Patent ID: 7248092

Claim:
A clamp circuit device comprising: an adder circuit for adding a power-supply-side reference voltage set close to a power supply voltage and a predetermined clamp control voltage; a subtractor circuit for subtracting the clamp control voltage from a ground-side reference voltage set close to a ground level; a power-supply-side clamp element that is connected between a power supply and a protected terminal and is caused to conduct and perform a clamping operation when a voltage of positive polarity higher than its conduction threshold set up based on an output voltage of the adder circuit is applied to the protected terminal; a ground-side clamp element that is connected between the ground and the protected terminal and is caused to conduct and perform the clamping operation, when a voltage of negative polarity higher than the conduction threshold set up based on an output voltage of the subtractor circuit is applied to the protected terminal, wherein the power-supply-side clamp element includes a P-channel MOSFET, a gate of which is connected to an output terminal of the adder circuit, wherein the ground-side clamp element includes an N-channel MOSFET, a gate of which is connected to an output terminal of the subtractor circuit; and a series circuit of a P-channel MOSFET, a resistor, and an N-channel MOSFET that is connected between the power supply and the ground, wherein a drain and the gate of the P-channel MOSFET are connected to one end of the resistor and also to the input terminal of the adder circuit, and wherein a drain and the gate of the N-channel MOSFET are connected to the other end of the resistor and also to the input terminal of the subtractor circuit to set up the power-supply-side and the ground-side reference voltages.