Re: PLL-controlled SSTC?

["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:
> 
> Original poster: "Daniel McCauley by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>
> 
> After some thinking. . .
> 
> Actually a PLL circuit really wouldn't work in this case.  The problem is
> that when a arc streamer propogates it actually changes the resonant
> frequency of the secondary and this ultimately kills the propogation of the
> streamer.  The output frequency of the oscillator doesn't really change much
> during such a propogation.
> A PLL on the output oscillator really wouldn't do anything since the
> frequency is relatively constant.
> 
> What would be needed is some kind of feedback to detect when the output
> current begins to drop or something similar.
> Richie Burnett uses a simple technique to simply feed back some of the
> output voltage back into the feedback of the TL494 chip (See his website).
> Its not very elaborate, but pretty effective for what its worth.
> 
> Dan

I am not convinced that this wouldn't be a worthy project.  You could
use one of the old Motorola Phase-frequency detector chips (MC4044?)
hooked up to a TLC555.  The 555 has a pin already for VCO shifts.  Maybe
an LM565 (part# ?) PLL would even work.

As long as you kept the VCO range small, harmonics would not be a
problem.

And since modern FET drivers switch at CMOS levels, the interface
wouldn't be difficult.

The TLC555 and output from a "SMPS current transformer" sensing coil
current would be fed into the phase-freq detector.

Rob.
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