Re: phase locked loop SSTC

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

Original poster: "John Tomacic by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla_ownz_u-at-hotmail-dot-com>

Hi,
I just joined the Tesla List this week, however I have been experimenting 
with SSTC's for last five years. I just finished a 4 kWatt (peak) full 
bridge MOSFET magnifier coil driver (I have lot's of digital pictures of 
discharges and construction of contoller/coil, if anyone want's to see, let 
me know)and my next step will be design and construction of a 11 kWatt SSTC.
Regarding keeping the coil always in tune, rather than using a PLL, a more 
stable and reliable method would be to use a current sense transformer in 
series with the secondary driving the magnifier coil (placed in between the 
secondary and ground).  The signal from the sense tx should be rectified, 
filtered then fed to a comparator.  Since maximum current is drawn through 
the coil at resonance, the frequency of the driver can be adjusted by the 
comparator through a vco to always keep the coil in resonance.  Initial 
measurement of the max current at resonance can be made then this value used 
as a setpoint for the comparator.  Hope this helps.

John T.



>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: phase locked loop SSTC
>Date: Tue, 18 Dec 2001 18:51:22 -0700
>
>Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
><m.j.watts-at-massey.ac.nz>
>
>Hi Jan,
>         It strikes me that the loop filter response time is a bit
>swift. Have you tried using a larger time constant?
>
>Regards,
>Malcolm
>
>
>On 18 Dec 2001, at 16:35, Tesla list wrote:
>
> > Original poster: "Jan Florian Wagner by way of Terry Fritz
><twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>
> >
> > Hi,
> >
> > I'm trying to do a simple phase locked loop to keep the SSTC driver &
> > sec always in tune, schematic is
> >  http://www.hut.fi/~jwagner/tesla/SSTC/PLL-schem.gif
> > for the PLL and the mains side is the half bridge as in
> >  http://www.hut.fi/~jwagner/tesla/SSTC/half-bridge.htm
> > and half-wave rectifier mains as input.
> >
> > But, well, something seems to be wrong with it... Has anyone else been
> > doing something like this? PLL coil?
> >
> > If I got it right then in this circuit the frequency lock range ==
> > frequency tracking range? At least, testing with a square wave input
> > suggested this is the case... I was careful to make the upper freq vs
> > lowest freq (R1 and R2) ratio 1.8 so it shouldn't lock on to TC sec
> > harmonics (with a ratio >2 this could happen??).
> >
> > The drive signal reacts just nicely to moving a hand towards the coil.
> > But, there's a changing phase shift in the signal, from about 40
> > towards 60 deg, so while the frequency is correct, the phase just
> > isn't. => mosfet switching losses go up and streamer output goes down.
> > In addition to this, slowly increasing the bridge input voltage keeps
> > everything in tune, but then most of the time if I try to draw an arc
> > to a screwdriver it just makes *zip*, one short spark, and then it is
> > totally out of tune and mains must be powered down and then up again.
> > Just to get a second small and unimpressive *zip*.
> >
> > On occaison it gives out some wimpy 5cm streamers, though. But that's
> > about 1/6th of the output possible with manual tune... :o(
> >
> > Any ideas whats going on here?
> >
> > every help would be welcome!
> > thanks,
> >  - Jan
> >
> > PS: A small current sense transformer senses the current into/out of
> > the primary coil (half-bridge). Specs: 1 pri turn, 100 sec turns, 820
> > ohm resistor, coupled via 10nF to CD4046 input incl two back to back
> > 6.2V Zeners. Then I'm using phase comparator II in the CD4046, which
> > should keep a 0deg phase shift between the sensed current and the
> > output drive signal, over the entire frequency range. Loop filter: 1nF
> > and 1.2kOhm
> >
> >
> > --
> > *************************************************
> >  high voltage at http://www.hut.fi/~jwagner/tesla
> >
> >
> >
> >
>
>
>
>




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