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

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

Original poster: "rob by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rob-at-pythonemproject-dot-com>

Tesla list wrote:
> 

> 
> Rob-
> 
> Thanks for the quick response.  I missed the notes.  Also, I see that the
> rep-rate is to be low: just the spark's rep-rate.
> 
> Even with 50 ns diodes, you do get current-spikes, do you not, when both
> transistors turn on and before the diodes turn off?
> 
> As to sockets for those transistors...BY ALL MEANS, USE THEM!!  I should
> have done that years ago.  I now use--for some of my TO-247s--DigiKey's
> S/N ED5031, a Mill-Max Co. individual press-in socket that nicely fits
> the TO-247's lead.  I bend the leads to form a triangular "footprint" for
> better stability in-place.
> 
> Can you contrive a circuit like this that is push-pull?  I'll have to
> think on that...
> 
> > Ken, I have blown up $50 of 1kV MosFETS and about $30 of 600V
> > MosFETs :)
> 
> $50?  $30??  What a piker!  Clearly, you have just begun.
> 
> Ken Herrick

Hi Ken,

I just put in an order for 10 6A 1000V IR Hexfets and 10 more 1200V
hexfreds :)  

I totally rebuilt my circuit yesterday.  I took a sheet of pad-per-hole
plated thru Vector board, built the section from 120VAC in to the first
high freq bypass cap normally with wire.  Split the low and high voltage
supplies so I can run the converter on any input voltage I choose.

Then I took a big flyback converter transformer and extracted the solid
copper ribbon they use for the LV winding.  Cleaned it in acetone, made
it straight in a vise, sanded with #600 emory, then sprayed it with
clear Krylon.  I've found Krylon to keep the copper shiny, yet not
impede soldering (it acts like flux).  Then I cut it in thinner strips
and used those to construct the switching portion of the converter. 
Looks really pretty.  And I used sockets for all the TO-247, incl. the
hexfreds.  Each MosFET has its own heatsink that floats at the drain
voltage.  I really need to get a digital camera and take some pics of
this, maybe the one at work.

Now I bet that the FETs will explode with violence :) instead of just
burning out.  Gee, then I don't have to probe them with an ohmmeter. 
Seriously, I also ordered a variety of  Panasonic 20mm varistors.  I'm
going to try those out as snubbers.  The high voltage ones have
relatively low capacitance.  I have a 100:1 scope probe here, so in
worst case, I will just run the supply on the lowest voltage before the
FETs get close to BV.

Rob.
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