Speed control device for transistor motor

Claim 1

A speed control device for a transistor motor having a stator provided with field windings and a rotor consisting of a permanent magnet, comprising position detecting windings wound at corresponding positions to said field windings, respectively, to detect the position of said rotor, a switching circuit including a plurality of driving transistors whose emitter-collector circuits are connected in series to said field windings, respectively, and whose bases are supplied with the outputs, respectively, from said position detecting windings, for changing-over in turn the currents of said field windings in accordance with the output signals from said position detecting windings, a base current control transistor for said driving transistors whose emitter-collector circuit is commonly connected through diodes to the respective bases of said driving transistors, and a servo circuit which is supplied with a speed control signal and supplies its output to said base current control transistor, for maintaining said base current control transistor to be inoperative during the starting period of said transistor motor and, as said transistor motor approaches a specified rotation speed, controlling in accordance with said speed control signal the base currents applied to the bases of the driving transistors from said position detecting windings.