METHOD AND CIRCUIT ARRANGEMENT FOR OPERATING A BRUSHLESS DC MOTOR

The invention relates to a method and a circuit arrangement for operating a brushless DC motor (10), having a rotor (14) excited by a permanent magnet and having different magnetic conductance values in different magnetic axes, particularly designed as a consequent pole rotor. The motor comprises a stator (12) having a multiphase, preferably three-phase stator winding and is controlled by an electronic control device (26) by means of a switching device (22) for consistently supplying current to the winding phases (U, V, W) of the stator winding and is supplied from a DC voltage source (23), test current impulses being connected to the stator winding by the switching device (22) and the current rise in the stator phases being monitored. According to the invention, the motor is operated as a stepper motor and the execution of the individual steps is checked by a sensorless position monitor, the step control being able to be superimposed with a current control for compensating for increased load on the motor, such as when starting. For the sensorless position determination of the rotor (14) and for monitoring the execution of the individual rotor steps, the stator windings (U, V, W) have test current impulses applied within the step pauses, the changing inductivity of the magnetic circuit determining the rise times of the current impulses and providing the position criteria.