Patent ID: 8093845

Claim:
A controller for controlling a 3-phase brushless direct current motor, said motor operating in phase sequences, said controller being capable of detecting a back electromotive force (BEMF) so as to produce a zero crossing point (ZCP) signal indicating a position of a rotor in said motor, thereby to perform a commutation operation for driving said motor, said controller comprising: a pulse width modulation (PWM) signal generation unit for generating a PWM signal, said PWM signal having a duty-on period; an analog to digital converter unit for performing an analog to digital conversion to convert said BEMF from an analog form into a digital form; an synchronization and extraction unit for extracting said BEMF in the digital form to obtain a corresponding ZCP signal; and an judgment unit for judging whether the commutation operation is to be performed according to a change of said ZCP signal, and outputting a commutation signal to said PWM signal generation unit after a predetermined time period if the commutation operation is determined to be performed, wherein said synchronization and extraction unit is adapted to operate in synchronization in part with said PWM signal such that the conversion by said analog to digital converter unit is delayed for a delay period from when said PWM signal switches to duty-on, the delay period being defined as Td=T duty −x, where Td denotes the delay period, T duty denotes the duty-on period of said PWM signal, and x is not less than a time period required by said analog to digital converter unit to complete the conversion.