Patent ID: 8606131

Claim:
A charging apparatus comprising: a charging member contacting an image bearing member to charge the image bearing member; an applying device configured to apply to said charging member a charging bias voltage including a DC voltage component and an AC voltage component; an AC detector for detecting an AC current flowing to said charging member; a DC detector for detecting a DC current flowing to said charging member; wherein the charging apparatus is operable in a mode for determining a peak-to-peak voltage of the AC voltage to be applied to said charging member during an image forming operation on the basis of a first detection result detected by said AC detector when at least an AC voltage having a first peak-to-peak voltage is applied to said charging member and a second detection result detected by said AC detector when an AC voltage having a second peak-to-peak voltage larger than the first peak-to-peak voltage is applied to said charging member; and a controller for controlling the first peak-to-peak voltage during the operation in the mode so as to be smaller than a peak-to-peak voltage Vo of the AC voltage at which a detection result of said DC detector starts saturating when the peak-to-peak voltage of the AC voltage applied to said charging member is increased, and for controlling the second peak-to-peak voltage during the operation in the mode so as to be larger than Vo.