| 摘要 |
PURPOSE:To suppress the output change of a light receiving element due to various optical causes and stabilize the output signal to obtain releable output by installing a feedback circuit controlling the operation current of a light emitting element through the photoelectric output of the light receiving element between light receiving and light emitting elements. CONSTITUTION:A transistor TR to control operation current is connected to the anode side of a light emitting diode D and the cathode side of the diode D is earthed. A phototransistor PT, light receiving element, is connected to a power source VCC through resistance R4, the potential V4 of a connection part Q between the resistance R1 and PT is taken out as optical output and the optical output is inputted to a comparator COMP whose another input is standard voltage VSO. An operation amplifier OP is installed between the base of TR connected to the diode D in series and the optical output of PT, and a feedback circuit with a time constant circuit composed of a capacitor C and a resistance R6 is connected between the inversion terminal and output terminal of the amplifier OP, controlling the operation current of the diode D and stabilizing the output of PT. |
