user1453 said:
ok, I've modified my circuit to include a variable length single shot pulse, the pulse cannot be retriggered until 1second has passed, how long is the maximum the pulse should be?
Looking at fig. 11, and working backwards to get maximum pulse width:
Device current=300V/(8+Rds)~35A
Device instantaneous power = PDM = I^2*Rds, PDM ~ 623W
From fig. 11: Tj=PDM*Zthjc+Tc
Tjmax=150C (from specs)
Solving for Zthjc,
Zthjc=(Tjmax-Tc)/PDM
Assume Tc = ambient temperature = 30C (Tc=case temperature)
Zthjc=(150-30)/623, Zthjc=0.192
Using the bottom curve of fig. 11 (duty cycle~0),
maximum pulse width~2.5ms.
This will, according to the spec, push the part to its limits. I would probably start with 1ms, and adjust it slowly upward until it fails, and then back off a little. However, if you go too far, it might still shorten the life of the part, so, for example, it might only last for 10 shots.
I don't think a heat sink will help, because of the short time involved.
Is 2.5ms long enough to appreciably accelerate your projectile? Seems pretty short to me. You might need something like an SCR with a capacitor-discharge scheme, or maybe an IGBT. Some of the other guys here have more experience with high-voltage, high-current applications than I do.