Patent ID: 8159795

Claim:
A protection circuit for protecting a semiconductor integrated circuit against a surge comprising: a surge detecting circuit for detecting the surge applied to the semiconductor integrated circuit; a protecting element for absorbing the surge, the protecting element being connected between a signal terminal for supplying a signal to the semiconductor integrated circuit and a power source terminal for supplying a power source voltage; and a power source voltage detection circuit for detecting the power source voltage applied to the semiconductor integrated circuit, wherein, when the power source voltage is smaller than a voltage enough to normally operate the semiconductor integrated circuit and the surge detecting circuit does not detect the surge, the protecting element is set at a current limiting state, and wherein, when the power source voltage is smaller than a voltage enough to normally operate the semiconductor integrated circuit and the surge detecting circuit detects the surge, the protecting element is set at a current non-limiting state, and wherein, when the power source voltage detection circuit detects that the power source voltage is not lower than the voltage enough to normally operate the semiconductor integrated circuit, a power source voltage detection signal is output to the surge detecting circuit, to set the surge detecting circuit at a non-detecting state, such that the surge detecting circuit sets the protection element at a current limiting state.