| 摘要 |
PROBLEM TO BE SOLVED: To control the drive current of an LD so that the light quantity of the LD becomes constant, when a power source is turned on by prolonging the active section of a first sampling signal after the power source is turned on and shortening those of a second and subsequent signals. SOLUTION: When the power source is turned on, a signal outputted from a voltage detector 21 is switched from L to H. The signal outputted from the detector 21 is applied to a one-shot multivibrator 22, and a signal outputted from the vibrator 22 is applied to the input terminal of an inverter 23 and one input terminal of an AND gate 25. Then, a signal outputted from the inverter 23 is applied to one input terminal of an AND gate 24, and a timer signal T4 having comparatively short pulse width T4 is applied to the other input terminal of the gate 24. Moreover, a timer signal T3, having comparatively long pulse width T3, is applied to the other input terminal of the gate 25. Then, respective signals outputted from the gates 24 and 25 are applied to an OR gate 26.
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