CONTROL CIRCUIT FOR A BRUSHLESS D.C. MOTOR

摘要

The present invention relates to a control circuit for a brushless self-starting D.C. motor. The motor comprises a permanent magnet rotor and a stator coil. A component is provided which is magnetic field-dependent and which is subjected to the rotor field to determine the rotary position. A controllable electronic servo-element is connected in series with the stator coil at a D.C. source. The servoelement controls the flux through the stator coil in dependence on the rotary position of the rotor. The magnetic dependent parameter changes of the magnetic field-dependent component are converted to a control signal for the servo-element. The control circuit comprises an oscillator having an LC resonant circuit of which the inductance is formed by the magnetic field-dependent component in the form of a sensing coil having a core. The oscillations of the oscillator are modulated in response to the induction generated in the sensing coil by the rotor field. The control signal for the servo-element is derived from the modulated oscillator output and the oscillator frequency is considerably higher than the rotor speed of the D.C. motor.