Motor system of accurate back-electromotive force detection and operation method thereof

A method of operating a motor system, the motor system comprising a brushless direct current (BLDC) motor, a voltage divider circuit, a switch and an analog-to-digital converter (ADC), the BLDC motor comprising a first winding, a second winding and a third winding, the first winding, the second winding and the third winding being coupled to each other at a neutral node, the driving circuit comprising a first set of switches coupled to the first winding and configured to output a pulse width modulation driving signal to the first winding, a second set of switches coupled to the second winding and configured to couple the second winding to a ground terminal, and a third set of switches coupled to the third winding and configured to float the third winding, the voltage divider circuit comprising a first resistor, a second resistor and a bypass diode, the first resistor comprising a first terminal coupled to the third winding and a second terminal, and a second terminal, the second resistor comprising a first terminal coupled to the second terminal of the first resistor, and a second terminal configured to optionally receive a control voltage or a ground voltage, the bypass diode comprising a first terminal coupled to the first terminal of the first resistor, and a second terminal coupled to the second terminal of the first resistor, the ADC being coupled to the voltage divider circuit, the method comprising:

• the ADC receiving a back-EMF signal from the second terminal of the first resistor;
• the ADC enabling the second terminal of the second resistor to receive the control voltage or the ground voltage according to the back-EMF signal;
• and
• the ADC determines a back-EMF zero crossing point according to the back-EMF signal.