LM317 Vin-Vout < 3V in constant current source

crutschow said:

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.

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