Re: Sheppard-Talyor circuit up on my website/ low Z construction technique

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

Original poster: "Daniel McCauley by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>


> So aside from that stage (the output stage I'll call it) the MOSFET's
> are no doubt operated as switches, meant to pull current into the
> 160uH inductance and "release" this current to the rest of the
> circuitry. So the MOSFET's are switched quickly here in order to
> minimize I^R power loss in the junction....and therefore there will
> most likely be large voltage spikes...
>
> So it is here in this stage (where there is high-speed switching of
> significant current) that I think there should be clamp diodes. Maybe
> even isolation of the MOSFET body diodes (with a series shottky) if
> it comes down to it...I've heard the body diodes can create damaging
> reverse recovery transients if driven into forward conduction too
> hard (from free-wheeling current).
>


Yeah, you definitely should bypass those internal MOSFET body diodes with
some external diodes.
I've built two solid state tesla coils already and currently use the MUR1660
type schottkey diodes (in a TO-220 package) to
bypass the MOSFETs internal body diodes.

Also, what kind of gate drive circuits are you using?  If you are operating
above 200kHz, you have to be able to switch those FETs on and off very fast
and a simple gate drive circuit isn't going to do it.

Dan