TL431A issue in voltage
This is an odd use of a TL431, which normally used as a voltage reference. In your circuit, the output phototransistor will be ON when the input (the righthand "A N"?) is greater than the TL431 reference, nominally 2.5V, assuming R145 is a sensible value. (Showing the values of the resistors would help greatly.) I suspect you need a rail-to-rail opamp as a comparator, plus a 4.7V reference (which could be a TL431).