| 摘要 |
PROBLEM TO BE SOLVED: To reduce an unwanted power consumption with no degradation in high speed which is required for switching of outgoing light quantity of a semiconductor laser. SOLUTION: An outgoing light quantity (b) of a semiconductor laser 2 is detected with a photodetector 3, coverted into a voltage signal (d), and calculated with a reference voltage signal by a differential amplifier 5 before fedback to a current source 1. A voltage signal (h) representing a forward voltage (operation voltage) of the semiconductor laser 2 is compared to a reference voltage signal (i) by a comparator 10, and imputed in a DC/DC converter 13. DC/DC converter 13 changes an output voltage to two stages according to an input signal (k). If, for example, the forward voltage is lower than the reference voltage, a voltage which is the lower of the two stages is outputted. The control speed of the control system fedback from the differential amplifier 5 is sufficiently fast even when the DC/DC converter 13 switches an output voltage, so no fluctuation in outgoing light quantity takes place. With this configuration, a reactive voltage at a power source 1 is suppressed low for a low power consumption.
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