Re: phase locked loop SSTC

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

Original poster: "Luc by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ludev-at-videotron.ca>

Hi list,

Not sure if I understand well; you told that one of the problem
of using a feedback loop ( like in fly back driver or VTTC ) is
because you feed the primary with square wave. May be you could
use a low pass filter between the FET and the primary, this way
you'll obtain near sinusoidal wave, any way the higher harmonic
present in the square wave just contribute to heat the coil ??????

Cheers,

Luc Benard  

Tesla list wrote:
> 
> Original poster: "Jan Florian Wagner by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>
> 
> Hi,
> 
> >         It strikes me that the loop filter response time is a bit
> > swift. Have you tried using a larger time constant?
> >
> > Regards,
> > Malcolm
> 
> [btw, has anyone made a PLL driven SSTC that really works? it'd be
> very relieving to hear from someone that he's done it, i.e. that it
> has real chances of working properly...]
> 
> Tried larger RC (single pole) loop filter, up to 250kOhm (with the
> same 1.0 nF). But the same thing happens - streamers grow to 5cm max
> and then suddenly zip and streamers turn off completely. An arc to a
> screwdriver looks like a short capacitive discharge, and that's it
> then. Rectified mains must go down to 0V and then up again to get any
> output from the secondary. I'd guess this is an issue with the current
> transformer? Although, the signal out is pretty clean... even though
> it is a square wave (overdriven and clipped sine wave).
> 
> Anyway I've started to suspect - is a phase locked loop of any use in
> driving a SSTC at all?
> 
> Because, when driving the TC at some more or less out-of tune
> frequency, the current drawn at the primary coil doesn't look like a
> sine wave. Instead it reminds more of a square wave at the driver
> frequency, except it has a large ripple / mess / "small bits" of sine
> wave on it here and there. Or, hmm..., is this really the signal I
> should be getting?
> 
> I mean if this is the case, and that messy signal is actually ok, then
> a phase locked loop wouldn't have any chance detecting the real
> resonant freq - because it appears just as that signal mess on top of
> the driving square wave waveform, which is "removed"/clipped off by
> the input amplifier of the PLL IC... ???
> 
> cheers,
>   - Jan
> 
> --
> *************************************************
>  high voltage at http://www.hut.fi/~jwagner/tesla