Patent ID: 7514894

Claim:
A driver for a brushless motor, comprising: a static position sensing device; a back EMF detector for detecting a back EMF signal; comprising: a filter for filtering the back EMF signal; an output stage comprising at least three modules for supplying a current to a respective phase coil of the motor; a commutating device for selectively enabling respective modules of the output stage depending on the position of the motor, which selectively enabling is alternated with a commutation frequency, the commutating device being controlled by the static position sensing device at startup of the motor and by the back EMF detector after the first detected back EMF pulse; a pulse width modulation unit controlling a strength of the current provided to the motor at a predetermined maximum value until the commutation frequency has a predetermined minimum value, and controlling the strength of the current at a value determined by an input signal when the commutation frequency has exceeded said minimum value, the filter having a relatively strong high frequency transfer characteristic at a relatively high commutation frequency and a relatively weak high frequency transfer characteristic at a relatively low commutation frequency.