Patent ID: 8378606

Claim:
A method for controlling speed of a sensorless brushless direct current motor which is controlled by N commutation periods wherein the N commutation periods define one rotation of the sensorless brushless direct current motor, said method comprising the steps of: determining the center of each commutation period in an electrical cycle of a sensorless brushless direct current motor by measuring back electromotive force voltage at each phase connection of the sensorless brushless direct current motor; generating pulse width modulation (PWM) control pulses, the PWM control pulses each having one on and one off transition during respective ones of the commutation periods, wherein each single PWM control pulse is substantially centered within its respective commutation period; and driving power switching transistors with the PWM control pulses for each of the commutation periods, wherein the power switching transistors are connected between stator coils of the sensorless brushless direct current motor and a direct current power source.