Patent ID: 8630324

Claim:
A semiconductor laser drive device, comprising: a semiconductor-laser drive element to generate a drive current according to an input control signal to supply the drive current to a semiconductor laser; a control circuit to control the drive current by controlling the semiconductor-laser drive element; and a drive current detection circuit to detect a current value of the drive current supplied to the semiconductor laser and generate a digital control signal representing the detected digital value of the drive current to output, wherein the drive current detection circuit comprises: a proportional current generator to generate a current proportional to the drive current for output as a monitor current; and a D/A converter to generate a current according to the input digital value of the digital control signal for output as a detection current, wherein the drive current detection circuit generates a drive-current detection signal indicating detection of the drive current for output when a predetermined relation between the value of the detection current and the value of the monitor current is established, and wherein the drive current detection circuit comprises a counter that increases or decreases the digital value of the digital control signal input to the D/A converter according to a clock signal to increase or decrease the value of the detection current output from the D/A converter.