LM317 Vin-Vout < 3V in constant current source

Thread Starter


Joined Jun 19, 2018
V+ is the Arduino supply voltage.
So when the Arduino input voltage gets more than a Schottky diode drop above the Arduino supply voltage, the diode starts conducting and clamping the voltage at the level through the resistor.
That should be sufficient to protect the Arduino input.

Similarly if the input voltage tries to go negative, it will be clamped at one Schottky diode drop below ground.
Still trying to understand.
What would be the benefit of this setup compared to a single zener diode to protect the over voltage?
The voltage I need to read and actually interests me to be as accurate as possible is between 0.4V and 3V. As far as I can see, the zener knee will not have an effect on this range.

Can't see where the under voltage could come from.