Compared to general transistors, general-purpose photocouplers that receive light with a phototransistor are operated in so-called "floating" state in which the base is completely free of circuit wires, so that noise may occur in unexpected situations. The following phenomena may occur.
(1) Noise generated by fluctuations in potential differences between the light emitting side and the light receiving side
(2) Noise generated at rising of light-receiving side power supply
(1) Addition of circuits suppressing sharp fluctuations in potential difference between circuits
(2) Speed down the rising of the power supply, and avoid use of output signal until the voltage has stabilized.
For details, refer to the following URL.
|Photocouplers / Optocouplers|