Patent ID: 7064940

Claim:
An over heat protection circuit for protecting a brushless dc motor, comprising: a thermal sensitive resistor having a resistance value adapted to change within a predetermined thermal preference in response to changing of an operational temperature of the motor; a resistor serially connected to the thermal sensitive resistor at a connection point at which to commonly provide an adjustable voltage value which is supplied from a voltage source; a transistor including a base, a collector and an emitter, wherein the base is connected to the connection point located between the thermal sensitive resistor and the resistor so that the adjustable voltage value is input to the base; the collector is connected to the voltage source; and the emitter is connected to the motor for controlling operation of the motor; wherein when the operational temperature of the motor is greater than a safety temperature or the motor is overheated, the resistance value of the thermal sensitive resistor is correspondingly adjusted with respect to a predetermined reference such that the adjustable voltage value of the thermal sensitive resistor and the resistor is inadequate to turn on the base of the transistor so as to cut off a motor current and thereby stop the motor to reduce the operational temperature of the motor; and wherein when the operational temperature of the motor is lower than the safety temperature or the motor has cooled, the resistance value of the thermal sensitive resistor is correspondingly adjusted with respect to the predetermined reference such that the adjustable voltage value of the thermal sensitive resistor and the resistor is adequate to turn on the base of the transistor so as to resupply a motor current and thereby restart the motor.