| 摘要 |
PURPOSE:To prevent thermal destruction of members having a low thermal resistance and thermal degradation of various parts constituting a heating device by detecting the abnormality of a temperature detecting means by off-start of power supply of a heating body. CONSTITUTION:When a timer 8 is started and a changeover switch 13 of a capacitor 11 is switched to start charging of the capacitor 11 through a fixed resistance 2a, the voltage outputted to a pulse width modulating circuit 3independently of the actual temperature of a fixing device falls to potential level 0 and is restored to a voltage level corresponding to a detected temperature S of the fixing device based on a prescribed time constant thereafter. When as voltage level Vs outputted to the pulse width modulating circuit 3 is lower than a voltage level corresponding to an upper limit reference temperature Tu after a prescribed time T elapses, it is judged that a thermistor 2b is short- circuited; and when the voltage level Vs is lower than a voltage T1 corresponding to the rise temperature, it is judged that the thermistor 2b is disconnected, and the control operation is stopped. Thus, degradation and thermal destruction of various parts constituting the heating device are prevented. |
