| 摘要 |
PURPOSE:To prevent deterioration in waveform of optical output, by controlling peak current flowing through a light-emitting element to be fixed even if temperature is varied while enabling a driving transistor to perform reliable switching operation. CONSTITUTION:A bias voltage between the gate and source of a field-effect transistor(FET) 2 driving a light-emitting element 3 by a control voltage generated by a voltage control section 7 is controlled, based on a value obtained by a current variation detecting section 5 detecting variation in current flowing through the light-emitting element 3 and a value obtained by a marking ratio variation detecting section 6 detecting variation in marking ratio of input pulses. Accordingly, peak current of the light-emitting element 3 which would be varied in association with variation in temperature is controlled to be fixed and the FET 2 can perform its switching operation reliably. Further, even if the marking ratio of input pulses is varied, the peak current flowing through the light- emitting element 3 can be controlled to be fixed. In this manner, no deterioration is caused in waveform of optical output. |
