Patent ID: 8278860

Claim:
A method for improving zero-crossing detection in a sensorless brushless direct current motor, said method comprising the steps of: generating a first plurality of pulse width modulation (PWM) control pulses at a first number of pulses per second until a certain time interval before a zero-crossing event is anticipated then generating a second plurality of PWM control pulses at a second number of pulses per second, wherein the second plurality of PWM control pulses at the second number of pulses per second is greater than the first plurality of PWM control pulses at the first number of pulses per second; detecting a zero-crossing event during the generation of the second plurality of PWM control pulses at the second number of pulses per second in at least one commutation period of an electrical cycle of a sensorless brushless direct current motor by measuring a back electromotive force voltage at an unexcited phase connection of the sensorless brushless direct current motor; and returning to generating the first plurality of PWM control pulses at the first number of pulses per second after the zero-crossing event has been detected.