I have a circuit for a model railway where the output from the mains transformer is 12 - 0 - 12 v. In the case of something causing a direct short across the lines, I would like the circuit to be shut down immediately before damage is caused to any of the components. Some years ago I saw a simple electronic circuit that was included in a model railway diagram that immediately cut out the power supply when a short occured across the tracks, but I can't find the circuit in question. Can someone help me with this?