| 摘要 |
PROBLEM TO BE SOLVED: To reduce the effect of a secular change in a transfer rate onto an optical transfer means by connecting 1st and 2nd photocouplers of the same kind to the output of an operational amplifier. SOLUTION: An input voltage Vi is given to an inverting input terminal 50 of an operational amplifier 51, a power supply voltage Vcc connects to ground via a resistor 58 and a phototransistor 53 of a 1st photo coupler 52 and a noninverting input terminal of the operational amplifier 51 is connected to one terminal of the resistor 58. The output of the operational amplifier 51 is connected to ground through a photodiode 56 of a 2nd photo coupler 55 and a photodiode 54 of the 1st photo coupler 52. The photodiode 54 and the phototransistor(TR) 53 form a feedback circuit of the operational amplifier 51. A power supply voltage V at an output connects to ground via the photo TR 57 of the 2nd photo coupler 55 and an output voltage V0 is outputted to an output terminal 61 in response to the output current of the operational amplifier. Since the 1st and 2nd photo couplers have the same characteristic, the effect due to recular change is not caused as a whole. |
