| 摘要 |
PURPOSE:To alarm the degradation of a laser diode accurately, by providing a means which monitors the driving current of the laser diode to make the result one input of a comparing circuit, another input of a storage circuit, and a coefficient discriminating circuit. CONSTITUTION:A monitoring circuit is constituted with said means which inputs the monitor result to one input of the comparing circuit, a storage circuit MEM which stores preliminarily the temperature characteristic of the driving current and outputs driving current information corresponding to the input of a temperature sensor THSEN, and a coefficient setting circuit COEF which generates a prescribed reference voltage Vr for alarm on a basis of driving current information and inputs it to the other input of the comparing circuit COMP. A voltage Va, which is proportional to an actual LD driving current detected by a current detecting resistance R and a current detecting circuit CURDET and can be applied to the circuit COMP, and the voltage Vr generated by the sensor THSEN are inputted to the circuit COMP as outputs of the circuit COEF. The circuit COMP compares both voltages with each other; and if the voltage Va exceeds the voltage Vr, an alarm output ALMOUT is generated. |
