Re: phase locked loop SSTC

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

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
> 
> 
> 
>