| 摘要 |
PURPOSE:To eliminate a fear of the stop without previous notice of the function of a photoelectric switch to improve the reliability of a system by regarding a semiconductor laser as degraded to give an output to the external when the integrals output of the current flowing the laser diode of the semiconductor laser exceeds a prescribed value. CONSTITUTION:If a laser diode LD of an APC circuit 3 is degraded and the optical output falls, the voltage between both ends of a resistance R4 falls in accordance with the current flowing to a photo transistor PD is reduced, and the emitter current of a current control transistor TR2, namely, the driving current of the laser diode LD is increased. Then, since the voltage between both ends of the resistance R2 is increased, it is inverted and amplified by a TR4 and the integral output of an integrating circuit is reduced gradually. When it level is lower than the threshold level determined by a Zener diode ZD and the voltage between the base and the emitter of a TR5, the TR5 is turned off and its collector voltage goes to the high level. Thus, the degradation of the laser diode LD is detected on a basis of this output.
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