| 摘要 |
PURPOSE:To control a driving current and to obtain a stable output light by providing an operational amplifier for converting the base potential of a PNP transistor in response to the variation in photocurrent detected by light detecting means. CONSTITUTION:A PNP transistor Tr2 for supplying a drive current to a light source 1 is provided. The driving current is controlled by an operational amplifier 9, which has one input set at a predetermined reference voltage and another input for receiving the difference between the photocurrent detected by light detecting means 7 and a bias current. The amplifier converts the differential current to a voltage for controlling the base potential of a PNP transistor Tr2 so that the base potential of the transistor Tr2 varies with a variation in the photocurrent. Thus, the variation in output light depending on the temperature characteristics of a control/drive circuit and the light source is suppressed, and stabilized light output is obtained. |
