Image forming apparatus and method of controlling transfer power thereof

An image forming apparatus comprising:

• a humidity sensor to measure humidity;
• a transfer unit configured to transfer an image on a photoreceptor to a transfer medium by a first output voltage;
• a power supply to apply a transfer current with a corresponding voltage to the transfer unit;
• and
• a controller to control the transfer power supplied by the power supply to the transfer unit,
• wherein the controller
• determines a sensing feedback voltage by applying a set sensing current to the transfer unit and measuring the first output voltage of the transfer unit during a time period before the image is transferred to the transfer medium,
• sets a target voltage based on the determined sensing feedback voltage when the humidity measured by the humidity sensor is higher than a set value, and
• controls the power supply to adjust the transfer current to cause the corresponding voltage to reach the target voltage to the transfer unit during a time period in which the image is transferred to the transfer medium.