Solid-state coil (gate xfrmr question)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <cwillis-at-guilford.edu>

Hi folks,

I just started toying with a solid-state coil setup that uses an IRF740
driven by a 556 timer and a gate driver chip.  The thing is working pretty
well, giving up to 5" of spark with about 70 watts in.  I'm confused about
one thing in particular, though- the problematic isolation transformers I
made to protect the driver circuit in case the transistor dies.  I have
made three of them now, all having about 12 turns on the primary and
secondary around different ferrite toroids I had lying around.  All have
the same effect of keeping the coil from putting out as big a spark as when
the gate is driven directly.  So, if you know what ferrite material to
select for a core, how big to make it, and how many turns should be
required, please let me know!

By the way...a big thanks to Richie Burnett for putting a great tutorial on
MOSFET coils on his website- it is really all I have had to go on and I
know it has saved me many a blown FET...at least so far I still have the
"original" one in there.

Carl