I have an input of pulse width 5 ms and which is fed to a Buffer IC and then the output of the buffer is FED to an opto isolator whose collector is pulled with a pull up of 7.5k resistor with an 24 V source. When no load is connected the output is fine but when connected to a load (PLC input pin) The output drops to 10V.
We increased the pull up to 15K the output is the same.
The opto used here is a 4N35
Please suggest some points to TAP on and a solution for the same.