Patent ID: 8030877
Filing Date: 2011-10-04
Classification: H02P

Abstract:
1. A device for detecting a back electromotive force phase of a motor coil of a two-phase excitation stepper motor that is driven with constant-current PWM, the device comprising: a timing generating unit for generating a timing signal indicating a start timing, an intermediate timing and an end timing of a 180-degree electrical angle period in a detection target phase, from excitation pulse signals indicating respective current passage directions of two current passage phases; and a difference calculating unit for receiving the timing signal, and calculating a difference between a total PWM control period of the detection target phase during a first-half 90-degree period defined by the start timing and the intermediate timing, and a total PWM control period of the detection target phase during a second-half 90-degree period defined by the intermediate timing and the end timing.