Developing device, image forming apparatus, and method for controlling developing device

摘要

A developing device includes a developing roller, a magnetic roller, a capacitor, a transformer, and a switching portion. The magnetic roller supplies toner to the developing roller or takes off the toner from the same. The capacitor is connected to a primary of the transformer, and the developing roller is connected to a secondary of the same. During a period while the voltage between electrodes of the capacitor is changing, the switching portion changes the duty ratio in a predetermined second time slot in which current flowing in the switching portion is smaller than that flowing in a first time slot.

主权项

1. A developing device comprising:
a developing roller which carries toner and is disposed to be opposed to a photosensitive drum; a magnetic roller disposed to be opposed to the developing roller so that the magnetic brush supplies the toner to the developing roller and takes off the toner from the developing roller; a capacitor; a transformer having a primary connected to the capacitor and a secondary which outputs an alternating voltage to be applied to the developing roller; and a switching portion including a control signal generating portion for generating a control signal, and a switching element connected to the capacitor so as to make and break current to a serial circuit of the capacitor and the transformer based on the control signal, wherein when the switching portion changes the duty ratio of the control signal step by step in a plurality of times toward a target duty ratio in a period after the change of the duty ratio in which the voltage between electrodes of the capacitor is changing, the switching portion changes the duty ratio in a predetermined second time slot in which current flowing in the switching portion is smaller than that flowing in a predetermined first time slot; wherein, the predetermined first time slot is a time slot in which the voltage between electrodes of the capacitor is smaller than a median of a fluctuation range, the predetermined second time slot is a time slot in which the voltage between electrodes of the capacitor is the median of the fluctuation range or higher, and the switching portion changes the duty ratio of the control signal in the second time slot.