Patent ID: 7443119

Claim:
A circuit for controlling the rotating speed of a brushless direct current (BLDC) motor, comprising: a target phase time circuit providing a target phase time signal proportional to a predetermined target rotating speed of the BLDC motor; an elapsed time counter providing an elapsed phase time signal proportional to an actual rotating speed of the BLDC motor; a time-out comparator providing a time-out signal according to the level of the elapsed phase time signal relative to the target phase time signal; an error amplifier providing an error signal according to the level of an actual phase time signal relative to the target phase time signal, wherein the actual phase time signal is obtained by sampling the elapsed phase time signal in response to a predetermined condition of the state of a Hall sensor signal, the state of the Hall sensor signal changes in response to the position of the rotor of the BLDC motor relative to the stator of the BLDC motor; a pulse width modulation (PWM) circuit providing a PWM signal, wherein the duty cycle of the PWM signal is determined according to the time-out signal and the error signal; and a motor drive circuit controlling the motor current of the BLDC motor according to the PWM signal and the Hall sensor signal, wherein the duty cycle of the PWM signal determines the duty cycle of the motor current and the state of the Hall sensor signal determines the direction of the motor current.