P-Channel MOSFET on the 12V (VCC) Side of the Load. Let's say you want to turn ON and OFF a 12V DC motor using an Arduino and a P-Channel MOSFET. The most intuitive way to archive this goal is to wire the MOSFET on the VCC side of the load (the motor in this case). Printopia big sur.

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• Infineon is one of the few semiconductor manufacturers worldwide to offer N-channel depletion mode MOSFETs. Compared to enhancement mode transistors, known as normally-off, depletion MOSFETs are in an on-state at zero voltage of gate-to-source (V GS), normally-on.This makes N-channel depletion mode MOSFETs a perfect constant current source.
• The formation of p channel depletion is just in reverse as compared with the n channel depletion MOSFET. Here the channel is pre-build due to the impurities of the p-type present in it. When the negative value of the voltage is applied at the terminal gate the free holes that represent the minority carriers at the n-type gets attracted towards.

A MOSFETs exhibit three regions of operation viz., Cut-off, Linear or Ohmic and Saturation. Among these, when MOSFETs are to be used as amplifiers, they are required to be operated in their ohmic region wherein the current through the device increases with an increase in the applied voltage. On the other hand, when the MOSFETs are required to function as switches, they should be biased in such a way that they alter between cut-off and saturation states. This is because, in cut-off region, there is no current flow through the device while in saturation region there will be a constant amount of current flowing through the device, just mimicking the behaviour of an open and closed switch, respectively. This functionality of MOSFETs is exploited in many electronic circuits as they offer higher switching rates when compared to BJTs (bipolar junction transistors).

Figure 1 shows a simple circuit which uses an n-channel enhancement MOSFET as a switch. Here the drain terminal (D) of the MOSFET is connected to the supply voltage V_S via the drain resistor R_D while its source terminal (S) is grounded. Further, it has an input voltage V_i applied at its gate terminal (G) while the output V_o is drawn from its drain.

Now consider the case where V_i applied is 0V, which means the gate terminal of the MOSFETis left unbiased. As a result, the MOSFET will be OFF and operates in its cutoff region wherein it offers a high impedance path to the flow of current which makes the I_DS almost equivalent to zero. As a result, even the voltage drop across R_D will become zero due to which the output voltage V_o will become almost equal to V_S.
Next, consider the case where the input voltage V_i applied is greater than the threshold voltage V_T of the device. Under this condition, the MOSFET will start to conduct and if the V_S provided is greater than the pinch-off voltage V_P of the device (usually it will be so), then the MOSFET starts to operate in its saturation region. This further means that the device will offer low resistance path for the flow of constant I_DS, almost acting like a short circuit. As a result, the output voltage will be pulled towards low voltage level, which will be ideally zero.

From the discussion presented, it is evident that the output voltage alters between V_S and zero depending on whether the input provided is less than or greater than V_T, respectively. Thus, it can be concluded that MOSFETs can be made to function as electronic switches when made to operate between cut-off and saturation operating regions.
Similar to the case of n-channel enhancement type MOSFET, even n-channel depletion type MOSFETs can be used to perform switching action as shown by Figure 2. The behaviour of such a circuit is seen to be almost identical to that explained above except the fact that for cut-off, the gate voltage V_G needs to be made negative and should be lesser than -V_T.

Next, Figure 3 shows the case wherein the p-channel enhancement MOSFET is used as a switch. Here it is seen that the supply voltage V_S is applied at its source terminal (S) and the gate terminal is provided with the input voltage V_i while the drain terminal is grounded via the resistor R_D. Further the output of the circuit V_o is obtained across R_D, from the drain terminal of the MOSFET.
In the case of p-type devices the conduction current will be due to holes and will thus flow from source to drain I_SD, and not from drain to source (I_DS) as in the case of n-type devices. Now, let us assume that the input voltage which is nothing but the gate voltage V_G of the MOSFET goes low. This causes the MOSFET to switch ON and to offer a low (almost negligible) resistance path to the current flow. As a result heavy current flows through the device which results in a large voltage drop across the resistor R_D. This inturn results in the output which is almost equal to the supply voltage V_S.

Next, consider the case where V_i goes high i.e. when Vi will be greater than the threshold voltage of the device (V_T will be negative for these devices). Under this condition, the MOSFET will be OFF and offers a high impedance path for the current flow. This results in almost zero current leading to almost zero voltage at the output terminal.

Similar to this, even p-channel depletion-type MOSFETs can be used to perform switching action as shown by Figure 4. The working of this circuit is almost similar to the one explained above except for the fact that here the cut-off region is experienced only if V_i = V_G is made positive such that it exceeds the threshold voltage of the device.

The table presented below summarizes the discussion presented above.

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.

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.
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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

P Channel Depletion Mosfet Symbol

P-channel Depletion Mode Mosfet