| 摘要 |
PURPOSE:To prevent the laser power from exceeding an allowable value by detecting that the monitor signal of a laser back beam is not returned and turning off the laser before the laser outputs an abnormal power. CONSTITUTION:The dark current of a solar battery 2 used for monitor of the back beam of the laser is detected to discriminate the connection state between an operational amplifier 4 and the solar battery 2 and the operating state of the solar battery 2. When the solar battery is used, the dark current exists, and the dark current is conducted from the solar battery 2 to the operational amplifier 4 even if the laser is turned off. As the result, a voltage V3 corresponding to the dark current is generated as an offset in the output of the operational amplifier 4. However, the voltage V3 is minute, and an abnormality detection signal 16 goes to the high level when this voltage is amplified by an amplifying circuit 15 and is compared by a comparator 14. If the solar battery 2 is broken, the dark current is not conducted and the abnormality detection signal 16 goes to the low level. Consequently, the abnormal state is detected with the laser turned off, and a laser turning-on command 12 is turned off after this detection. |
