P-Channel MOSFET is not popularly known compared to the N-Channel variant. Others said it is because difficult to deal with while others are saying it is not supply abundant and there are others saying that it is only limited to few applications. In this article, I will concentrate to the last reason, about applications. So, stay with me as I will be uncovering what are the common uses of a P-Channel MOSFET.
A P-Channel MOSFET is also called PMOS while the N-Channel is called NMOS. A P-Channel is characterized by negative values like negative VGS, negative drain to source voltage, and negative drain current.
What are the Common Uses of a P-Channel MOSFET?
Okay, let us go directly to answer the question what are the common uses of a P-Channel MOSFET. Basically, both NMOS and PMOS have same common uses. It could be either a switch or a reverse battery protection. As a switch, it could be as simple on/off switch or a continuous switch like in switching converters or switching power supplies. However, they differ on how the circuit is structured. In using NMOS as a switch, it is on the low side while PMOS as a switch will be on the high side. As a reverse battery protection, NMOS will be located in the negative side while PMOS on the positive side. This article will focus particularly on what are the common uses of a P-Channel MOSFET so I will only discuss the following circuits for the PMOS.
P-Channel MOSFET as a High Side Switch
Below is the circuit for this particular use. Once the PMOS is turn on, it will have a very low voltage drop thus ideally giving the load the same voltage level of the Vsource. Thus the term high side switch is used since it is switching the load to the high side, which is the positive part of the circuit.
The gate signal could be a ground level (or zero level) so that the PMOS will turn on or a high level and the PMOS will turn off. Take note that the high level of the Gate Signal must be at least equal to the level of the Vsource. If it is lower than Vsource, the PMOS will not turn off.
Another thing to consider though for this type of circuit is that it will allow reverse current flow. Imagine when the Vsource is connected in reverse, the source of the PMOS is negative and the body diode will be forward bias allowing reverse current flow then the load will see reverse voltage.
P-Channel MOSFET as a Reverse Battery Protection
Another interesting use of a P-Channel MOSFET is a reverse battery protection. It could be done like below simple illustration.
The PMOS is positioned in the high side or in the positive side of the battery. During initial turn on, the current will flow to the body diode of the PMOS (Literally there is no diode connected to the PMOS. The body diode is formed by the PN junction across drain to source.) Once the current reach the other side, there will be voltage across the “plus” and the “minus” of the device, which is a diode drop less. With this, the PMOS will turn on and then the current will flow to the PMOS channel instead to the body diode.
When the battery is connected in reverse, the body diode will not forward bias, thus current cannot flow to the other side. This means there is no reverse voltage transferred to the device. So, it is protected! If you are interested to dig deeper regarding reverse battery protection using MOSFET, read MOSFET Reverse Battery Protection.
Summarizing what are the common uses of a P-Channel MOSFET
- P-Channel MOSFET is also called PMOS
- PMOS uses negative parameter values
- PMOS and NMOS have same application, they only differ on how the circuit is constructed
- The most common application of a PMOS are high side switch and reverse battery protection
- To turn-off a PMOS, the gate voltage must be equal or higher than the source voltage
Should you have other ideas about PMOS uses, feel free to share and let us discuss!