STEP MOTOR CONTROL CIRCUIT

A permanent magnet step motor rotor is driven in response to oppositely directed magnetic fluxes coupled by a magnetic core to the rotor. The flux in one direction is derived by selectively feeding D.C. current in one direction through a winding means on the core and a transistor emitter collector path while a switch is open circuited to forward bias the transistor base emitter junction. Flux in the other direction is derived by closing the switch and thereby back biasing the transistor so that D.C. current flows in the winding means in the opposite direction. The rotor is locked in place under steady state conditions with a D.C. current derived from the circuit including the transistor and switch. The steady state current is less than the current required to drive the rotor and is maintained at the lower level by including capacitors in bias circuits for the transistor. To drive the rotor in response to changing magnetic fluxes there may be provided either shading rings, extended, segmented core pole faces, or a rotor having major and minor permanent magnet poles. To provide balanced magnetic flux in opposite magnetic core pole faces coupling flux to the rotor a low resistivity slotted ring is provided.