Design of anti-reverse connection circuit

1. Diode anti-reverse connection circuit

1.1. Working Principle

When the power supply is connected in the forward direction, the diode D1 is in the conducting state. At this time, the voltage of V+ input to the load is equal to V+ minus the voltage drop on the diode D1. When the power supply is reversed, the circuit cannot be turned on because the diode has unidirectional conductivity.
1.2. Precautions
1.2.1. In the process of using the diode, it is necessary to ensure that the actual current flowing through the diode is not higher than its rated current value. It is also necessary to pay attention to the transient current generated at the moment of power-on of the system to prevent the current from exceeding the maximum rated peak current that the diode can withstand.
1.2.2. When the diode is reverse biased, the voltage it withstands cannot exceed its reverse breakdown voltage.
1.2.3. In a low-voltage environment, the voltage drop of the diode may be too large, which may easily cause insufficient voltage of the subsequent load; in a high-current environment, the power consumption of the diode will increase significantly, and its own voltage drop is large, resulting in high losses. Although the use of Schottky diodes can reduce losses to a certain extent, when the power supply voltage is lower, even if Schottky diodes are used, it will still have a greater impact on the circuit.
1.2.4. When using a diode, pay attention to several important parameters in the manual: Peak Repetitive Peak Reverse Voltage (repetitive peak reverse voltage); RMS Reverse Voltage (reverse effective value voltage) should be designed with a margin, and the margin is recommended to be designed at 80%; Average Forward Rectified Current (average forward rectified current) is the average current flowing through the diode when it is forward-conducting. Pay attention to the margin in the design, and the margin is recommended to be designed at 80%. The instantaneous peak current can exceed this value; Peak Forward Surge Current (peak forward surge current).

2. Rectifier bridge type anti-reverse connection circuit

2.1. Working principle

Whether the input AC power is positive or negative half-cycle, the direction of the current on the load is always consistent, thus realizing the function of converting AC power into DC power.

2.2. Precautions

1. Through the action of the rectifier bridge, AC power is converted into DC power, but the output DC power still has certain fluctuations. In order to obtain more stable DC power, a filter circuit is usually connected to the output end of the rectifier bridge to further smooth the DC voltage.
2. When using the rectifier bridge, a voltage drop of 1.2-1.4V will be generated. This voltage drop will make the output DC voltage lower than the peak value of the input AC voltage. This needs to be taken into account when designing the circuit to ensure that the subsequent circuit can obtain a suitable operating voltage. Using MOSFET tubes or Schottky diodes instead of ordinary diodes will effectively reduce the voltage drop and power consumption of the rectifier bridge.

3. Zener diode and fuse anti-reverse connection circuit

3.1. Working Principle

Due to the voltage drop problem of the diode, which will affect the power supply voltage of the circuit, we use a combined anti-reverse connection circuit of the fuse and the diode to replace the separate diode anti-reverse connection circuit. When the power supply is connected in the forward direction, the circuit will produce a very small voltage drop. When the power supply is reversed, the diode D1 is turned on, clamping the reverse voltage at both ends of the load at the diode's conduction voltage drop (about 0.7V), so that the load is equivalent to being bypassed and protected. The voltage basically falls on the fuse F1. When the current exceeds the fuse current of F1, the fuse F1 disconnects the power supply.

3.2. Precautions

3.2.1. If you want to output a stable voltage to the load, you can replace the ordinary diode with a voltage regulator diode.
3.2.2. When the power supply is reversed, it will give the load a negative voltage, which may cause damage to the subsequent load equipment.
3.2.3. The fuse can use a self-recovery fuse.

4. MOS tube anti-reverse connection circuit

4.1. NMOS tube anti-reverse connection circuit

1. R2 and R3 are a resistor divider to provide a turn-on voltage for the G level of the MOS tube.
2. The internal parasitic diode of the MOS tube has a breakdown voltage. When the breakdown voltage is not reached, the internal parasitic diode will not conduct. Therefore, when the power supply is reversed, the circuit of this MOS tube anti-reverse connection circuit is turned off.
3. For the voltage-stabilizing diode connected in parallel to the voltage-dividing resistor in the circuit, because the input resistance of the field effect tube is very high, it is a voltage-controlled device. The voltage of the G level should be controlled within 20V. Excessive voltage pulses will cause the breakdown of the G level. This voltage-stabilizing diode plays a role in protecting the field effect tube from breakdown.
4. The RC series circuit connected in parallel between the field effect tube D and S is used for pulse absorption or delay. It depends on the load situation here. It may not be good to add it. After all, this will cause a short turn-on pulse when the power supply is reversed.

4.2. PMOS tube anti-reverse connection circuit

4.2.1. The function of the resistor in parallel between the G and S levels is to release the current of the parasitic capacitor C3 and ensure that the MOS tube is effectively turned off.
4.2.2. The function of the G-level series resistor is to reduce the instantaneous value of the G-level current and form an LC oscillation circuit together with the parasitic inductance of the MOS tube to reduce oscillation.