| 摘要 |
PURPOSE:To prevent the flow of overcurrent to a semiconductor laser at the time of superposition of amplitude noises or surges by a method wherein a Zener diode having a fixed Zener voltage is connected to the base of a laser drive transistor. CONSTITUTION:The semiconductor laser 2 is connected to the collector circuit of the transistor TR1, and then the semiconductor layer 2 is driven at a constant output by connecting the base of the TR1 to the constant voltage EB. For the purpose of protection of the laser 2 in such a circuit, the Zener diode 4 is connected to the base of the TR1. The Zener voltage VE of this diode 4 is designed approximately equal to the constant voltage EB. By such a circuit, when noises or surges superpose on the base voltage EB, and then the value exceeds VE, the excess part thereof is absorbed to the diode 4. Therefore, the flow of overcurrent to the semiconductor laser can be prevented at the time of superposition of amplitude noises of surges. |
