| 摘要 |
PURPOSE:To prevent the flowing of large currents through a semiconductor laser, and to ensure stability and reliability by mounting an overcurrent detecting circuit and a current cut-off circuit to a driving circuit for the semiconductor laser. CONSTITUTION:A driving circuit 10 is operated normally and a beam output from a semiconductor laser 1 is kept constant for a time T1. When an insufficient state is still brought even when DC driving currents Idc exceed threshold currents Ith for some cause at a time TA, DC driving currents Ids for the semiconductor laser 1 continuously increase, and the beam output rapidly augments. When driving currents for the semiconductor laser 1 exceed limit currents at a time TB, however, output voltage from an error amplifying circuit 9 exceeds the limit voltage of a comparator 11, thus operating a current cut-off circuit 12, then cutting off the DC driving currents Idc of a DC current source 3. The driving circuit 10 is reset, and driving currents automatically flow through the semiconductor laser 1 again, thus eliminating trouble of which currents flowing through the semiconductor laser 1 are left as they increase on occasional abnormality and on the transition of the making of the power supply, etc. |
