Power Anti-reverse connection protection circuit

1, usually the DC power input anti-reverse protection circuit is to use the unidirectional conductivity of the diode to achieve anti-reverse protection. As shown in 1:

This method of connection is simple and reliable, but the power dissipation effect is very large when the large current is input. To the input current rating of 2A, such as the use of Onsemi fast recovery diode mur3020pt, the nominal tube pressure drop of 0.7V, then the power consumption at least to achieve:pd=2Ax0.7v= 1.4W, so the efficiency is low, heat is big, need to add radiator.

2, you can also use a diode bridge to the input rectifier, so that the circuit will always have the correct polarity (Figure 2). The disadvantage of these schemes is that the pressure drop on the diode consumes energy. When the input current is 2A, the circuit power consumption in Figure 1 is 1.4W, and the power consumption of the circuit in Figure 2 is 2.8W.

Figure 1, a series diode protection system is not affected by reverse polarity, the diode has a 0.7V pressure drop

Figure 2 is a bridge rectifier, no matter what polarity can work normally, but there are two diode conduction, the power consumption is figure 1 twice times

MOS tube Type anti-reverse protection circuit

Figure 3 Using the MOS tube switching characteristics, control circuit on and off to design anti-reverse protection circuit, due to the low internal resistance of the Power MOS tube, now MOSFET Rds (on) has been able to achieve a non-European level, It solves the problem that the voltage drop and power dissipation in the current anti-reverse solution of diode power supply are too large.

Reverse polarity protection will protect the use of the effect tube in series with the protected circuit connected. The protective effect tube is a pmos field effect tube or a nmos field effect tube. For PMOs, the gate and source are respectively connected to the grounding and power ends of the protected circuit, and the drain is connected to the substrate of the PMOS element in the protected circuit. If nMOS, its gate and source are connected to the power and ground ends of the protected circuit respectively, and its drain is connected to the substrate of the NMOS element in the protected circuit. Once the power supply polarity of the protected circuit is reversed, the protective effect tube will form a circuit breaker to prevent the current from burning the FET element in the circuit and protecting the overall circuit.

Specific n-Channel MOS tube anti-reverse protection circuit circuit 3 shows

Figure 3. nMOS Tube Type anti-reverse connection protection circuit

The N-Channel MOS tube is threaded between the power supply and the load through the S-pin and D-pins, and the resistor R1 provides a voltage offset for the MoS tube, which uses the switching characteristics of the MOS tube to control the conduction and disconnection of the circuit, thereby preventing the power supply from being reverse-connected to the load causing damage. The R1 provides VGS voltage and MOS saturation conduction when it is connected. When reverse, the MOS is not able to conduction, so it plays anti-reverse effect. the Power MoS tube Rds (on) only 20mω actual loss, 2 A of current, power dissipation (2x2) x0.02=0.08w no need to use the heatsink. It solves the problem that the voltage drop and power dissipation in the current anti-reverse solution of diode power supply are too large.

VZ1 for the regulator to prevent the gate source voltage high breakdown of the MoS tube. nMOS the resistance of the tube is smaller than the PMOs, the best choice is nmos.

The nMOS is connected to the negative of the power supply and the gate is high-level.

The PMOs is connected to the positive of the power supply and the gate is low-level conduction.

Power Anti-reverse connection protection circuit