| 摘要 |
PROBLEM TO BE SOLVED: To detect a semiconductor laser not illuminating among a plurality of series-connected semiconductor lasers, without causing a circuit to become complex, and so on. SOLUTION: A light output change value measured at a point "t=0" of time is stored as a reference light output change value ΔW0. It is determined whether there is a difference between the stored reference light output change value ΔW0 and a light output change value ΔW measured, when a power source is turned on, this time. At this time, even after usage time elapses, the light output change value ΔW measured this time is equal to the reference light output change value ΔW0 as long as the first to third semiconductor lasers are all turned on. However, if any of the first to third semiconductor lasers is not turned on at "t=1" time, the light output change value ΔW becomes smaller than the reference light output change value ΔW0 so that "ΔW0≠ΔW" is satisfied. Hence, the number of semiconductor lasers among the three series-connected semiconductor lasers which are not turned on, can be calculated from the difference value "ΔW0-ΔW". COPYRIGHT: (C)2011,JPO&INPIT
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