Re: DRSSTC Primary Circuit Feedback Control

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jimmy Hynes <jphynes@xxxxxxxxx>

Hi Terry,


On Mon, 06 Dec 2004 21:09:37 -0700, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi Jimmy,
>
>
>
> At 08:50 PM 12/6/2004, you wrote:
> >Hi Terry,
> >
> >The little IGBTs should be practical anyway. Based on some
> >measurements taken on my DRSSTC, I'm convinced that a half bridge of
> >little TO-247 IGBTs could get me to 5'.
> >
> >You have to be a little careful with primary feedback, because if it
> >isn't tuned, the secondary won't be sucking much out, and it will
> >build up more than normal
>
> Yes!!  The models show that for sure.  If the primary and secondary are not
> tuned, then the primary voltage just keeps rising pretty much till
> something blows up!!  A spark gap might "still" be a good idea ;-))

As long as you limit burst time, you should be fine ;-)

>
> The models (not real confident in the numbers..) say the IGBTs will do
> about 40 watts of heat as is.  But with "perfect" zero cross switching,
> that goes down to 1.2 watts!!

Huh? What frequency and switching times? My simulations showed about a
factor of 2 increase in loss when hard switching about 80% of peak
current. A factor of 30 is hard to believe.

> This is no different than any other
> switching resonant thing and they are all using "little" FETS and
> IGBTs...  We just have to refine ours...  I also seem to be able to keep
> the peak primary currents at just 80 amps which is trivial for the
> IGBTs.  Almost could use FETs again...
>

80 amps? Where's the power? I don't think you'll get very big sparks
with only 80 amps. If we're going by the 'semi-cw' theory, then you
need a lot of power to push the sparks out.  If you use a toroid with
no breakout point, then it might work...

> Cheers,
>
>         Terry
>
>