Patent ID: 8810183
Filing Date: 2014-08-19
Classification: H02P

Abstract:
1. A PWM signal output circuit configured to output a PWM signal with a duty cycle corresponding to a duty cycle of an input signal to a drive circuit configured to drive a motor based on the PWM signal, the PWM signal output circuit comprising: a detecting circuit configured to detect a time period in which a speed signal is at one logic level or at an other logic level, based on the speed signal whose logic level changes in an alternate manner, the speed signal having a period corresponding to a rotation speed of the motor; a dividing circuit configured to divide each of the time periods detected by the detecting circuit into first to third time periods; a PWM generating circuit configured to control a duty cycle of the PWM signal so that the duty cycle of the PWM signal changes in a stepwise manner toward a duty cycle of the input signal, in order to increase a current flowing through a motor coil of the motor, in the first time period, and output the PWM signal with the duty cycle; the PWM generating circuit configured to control the duty cycle of the PWM signal so that the duty cycle of the PWM signal becomes equal to the duty cycle of the input signal, in order to maintain the current flowing through the motor coil constant, in the second time period; and the PWM generating circuit configured to control the duty cycle of the PWM signal so that the duty cycle of the PWM signal changes in a stepwise manner from the duty cycle of the input signal, in order to decrease the current flowing through the motor coil, in the third time period, and output the PWM signal with the duty cycle.