Description has been made with reference to FIG. 6A and FIG. 6B (or FIG. 7A and FIG. 7B) regarding an arrangement in which, in the second mode, the second overcurrent detection circuit 150_2 (or the second peak detection circuit 160_2) on the slave side is disabled. However, the present invention is not restricted to such an arrangement. Also, such a detection circuit may be operated in parallel with the first overcurrent detection circuit 150_1 (or the first peak current detection circuit 160_1) on the master side. In this case, one from among the outputs of the two detection circuits 150_1 and 150_2 (160_1 and 160_2) that shows a quicker response may be used to provide a control operation or a protection operation.

Description has been made in the embodiment regarding a two-channel arrangement. However, the present invention is also applicable to an arrangement in which the number of channels N is a desired integer of three or more. In this case, an arrangement may be made configured to select a mode from among a mode in which all N channels are operated independently and a mode in which M channels (M≤N) from among the N channels are coupled to a common inductor, and one from among the M channels is operated as a master while the remaining channels are operated as slaves.