Abstract: An image forming apparatus includes a fixing unit, a switching element, and a controller. The controller controls the switching element on a half-cycle basis of an alternating current. A period in which the electric power is supplied to the heater within a period of a half-cycle of the alternating current is divided into at least one first power supply period and a second power supply period longer than one first power supply period. A length of a sum of the at least one first power supply period is a length from 1/6000 to 1/40 of one cycle of the alternating current. A sum of electric power supplied in the at least one first power supply period and electric power supplied in the second power supply period is determined depending on a difference between a temperature and a target temperature of the fixing unit.

Abstract: A heater for an image heating device includes a substrate having first and second surfaces, a heat generating element electrically connected to a first electrode group, both formed on the first surface, a temperature detection element electrically connected to a second electrode group, both formed on the second surface. A plurality of first feed terminals provided in the image heating device in contact with the first electrode group. A plurality of second feed terminals provided in the image heating device in contact with the second electrode group. The first and second electrode groups are disposed on the same side of a midpoint of the substrate in a longitudinal direction. The second electrode group is disposed closer to the midpoint than the first electrode group in the longitudinal direction. The first and second electrode groups are disposed with a gap between the first and second electrode groups in the longitudinal direction.

Abstract: An image forming apparatus includes a fixing unit, a switching element, and a controller. The controller controls the switching element on a half-cycle basis of an alternating current. A period in which the electric power is supplied to the heater within a period of a half-cycle of the alternating current is divided into at least one first power supply period and a second power supply period longer than one first power supply period. A length of a sum of the at least one first power supply period is a length from 1/6000 to 1/40 of one cycle of the alternating current. A sum of electric power supplied in the at least one first power supply period and electric power supplied in the second power supply period is determined depending on a difference between a temperature and a target temperature of the fixing unit.