| 摘要 |
PURPOSE:To detect an object intercepting or reflecting light accurately by switching the load resistance of a phototransistor (PT) and a power source voltage according to the output voltage of the PT to hamper effect of disturbed light. CONSTITUTION:To the power source voltage VCCH is higher substantially than the power source voltage VCCL. When the output voltage of a PT2 is higher than the voltage VCH of the non-inversion input of a comparator 14, an analog switch 13 is turned ON by the output of an inverter 15 and a load resistance 11 is connected to the PT2 to apply a low voltage VCCL thereto. On the other hand, when the voltage of the PT2 is lower than the voltage VCH, an analog switch 12 is turned ON and a load resistance 10 is connected to the PT2 to apply the voltage VCCH. The load line of the circuit forms a broken line 16 in which the output voltage at the broken point indicates the voltage VCH. So to speak, the output voltages V01-V03 has a sufficient room for the threshold voltage VTH of a binary-coding circuit 4 with respect to light inputs P11-P13. Thus, normal operation can be done even with the light input P13 thereby hampering effect of disturbed light. |
