Fixing Device and Image Forming Apparatus Including the Fixing Device

An image forming apparatus, comprising:

• a transport unit configured to transport a sheet;
• an image forming unit configured to form a toner image, which is transferred on the sheet;
• and
• a fixing device configured to fix the toner image, which is transferred on the sheet, to the sheet,
• wherein the fixing device includes
• a heat rotational member configured to contact the sheet on which the toner image is transferred and to fix the toner image to the sheet;
• a pressure rotational member configured to press the heat rotational member to form a nip, to apply a pressure to the sheet, which passes through the nip, and to fix the toner image to the sheet;
• a magnetic-flux generation unit including
• a resonant circuit including a coil that generates a magnetic flux, which causes the heat rotational member to generate heat by induction heating, and a capacitor, and
• a switch unit that is connected to the resonant circuit and performs switching of power supply to the resonant circuit;
• a detector configured to detect power consumption of the magnetic-flux generation unit;
• and
• a fixing controller configured to recognize the power consumption of the magnetic-flux generation unit based on an output of the detector in response to an instruction of a target power applied to the magnetic-flux generation unit from the outside, to set a switching frequency of the switch unit in accordance with the target power if current power consumption of the magnetic-flux generation unit is smaller than the target power, to adjust the switching frequency to move closer to a reference frequency, and to cause the switch unit to stop the power supply to the resonant circuit if a difference between the switching frequency set in accordance with the target power and the adjusted switching frequency exceeds a predetermined change width.