Over current crowbar

[Phil1977]

Hi together,

please apologize if the idea was already discussed, but I couldn't find it using the search.

Has anyone ever tried to build an overcurrent-crowbar with a SCR?

I would like to have some protection device that prevents LEDs from getting destroyed when they are unintentionally connected to a live PSU with some output capacitance.

So far I tried fast current limiters with MOSFETs, but I´m thinking if it could be done better by this circuit:


       |---|<---|
(+) ------vvvv--------------------(+)
           L               |
PSU                       SCR     Output
                           |
(-)-------------------------------(-)


The inductance L is intended to limit the current gradient if the output is suddenly loaded. A trigger circuit watches the voltage over L and fires the SCR if it is too high. By rough estimations a small inductor of around 20uH delivers 1V at a current gradient of 50kA/s which would be clear indication of a dangerous load condition. A freewheel diode over L prevents voltage spikes at sudden load disconnection.

The circuit needs no self-reset capability, it´s just a line of defense against LED damage.

What do you think? Any ideas or comments before soldering it to a testboard?