In circuit design, both diodes and MOS tubes can be used to prevent reverse connection. However, diodes have voltage drop and power consumption problems and are only suitable for low current and low power consumption scenarios. Therefore, in most cases, we will use MOS tube reverse connection protection circuits.

At this time, the question arises: should we choose NMOS tube or PMOS tube?

Usually, we give priority to NMOS tubes because the on-resistance of NMOS is usually smaller than that of PMOS.

NMOS tube reverse connection protection circuit

 The NMOS tube is connected to the negative pole of the power supply, and the MOS tube is turned on when a high level is applied to the gate. Resistor R1 provides voltage bias for the MOS tube, and uses the switching characteristics of the MOS tube to control the conduction and disconnection of the circuit, thereby preventing the reverse connection of the power supply from damaging the load.

When the power supply is connected in the forward direction, R1 provides the VGS voltage to the MOS tube, making it saturated and turned on; when the power supply is connected in the reverse direction, the MOS tube cannot be turned on, playing a role in preventing reverse connection. This effectively solves the problems of excessive voltage drop and power consumption in the traditional diode power supply reverse connection protection solution.

In addition, D1 in the circuit is a voltage regulator, which can prevent the gate-source voltage from being too high and avoid the MOS tube from being broken down.

PMOS tube reverse connection protection circuit

 The PMOS tube reverse connection protection circuit can also realize the reverse connection protection function. The PMOS tube is connected to the positive pole of the power supply, and the MOS tube is turned on when a low level is applied to the gate. However, since the NMOS tube not only has a smaller on-resistance than the PMOS tube, but is also relatively cheaper, in practical applications, the NMOS tube is often a better choice.