Polyfuses have the great advantage that they need not to be replaced after a "blow". But this is the only advantage of this type of fuse. A big disadvantage is the big manufacturing tolerances of polyfuses refering to trip current, cold resistance, etc. and the huge heat transfer tolerances caused by varying mounting conditions. The result is a derating with ambient temperature which is more than twice as bad as that of a standard melting fuse.

Another huge disadvantage of the polyfuse is the recovery characteristics after a "blow". Sometimes they need more than one hour to recover to their cold resistance! Any attempt to restart the circuit before the polyfuse could fully cool down can result in very very strange behaviour.

Again, why using such a crowbar at all and why not using a comparator with P-MOSFET as high side switch, as I have suggested earlier?

Kai Klaas