This is my first time working with an optocoupler and I'm trying to find the right resistors for a zero crossing detector circuit that has a 4N25 optocoupler, but the values I've calculated are not giving the expected result for the circuit.
For the 4N25, I've used a forward voltage of 1.3V, forward current of 50mA,and a CTR of at least 20%.
If VCE = 0.2V, and IcMax = 50mA R2 = 9.8V/IcMax R2 = 196 ohm
With CTR of 20%, the forward current is: If = Ic - Ic.0,2
If = 40mA
Then for R1: R1 = (Vp - 1.4V - Vf)/If
R1 = 356.75 ohm
But I'm not getting the cut-saturation state as output in the VCE as it goes from 8.5V to 10V :
Are the calculations wrong?, is there something else I should consider ?