| 摘要 |
PURPOSE:To enable to largely reduce the loss due to a base current by varying the base current of a drive transistor in response to the coil current by the operations of a current detector, a current supply unit and a selector. CONSTITUTION:The base currents of the first drive transistors 1a, 1b are varied in response to the current IM of a coil 4 by the operation of a current detector 11, a current supply unit and the first selector 13, and the loss due to the base currents is reduced. In other words, the base current is set to 102mA when the large current operation (IM=2A) at the starting time of the motor and the base current is set to 7mA in the small current operation (IM=100mA) of the normal state of speed control. Then, the first drive transistors 1a, 1b are effectively turned ON and OFF, and the base current loss corresponding to (102-7)=95mA is reduced. The base currents of the second drive transistors 2a, 2b are varied in response to the current IM of the coil 4, thereby reducing the loss. |
