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Re: Small DRSSTCs
Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>
Hi Steve,
At 07:25 PM 12/3/2005, you wrote:
1) The list has been buzzing with the success of ever-larger and more
impressive DRSSTCs, with even larger ones on the drawing board. But what
about the other end of the spectrum? Some of us may wish to build much
smaller versions for tabletop fun and portability. But as size goes down,
the secondary resonant frequency goes up, and can be in the 200-500 kHz
range.
Perhaps super high primary current are not needed for smaller
coils. Thus, FETs could be used that have very fast
speeds. Resonant gate drive could also be used to speed the H-bridge
but "control" gets "odd" in that case.
I was working on a pure Sidactor driven coil thing too (apparently
they can be parralleled). But the powers were not coming out very
good. But for a little coil, that would certainly be an
""extremely"" cheap simple design. I sort of gave up on it since the
streamer lengths we only three inches... It really needed 240 VAC,
or more, of line voltage.
Question - are IGBTs available that can work well at much higher Fs?
IGBTs can be driven very fast!! Forget what the data sheets
say... Since we have a low pulsed duty cycle, we can slam them real
hard and fast. The usual problem is aligning the H-bridge transition
with the true current crossing point.
If we switched them that hard "continuously, they would fry, but at
say a 5% duty cycle, the switching losses at high speed are very acceptable.
Current capacity & voltage rating need only be enough to produce leaders
measured in inches for tiny coils, to about 3 feet for larger desktop
models. Any suggested manufacturers & products?
IR, APT, IXYS, Toshiba, Powerex are the big power semi players....
Any general design advise
for building small DRSSTCs?
Lower Fo frequencies are not so much a need for the power
devices. But we need low Fo to allow for reasonable primary
inductances with a primary cap that can store enough energy to make a
reasonable spark.... But that may not make sense... I am thinking
of yet another topology...
2) Suppose one wanted to buiild a twin coil DRSSTC. Does anyone see a
problem in using feedback from just one of the primaries or secondaries? I
think all would be well for leaders jumping between the coils, but what if
one coil experiences a ground strike and the other one doesn't, etc?
Experts, any thoughts?
I would think a twin coil system would have a common primary current
path??? Since the secondaries are coupled loosely, what happens at
the end of the secondaries is just the way it is... If one secondary
system gets drained of power through an arc, not a big deal... Just
keep pumping power, in phase, to the primary
Cheers,
Terry
--Steve Y.