| 摘要 |
PURPOSE:To obtain excellent print quality by varying the light emission intensity of a light emission source by an intensity control pat according to specified resolution, and varying an apparent spot diameter and setting an optical spot diameter within a constant range. CONSTITUTION:When an intensity specifying signal SD indicates that a high resolution mode is off, a transistor (TR) Q1 turns off and a modulated signal LEDS, on the other hand, is inputted to a modulating circuit 210 to drive a laser diode 12a with a driving current obtained by superposing the modulated signal upon a bias current ic. Namely, the potential is raised almost to a threshold value T with the bias current ic and the diode is driven with the current having the modulated signl LEDS superposed thereupon. When the optical spot diameter is set within the range shown by an expression, a sufficient voltage margin is obtained even if the intensity is varied by switching the resolution, and excellent print quality is obtained even if a photosensitive body varies in potential. Bleeding due to a scatter is minimized at such an electrostatic charging potential at which the print density is small, and large with high print density and small with low resolution, but when the resolutio is low, unit line width is large and there is no apparent variation. |
