| 摘要 |
PURPOSE:To detect the intensity of light of laser beam on a photosensitive plane easily by switching the gain of a photodetector for picture write synchronism of laser beam so as to obtain an electric signal proportional to the intensity of light of laser beam. CONSTITUTION:The beam irradiated from the laser 1 scans optically a photosensitive drum 12 through an optical system. A photodetector PD13 is provided at the vicinity at the outside of the picture recording area of the drum 12, and every time the laser beam applies main scanning on the drum 12, a pulse signal is outputted from the photodetector 13, and the output signal is used as a periodic signal for the picture write via an operational amplifier OP-AMP and a comparator COMP. A control signal CS is applied to an FET provided to a feedback resistor RF of the OP-AMP so as to switch the gain to a gain where the output of the OP-AMP is not saturated, the output of the OP-AMP is held 14 in terms of peak value and this output drives 15 a meter 16. |
