help: HV SMPS coil driver

["Jan Florian Wagner" <jwagner-at-cc.hut.fi> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

[second try to send]

Hi,

Dreaming of a compact TC power supply and RF base feed driver...
...so I'm in the process of building a small, modular, directly mains fed
500W SMPS power supply to drive a TC secondary, 100..300kHz adjustable.
Got some stuff for the SMPS already assembled, but I've a few questions
yet. 

Maybe someone experienced with HV SMPS' could help?

The ferrite xfrm is about ready, should give 3..5kV, but I've now started
wondering about insulation (a bit late maybe... ;). I've used LD-PE
plastic bags and transparency sheets as insulation between primary and
secondary, and also between each secondary layer (turns, one layer PE,
one wire led across, one layer of transp sheet, next turns). Plus,
poly-urethane varnish. 

Does that sound ok?

The ferrite xfmr runs at about 1/50 of critical B-saturation, has lots of
primary turns, big 5cm x 5cm x 2cm core of 3C85 material. Two 
non-connected 8 turn primaries, one tapped 120 turn secondary.

I designed the xfmr for push-pull, but with my lack of experience and
those symmetry/saturation problems I've for now dropped that idea.

I'm using a CA3825 PWM chip (with dead-time expansion), but couldn't find
any FET buffer chip so looks like I can use only two FETs safely (?).

Sooo... what is the "best" way to hook up that xfrm? 

What would put minimal strain on the switch MOSFETs? 
(They are 500V 8A, mains is 220V 50Hz.)

Other thing, I was wondring with voltage feedback from the secondary...

How is that done? Divider network with a small well insulated transformer?
Or just 1-2 feedback turns on the xfmr, no messing around with secondary
HV?


And last but not least, how do you go about designing the FET snubber
network? 

Do you use a series cap on the fet to cancel out xfmr reactance? That
sounds wrong somehow - but how do you do it otherwise?
Any ready formulas?

(By the way I've never built a SMPS before but've tried to gather as much
knowledge as possible for starters. If you happen to know any good web
site on SMPS, I'd be very much interested.)

Many thanks in advance for any help!

thanks,
Jan
--
*************************************************
 Jan Florian Wagner
 http://www.hut.fi/~jwagner