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Protect selfmade PSU sense input from reverse voltage, etc.

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nemail2:
Ok, how about this? Did I misunderstood ZD2? Not sure if you meant that there should be one, @Kleinstein...
I have put red circles on the changed parts of the schematic...

Btw. I'm not quite sure about C46 - is that correctly connected? SENSE_GND against SENSE?

D5 and D7 could be something like BAV199 or BAV99, right?

nemail2:
Or, what about this solution...?

- Sense has a flyback diode connected (D5) which should do the business for things like motors and coils discharging themselves while connected to the sense wires but disconnected from the PSU output (because the relais disconnected the output but not the sense wires - btw. should the relais actually disconnect the sense wires as well??)

- OPA2197 has integrated clamping diodes according to the datasheet and should be reasonably protected by R14 as Kleinstein pointed out already.
- OPA2197 still has 15V supply voltage so voltage on SENSE may be as high as 150V without harming the OPA2197-
- IC11 (OPA2197) will in that case output 15V which would be clamped by the zener diode ZD1 and through T10 there would only be 3.3V minus T10 forward drop voltage anyway.
- Series resistor R39 will further limit current to the ADC input pin, which in turn has clamping diodes by itself as well, if everything goes wrong.

SENSE_GND has a series resistor R27 which limits current + acts as a RC filter with C46 and clamps to 2.7V with ZD3. If SENSE_GND sees negative voltages, ZD3 should clamp as well, depending on its characteristics...

Am I missing anything?

edit: seems to work quite well in the attached simulation. even added the opamp supply pin series resistor to limit current through the zener.
sorry for the crudity, I'm no LTSpice Pro...

nemail2:
just a quick update:
stupid me just realized that my whole sense input is absolutely pointless, as it is not integrated into the control loop and therefore doesn't do anything besides showing the value which was read by the ADC on the display.
I simply didn't know and didn't think about that, that a sense input is supposed to be part of the control loop and as I don't want to extend my control loop outside of the PSU, I ditched the whole idea of a sense input completely.

for me that means:
- less PITA with protection
- more space on the PCB
- more space on the display
- less components
- simpler design (actually I'll go with the quad OPAx197 version, the OPA4197 + 1x OPA197 for onboard voltage measurement now, instead of 3x OPA2197)

still, I have learned much about circuit protection so it is still a win for me, from all perspectives.

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