555 overcurrent detection

This circuit uses a 555 timer to detect the event of overcurrent. The trick is that the current drawn by the load makes the voltage on 555's VCC drop. Inside the NE555, there is a comparator that compares THR and VCC. We can then set the voltage on THR with the potentiometer. If the load draws too much current, the voltage on VCC will drop below the voltage on THR, and therefore trigger the ouput. Instructions to use included in the schematic. This circuit detects the event of overcurrent through the load (lightbulb). To operate : 1) Run the simulation 2) Open the switch S2 below the lightbilb (load not connected) 3) Click the reset switch S1 (close and reopen) 4) The LED should be ON now. 5) Close the switch S2 (connect the load). 6) You can see that the voltage at PR2 goes below the voltage at PR3, and triggers the output, turning off the LED. 7) To restart, simply switch off the bulb and reset the circuit with S1. The current limit can be set with R2, the potentiometer.