Figure 7. Non repetitive surge peak on-state current for a sinusoidal pulse with width tp < 10 ms. The graph shows, as the surge gets shorter and shorter than 10 milliseconds, the allowed surge current goes from 600 amps to 4000+ amps at 0.15 milliseconds. But when the surge gets shorter than 0.15 milliseconds, the allowed surge starts to go from 4000+ amps down to 300 amps at 0.01 milliseconds, because the device's di/dt limitation is 100 A/µs.

Notices where this attachment appears

1. Embed this notice
   niconiconi (niconiconi@cybre.space)'s status on Sunday, 07-Aug-2022 16:25:34 JST niconiconi

   in reply to

   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