Hi Daku, I just got a crowbar protection circuit working for my negative regula ted supply. I had looked at this thread, earlier, but didn't get a clear p icture from the comments, so far. So, I sat down with a lab supply and so me components and alligator clip leads and got a solution which I thought I 'd share for the sake of this thread. I started with a schematic that I found online (by Ravi Sumithraarachc hi) for a positive regulated supply. In my application, the negative regul ation is provided by a normally-positive regulator (7815 (TO-3 package)) th at has its (normal) output connected to Earth, and its ground pin is used a s the negative supply. Of course, there are negative regulators, but this implementation works, too. So, I put the fuse on the (normally positive) output on its way to Eart h and put the cathode of the SCR to the (normally Earthed) negative supply. The cathode of the 16 V Zener is still sensing the (electron-hole)input s ide of the fuse, but, in effect, I've fused the conventional return path, r ather than the conventional send path.
Please check out this drawing:
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Maybe it will give you or someone else some ideas about how to impleme nt your own CPC...
servus, Andrew