Original poster: Ken or Doris Herrick <kchdlh@xxxxxxxxx> Never fear: Doris pays NO attention to this "electronic poo-poo".My 1st--& only, so far--s.s.t.c. used a >>whole bunch<< of TO-247 MOSFETs & today I wouldn't recommend that at all: too many parts to fail. Surplus "bricks" would seem to be the way to go now. A failure costs more but at least it's easier to identify where the failure is.
As to what I'm doing, check out <http://www.pupman.com/current/kcherrick>http://www.pupman.com/current/kcherrick, image 4. It's a simulation schematic of 1/2 of what I'm building. At the (gated) start, oscillator U4 via E1 & S1 drives Q4. As soon as TX1's secondary draws current, feedback-voltage across D2, D3, D4 & D7 entrains the frequency to the Fr of the secondary. During positive half-cycles, Q4 conducts; Q1 is not used. When Q4 cuts off, D6 conducts, charging up C3 to snub the voltage overshoot--with the precautionary help of some MOVs not shown--to 900 V or so in the hardware. At alternate half-cycles, Q4's collector going negative discharges C3 thru the "snub primary", delivering that charge by transformer action back into the mains supply. You can see the effect on C4's charge from the accompanying waveform.
My push-pull circuit doubles that up, with a 2-secondary xfmr driving the pair of IGBT bricks and fancier driving electronics providing -27 V or so at the gates until each spark-burst is to occur. So I end up with 4 primaries with leads physically crossing over, which led me to the confusion (see my other post of today).
It seems like a nutty circuit since the snub-primary's field would seem to buck, to some extent, the field of the main primary. But as I see it so far, power that doesn't get back to the mains supply that way has nowhere else to go but into the secondary. And the simulation runs fine. I'll soon find out, I trust...
KCH Mike wrote:
I think this is for Ken, but if not......Doris...forgive me, plz.I guess I'd like to see exactly what you are hoping ot achieve.......I know IRFP30's are pretty good, but I was plannng on using a bank of them just to run an xray trannie.....Don't give up.....you'll be teaching us how to make 'em bigMike <http://us.rd.yahoo.com/evt=49938/*http://tools.search.yahoo.com/toolbar/features/mail/>