Sensorless motor circuit providing accurate back electromotive force zero-crossing point detection and operation method thereof

A method of operating a sensorless motor circuit, the sensorless motor circuit comprising a BLDC motor, a driving circuit, a voltage adjustment circuit, a virtual neutral point circuit, a comparator and a control circuit, the BLDC motor comprising a first winding, a second winding and a third winding, each of the second winding and the third winding comprising a first terminal having a terminal voltage, and a second terminal, the driving circuit being coupled to the BLDC motor, the voltage adjustment circuit being coupled to a first terminal of the third winding, and the virtual neutral point circuit being coupled to a first terminal of the first winding, a first terminal of the second winding and a first terminal of the third winding, the comparator being coupled to the voltage adjustment circuit and directly coupled to the virtual neutral point circuit, the control circuit being directly coupled to the comparator, the method comprising:

• the driving circuit outputting a PWM signal to a first terminal of the first winding, coupling a first terminal of the second winding to a ground terminal, and setting the first terminal of the third winding to a floating state;
• the voltage adjustment circuit generating a divided voltage according to a terminal voltage of the third winding;
• the virtual neutral point circuit generating a virtual neutral voltage;
• the comparator comparing the divided voltage with the virtual neutral voltage to generate a comparison signal;
• the control circuit determining a sampling time of the comparison signal according to a duty cycle of the PWM signal;
• and
• the control circuit sampling the comparison signal at the sampling time to detect an EBMF zero-crossing point.