Patent ID: 8704578

Claim:
A protection circuit provided between a power supply and a circuit to be protected to protect the circuit to be protected from a surge voltage, the protection circuit comprising: a p-channel transistor including a source coupled to the power supply and coupled to a backgate thereof, a drain coupled to the circuit to be protected, and a gate; a first zener diode that causes a breakdown when a voltage from the power supply rises to or above a breakdown voltage, a cathode of the first zener diode being connected to the source of the p-channel transistor, and an anode of the first zener diode being connected to the gate of the p-channel transistor; a second zener diode, a cathode of the second zener diode being connected to the drain of the p-channel transistor, and an anode of the second zener diode being connected to a ground; and a resistor connected between the gate of the p-channel transistor and the ground.