Patent ID: 8351175

Claim:
A protective device for a load circuit, in which a plurality of load circuits in each of which a semiconductor switch and a load are connected through a load connection wiring line are connected in parallel, each of the load circuits and a power source are connected through a common wiring line that is common to each of the load circuits, and when an over-current has been generated in at least one of the load circuits, the load circuit having undergone the over-current is cut off, the protective device comprising: a first counter-electromotive force detection unit for detecting a first counter-electromotive force which appears in the common wiring line, and second counter-electromotive force detection unit disposed in at least one of the load circuits, and for detecting whether or not a second counter-electromotive force which is the same direction as the first counter-electromotive force is induced in the load connection wiring line; and a cutoff control unit for cutting off the load circuit which has the load connection wiring line, in a case where the first counter-electromotive force has exceeded a predetermined threshold value and where the second counter-electromotive force has been induced in the load connection wiring line.