An image forming apparatus executes processing for calculating a complex number of a discharge current waveform which is a discharge current component of a current waveform in discharge based on a first complex number at an analyzing frequency near a charging frequency of a current waveform in non-discharge, a second complex number at the analyzing frequency of the current waveform in non-discharge, a third complex number at an analyzing frequency of the current waveform in discharge, and a fourth complex number at the analyzing frequency of the current waveform in discharge, and then for determining an AC voltage value of a charging voltage during image formation based on a calculation result of the complex number of the discharge current waveform. The controller controls a power supply portion to apply, to the charging member, the charging voltage including an AC voltage component with the determined value.

A control circuit of an image forming apparatus outputs a pulse signal. A clock signal generation circuit generates a clock signal, based on the pulse signal. A pulse signal conversion circuit generates a pulse conversion control signal of a voltage value associated with a duty ratio of the pulse signal. An AC voltage generation circuit generates an AC voltage of a frequency based on the clock signal. Either the AC voltage generation circuit or a DC voltage generation circuit generates a voltage whose amplitude or voltage value increases as a voltage value of the received pulse conversion control signal increases, and whose amplitude or voltage value decreases as a voltage value of the pulse conversion control signal decreases.

An image forming apparatus is configured to control a generation circuit to modulate a DC component of a developing voltage based on a first correction component such that a density unevenness is reduced. The image forming apparatus is further configured to restrict the first correction component for modulating the DC component of the developing voltage such that fogging of toner that may occur on a non-exposure region which is not exposed by an exposure unit and adhesion to a photosensitive member of carrier included in a developer are reduced.

A high-voltage power supply includes: a first high-voltage output circuit having a first output connected to a first load, and a second output, and capable of outputting a first voltage having a first polarity to the first load; a voltage clamping element connected to the second output and configured to clamp a voltage at the second output to a second voltage having a second polarity opposite to the first polarity; a second high-voltage output circuit having a third output connected to the second output and a fourth output, and capable of outputting a third voltage having the first polarity; and an output circuit connected to the fourth output and a second load, and configured to produce a voltage having the first polarity and a voltage having the second polarity using the third voltage and a voltage derived from the second voltage and output the produced voltages to the second load.

An image forming apparatus including a control unit configured to execute a first mode and a second mode of forming images on first through third image bearing members. In the first mode, a toner image is formed on a third image bearing member without having toner images formed on first and second image bearing members in a state where the first through third image bearing members are abutted against an intermediate transfer body. In the first mode, the control unit controls at least a first charging device such that a primary transfer contrast in a first primary transfer portion is set equal to or greater than a discharge starting voltage, and applies an AC voltage to a second charging device such that a discharge current having a current quantity smaller than that in the second mode.

A coil spring includes a resilient portion having a first diameter defined by a first central axis that is hypothetical and an end coil abutting on one end of the resilient portion in an axial direction of the resilient portion. The end coil has a second diameter defined by a second central axis that is hypothetical and shifted from the first central axis of the resilient portion in parallelism with the first central axis of the resilient portion by a predetermined shift amount. A coupler has a first width that is smaller than the first diameter of the resilient portion and greater than a second width obtained by subtracting the predetermined shift amount from the first diameter of the resilient portion. The coupler is inserted into the end coil to secure the end coil to the coupler.

A half bridge circuit of a class-D amplifier outputs a voltage in accordance with switching of a first switching element and of a second switching element, to a load. A high side gate drive circuit and a low side gate drive circuit respectively drive the first and second switching elements. A bootstrap capacitor connected between the high side gate drive circuit and an output terminal of the half bridge circuit is charged by a charging current from a second direct-current power supply while the first switching element is off. An inductance component for noise suppression, and a voltage limit element that is connected in parallel with the inductance component and is for limiting a voltage that occurs at the inductance component are provided on a path in which the charging current flows.

An image forming apparatus includes a rotatable photosensitive member (drum), a first corona charger, a second corona charger, an image forming portion, a voltage applying portion, a surface potential detecting portion, a controller. The controller determines a condition of voltages applied to the first and second corona chargers during image formation, by setting a first voltage condition for the first corona charger so that the surface potential of the drum is a second potential lower in absolute value than the first potential in a state in which the first corona charger operates, and the second corona charger does not operates, and then by setting a second voltage condition for the second corona charger so that the surface potential of the drum is the first potential in a state in which the first corona charger operates under the first voltage condition, and the second corona charger operates.

A power supply applies a first charged voltage to a charging section disposed near an image carrier during a predetermined process and applies second charged voltages sequentially to the charging section in obtaining a predetermined peak-to-peak voltage value for an alternating-current voltage of the first charged voltage. Each of the second charged voltages includes an alternating-current voltage having a peak-to-peak voltage value varying between a forward discharge range and a back discharge range. A current sensing section senses the alternating-current running through the charging section upon application of each of the second charged voltages. A control section derives a first approximation function and a second approximation function on the basis of the alternating-current values sensed by the current sensing section and sets a peak-to-peak voltage value as the predetermined peak-to-peak voltage through a difference function representing a difference value between the first approximation function and the second approximation function.

An image forming apparatus includes: an image carrier having a first rotation axle, a charging roller having a second rotation axle, a conductive member to contact a surface of the image carrier, a gap size acquisition device, and a gap adjustment device. The charging roller is disposed adjacent to the image carrier in a non-contact manner across a gap to charge the image carrier. The gap size acquisition device acquires a size of the gap. The gap adjustment device adjusts a distance between the first rotation axle and the second rotation axle based on information from the gap size acquisition device to maintain the size of the gap within a predetermined range.