What should I do if reverse current occurs? How to better block the reverse current?

 What to do when reverse current is generated?

 You can use a back-to-back MOSFET! When the MOSFET is turned off, it can block the current from both directions.

 How is reverse current blocked?

 There are two general reasons for reverse current: The first is that when the power supply is disconnected from the system, the input voltage drops suddenly, leaving a higher voltage at the output, resulting in a temporary reverse current.

 The second is when the MOS tube is used for load switching, the diode is forward biased, the reverse current can flow through its body diode in the reverse direction, the output voltage is greater than the input voltage, the reverse voltage will be generated, resulting in a linear increase in the power dissipation at both ends of the body diode.

 So what is the danger of reverse current?

 It can damage internal circuitry and power supplies, plus reverse current spikes can damage cables and connectors.

 How to block reverse current? There are three common ones:

 1. Utilizing a diode, but it will cause the forward voltage to drop, the total power consumption will increase, and the power supply will drop 0.6V to 0.8V as a result, resulting in shorter battery life.

 2. The second, which is the back-to-back MOSFET we mentioned at the beginning, blocks the current in both directions when the MOS tube is turned off. It has a lower voltage drop compared to a diode, though it requires more space.

 3. In the last type, the MOS tube is positioned so that the body diode goes from the input to the output, and when the MOS tube is turned off or on, no reverse current flows.

 The disadvantage of this circuit, however, is that the power supply cannot be turned off. This is because the diode is always conducting between the power supply and the load.

 So when is it usually necessary to block reverse current?

 1. In the case of power multiplexing, where 5V is applied to the system when the 3.3V power switch is on, for the switch, a simple FET solution is used, where the reverse current is able to flow through the FET body diode even when the switch is off.

 2. or gate applications when similar to power multiplexing, except that the highest voltage is always supplying the system, rather than selecting a power supply to power the system.

 3. Large capacitors, where the supercapacitor maintains the output when the input power drops, require reverse current protection in order to protect the upstream power supply or components.

 4. Sudden loss of input power may generate reverse current. The capacitance at the output of the switch is larger than that at the input, and the voltage at the output decays very slowly, which means that the voltage at the output of the switch falls slower than that at the input. At this point the voltage on the switch output will be greater than the input and reverse current will flow through the switch.