| 摘要 |
PURPOSE:To determine exactly the threshold value of the electric current and to contrive to improve the service life and the reliability of a device by a method wherein the reference value of the judgment is changed by detecting the temperature of a semiconductor laser. CONSTITUTION:The semiconductor 1 is provided between the ground point and the minus V electric power source, said semiconductor laser being connected to a transistor 4 for controlling the current which determines the bias current of said laser and a bias current limiting resistor 5 in series. A temperature sensor 2 which detects the laser temperature is provided near the semiconductor laser 1, and one end of it is connected to the ground point and the other end is connected to the minus V electric power source through a resistor 7 and a variable voltage source 3 which sets the judging reference value. Furthermore, connecting points of the temperature sensor 2 and the resistor 7 are connected to one input terminal of a comparator 6, and the connecting points of the transistor 4 and the resistor 3 are connected to other input terminal of comparator 6. The magnitude of voltage between both terminal voltage of the resistor 5 which detects the laser current and the reference voltage VRef which changes with the resistance value of the temperature sensor 2 are compared with the comparator 6, and the life of the semiconductor laser 1 is predicted. |
