Count several commonly used protection circuits (II)

Protection circuit in inverter power supply:

Inverters often need to perform current conversion. If the current in the circuit exceeds the limit, it will cause great damage to the circuit and key components. Therefore, the protection circuit is especially important in the inverter power supply.

Anti-reverse protection circuit:

If the inverter does not have an anti-reverse circuit, it will often have catastrophic consequences when the input battery is reversed. It will burn the fuse and burn most of the circuit. There are three main types of anti-reverse protection circuits in the inverter: anti-reverse protection circuit composed of anti-transverse Schottky diodes.

When the battery is reversed, the Schottky diode D is turned on and the F is burned. If the main conversion circuit of the push-pull structure is followed by the parasitic diode of the two push-pull switch MOS transistors, it is also equivalent to parallel with D, but the voltage drop is much larger than the Schottky, and the impact resistance against transient current is lower than that of Schott. The base diode D prevents the high current from passing through the parasitic diode of the MOS transistor, thereby protecting the two push-pull switch MOS transistors.

The anti-reverse protection circuit has a simple structure and does not affect the efficiency. However, after the protection, the fuse F is burned and needs to be replaced again to resume normal operation.

The anti-reverse protection circuit of the relay is adopted, and the basic circuit is as follows:

If the battery is reversed, D is reversed, no current flows through the coil of relay K, the contacts cannot be closed, and the power supply to the inverter is cut off. This anti-reverse protection circuit has a better effect and does not burn the fuse F, but the volume is relatively large, and the life of the contacts of the relay is limited.

The anti-reverse protection circuit of the MOS tube is used, and the basic circuit is as follows:

D is a parasitic diode for anti-reverse MOS, which is easy to draw for analysis. When the polarity of the battery is not reversed, D is positively biased, and the GS pole of Q is turned forward by the positive pole of the battery through F, R1, and D to return to the negative pole of the battery. The voltage drop after Q is turned on is much smaller than the voltage drop of D, so after Q is turned on, D will not get enough forward voltage and cut off;

When the battery polarity is reversed, D will be terminated due to reverse bias, and Q will also be terminated due to GS reverse bias, and the inverter cannot be started. This anti-reverse protection circuit has a long service life because it does not use a mechanical contact switch, and does not burn the fuse F like the anti-reverse protection circuit composed of a reverse Schottky diode. It is a certain loss when the MOS is turned on. It is sufficiently unobstructed to maintain relatively low losses through relatively large currents.