Over voltage and surge voltage preventing circuit

An over voltage and surge voltage preventing circuit comprising:

• an input voltage source;
• first and second resistors connected in series to the input voltage source;
• a first switching device including a first control terminal between the first and second resistors and a first input terminal connected to the input voltage source via a third resistor;
• a second switching device including a second control terminal connected to the first input terminal and a second input terminal connected to the input voltage source via a fourth resistor;
• a third switching device including a third control terminal connected to the second input terminal, a third input terminal connected to the input voltage source, and a third output terminal connected to an output voltage line;
• and
• a time constant circuit including the third resistor, the time constant circuit connected to the second control terminal of the second switching device.

A method of protecting an electronic device from an over voltage and surge voltage applied from a power source, comprising:

• providing, in series, first and second resistors connected to an input voltage source;
• connecting a first control terminal of a first switching device between the first and second resistors and a first input terminal of the first switching circuit to the input voltage source via a third resistor;
• connecting a second control terminal of a second switching device to the first input terminal and a second input terminal of the second switching device to the input voltage source via a fourth resistor;
• connecting third control terminal of a third switching device to the second input terminal, a third input terminal of the third switching device to the input voltage source, and a third output terminal of the third switching device to an output voltage line;
• and
• providing a time constant circuit, wherein the time constant circuit includes the third resistor and is connected to the second control terminal of the second switching device.