| 摘要 |
PURPOSE:To prevent the deterioration and breakdown of a laser diode due to excessive current by a method wherein a protective device, with which current will be suppressed or cut off in accordance with the intensity of the current running on the laser diode, is provided. CONSTITUTION:When a trouble occurred between the emitter and the collector on a driver transistor 6 due to some reason and it developed into a short-circuit, the current flowing to a diode 1 is restricted because the current determined by the Zener voltage V2 of a Zener diode 14, the forward voltage of a laser diode 1 and the resistance value of a resistor 10 runs to the laser diode 1 and the current in excess runs to the Zener diode 14. As a result, the deterioration and the breakdown of the diode 1 can be prevented by properly selecting the Zener voltage of the Zener diode 14 and the resistance value of the resistor 10. |
