To suppress the generation of high frequency by supplying a power to a heating device while regularly making the ac voltage supplied to the heating device ON in a prescribed frequency and OFF in a prescribed frequency every half-cycle of the waveform of the ac voltage.
A CPU 13 detects the ON time of a heater temperature regulating signal and the OFF time thereof, and transmits a heater control signal for controlling the time of actually applying an ac voltage to a heat fixing heater 9 from the duty ratio. The heater control signal is formed of a signal consisting of a prescribed frequency of ON and a prescribed frequency of OFF which is regularly changed every half-cycle. According to ON and OFF of the heater control signal, a switch element 11 is switched to actually supply a power to the heat fixing heater 9. The control is performed so that a prescribed frequency of ON and a prescribed frequency of OFF are regularly provided very half-cycle of the ac voltage waveform, whereby the power according to the excess and shortage of the heating quantity of the heater 9 is supplied according to the surface temperature of the fixing roller 4.
KAWADA SATORU
NAITO MASAO
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