An image forming apparatus includes a fixing member, a heating portion configured to heat the fixing member by being supplied with electric power, a power source configured to supply electric power to the heating portion, a temperature detector, a controller configured to control power supply from the power source to the heating portion based on the output voltage from the temperature detector, a reference voltage generator configured to generate a reference voltage, and a breaker configured to stop the power supply from the power source to the heating portion. The reference voltage generator is configured to output the reference voltage that changes with time having elapsed since a start of heating at which the power supply to the heating portion was started by the controller.

According to one embodiment, the power converter includes a power conversion circuit and a power outage detection circuit. The power converter includes a power conversion circuit including an isolation transformer including a primary winding, a secondary winding electromagnetically coupled to the primary winding, and an auxiliary winding, a first DC voltage source which outputs DC power with an input AC power, a switching circuit which switches connection between the first DC voltage source and the primary winding, an auxiliary power supply circuit which supplies the DC power to the switching circuit using a power generated in the auxiliary winding, a second DC voltage source which rectifies and smooths the power generated in the secondary winding and outputs DC power to a load.

A metal frame provides a ground potential. An image forming unit forms a toner image on a sheet. A fixing apparatus fixes the toner image on the sheet. The fixing apparatus comprises a heating element for generating heat by being supplied with power from an alternating current power source. An insulating layer covers the heating element. A conductive layer contacts the insulating layer and insulated from the metal frame. A tube-shaped member is heated by the heating element. A pressing member is arranged opposing the tube-shaped member and forms a nip portion in cooperation with the tube-shaped member. A capacitive element whose one end is connected to the metal frame and whose other end is connected to the conductive layer of the fixing apparatus.

An image forming apparatus includes an attachment portion to which any one of a first fixing apparatus and a second fixing apparatus is selectively attached, and a power supply circuit including a plurality of power supply paths. The first fixing apparatus includes a plurality of first heating elements grouped into a plurality of groups, and a number of the plurality of groups is equal to a number of the plurality of power supply paths. The second fixing apparatus includes at least one second heating element grouped into at least one group whose number is smaller than the number of the power supply paths. In a state where the second fixing apparatus is attached to the image forming apparatus, a power supply path of the plurality of power supply paths in which a power line has a largest allowable current value is electrically connected with the second heating element.

According to one embodiment, the power converter includes a power conversion circuit and a power outage detection circuit. The power converter includes a power conversion circuit including an isolation transformer including a primary winding, a secondary winding electromagnetically coupled to the primary winding, and an auxiliary winding, a first DC voltage source which outputs DC power with an input AC power, a switching circuit which switches connection between the first DC voltage source and the primary winding, an auxiliary power supply circuit which supplies the DC power to the switching circuit using a power generated in the auxiliary winding, a second DC voltage source which rectifies and smooths the power generated in the secondary winding and outputs DC power to a load.

A bias circuit includes one or more first Zener diodes electrically coupled to a member provided in a replacement unit, the one or more first Zener diodes being coupled in series. When the replacement unit is removably attached to a main unit including a power supply that has one or more second Zener diodes coupled in series, the first Zener diodes are electrically coupled to the second Zener diodes in parallel to change a bias voltage to be applied to the member, the bias voltage being supplied by the power supply. A total absolute value of breakdown voltages across the first Zener diodes is lower than a total absolute value of breakdown voltages across the second Zener diodes.

A power supply apparatus includes a predetermined mode in which power consumption is suppressed and a normal mode in which the power consumption is not suppressed and which supplies power to an apparatus. the power supply apparatus includes the following, a cutting member which cuts off supply of the power to a fixing heater; a noise removing member which is positioned in a later stage of the cutting member and which removes noise in the power; and a controller which controls the cutting member. The controller controls the cutting member to cut off supply of the power to the noise removing member in the predetermined mode.

A control portion determines the lengths of time required to raise a plurality of heat generating elements to prescribed start-up completion target temperatures, and when a heat generating element determined to have the longest start-up requirement time among a plurality of heat generating elements is a second heat generating element, and a heat generating element determined to have shorter start-up requirement time than that of the second heat generating element among a plurality of heat generating elements is a first heat generating element, the control portion controls power to be supplied to the first heat generating element by changing a start-up control parameter for the first heat generating element with reference to the start-up performance of the second heat generating element.

A bias circuit includes one or more first Zener diodes electrically coupled to a member provided in a replacement unit, the one or more first Zener diodes being coupled in series. When the replacement unit is removably attached to a main unit including a power supply that has one or more second Zener diodes coupled in series, the first Zener diodes are electrically coupled to the second Zener diodes in parallel to change a bias voltage to be applied to the member, the bias voltage being supplied by the power supply. A total absolute value of breakdown voltages across the first Zener diodes is lower than a total absolute value of breakdown voltages across the second Zener diodes.

An image forming apparatus includes a power controller that starts an examination mode by an external operation. The examination mode detects a temperature-resistance property of a resistive heat generator. The power controller supplies power at a predetermined power duty cycle to the resistive heat generator, The power controller obtains the power supplied to the resistive heat generator and a change in a temperature of the resistive heat generator, that is detected by a temperature detector, while the power controller supplies the power at the predetermined power duty cycle to the resistive heat generator. The power controller calculates the temperature-resistance property of the resistive heat generator based on the power and the change in the temperature that are obtained. The power controller adjusts a power duty cycle at which the power is supplied to the resistive heat generator based on the temperature-resistance property.