| 摘要 |
PURPOSE:To quickly detect the non-electrified state with a simple constitution by detecting the non-electrified state of a fixing heater on the basis of magnitude relations between the temperature detection signal of a thermistor and the integral signal obtained by integrating this detection signal. CONSTITUTION:The time constant of discharge passing a resistance 11 in an integrating circuit 9 is so set that it approximately coincides with the detection temperature drop curve after disconnection of the fixing heater is generated. If disconnection of the fixing heater or the like occurs, the temperature detection signal at a connection point 3 between a thermistor 1 and a variable resistance 2, namely, the output signal from an amplifier 4 is kept at a certain value. This output signal is supplied to the circuit 9 through a switch 8 interlocking with a power switch, and the integral output signal from the circuit 9 is supplied to the reference input terminal of a comparator 7 whose comparison input terminal the output signal from the amplifier 4 is supplied to. Then, magnitude relations between both signals supplied to the comparator 7 are inverted in a short time after making of the power switch, and the signal indicating the non-conductive state of the fixing heater is supplied to a fixing heater control part 6.
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