A power supply device includes a DC power supply circuit to output a DC voltage, an AC power supply circuit to generate an AC voltage, and a power supply control circuit to control the DC power supply circuit and the AC power supply circuit. The AC power supply circuit outputs a superimposed voltage in which the DC voltage is superimposed with the AC voltage. The power supply control circuit controls the DC power supply circuit to output the DC voltage according to a DC output value corresponding to the AC voltage.

An image forming apparatus including an image bearer, a transfer-bias power source, an environment sensor, and a controller. The controller controls the transfer-bias power source to change the DC component and the AC component, according to the at least one of temperature and humidity detected by the environment sensor and a duty of the transfer bias. The duty is A/(A+B)×100[%] where A denotes an area on a return-directional side to move toner from the recording sheet back to the image bearer, relative to a center value (Voff) of a maximum value and a minimum value of the transfer bias in one cycle of a waveform of the transfer bias, and B denotes an area on a transfer-directional side to move the toner from the image bearer to the recording sheet, relative to the center value (Voff) in the one cycle.

An image forming apparatus including an image bearer; a nip forming member, a nip width changing device, a power source; and a controller. The controller switches between a first mode and a second mode according to a predetermined condition. In the first mode, a duty of the transfer bias is a first duty and a width of a transfer nip is a first width. In the second mode, the duty of the transfer bias is a second duty lower than the first duty and the width of the transfer nip is a second width greater than the first width. The duty is (T−Tt)/T×100% where T denotes one cycle of the transfer bias, and Tt denotes a time period, in which the transfer bias is on a transfer-directional side relative to a time-averaged value of the transfer bias, in the one cycle.

An image forming apparatus includes an image bearer, an image forming device to form a toner image on the image bearer with toner, a power source to output a bias to transfer the toner image onto a recording medium, and control circuitry. The circuitry controls the power source to decrease a peak-to-peak voltage of the bias in response to increase in at least one of temperature and humidity, when a time-averaged voltage of the bias is on a transfer side of transferring the toner to the recording medium, from a median value of maximum and minimum voltages of the bias. The circuitry controls the power source to increase the peak-to-peak voltage of the bias in response to increase in at least one of temperature and humidity, when the time-averaged voltage of the bias is on a return side of returning the toner to the image bearer, from the median value.

In an image forming apparatus including a power source for forming a secondary-transfer electric field at a secondary-transfer position and for forming a primary-transfer electric field at a primary-transfer position by applying a voltage to a transfer member to pass a current through a constant-voltage element, a potential of an image portion is controlled depending on a detection result of a detecting member.

An image forming apparatus (1) includes image bearing members (31), transfer members (52), and a power supply section (57). The image bearing members (31) each bear one of toner images in different colors from one another. The transfer members (52) are located opposite to the image bearing members (31). The power supply section (57) charges the transfer members (52). Through the above, the toner images on the respective image bearing members (31) are transferred to a moving transfer target (51). The power supply section (57) includes a power supply device (58 or 58a) connected to at least two of the transfer members (52). The transfer members (52) connected to the power supply device (58 or 58a) are each located at a position shifted upstream or downstream of a corresponding one of the image bearing members (31) in a moving direction (X) of the transfer target (51).

An image forming apparatus (1) includes photosensitive drums (41y, 41c, 41m, and 41k), static eliminators (45y, 45c, 45m, and 45k), transfer rollers (54y, 54c, 54m, and 54k), a power source (55a) for transfer, and load resistors (47y, 47c, 47m, and 47k). The static eliminators (45y, 45c, and 45m) perform static elimination on adjacently upstream or downstream photosensitive drums (41y, 41c, 41m, and 41k) in a movement direction of a transfer target. The transfer rollers (54y, 54c, 54m, and 54k) are disposed opposite to the respective photosensitive drums (41y, 41c, 41m, and 41k). The power source (55a) for transfer applies potential to the transfer rollers (54y, 54c, 54m, and 54k). The load resistors (57y, 57c, 57m, and 57k) are respectively connected in parallel to one another and in series between the power source (55a) for transfer and the respective transfer rollers (54y, 54c, 54m, and 54k).

A transfer apparatus includes a transfer unit, a detector, a supplying unit, and a controller. The transfer unit transfers a toner image onto an object onto which transfer is to be performed. The detector detects humidity. The supplying unit includes a constant voltage supplying unit that supplies a transfer voltage that is a constant voltage to the transfer unit, and a constant current supplying unit that supplies a transfer current that is a constant current to the transfer unit. The controller controls the supplying unit such that the transfer voltage is supplied from the constant voltage supplying unit to the transfer unit when transfer is performed in a case where the detected humidity is not greater than a threshold, and the transfer current is supplied from the constant current supplying unit to the transfer unit when transfer is performed in a case where the detected humidity exceeds the threshold.

There is provided an image forming apparatus including: an intermediate transfer belt; a photosensitive drum; a primary transfer member; a secondary transfer member; a first backup member; a first power supply electrically connected to the primary transfer member and to the secondary transfer member; and a first resistor electrically connected to the first power supply and to the primary transfer member. A first current route, in which the first resistor, the primary transfer member, and the photosensitive drum are connected in series in that order, is connected to the first power supply and to a basis potential. A second current route, in which the secondary transfer member and the first backup member are connected in series, is connected to the first power supply and to the basis potential. The first current route is connected in parallel to the second current route.

An image forming apparatus includes a photosensitive member, a transfer member, a transfer power source, and a control unit. At a start time of a start-up operation at the time of starting an image forming operation, on the surface of the photosensitive member, a first position coincides with a charging position, and a third position coincides with a transfer position. During a period in which an area on the photosensitive member located between the first position and the third position in a rotation direction of the photosensitive member passes the transfer position, the control unit performs control of applying a first voltage having the same polarity as a normal charging polarity of toner to the transfer member by the transfer power source, and, at a predetermined timing, changing a voltage from the first voltage to a second voltage having an absolute value less than that of the first voltage.