| 摘要 |
PURPOSE:To make it possible to control the quantity of emitted light at a state close to a specified value in correspondence with the characteristics of a light source, by performing feedback control based on the sum of the output voltage of a light receiving element and a constant voltage each having a specified ratio. CONSTITUTION:Light emitted from an LED 1 is propagated through an optical fiber 4 and optical measurement is performed. Said emitted light is received by a photodiode 11 of a monitoring light receiving element. The output voltage Vm of the received light is made to be the voltage having a specified ratio by a voltage divider 13 through a sample and hold circuit 12. Meanwhile a constant voltage Vc is also made to have a specified ratio by a voltage divider 14 and added to the output voltage of the voltage divider 13 by an adder 15. The added voltage is made to be a feedback voltage, and the light emission of the LED 1 is controlled. The quantity of the light emission of the LED 1 can be controlled in a state C, which is close to a specified value between a case A, wherein the LED 1 is driven by a constant current, and a case B, wherein the quantity of light is decreased conversely with the temperature increase due to the increase in the quantity of light based on the feedback control, by which the difference between the monitoring voltage and the reference value becomes zero. |
