Switching transistor protection circuit for DC low inertia motor - uses four switching transistors and compares motor power with that transistor to limit max. starting current

摘要

Four switching transistor units are driven from a single control circuit which is itself fed from a phase shifting circuit. The power threshold handled by any one transistor is compared with that of the motor, obtained from an isolated series resistance in the motor supply. The output is used to limit the max. starting current as a function of the motor. The circuit comprises a motor speed reference, an error detection and measurement device, an operational amplifier for amplifying the errors and an oscillator. The oscillator is coupled to a pulse generator. Safety devices control the low voltage power to the motor. The circuit uses two auxiliary voltages of + 8v and -8v to improve switching.