Motor control apparatus

A motor control apparatus comprising:

• a motor generating a back electromotive force when in rotation;
• designation means for providing a signal for specifying the operational condition of said motor;
• drive means coupled to said designating means to said motor for driving said motor when said first signal is at a first level and for providing a second signal when said first signal is at a second level;
• comparator means coupled to said motor for comparing the back electromotive force of said motor with a reference level when said first signal is at said second level and for providing a third signal at a terminal when said back electromotive force is within a given level range prescribed by said reference level;
• and
• braking means coupled to said motor applying magnetic braking with respect to the rotation of said motor by shunting the path through which the back electromotive current flows when said second and third signals are provided, said braking means including a switch circuit forming a positive feedback loop and turned on when applying electromagnetic braking to said motor, said switch circuit including a thyristor-connected semiconductor switch connected in series with the current path of the back electromotive force current, said semiconductor switch including:
• a first switching transistor having a base, an emitter connected to one end of said motor and a collector connected to the other end of said motor;
• and
• a second switching transistor having a base connected to the collector of said first switching transistor, a collector connected to the base of said first switching transistor and an emitter connected to a terminal to which said third signal is applied, said back electromotive force current flowing through the emitter-collector path of said first switching transistor.