I am studying a DC-DC converter circuit design which has PC817 photocoupler in it. I am confused with the way PC817 behaves. My friend says that it is an analog photocoupler. I have tested it myself and it appears to work as digital photocoupler. Here are the test cases and results I got:
For input voltage less than 2V (10k ohm in series with supply), the output is 4.3V.
For input greater than 2V (10k ohm in series with supply), the output drops to zero volts.
For voltages closely around 2V (10k ohm in series with supply) the output varies between zero and 4.3V.
(4.3V is due to voltage sources at output side of IC)
I don't know how it is a analog optocoupler. Can anyone explain exactly how this IC operates?