| 摘要 |
PURPOSE:To enable a laser diode drive circuit to be simplified in circuit structure and manufactured at a low cost by a method wherein a pull-up resistor and an output terminal of an open collector are connected to the base of a transistor, and a voltage applied to the pull-up resistor is set variable. CONSTITUTION:A voltage applied to a pull-up resistor 7 is made variable through a photodiode 3, an APC control circuit 10, and a voltage variable circuit 8, whereby a transistor 5 becomes apparently variable in operation level, therefore a laser diode 2 can be changed in duty of optical output. For instance, in a write control circuit 9, the emitted light volume of the laser diode 2 is monitored by a photodiode 3 when pulses of 50% ON/OFF are inputted into a video signal/VIDEO, and the APC control circuit 10 feeds back its output to the voltage variable circuit 8 through the intermediary of a control wire 12 so as to set the average emission light volume of the diode 2 to 50% of its emission peak, whereby the laser diode 2 can be kept constant in duty of optical output. |
