Re: Is a PLL-synchronised SR SSTC possible?

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

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

Although your idea is interesting, I'm not sure how much its going to buy
you.  I've tried something similar, but only managed to get a very small
increase in performance.

I think it would be much more advantageous to spend the time, money, and
energy into going into one of the following directions:

1)  Improve SSTC to handle much higher input voltages (240VAC up to 480VAC)
for starters.  From my experiences, I get approximately 10 inch streamers
per 120VAC input at
half-rectification.  My maximums were above 36" streamers before my SSTC
bridge circuit blew up. This is all without any type of feedback system.  A
PLL system may only give
you an inch or two at best in tracking the changing secondary resonant
frequency.  I'm currently working on a 1500V solid state modulator using (6)
IXFN24N100 FETs using
a CASCODE type topology.  This should be a vast improvement to the
full-bridge designs currently being used now.  I'll be posting this design
shortly to the group.

2) Improve SSTC by using "magnifier" type design.  Which would be stepping
the voltage up by up to 5-10 times the output voltage after the full bridge.
I'm currently exploring this
option as well, but I am still waiting for some high frequency U-Cores I
ordered a few months ago.  The difficulties here are getting a suitable core
for the high frequency and currents
as well as voltage stand-off on the core.

The Captain


 > I have drawn a diagram (below) for a self-resonant SSTC using a
 > Phase-Locked Loop
 > to synchronise oscillation of the VCO to the resonant frequency of the
 > secondary. What if any are the reasons why this topology will not work?
 >
 > Assuming that it could be made to work would a normal or a quadrature
phase
 > detector need to be employed/would the LM567 Tone Decoder IC be of any use
 > in this application?
 >
 > Wouldn't the choice of quadrature or normal phase detector depend on type
 > of feedback transducer used (eg pickup antenna, current transformer or
 > current-sense resistor) and in the case of the current transformer or
 > resistor, whether it was connected in series with the primary or the
 > secondary windings?
 >
 > Isn't the technique I have illustrated basically a matter of simpy
 > frequency-modulating the oscillator to keep it in step with the resonant
 > frequency?
 >
 > NB:or reasons of simplicity in the diagram, I have shown only a SINGLE
 > transistor output stage.
 >
 > pickup antenna
 >        \|/
 >         |
 >   phase detector----low pass filter-+
 >         |                           |
 >         |                           |
 >         |                           |
 >         |         (-+-)             |
 >         |           |               |
 >         |   Vcc+   <                |
 >         |     |    <                |
 >         |  pri>    <sec             |
 >         |     >    <                |
 >         |     |    |               |
 > Contr. |   b /c    |               |
 > +--vco-+----|      |               |
 > |      O/P   \e    |               |
 > |            |     |               |
 > |            +-----+               |
 > |            gnd                   |
 > |                                  |
 > +----------------------------------+
 >
 > Jolyon
 >
 >
 >
 >
 >
 >