| 摘要 |
PURPOSE:To execute sufficiently driving even in case of a heavy load by varying a reference voltage compared with a voltage of a load circuit in synchronization with a variation of a pulse signal for starting a current supply to the load. CONSTITUTION:When a pulse signal P of short width is generated from a pulse signal outputting circuit 14, a transistor TR13 is driven through an OR circuit 12 and an AND circuit 11, and a current is made to flow to a load 15. In this case, a voltage VS of a load point 16 is compared with a varialbe reference voltage VREFV by a comparing circuit 17. The voltage VREFV is set to a large value V1 in synchronization with rise of the signal P by a reference voltage varying circuit 18, and thereafter, dropped successively by a prescribed incline, and when its value reaches V2, it is held at a constant value. When the load 15 is a light load, a load voltage VS1 drops to a value of about the ground potential, therefore, an output of the circuit 17 becomes logic ''1'', also in case of a heavy load, a load voltage VS2 drops from the VREFV while the signal P is logic ''1'', the circuit 17 outputs logic ''1'', and the conduction of the TR13 is held. When the load 15 is in a short-circuit state, a voltage VS3 of the point 16 becomes higher than the VREFV, and when the signal P becomes ''0'', the TR13 is cut off. |
