Thanks for the info (and being patient, ;-P)
One *last* question. As you can see by my schematic I posted, I have a slow discharge of my 300V cap bank through a large resistor and a relay. Its working pretty good thus far. I would also like to figure how to do a safe, but single pulse, quick discharge of the bank (through a inductor/solenoid load). So, I wanted to use my IRF840. It is rated at 500V and has an RDS of .850. I prefer not not have this directly connected to my pic. I have an extra mosfet driver channel. Is it stupid or beneficial to use this driver? If it is not impractical, can you tell me:
-with a 500V Vds AND Vgs, is there ANY reason to add protection? If so, what type of diode? I have not looked into zeners at that rating, but the UF4007 is rated here. Would this be fine?
-with the power mosfet, I understand applying more gate voltage/current may be better, so a smaller base resistor may be better. In the case of a irf840, is this true? It seems as though I would want a larger resistor on the gate for damage immunity to the driver. Also, since I am also going for a single pulse, would a lower resistor value mean that the discharge time be significantly different?
EDIT- I overlooked that the GS voltage is 20V, so I should clamp it. I guess the questions is then....do I clamp at 20V or 15V? Base resistor size needed from driver output? I suppose the uf4007 can then go reversed biased on the inductor leads.