| 摘要 |
PURPOSE:To detect electromotive force of a motor accurately during OFF duty interval in a system for controlling the duty ratio based on a signal rele vant to the speed which is obtained from the electromotive force of motor during OFF duty when the motor speed is subjected to duty ratio control. CONSTITUTION:A pulse width elongating circuit 10 is additionally provided in order to extend the interval of motor voltage, which is not inputted to a comparing circuit 6, not only through ON duty interval but also immediately thereafter. An average voltage holding circuit 2A is also provided in order to input not the instantaneous value but the average value of voltage to the comparing circuit 6. |
