CONTROLLER FOR POWER SUPPLY OF HEAT ROLL IN THERMAL FIXING DEVICE FOR PAGE PRINTER

PURPOSE:To surely prevent overheat of a heat roll by providing an overheat preventing circuit which forcibly immediately fusing a fuse at the time of continuously supplying power to the heat roll over a set time. CONSTITUTION:An AC power source 30 is used for power supply to a heat roll 10, and the temperature of the heat roll 10 is detected by a temperature detector 12, and heating of the heat roll 10 is controlled in accordance with the detected temperature by a heating control circuit 14. A thermistor is used as the temperature detector 12, and the heating control circuit 14 consists of a triac control circuit 32, a photocoupler 34, and a triac 36. A fuse 16 is inserted to the power path of the heat roll 10, and the fuse 16 is immediately and forcibly fused by an overheat preventing circuit 18 when power is continuously supplied to the heat roll over the set time. Since the power path is immediately opened at the time of the control abnormality of continuous power supply for heating of the heat roll in this manner, overheat of the heat roll is surely prevented.