The present invention provides systems and methods for power factor control of a motor. A phase detector uses a line voltage of a power supply and a motor terminal voltage of a motor. The output of the phase detector is synchronized to a zero crossing of the motor current of the motor and a zero crossing of the line voltage. A digital microprocessor connected between the output of the phase detector and a rectifier driver senses a first time at which a phase of the motor voltage is crossing zero volts and a second time at which a phase of the motor current is crossing zero current. The digital microprocessor calculates the difference in time between the first and second times and uses the difference in time to calculate a phase lag of the motor. The digital microprocessor uses the phase lag to calculate a firing time of a rectifier to command power efficiently to the motor.