Patent ID: 7242160

Claim:
A method for starting a brushless DC motor (BLDCM) having a stator, a rotor, a winding and an asymmetrical air gap, wherein said stator has a specific tooth and said rotor has a specific magnetic pole, comprising the steps of: (a) exciting said winding with a current impulse such that said stator generates a magnetic field and then going to one of steps (b) and (d); (b) driving said rotor to rotate in a first direction with said current impulse if a polarity of a portion of said specific tooth of said stator close to said air-gap and a polarity of said specific magnetic pole of said rotor corresponding to said specific tooth are opposite and then going to step (c); (c) stopping said current impulse at a specific moment such that said rotor is rotated in a second direction by a cogging torque and then going to step (f); (d) driving said rotor to rotate in a specific direction with said current impulse if a polarity of a portion of said specific tooth of said stator close to said air-gap and a polarity of said specific magnetic pole of said rotor corresponding to said specific tooth are the same and then going to step (e); (e) stopping said current impulse at a specific time such that said rotor is rotated in said specific direction by an inertia and then going to step (f); and (f) detecting a back electromotive force (BEMF) in said winding when said rotor rotates such that said motor is controlled for commutating according to said BEMF.