Patent ID: 8532516

Claim:
A fixing device comprising: a heating unit that is heated by supply of an alternate-current power; a heating control unit that executes a phase control to supply the alternate-current power to the heating unit for an ON-width in at least a half-wave period of the alternate-current power; and a storing unit that stores therein parameters for calculating the ON width and a duty step that defines an amount of increase or decrease in the ON width, wherein the heating control unit calculates the ON width based on the parameters and the duty step stored in the storing unit and executes the phase control using a calculated ON width, wherein the heat control unit calculates the ON width based on the duty step that defines an amount of increase in the ON width in case of a soft-start period, and the heat control unit calculates the ON width based on the duty step that defines an amount of decrease in the ON width in case of a soft-end period, wherein the parameters include: the duty step that defines an amount of increase in the ON width, and a phase control period that defines a period during which the phase control is executed, and the heating control unit calculates a number of half-wave periods for which the duty step is added based on the phase control period and the half-wave period, and calculates the ON width based on the calculated number of half-wave periods and the duty step.