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 adsorbing member includes a plurality of adsorbing sheets and a plurality of spacers. The plurality of adsorbing sheets adsorb a floating matter. The plurality of spacers are each provided between the adsorbing sheets to form a laminate that the plurality of adsorbing sheets are overlapped via a gap.

A first high-voltage power supply includes a first transformer configured to generate a voltage to be supplied to a first wire of a charger, and a second high-voltage power supply includes a second transformer configured to generate a voltage to be supplied to a second wire of the charger. The first and second high-voltage power supplies respectively drive the first and second transformers in accordance with pulse signals that are supplied from a CPU and that have the same frequency and phase. The first and second high-voltage power supplies respectively supply, to the first and second wires of the charger, voltages generated by driving the first and second transformers.

In a case where a collection mode in which a exposure unit forms a first potential on a photosensitive member and a developing unit collects discharging toner discharged from the developing unit to a position where the first potential is formed is executed, a potential forming unit forms, on an intermediate transfer member, a potential same as a normal charging polarity of toner and an absolute value greater than an absolute value of the first potential, and a charging power supply applies, to a charging member, a voltage having a polarity same as the normal charging polarity and an absolute value greater than an absolute value of the first potential.

An image forming apparatus includes a photosensitive member, a corona charger including a discharging electrode and a grid electrode having a surface layer containing a carbon atom as a main component and configured to electrically charge the photosensitive member under application of a voltage to the discharging electrode and the grid electrode, and an output portion configured to output information on a lifetime of the grid electrode. The output portion outputs the information on the basis of an index value of an amount of use of the grid electrode correlating with a product of a value of a grid current flowing through the grid electrode and a time of flowing of the grid current through the grid electrode.

An image forming apparatus includes a photoconductor, a charging roller for charging the photoconductor, a current sensor for detecting a value of current flowing through the photoconductor or the charging roller as a result of application of voltage to the charging roller, an acquisition sensor for acquiring an environment value representing an environment state inside the image forming apparatus, and a processor configured to estimate a film thickness of the photoconductor, based on a value of current detected by the current sensor when a state in which the environment value falls within a predetermined range continues for a predetermined time or longer.

An image forming apparatus includes an apparatus main body, a conductive member, a contact spring, a hollow cylinder, and a drum unit attachable to and detachable from the apparatus main body. The conductive member is disposed in the drum unit. The contact spring is disposed in the apparatus main body and comes in electrically conductive contact with the conductive member. The hollow cylinder is disposed in the apparatus main body. The contact spring has a contact part and a helical spring part. The contact part is provided on the helical spring part. The contact part is retractable in and out of the hollow cylinder. The helical spring part is contained in the hollow cylinder and urges the contact part in a direction for causing the contact part to protrude from the hollow cylinder. The contact part has a longitudinal shape elongated along an axis of the helical spring part.

After a predetermined period elapses since the start of use of a photosensitive member, if a calculated value calculated from a detection current between a charging unit and a photosensitive member is out of a predetermined range, a determining unit does not perform determination using a currently calculated value and, if the calculated value is within the predetermined range, the determining unit performs determination using the currently calculated value.

A bias power-supply device of an image forming apparatus includes a transformer that includes a first winding and a second winding, and outputs an alternating-current output signal from the second winding when the first winding is supplied with current; a switch circuit that includes a switching element, and supplies the first winding of the transformer with the current by switching the switching element in accordance with a received modulation output signal; and a modulation circuit that receives a frequency setting signal of setting a frequency of the alternating-current output signal and a modulation signal, and generates the modulation output signal having a modulated pulse width. A frequency of the modulation signal and a frequency of the alternating-current output signal are set to cause an interference frequency between the modulation signal and a harmonic of the alternating-current output signal is higher than a predetermined frequency.

An image forming apparatus provided with a charging member to charge a surface of a photoreceptor, includes: a power supply that applies to the charging member a first bias in which an AC voltage is superimposed on a DC voltage or a second bias which is a simple DC voltage; and a hardware processor that causes the power supply to apply the first bias until an amount used of the photoreceptor reaches a predetermined value, and causes the power supply to apply the second bias when the amount used of the photoreceptor reaches the predetermined value.