DEVICE FOR CONTROLLING DRIVE OF DC BRUSHLESS MOTOR

PURPOSE: To provide a drive controller for brushless motor which can prevent the pulsation of the operating frequency of a DC brushless motor caused by a feeding-back time lag when an actual frequency is very close to a command frequency and, at the same time, can prevent the over-speed operation of the motor when the motor is overloaded. CONSTITUTION: A device for controlling drive of DC brushless motor is provided with a dead zone adding means 13 which makes a command frequency to be compared with an actual frequency to have a prescribed width so that a frequency comparing means 11 can output such an output that changes the duty ratio of PWM waveform signals only when the actual frequency does not fall within the prescribed width of the command frequency added by the adding means 13 to a PWM waveform signal generating means 12 and, at the same time, a duty ratio regulating means 14 which controls the duty ratio of the PWM waveform signals so that the duty ratio cannot exceed the upper limit values set at every frequency. Therefore, the reliability of a DC brushless motor is improved, because the motor can be controlled stably without causing pulsation nor hunting and the motor is not burnt nor stopped even when the motor is overloaded.