Patent ID: 8022578

Claim:
An electric power supply cut-off circuit which cuts off an electric power supplied from a power source, the electric power supply cut-off circuit comprising: an IC having an IC operation signal output circuit which outputs an IC operation signal indicating that the IC is in operation, which outputs a normal operation signal when the IC is operated normally, and which does not output the IC operation signal or outputs an abnormal operation signal when any abnormal situation arises in the IC, the normal operation signal being composed of the IC operation signal and indicating that the IC is operated normally, and the abnormal operation signal having a waveform different from that of the normal operation signal; a switch which makes a switching operation between the IC and the power source; and a switching control circuit which controls the switching operation of the switch and which continuously outputs, to the switch, a connection instruction signal to instruct a connection between the IC and the power source during a period in which the normal operation signal is inputted from the IC operation signal output circuit; wherein the switch makes the connection between the IC and the power source when the connection instruction signal is inputted to the switch, and the switch cuts off the connection between the IC and the power source when the connection instruction signal is not inputted to the switch, when the IC operation signal is inputted, the switching control circuit outputs the connection instruction signal to the switch only for a predetermined period of time; and when the IC is operated normally, the IC operation signal output circuit outputs, to the switching control circuit, the IC operation signal as the normal operation signal at a time interval which is not more than the predetermined period of time, and when the abnormal situation arises in the IC, the IC operation signal output circuit outputs, to the switching control circuit, the IC operation signal as the abnormal operation signal at a time interval which is longer than the predetermined period of time.