Once the positive and negative poles are reversed, many electronic components will be burned out.
At this time, we will use the anti-reverse circuit to prevent the positive and negative poles from being reversed, so how does it protect?
There are four common anti-reverse circuits: diode series, rectifier bridge, NMOS, and PMOS
Diode series: Using the unidirectional conductivity of the diode (forward conduction, reverse cut-off), a diode is connected in series at the output end of the positive power supply for normal conduction, and if the power supply is reversed, it will be shut off because it cannot form a loop.
The question is, is there a circuit that can be turned on by both positive and negative connections?
Of course, that's the rectifier bridge circuit.
Whether the rectifier bridge is connected forward or reversed, its output is always fixed, and the circuit can remain functional.
However, whether it is one diode or several, it will generate a tube voltage drop and consume electrical energy.
At this time, the anti-reverse circuit design of the MOS tube can be used.
Anti-reverse circuit design for NMOS and PMOS
When the input is positive and negative, the current passes through R1, R2 and the parasitic diode of the mos transistor to the ground, after R1 and R2 divide the voltage, the GS voltage is greater than the on-voltage Vgs of the MOS transistor, and then the mos transistor is turned on.
When the polarity is reversed, that is, the upper negative and the lower positive, the current path will be reversed by the parasitic diode of the MOS transistor, and the GS will be cut off due to the lack of voltage, and the circuit circuit will be cut off.
The anti-reverse principle of PMOS is the same as that of NMOS, but the position is different, and PMOS generally puts it on top.