Back to switch selection... At millisecond-scale, the limitation of SCRs in an non-repetitive, oneshot pulse is thermal, as the pulse gets shorter, the allowable surge current goes up significantly, a SCR only rated for 60 A steady-state can switch even 2000 A. But at microsecond-scale, di/dt becomes the new problem, and that makes the allowed surge current to go down significantly... Apparently the responsible mechanism is localized hotspots in the silicon before it fully turns on.

Most SCRs have di/dt (max) = 50 - 100 A/μs. So for a 8/20 µs surge, the current peak must be less than 400-800 A. With a standard 2 Ω effective ESR, surge voltage is restricted to 800-1600 V. Let's see if an IGBT does this better... #electronics