| 摘要 |
PURPOSE:To make a reproduction output and a recording output constant even when a characteristic change takes place in a laser diode by detecting a ratio of a reference constant current to a monitoring current from a prescribed ratio to control a driving current flowing to the laser diode. CONSTITUTION:A monitoring current I2 always keeping a prescribed ratio to a reference constant current I0 flows to a monitoring diode (MD) 2 when a laser diode (LD) 1 gives a prescribed output with a constant current circuit 10 composed of a current mirror circuit 10c whose load is the MD 2. A charac teristic change in the LD 1 is taken place and its output is changed and a monitoring current flowing to the MD 2 is changed and a deviation is generated between the ratio of the I2 to the Io and the prescribed ratio. The deviation is detected by a feedback circuit 20 and the output of the circuit 20 keeps the output of the LD 1 by a driving circuit 30 to have a prescribed ratio. Thus, the reproduction output and the recording output are made constant. |
