| 摘要 |
PURPOSE:To prevent a carrier from sticking to a photosensitive drum when failures occur by providing a developing bias control part with a developing bias delaying circuit. CONSTITUTION:The title device is provided with a developing bias power source part 20 and the developing bias control part 30. The developing bias delaying circuit 33 is in the control part 30. The circuit 33 consists of a diode D, a condenser C, resistance R and a switching transistor TR. When the failures occur at a timer Tx, the surface potential VDS of a developing sleeve is prevented from stopping by the failures and a developing bias voltage is held at about -450V for a specified time, whereby difference between the developing bias voltage and the surface potential VS of the photosensitive drum is held at 150V. The developing bias delaying circuit 33 delays the change in the surface potential VDS of the developing sleeve for a specified time and holds the change. The surface potential VDS is changed from the time Tx according to a specified time constant and the time constant is set based on the value of the condenser C and the resistance R of the circuit 33. |
