| 摘要 |
PURPOSE:To obtain a recording picture with high quality by detecting luminous intensity of a laser beam by a photodetector at the stand-by mode in a laser printer, storing it in a storage means and controlling laser beam power with an output signal of a storage means at the print mode. CONSTITUTION:A comparator COMP2 compares an output signal of a peak hold circuit pH with a reference voltage Vref and outputs its difference signal to a driver DR. The gain of the driver DR is controlled by an output signal of the comparator COMP2 so as to control the power of laser beam to a constant value. The control signal goes to a low level at the print mode, a field effect transistor (TR) FET is turned off and a feedback resistance of an operational amplifier OP becomes a resistor R1 only. The output signal of the operational amplifier OP is binary-coded by a threshold voltage from a power supply E1 at the comparator COMP and becomes a synchronizing signal SYNC. An analog switch SW2 is turned off in this case, the laser beam power is made constant and a recording picture with good quality is obtained against deterioration in a laser tube or the like.
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