Driving methods and driving circuits for brushless dc motors without rotor position sensors

Claim 1

A driving circuit for a sensorless and brushless DC motor comprising: a plurality of phase-corresponding coils having respective back electromotive forces when the motor is activated; a first plurality of comparators for comparing said back electromotive forces and outputting a plurality of position detection signals; a second plurality of comparators for comparing said back electromotive forces with a common voltage and outputting phase-corresponding turn-on signals; a first plurality of transistors connected to said phase-corresponding coils for turning on said phase corresponding coils when receiving the turn-on signals; a rotation direction control section having inputs for receiving said phase corresponding turn-on signals and a forward/reverse direction control signal, and outputs for outputting a plurality of direction control signals; a charge/discharge control section having inputs for receiving said direction control signals and said position detection signals, and outputs for outputting charge/discharge control signals; a charge/discharge section connected to the outputs of the charge/discharge control section for outputting a turn-off decision signal; a turn-off signal generating section having inputs for receiving said turn-off decision signal, said position detection signals and said forward/reverse direction control signal and having outputs for outputting a plurality of turn-off signals; and a second plurality of transistors connected to said first plurality of transistors for turning off said first plurality of transistors when receiving said turn-off signals.