Re: SSTC problems1 (no its not a PlasmaSonic ;-))

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

Original poster: "Jim Mitchell" <electrontube-at-sbcglobal-dot-net> 

The IN34A just protect the chip from high antenna voltage!

Regards - Jim Mitchell
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, January 29, 2004 11:28 PM
Subject: RE: SSTC problems1 (no its not a PlasmaSonic ;-))


 > Original poster: sebastian gaeta <sgtporky-at-prodigy-dot-net>
 >
 > Hi David,
 >
 > I built the full bridge Feedback coil at:
 > <http://dave.golfbuddys-dot-com/hvguy/>http://dave.golfbuddys-dot-com/hvguy/
 >
 > My coil needs a lot of improvement though. If I had it to do over again,
 > (and I AM doing it over again!) I would use the same driver that they use
 > for their 10 KW design, even for the P460s because it is more rugged, and
 > the parts are more available. I saw a scope picture of someones gate
 > waveform using that design, and it even appears to be a faster switcher
 > than the one I am using. If you look at my picture, the gate drive
 > transformer is not in a good place because the back fets are too far away
 > from it. My new one will have the GDT in the middle of the heatsinks and
as
 > close to each fet as possoble. I also put 10 ohm resistors in series with
 > each gate with a schottky across each one to speed up the fall times.
 >
 > I rewired my bridge rectifier to do half wave instead of full wave because
 > my mosfets get too hot. And half of them get hotter than the others so my
 > duty cyle stinks too. I played around some more last night by powering the
 > H bridge with 12VDC, and probing around with a scope. You need something
 > like 100 volts on the antenna to give steep enough rise and fall times to
 > create a decent enough square wave with your 1N34 'chopping diodes'. If
the
 > feedback voltage is too small, the duty cycle is uneven, and one set of
 > mosfets work harder than the other set. Just something to keep in mind if
 > the same thing is happening to anyone else. Rewiring the bridge was the
 > last thing I did before I went to bed last night, so I haven't even tried
 > it yet with half wave rectification. This should force things to run
cooler
 > even if my circuit is messed up!
 >
 > A properly switching MOSFET should never even get warm because it should
 > never be dissapating power. When the current is max. the voltage should be
 > 0 and when the the voltage is max there is no current! Power dissapation =
 > 0 = I am doing something wrong! The "beast09" does not look like a typical
 > MOSFET switching waveform though! If you look hard and long enough, you
can
 > almost make out a square wave buried in there!
 >
 > If you want to look at my coil, it's at:
 >
<http://community.webshots-dot-com/album/113763981zJBnik>http://community.websho
ts-dot-com/album/113763981zJBnik
 > The Mosfets are on the light colored rectangle heatsinks and the
 > freewheeling, and mosfet body diode disabling diodes are on the small
black
 > individual heatsinks. I'll bet they get really hot, but the fans cool
every
 > thing off before I can get my fingers down in there in time to feel them.
 >
 > Sue
 >
 > Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "David Trimmell"
 >
 > Hi Sue, do you have a schematic of your SSTC design? I am still trying
 > to decide what kind of driver circuit I want to use for my first
 > self-designed Half Bridge. I am ready to populate my second PlasmaSonic
 > board from Dan, but also want to try for some Solid State Sparks (as
 > apposed to audio)! But being a newbie to FETs makes for slow progress,
 > but Richie's website (http://www.richieburnett.co.uk/tesla.shtml) sure
 > is a great wealth of information! It sure is great to see the natural
 > evolution of Tesla's technology.
 >
 > Regards,
 >
 > David Trimmell
 >
 >