Patent ID: 8331819

Claim:
An image forming apparatus, comprising: a fixing portion that heat-fixes an unfixed toner image formed on a recording material onto the recording material, the fixing portion comprising: an endless belt; and a heater that contacts an inner surface of the endless belt and generates heat by power supplied from a commercial alternating current power source; a temperature detection element that detects a temperature of said fixing portion; and a power control portion that controls the power supplied from the commercial alternating current power source to the heater according to the temperature detected by the temperature detection element, wherein the power control portion is configured to set: a first power supply control mode, with a predetermined number of half waves more than two continuous waves in an alternating current waveform set as one control cycle, for supplying power to the heater according to the detected temperature for each one control cycle; a second power supply control mode, with a predetermined number of half waves equal to or less than the two continuous waves in the alternating current waveform set as one control cycle, for supplying power to the heater according to the detected temperature for each one control cycle; and a third power supply control mode for supplying predetermined power to the heater, wherein the power control portion switches, before a leading edge of the recording material enters the fixing portion, a state of supplying the power in the first power supply control mode to a state of supplying the power in the second power supply control mode, then switches the state of supplying the power in the second power supply control mode to a state of supplying the power in the third power supply control mode, and further switches the state of supplying the power in the third power supply control mode to the state of supplying the power in the first power supply control mode, and wherein the fixing portion fixes the unfixed toner image onto the recording material in the state of supplying the power to the heater in the first power supply control mode.