| 摘要 |
PURPOSE:To eliminate the need for the preparation of other temperature compensation element by using a bias current conversion value of a standby light emitting element as a reference signal for measuring the progressing degree of deterioration. CONSTITUTION:An output voltage of a current-voltage conversion circuit 11 being the result of converting a bias current 1'B of an LD 8 of a standby system is used for a reference voltage for measuring the degree of progress of deterioration. The reference signal includes the correction of a reference voltage against temperature fluctuation at all times. The reference signal is subtracted from the conversion voltage of a bias current of the LD 4 increased by the repetition of lighting drive by the subtraction circuit 14. The difference signal is compared with a deterioration discrimination level VS and when the value exceeds the level VS, an output signal is generated from a comparator circuit 16. The said output signal is used for the changeover from the active to the standby system in a changeover circuit 18. Thus, it is not required to provide a temperature compensation element separately. |
