| 摘要 |
PURPOSE:To prevent input of a feedback signal to driving means of a laser diode by providing a limit controller which outputs a drive signal for driving the driving means when the feedback signal from a feedback controller is a predetermined value or more. CONSTITUTION:A feedback signal of a voltage responsive to the intensity of a laser light L to be detected by a photodetector 8 from a feedback controller 21 is outputted to a limit controller 22. If the feedback signal is larger than a set voltage applied previously to a fourth differential amplifier 32, a drive signal responsive to the difference is output to a driver 7. Thus, since the driver 7 drives a laser diode 6, the output of the light L is maintained constantly. That is, if the feedback signal is higher than the vicinity of a threshold value, a drive threshold value is outputted from a limit setter 22 to the driver 7, and hence the diode 6 is controlled to be driven so that the output of the light L becomes constant by the drive signal. |
