Patent ID: 8483250
Filing Date: 2013-07-09
Classification: H01S

Abstract:
1. A semiconductor laser driving device that includes a semiconductor laser driven by a driving current which is a combination of a bias current and a switching current and that is capable of automatically controlling a current supplied to the semiconductor laser so that a light amount of the semiconductor laser is substantially equal to a predetermined light amount, the semiconductor laser driving device comprising: a switching current generating circuit unit generating the switching current in accordance with an input switching current setting signal and supplying the generated switching current to the semiconductor laser in accordance with an input control signal; a bias current generating circuit unit generating the bias current in accordance with an input bias current setting voltage and supplying the generated bias current to the semiconductor laser; a control circuit unit detecting an emitted light amount of the semiconductor laser and controlling an operation of the bias current generating circuit unit by generating the bias current setting voltage so that the detected emitted light amount is substantially equal to a desired value; and a deterioration detecting circuit unit detecting a deterioration of the semiconductor laser based on the bias current setting voltage transmitted from the control circuit unit and generating and transmitting a deterioration detecting signal indicating a result of the deterioration detection, wherein the deterioration detecting circuit unit is configured to generate and output the deterioration detecting signal indicating the deterioration detection of the semiconductor laser when the bias current setting voltage based on which the bias current generating circuit unit generates the bias current is equal to or greater than a reference voltage corresponding to a current value obtained by subtracting the switching current from a maximum driving current of the semiconductor laser, wherein the bias current generating circuit unit includes a bias current setting resistor and a first voltage-current converting circuit connected to each other serially between the semiconductor laser and ground voltage, and the first voltage-current converting circuit controls a voltage output to a connection node between the bias current setting resistor and the first voltage-current converting circuit to match the bias current setting voltage and thereby convert the bias current setting voltage into a current flowing through the bias current setting resistor, and wherein a resistance value rbi of the bias current setting resistor is set to match the following equation: