Motor over-heating protection circuit

Abstract

A motor overheating protection circuit includes an enabling circuit which responds to a trigger signal provided by a reset circuit upon application of power to the protection circuit to enable a motor drive circuit to effect energization of the motor. A temperature sensing circuit provides a control signal indicative of the temperature of the motor, and should the control signal exceed the set point of a threshold detecting circuit of the enabling circuit, indicative of overheating of the motor, the enabling circuit inhibits the motor drive circuit deenergizing the motor. Once the motor has been deenergized as the result of an overheating condition, the reset circuit maintains the enabling circuit locked out until the protection circuit is deactivated and then reactivated. If the sensor or its input leads are open, then the control signal provided by the temperature sensing circuit will exceed the detection threshold of the threshold detecting circuit and the enabling circuit will maintain the motor deenergized. If the sensor or its input leads are short circuited, then the control signal provided by the temperature sensing network will be less than the threshold level for a minimum voltage detector circuit of the enabling circuit and the enabling circuit will maintain the motor deenergized.