Patent ID: 6181093
Filing Date: 2001-01-30
Classification: H02P

Abstract:
A commutation circuit for a sensorless three-phase brushless DC motor, comprising:a starting circuit adapted to generate a selection signal that indicates whether a motor is in a starting mode or a constant velocity mode by detecting the size of each phase voltage of the motor stator coil and to generate a starting clock signal to forcibly start the motor without information associated with the position of the motor rotor, and being further adapted to generate first, second and third reference clock signals having respective phase differences of 120.degree. and that are synchronized with the starting clock signal;a constant velocity controlling circuit adapted to compare each phase voltage and a neutral point voltage of the stator to generate first, second and third comparison signals and a constant velocity clock signal having a frequency three times the frequency of the comparison signals;a stair/common voltage generating circuit, which in response to the selection signal generated from the starting circuit in the starting mode is controlled by the reference clock signals to simultaneously generate a first group of three stair voltages having respective phase differences of 120.degree. when iterating three-phase with a first voltage equal to a reference voltage during a first period of the starting clock signal, iterating three-phase with a second voltage less than the reference voltage during subsequent second and third periods of the starting clock signal, iterating three-phase with the reference voltage during a subsequent fourth period of the starting clock signal, and iterating three-phase with a third voltage greater than the reference voltage during subsequent fifth and sixth periods of the starting clock signal, and, in the constant velocity mode of the motor, is controlled by the reference clock signals to simultaneously generate a second group of three stair voltages having respective phase differences of 120.degree., when iterating three-phase with a fourth voltage equal to a second reference voltage during a first period of the constant velocity clock signal, iterating three-phase a fifth voltage less than the second reference voltage during subsequent second and third periods of the constant velocity clock signal, iterating three-phase with the second reference voltage during a subsequent fourth period of the constant velocity clock signal, and iterating three-phase with a sixth voltage greater than the second reference voltage during subsequent fifth and sixth periods of the constant velocity clock signal; andan output driving circuit, controlling the direction of the current in the respective phases of the stator coil in response to the voltage differences between the first group of stair voltages and a first common voltage in the starting mode of the motor and in response to the voltage differences between the second group of stair voltages and a second common voltage in the constant velocity mode of the motor.