminal is where we connect about -3 volts to power on the transistor (to make it turn on).
The source terminal is where we connect our output device that we want to power. And when connecting our load, if the device is polarity-sensitive, such as LEDs and buzzers are, the anode terminal must be connected to the positive voltage, while the cathode end connects to the source terminal. Or else, it won't work, because current in an P-channel MOSFET flows from source to drain. If we hooked up an LED, reverse biased, so that its anode was connected to the drain terminal and its cathode was connected to the positive voltage source, it would not work.
The last terminal, the drain, simply connects to ground. Since current flows source to drain, the drain must be grounded to create a return path.
The IRF9640 datasheet is can be be viewed here: IRF9640 MOSFET datasheet.
P-Channel MOSFET Circuit Schematic
The schematic for the P-Channel MOSFET circuit we will build is shown below.
So, this is the setup for pretty much any P-Channel MOSFET Circuit.
Negative voltage is fed into the gate terminal. For an IRF9640 MOSFET, -3V at the gate is more than sufficient to switch the MOSFET on so that it conductsacross from the source to the drain. Now that we have hooked up sufficient voltage to the gate to turn on the transistor, then we must supply voltage to our load on the source terminal of the transistor. Remember, one voltage is to turn on the transistor and the other voltage is to power the load once the transistor has been turned on.
The amount of voltage that needs to be connected to the load depends entirely on how much voltage the load needs to be powered on. If you are using a 6V DC motor or buzzer, then you connect 6V to the source terminal. If you are powering a 12V motor or buzzer, then you connect 12V.
Since the buzzer we are using in this circuit requires 6V, 6V is connected to the source terminal.
And this is how an P-Channel MOSFET is set up and works.
To see how this circuit works in real life, see the video below.
Related Resources
P Channel MOSFET Basics
How to Connect a Transistor as a Switch in a Circuit
How to Connect a (NPN) Transistor in a Circuit
Types of Transistors
Bipolar Junction Transistors (BJTs)
Junction Field Effect Transistors (JFETs)
Metal Oxide Semiconductor Field Effect Transistors (MOSFETs)
Unijunction Transistors (UJTs)
What is Transistor Biasing?
How to Test a Transistor
Arduino pins can directly turn ON very low power components like small LEDs. MOSFETs are great if you need to switch ON and OFF more powerful devices that also may use higher input voltage than Arduino's 5V.
So, which type of MOSFET should you use? If you need to turn ON a device that consumes more power than an Arduino pin can provide, then you should use a Logic Level Enhancement-Type N-Channel MOSFET. It's easy to wire it up to be OFF by default and switched ON when Arduino pin goes HIGH. I have used 30N06L MOSFET to switch ON 12V motors and lamps.
In this article, I will talk about different types of MOSFETs, and give the reasons why I think you most likely want to use an N-Channel MOSFET:
Logic leve N-Channel and P-Channel MOSFETs
Disclosure: Bear in mind that some of the links in this post are affiliate links and if you go through them to make a purchase I will earn a commission. Keep in mind that I link these companies and their products because of their quality and not because of the commission I receive from your purchases. The decision is yours, and whether or not you decide to buy something is completely up to you.
What Kinds of MOSFETs There Are?
MOSFET can be either Enhancement-Type or Depletion-Type and N-Channel or P-Channel. Roughly speaking, we have four different kinds:
- Enhancement-Type N-Channel
- Enhancement-Type P-Channel
- Depletion-Type N-Channel
- Depletion-Type P-Channel
All MOSFETs have Gate (G), Source (S), and Drain (D) pins. The voltage between Gate and Source (Vgs) determines if the current is flowing through Source and Drain or not. Each kind has its own logic of when the MOSFET is turned ON or OFF. I will explain it in detail in the next two chapters.
Symbols for MOSFETs:
A MOSFET is classified as Logic Level MOSFET if it gets fully turned on with Vgs in the range of 3 to 5 volts. If you use a 5V Arduino board, then all Logic Level MOSFETs should be OK. If you are using a 3.3V board, then you have to check that the MOSFET you are using is compatible with 3.3V switching.
Normal MOSFETs typically need Vgs to be 10V or more to be fully ON.
Enhancement-Type MOSFET vs Depletion-Type MOSFET?
Every MOSFET is either Enhancement-Type or Depletion-Type.
Of the two types, the more common Enhancement-Type is not conducting electricity, when Vgs (voltage between Gate and Source) is zero - 'Normally OFF.' Depletion-Type is logical inversions of that, and is conducting when Vgs is zero - 'Normally ON.'
For example, an Enhancement-Type N-Channel MOSFET with a pull-down resistor will be OFF while your Arduino pin is not initialized as output (the first few seconds on startup). But a Depletion-Type will be ON in the same conditions.
When deciding between those two types, you have to think of what do you want to happen while your controller board is not actively driving the MOSFET Gate. If you don't know, then pick the Enhancement-Type. It's easy to put a 10k resistor between the Gate and the Source, which makes it OFF by default.
In the rest of the article, all the examples are about Enhancement-Type MOSFETs. Everything also applies to the Depletion-Type, just the ON/OFF status would be inverted.
N-Channel MOSFET vs P-Channel MOSFET
The main difference between an N-Channel and a P-Channel MOSFET is that N-Channel usually goes to the Ground (-) side of the load (the device you are powering), and P-Channel to the VCC (+) side.
But why do you have to connect one to the negative and the other to the positive side?
Far harbor memory puzzle 5. Enhancement-Type ('Normally OFF') N-Channel MOSFET starts to conduct if Gate value is sufficiently higher than Source. For Logic Level MOSFETs, it's typically 3 to 5 volts. If you connect the Source to the Ground, then you can use a voltage between Ground (-) and VCC (+) to activate it.
If you decided to connect it to the VCC side of the load, then the value of the Source would also be very close to VCC. It means that you need to apply a higher voltage than VCC to the Gate to active the MOSFET. Typically you don't have this higher voltage readily available, and it makes more sense to connect the Source of an N-Channel MOSFET to Ground.
Enhancement-Type ('Normally OFF') P-Channel MOSFET is like an upside-down N-Channel MOSFET. It starts to conduct if Gate value is sufficiently lower than Source. If you connect the Source of a P-Channel MOSFET to VCC, then you can use a voltage between VCC (+) and Ground (-) to turn it ON and OFF.
Connecting it to the negative side of the load has a similar problem that the N-Channel MOSFET had. Only this time, Source would be too close to Ground. You would need to apply a negative voltage (compared to Ground) to the Gate to activate it.
It is easy to remember: you should connect the Source pin of an N-Channel MOSFET to the negative output of your power supply, and the Source pin of a P-Channel MOSFET to the positive output of your power supply.
The same rules apply to Depletion-Type N-Channel and P-Channel MOSFETs. Real rock riddim rar. Only ON and OFF state is inverted.
Why Prefer an N-Channel MOSFET to a P-Channel MOSFET?
Functionally you could design your circuit in a way that you could use either of them. If you have an Arduino that runs on 5V and the device you are turning ON also runs on 5V, then it doesn't even matter. You could use an N-Channel or P-Channel MOSFET as long as you wire it accordingly.
Common P Channel Mosfet Vs
Then why prefer N-Channel over P-Channel?
- You can have a Common Ground between the 12V power source and your Arduino.
With a P-Channel MOSFET, you have to create a Common VCC instead of a Common Ground. But it's standard practice to have a Common Ground between connected devices and modules. You can easily have that with an N-Channel MOSFET.
- You can power your Arduino from the same 12V power source by connecting the Arduino's barrel jack or the Vin pin to the power supply.
The negative input of the barrel connector leads directly to Arduino Ground. When you are using an N-Channel MOSFET as a power switch, then that is not a problem. The Grounds are connected anyways. With a P-Channel MOSFET, we can't connect the negative output of the power supply to the Arduino Ground since the 5V pin has to be pulled up to the positive output of the power supply. By also connecting the Grounds, you will send 12 volts through the Arduino.
- N-Channel MOSFETs are more efficient than P-Channel MOSFETs.
It comes down to physics. N-Channel MOSFETs use electron flow as the charge carrier. P-Channel MOSFETs use hole flow as the charge carrier, which has less mobility than electron flow. And therefore, they have higher resistance and are less efficient. In other words, a P-Channel MOSFET will get hotter than an N-Channel MOSFET with higher loads.
P Channel Mosfet Driver Circuit
There are use-cases where P-Channel MOSFET is preferred or even required. For example the Arduino self-power-off circuit needs both: https://circuitjournal.com/arduino-auto-power-off