Re: SSTC, Modes and soft switching

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

Original poster: "Antonio Carlos M. de Queiroz" <acmdq-at-uol-dot-com.br> 

Tesla list wrote:

 > Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>

 > 1. It looks like it is possible to get soft switching all the way through a
 > burst, no matter what the tuning and coupling of your DRSSTC. You use a
 > phase locked loop or self-resonant driver circuit, sensing the primary
 > current, to force the phase angle betwen inverter voltage and primary
 > current to zero. The system then operates at a frequency where this phase
 > condition holds true.

The pll idea is conceptually elegant, but there is a problem:
How can the pll lock immediately, considering that the bursts are of
just a few cycles, and that the spacing between the zero crossings may
be not uniform? With any conventional pll, the first cycles would be
severely out of phase. Maybe better to use just a comparator sensing
the sign of the input current, that would act instantaneously.

 > 2. With a driver like this, that forces zero phase shift, you then have to
 > tune your primary to find the point of maximum primary current. This also
 > seems to be the point of highest output voltage, and largest and fiercest
 > sparks :)

Makes sense.

 > 3. When I checked my coil with a frequency sweep after tuning it like this,
 > I found the primary was tuned surprisingly low (lower than the optimum
 > tuning when I used the same coil with spark-gap excitation) and the lower
 > mode was emphasized compared to the upper one.

My idealized analysis resulted in a driving frequency identical to the
resonance frequency of the secondary+topload alone, and a tuning
relation 1/(L1*C1)=(1-k^2)/(L2*C2). The primary shall really be tuned
to a lower frequency, specially for high coupling. Of course there is
the question of streamer loading too.

Antonio Carlos M. de Queiroz