Over -voltage and under -voltage protection circuit

The utility model relates to an over -voltage and under -voltage protection circuit, including the voltage input end, the voltage output end is connected through overvoltage crowbar, undervoltage protection circuit and control circuit to the voltage input end, be equipped with a zener diode among the overvoltage crowbar, be equipped with the 2nd zener diode in the undervoltage protection circuit, a zener diode's breakdown voltage is greater than the 2nd zener diode, and the voltage of working as the voltage input end is between a zener diode and the 2nd zener diode breakdown voltage, and voltage output holds and just has voltage output, the utility model discloses a whether a zener diode and the 2nd zener diode control overvoltage crowbar open with the undervoltage protection circuit, further control the triode among the control circuit again, and the triode is equivalent to the switch to whether the control voltage output has voltage output, the utility model provides a simply, convenient over -voltage and u