| 摘要 |
PURPOSE:To prevent inputs of overcurrents and surge currents to a semiconductor laser, and to avoid the breakage of the semiconductor laser by mounting a protective circuit at an input stage. CONSTITUTION:In a semiconductor laser drive circuit provided with a semiconductor laser 13 and a P-I-N photodiode 14, resistors 1, 2 for setting the base voltage of a transistor 3 at an input stage are selected to fixed values under the state in which both positive and negative power supplies are inputted to both (+)and (-) terminals. When negative voltage is made higher than a first set value for some reason in the circuit, the transistor 3 is brought to an ON state, and potential at a point B drops. Consequently, a protective circuit functions even when negative voltage rises, and breakdown voltage is not applied to the semiconductor laser 13. Surge currents do not flow transiently through the semiconductor laser 13 because operating currents are fed to the semiconductor 13 and the state of constant currents is brought by changing the point B into positive potential after an APC circuit is prepared so as to normally operate in the drive circuit. |
