C MOTOR CONTROL SYSTEM UTILIZING A SELECTIVELY ENERGIZABLE SEMICONDUCTOR SWITCH MEANS

A control system is disclosed for an electrical motor having a run winding and a start winding. The system includes a gate-controlled current switch device connected between the start winding and a source of power as well as trigger means including a thermistor adapted for operation in a self-heating mode coupled to the gate of the current switch device. The trigger means is adapted to apply triggering current to the gate only for a predetermined time interval to cause sufficient self-heating of the thermistor for effecting operation thereof in a high-resistance mode so as to cause a reduction in the flow of current therethrough and effect deenergization of the switch device at the expiration of the predetermined time interval. Means are also provided for energizing the start winding and the trigger means to permit current to flow to the start winding during the predetermined time interval in order to effect starting of the motor. In addition, the system may include a thermal protection means coupled to the motor in order to disrupt the flow of current to the run winding in response to a sensed motor temperature in excess of a preselected temperature level.