Motor control circuit for a brushless DC electric motor

The motor has plural sets of windings 45,46 and plural drive sections 27,28 each operative to commutate one of the sets of windings. The drive sections are coupled to a power source 32 by a switching circuit 30,35,36 which, in response to the speed of the motor, places the drive sections and thus the winding sets either in a series or in a parallel configuration across the terminals of the power source. As a result, the winding impedance and the back electromotive force reflected back to the power source is varied in accordance with the motor speed, thus enabling high torque at low speed and low torque at high speed.