Difference Between P Channel and N Channel on MOSFET

MOSFETs

• A MOSFET is a three-terminal device; the terminals are called the gate, drain and source. A voltage applied at the gate controls the flow of electrons from the source to the drain. As the gate voltage passes a threshold value, the transistor goes from non-conducting to conducting. The gate resistance is extremely high, on the order of millions of megohms. Because of this high resistance, the MOSFET̵7;s current consumption at the gate is very low. The resistance between the source and drain becomes low when the device conducts; a MOSFET can handle tens of amps of current with very little loss.
  In addition to P and N channel types, MOSFETs are made as enhancement-mode or depletion-mode devices. An enhancement-mode transistor is normally off and turns on with a voltage; a depletion-mode device is normally on and turns off with a voltage. The descriptions that follow apply to enhancement-mode MOSFETs.

P Channel

• To turn a P channel MOSFET on, you apply a negative voltage to the gate. This voltage is negative relative to ground. In a circuit, you connect the P channel MOSFET̵7;s source terminal to a positive voltage supply and the drain to a resistor connected to ground; the resistor limits the current flowing through the transistor. The circuit diagram symbol for a P channel MOSFET has an arrow pointing away from the gate.

N Channel

• An N channel MOSFET turns on when you apply a positive voltage at its gate terminal. The voltage is greater than the positive voltage supply at the drain terminal. A resistor between the positive supply and the drain limits current; for an N channel MOSFET, the source terminal connects to ground. The circuit symbol for an N channel MOSFET has an arrow pointing toward the device̵7;s gate.

Low Side and High Side

• A circuit called a low side driver uses an N channel MOSFET; it is called ̶0;low side̶1; because the transistor connects to the circuit ground connection. A positive supply voltage drives a device when the MOSFET turns on. A high side driver, on the other hand, has a P channel MOSFET connected to the positive supply, with the switched device connected to the transistor̵7;s drain terminal and ground. The low side driver is a simpler circuit; the high side driver, however, lets you switch the direction of current through the device.