| 摘要 |
PROBLEM TO BE SOLVED: To effectively protect a driving transistor even if a short circuit abnormality occurs in a motor in a configuration in which the motor and the driving transistor are connected in series.SOLUTION: When a supply voltage V1 drops to or below an undervoltage protection value, a control circuit 30 outputs a low duty signal from a drive circuit 36 for a predetermined monitoring time. This prevents an excessive current from flowing to a driving transistor 22 to protect the driving transistor 22 even if a short circuit abnormality occurs in a motor 10. The control circuit 30 is provided with a capacitor 48 for providing a power backup such that an internal power supply 46 can supply an operating voltage at least for the monitoring time even if the supply voltage V1 drops to such a level as disables the internal power supply 46 from generating the operating voltage. The control circuit 30 can thus protect the driving transistor 22 effectively without losing the function of protecting the driving transistor 22 even if the supply voltage V1 drops. |
