Patent ID: 9692331
Date: 2017-06-27
CPC Classifications: H02P

Claim:
1. A method for zero crossing detection for a brushless direct current (BLDC) motor, said method comprising the steps of: driving two phases of the three phase BLDC motor with pulse width modulation (PWM) drive voltage pulses, each PWM drive voltage pulse having a period and a duty cycle, and a voltage from a power source; coupling an un-driven third phase of the three phase BLDC motor to a voltage comparator for comparing back electromotive force (BEMF) voltages thereof; comparing the BEMF voltages to a reference voltage with the voltage comparator; measuring a falling time interval during a falling BEMF period when the BEMF voltages are less than the reference voltage; storing the falling time interval; measuring a rising time interval during a rising BEMF period when the BEMF voltages are greater than the reference voltage; storing the rising time interval; and comparing the stored falling and rising time intervals, wherein if the stored falling and rising time intervals are substantially the same then do not change the reference voltage, and if the stored falling and rising time intervals are not substantially the same then change the reference voltage.