Patent attributes
A developing unit is adapted to an image forming apparatus of an electrophotographic system that has a two component developing agent. The developing unit deposits a thin layer of toner on a developing roller by way of a magnetic brush on a magnetic roller. The toner then is transferred from the developing roller to a photosensitive drum. Developing bias voltages applied to the rollers have DC and AC components. Thus, electric current alternately flows in the magnetic roller and the developing roller to accelerate toner transfer. Sufficient toner is supplied from the magnetic roller to the developing roller, and sufficient toner is recovered from the developing roller to the magnetic roller. This arrangement lowers the amplitude of the AC bias voltage, thereby eliminating an influence on the photosensitive drum. Further, the frequencies of the AC bias voltages are constant. Thus AC bias voltage generating circuits have a low cost.
