Patent ID: 6842469

Claim:
A laser driving device for driving a semiconductor laser, comprising: an operating voltage detecting circuit connected to said semiconductor laser for detecting an operating voltage of the semiconductor laser; a voltage converter connected to said operating voltage detecting circuit for converting an input second voltage input from an external power supply into a first voltage greater than the input second voltage on the basis of the detected operating voltage; the input second voltage being the only externally supplied voltage to the laser driving device; control means for generating control signals to control the laser driving device; the control means being powered by the input second voltage; and a laser driving circuit connected to said voltage converter, said semiconductor laser, and said control means for driving the semiconductor laser on the basis of the first voltage from the voltage converter and the control signals from said control means; said operating voltage detecting circuit including a hold circuit for detecting and holding an operating voltage of the semiconductor laser on the basis of a hold control signal and a hold voltage initial value; and wherein the voltage converter adjusts the first voltage converted from the input second voltage on the basis of the held operating voltage.