How to use MOS tube to realize the anti reverse connection circuit of power supply

When connecting the power supply to the board , If an oversight is reversed , It is very likely to burn the chip or device , So we need to design anti reverse connection circuit . This article introduces how to use MOS Tube to realize the anti reverse connection circuit of power supply .

Use PMOS perhaps NMOS It's all right , Let's take a look at PMOS How to achieve .

As shown in the figure ,MOS tube G Pole grounded ,D Extremely VBAT, The freewheeling diode is on , bring S Extremely VBAT-0.7V about ,Vgs<Vgs(th),MOS The pipe is open , after DS Equivalent to direct connection , The diode no longer works ,S The voltage of the pole is basically VBAT.

If the power supply is reversed ,G The voltage of the pole is VBAT, If it is resistive or inductive load ,S The voltage of the pole is also VBAT,Vgs>Vgs(th),MOS The tube doesn't work , Circuit inoperative . In case of capacitive load , The circuit is open ,Vgs>Vgs(th)（ here S I don't know how to determine the state of pole , Only know that it can't be greater than G extremely , Ask your partner to answer ）, Again MOS The tube cannot be connected .

here MOS Tubular DS It is extremely impossible to switch , Otherwise, when reverse connection D The pole voltage will be greater than S The pole makes the freewheeling diode turn on .

If you use NMOS, Need to put MOS Connect the tube to the bottom of the circuit , As shown in the figure below .

Under normal circumstances ,G Extremely VBAT, If it is resistive or inductive load ,S The voltage of the pole is greater than D extremely , The freewheeling diode is on , And then pull down S The voltage of the pole ,Vgs>Vgs(th),MOS The pipe is open . Capacitive load directly G The pole voltage is higher than S extremely ,MOS The pipe is open .

If the power supply is reversed ,G Pole voltage is 0V, Under normal circumstances, it will not be greater than S The voltage of the pole , therefore MOS The tube will not conduct , Circuit inoperative .

Again , here MOS Tubular DS It is extremely impossible to switch , Otherwise, when reverse connection S The pole voltage will be greater than D The pole makes the freewheeling diode turn on .