| 摘要 |
An apparatus for producing a bias voltage for use in an electrophotographic copying machine including a developing electrode, which apparatus assures a bias potential of a proper magnitude in response to a variation in the amount of light emitted by a light source of an exposure optical system. The apparatus comprises a transducer for converting the amount of light into a corresponding electrical quantity, and an amplifier for amplifying the electrical quantity. The apparatus also includes a differential amplifier which produces a bias potential corresponding to the variation in the amount of light to which a reference bias potential is added.
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