Image forming apparatus controlling transfer power source based on detection result of detection unit connected to transfer portion

An image forming apparatus comprising:

• an image bearing member configured to bear a toner image;
• a transfer member configured to be brought into contact with the image bearing member to form a transfer portion and transfer the toner image from the image bearing member onto a transfer medium in the transfer portion;
• a transfer power source configured to apply a voltage to the transfer member;
• a fixing unit situated downstream of the transfer portion in a direction in which the transfer medium is conveyed, the fixing unit including a heating member and a pressing member configured to face the heating member to form the fixing portion, wherein the heating member includes a heating unit situated to face the transfer medium held in the fixing portion and a voltage is applied from an alternating-current power source to the heating unit so that the heating unit heats the transfer medium held in the fixing portion;
• a first detection unit situated between the transfer member and the transfer power source and configured to detect a current flowing in the transfer member;
• and
• a control unit configured to control the transfer power source based on a first detection result input from the first detection unit,
• wherein the control unit determines a first voltage to be applied from the transfer power source to the transfer member in the case of transferring the toner image from the image bearing member onto the transfer medium in the transfer portion, based on a value of the voltage applied from the transfer power source to the transfer member when the control unit controls the transfer power source such that a current of a predetermined value flows to the transfer member while the transfer medium is not held in the transfer portion, and
• wherein in a case of transferring the toner image from the image bearing member onto the transfer medium in the transfer portion, the control unit controls the transfer power source based on a result of a comparison between a frequency obtained from the first detection result and a predetermined frequency range including a frequency of the alternating-current power source.