Patent ID: 8680799

Claim:
A method for reducing acoustic noise in a brushless direct current (DC) motor, the method comprising: applying a drive signal to a drive circuit; determining a zero-crossing for a back electromotive force (back-EMF) voltage for the brushless DC motor based at least in part on the drive signal; measuring an applied current applied to the brushless DC motor by the driver in response to the drive signal; comparing the zero-crossing for the back-EMF voltage to a zero-crossing for the applied current; and incrementally adjusting the drive signal so as to substantially align the zero-crossing for the back-EMF voltage and the zero-crossing for the applied current, wherein the step of determining further comprises determining a position for the zero-crossing for the back-EMF voltage within a window, wherein the step of comparing further comprises: determining a plurality of signs of a magnitude of the applied current within the window, wherein each sign is determined at a predetermined interval; incrementing a counter for each sign that is one of positive and negative to generate a position for the zero-crossing for applied current; and comparing the position for the zero-crossing for the back-EMF voltage to the position for the zero-crossing for the applied current to generate a position difference.