Sensorless commutation circuit and sensorless driving apparatus for brushless motor

A sensorless driving apparatus for a brushless motor, comprising:

• a micro controller, outputting a pulse width modulation control signal according to a phase voltage signal;
• an inverter, coupled to the micro controller, for switching the pulse width modulation control signal to a phase voltage signal of the brushless motor;
• and
• a sensorless commutation circuit, coupled to the micro controller and the inverter, the sensorless commutation circuit comprising:
• a voltage divided unit, outputting a voltage divided signal according to the phase voltage signal of the brushless motor;
• a control signal output unit, outputting a filter control signal, wherein the filter control signal has a same switching cycle as the pulse width modulation control signal;
• a switch unit, coupled to the control signal output unit and the voltage divided unit, outputting a comparison signal according to the filter control signal and the voltage divided signal;
• and
• a comparison unit, coupled to the switch unit, and outputting the correct commutation signal according to the comparison signal,
• wherein the switch unit is switched in response to the filter control signal to output the voltage divided signal as the comparison signal.