I'm having a hard time finding a good way to protect a radio module if the voltage regulator fails and injects the battery's input voltage. The module is expensive, so I would like to protect it from voltage above 3.6V.
The module works in 3.3V up to 3.6V, higher voltage can burn it.
The circuit that I thought would solve my problem:
The idea looks to be correct but it doesn't look like you will be supplying the relay enough voltage to activate. So you need to add a stage there. The zener will supply a reference voltage to a comparator or something similar. The output of the comparator will then operate the relay ( possibly off a separate supply ). You might need to add a driver for the comparator to supply enough current for the relay to operate. However, a relay is a bit of clunky solution. It is mechanical, high failure device of its own, maybe too slow to react to protect your circuit. Why not replace the relay with a MOSFET or BJT switch? Also, transients can be removed with some bypass capacitors on your 3.3V regulator.
A mechanical relay will be way too slow to protect electronics.
You could add a regulator in front of the 3.3V regulator, preferably a switching regulator (for efficiency, though noise might be an issue), and then there would have to be two failures for the module to see the input voltage. Make sure the second regulator has adequate protection and rating to not fail if fed 12V directly (could be thermal overload protection and adequate input voltage/SOA rating).
No, that won't work. If the voltage regulator failed and did output 12V, the RF module will be damaged by 12V before the relay coil actuates and disconnects 12V from RF module input.
Your setup reacts far away from 3v6 voltage. Btw, the the relay is too slow to protect sensitive load.
The schematic below should works better. (The U1 is still LM60430, I could not find a model in library, also the input diode)
simulate this circuit – Schematic created using CircuitLab
