mike_kilroy
Senior Member
- Location
- United States
1)Surge current is not the same as short circuit current.
2)It's a heat issue whichever way you cut it.
V*I*t.You simply cannot treat them as independent variables as you seem to have done.
That's basic physics.
3)If you had ever examined the nature of the damage to the silicon chip from a failed large diode or SCR, you would have observed that the damage, whatever the mode of failure, is some or all of the chip had melted. You can sometimes determine the cause of the failure by the position and area of the chip that melted. But melted it has. And melting needs heat.
It really is that simple.
1) For reference, I never once said short circuit current was surge current; I always said what I meant, max current, ie., max surge current. The short circuit words were other posts you are for some reason attributing to me.
2) no, it is not. Read the ref in post above this and perhaps you will agree that there is a real rating limitation called max surge current that degrades and kills MOVs - not watt-seconds, max current number only.
3) unfortunately you choose to ignore my posted comment that exceeding a rating - PIV - not a watts for some seconds as energy rating - will kill a transistor. THEN after it shorts, the hi watt-seconds flow, melt it, and blow it up. You will never get a 3"x3" semiconductor device make a shock wave while failing with a 2 joule spike - it needs the 460v@1000amp short circuit current that follows to make that sound. Yes, a semiconductor can overheat and fail shorted and thus melt and blow, but quit a few failures are actually from voltage spikes - without much energy behind them - that exceed PIV causing the semiconductor to fail - when it fails in a short circuit mode it THEN AFTER THE FAILURE FACT melts and blows up. You have to be ready to look beyond the obvious "it melted." Same with MOVs - quite often they degrade from the surge currents (pronounced "low joules") that degrade them so their turn on voltage reduces - per above article typically 10% per over max current surge, until it turns on at the AC voltage it is meant to protect, THEN conducting, melting, and failing fully.