Current flows through the load (blue) and through the power transistor (right) to ground. If the current through load gets too high, the signal transistor (left) turns on, turning the power transistor off, and the LED indicates a problem.
The signal transistor stays on until the circuit is reset by the power switch with the load current below the trigger level. The trigger level is set by the bias resistor on the signal transistor.
Run the sim and flick the power switch. Adjust the blue load resistor to increase the current and adjust the green bias resistor to set the load current amount that will trip the circuit into overload mode.
