| 摘要 |
PURPOSE:To simplify circuit constitution and to facilitate control operation by eliminating the need to provide a special discharging means only by adding a grounding resistance and also eliminating the need to output a discharge command signal from a control circuit at every end of the writing of one scanning line. CONSTITUTION:The input side of a switch means which reacts based on the synchronizing signal for position detection of a laser beam is grounded through a resistance R2. Therefore, when the detection voltage of a monitor detector 6 is charged in a capacitor C1 as a holding voltage at every start of beam scanning, the voltage is charged superposed upon the last charging voltage if the current detection voltage is larger than the charging voltage at the time of last scanning and the difference voltage is discharged through the resistance R2 all the time if the current voltage is smaller. The output voltage of a sample holding circuit 20 is utilized as the comparison voltage of a comparator 23 and the reference voltage of the comparator 23 is obtained from another stationary power source, so an accurate difference signal corresponding to the detection voltage is outputted by the comparator 23. Therefore, the driving current of a semiconductor laser 1 is controlled according to the difference signal to stabilize the output of the semiconductor laser 1 more.
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