Patent US 4,092,572

A stator winding drive circuit for a brushless d.c. motor having a permanent magnet rotor and a plurality of stator poles unequal to the number of rotor poles. Hall elements sense the rotor position, but due to the unequal number of rotor and stator poles, if the amplified Hall element outputs are used to directly drive the stator windings some drive signal overlap will exist resulting in torque ripple. Therefore, the true and reciprocal Hall element outputs are applied to a resistive addition network to produce staircase waveforms, portions of which have the desired sequential timings and non-overlapping electrical durations. These waveforms are applied to threshold switching circuits triggered by such desired portions, and the switching circuit outputs feed the stator windings.