MOS Tube Anti-overvoltage Circuit
NMOS tube back connection circuit
When the power is properly connected. The current flows from VIN to the load, through NMOS to GND. At the beginning of power on, because the body diode of the NMOS tube exists, the ground circuit is connected through the body diode. Later, because the VGS is greater than the threshold voltage of VGSTH, the MOS tube conducts.
Fig.1
When the power supply is connected backward, the body diode does not work, and the VOLTAGE of VGS will not meet the requirements, all NMOS tube is not connected, there is no current loop in the circuit, the circuit is open, the load does not work, will not burn out, to achieve protection.
It is important to note that the current in the circuit goes from S to D when the power supply is normally connected. The current direction used by conventional NMOS tubes is different.
It should be noted that the VGS should not exceed the maximum VGS withstand voltage value of the NMOS tube under normal circumstances. If the VGS exceeds the maximum VGS withstand voltage value, a regulator tube can be bonded on the VGS to prevent burnout.
PMOS tube backconnection circuit
Fig.2
The principle of the circuit is similar to that of the NMOS anti-backconnection circuit
Overvoltage proof circuit
Fig.3
When the VIN input voltage is normal, there is no reverse breakdown of the regulator, and the current in R3 and R4 is basically 0. VBE=0 of PNP triode, that is, PNP triode does not conduct. The VGS of PMOS tube Q4 is determined by the partial voltage of resistor R5 and R6. The conduction of PMOS tube means that the power supply works normally.
When the VIN input is greater than the normal input voltage, the VIN>VBR is broken down, and the voltage on the VIN is VBR. PNP triode Q1 conduction, VCE≈0, that is, THE VGS≈0 of PMOS tube, PMOS tube is not conductive, circuit is open, that is, overvoltage protection is realized.
Anti - anti - overvoltage circuit integrated
Fig.4
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