Protective circuit capable of preventing error voltage access

A protective circuit capable of preventing error voltage access, comprising a voltage input end, a voltage output end, a first unidirectional conduction element, a triode control circuit, a first triode, a first capacitor, a Darlington transistor or a second triode, a first resistor, a second resistor and a relay;

• a normally open contact of the relay is connected in series between the voltage input end and the voltage output end;
• the first unidirectional conduction element has a first end and a second end and allows a current to flow from the first end to the second end, the first end of the first unidirectional conduction element is connected to the voltage input end, and the second end of the first unidirectional conduction element is connected to a first end of the first resistor, a first end of the first triode, a first end of the first capacitor, and a first end of the Darlington transistor or the second triode respectively;
• a first conduction end of the triode control circuit is connected to a second end of the first resistor and a controlled end of the first triode respectively, and a second conduction end of the triode control circuit is grounded;
• the triode control circuit is used for disconnecting the first conduction end from the ground when a voltage of the voltage input end is lower than or equal to a preset voltage, and connecting the first conduction end to the ground to turn on the first triode when the voltage of the voltage input end is higher than the preset voltage;
• a first end of the second resistor is connected to a common contact of a second end of the first triode, a second end of the first capacitor and a controlled end of the Darlington transistor or the second triode, and a second end of the second resistor is grounded;
• a second end of the Darlington transistor or the second triode is connected to a controlled end of the relay.