In HCNR200 Datasheet, the page 11, figure 13-A, there is a sample that confused me. In this sample, the Vin is applied to the inverting input and if the electric current passes through PD1, PD1 voltage goes to zero and finally when PD1 voltage reached to zero, the voltage on inverting input is around zero, but a bit more than non-inverting input voltage. So, how does op-amp output go to higher than zero and adjust the current of LED? And for right side op-amp, how does op-amp output go to more than zero while its non-inverting input is connected to ground and inverting input is going to higher than it?
*Op-Amps are powered by a single supply.