I am working on a thyristor (in my case: Semikron SKKT 253/08) circuit operating at 400 V mains (3 phase). What I'm wondering is how one can calculate a thyristor gate resistor so 12 VDC applied at pulse transformer can't damage the thyristor gate as in the following circuit:
In SKKT 253's datasheet, it states that minimum gate voltage is 3V and minimum gate current is 200 mA is required to turn on the thyristor. So I decided to drive a 1A pulse into its gate using factor of 5 according to Semikron manual page 152. Now back to my circuit:
Ig = Ir2 = 1A (1) Vg + Vr2 + Vd2 = 12V -> Vg + (Ir2 x R2) + 0.7V = 12V (2) From equation (1) and (2), we have: R2 = (11.3 - Vg)/(Ir2) = (11.3 - Vg)/1 -> R2 = 11.3 - Vg (Ohm) (3)
Now I'm stuck at equation (3) because I can't decide which voltage Vg will be in case Ig = 1A. According to SKKT 253's gate trigger characteristic:
when Ig = 1A, Vg can be from 1V to 6V. Could anyone please enlighten me on this problem ?