Ground loss protection
I have a hat board that has some high power solid state switches (mosfets).
The hat is controlled by the main board.
The hat and the main board are connected via pin headers, like an arduino.
The hat board contains some connectors for the power and also the outputs.
My main concern is how to avoid high current flowing back and down to the main board in case the ground disconnects from the hat board.
A schematic below:
Blue box represents the high power part of the hat board and the rest is the control circuit.
SW2 represents the external ground wire of the output connector the hat board.
In theory, if the wire cuts off, SW2 opens. No current will flow back to the control circuits due to high resistance of R3.
I could also leave R3 unconnected but I Don't know how the circuit will behave with a floating source pin.
I can't have an isolated supply for 3.3V (V2). As the main board exists already. The main board contains a DC/DC that steps down 24V to 3.3V.
There will be two power lines. One for the main board, its operation (steps down to 3.3V). And one for the top board, the high power part. Those two are exactly the same source.
1 answer
It all depends on what is connected between the main board and this "hat" board. Your schematic doesn't show any of these connections, so we can't really tell.
In the end, the high current loop should be isolated from everything else. In your context, V3 would be an isolated supply. The circuit in the blue box would be referenced to the same isolated ground as that supply. You will then need some sort of isolation for the signal that turns on M1. One obvious way to do that would be to replace Q1 with an opto-isolator. Of course you need to check that the reaction time is still fast enough in that case.
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