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Press switch on the right to simulate shortout. Press switch on the left to release protection after you've fixed the short out. Now that the sensing side is at the positive supply rail, there won't be any problems with ground loops and whatnot. The circuit is just exemplary, might cause some problems with stability in reality, but you get the point. The first top left op amp, measures the voltage drop between the 100mOhm resistor. A perfect indication is not necessary, because the secons op amp works as a Schmitt trigger, and has an adjustable threshold level. The transistor part on the right is a bistable latch
Once the schmitt trigger figures out theres a short somewhere it generates a square wave that enables and latches the relay so that is disengages the load. Right now the protection should work at 4.25A. The circuit is open to criticism, I designed it in 20 mins or so and haven't had the time to work out the kinks yet.
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