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 Paul,

Can you share your self-oscillating sstc design with os please, Tx.

Cheers,

Luc Benard

Tesla list wrote:
> 
> Original poster: "Paul Nicholson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
> 
> Malcolm wrote:
> > If you apply one signal to the "D" input and the other to the
> > clock ... An XOR gate fed from the same signals gives the degree
> > of difference
> 
> Ah, I see what you mean,  but the trouble is, John has rectified
> and smoothed the feedback signal, so this won't work.
> 
> John Tomacic wrote:
> > I always operate my coil just below resonance or at resonance, so
> > an increase in current amplitude would mean that the comparator
> > would drive the VCO input voltage lower, lowering the frequency to
> > compensate for the increase in current
> 
> Thanks, I'm clear on that now.  That sounds a little delicate - if
> the resonance of the coil ever fell below the VCO frequency...
> I wondered if you were using some sort of control logic, eg
>  1. Tune the VCO a tad in some direction
>  2. Secondary current higher?   If not, change direction.
>  3. goto 1.
> 
> Jan Florian Wagner wrote:
> > ... phase locked loop seems to work if and only if the upper
> > freq of the VCO is set to the unloaded reso freq of the secondary
> > and the lowest freq is maybe 50kHz below this (300kHz coil).
> 
> How far above Fres can you set the upper freq before problems occur,
> and what are those problems?  When you get things settled down, it
> would be interesting to see, by looking at the vco control voltage,
> just how low the secondary Fres can dip during heavy arc loading of
> the secondary.
> 
> I've always built self-oscillating sstc, ie direct RF feedback from
> the secondary, but I'm a bit reluctant to use this method at higher
> power.  Hence, I'm keen to learn about how others are using PLLs.
> Does anyone have any good links?
> 
> > not a "plug'n'play"-for-any-secondary thing like I had wished...
> 
> That would be tricky, for impedance matching as well as frequency
> control.  I think there'd have to be some preset constraint on the
> vco range to avoid it latching on to an unwanted mode of secondary
> resonance.
> 
> Regards,
> --
> Paul Nicholson,
> --