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,

Could someone here be enough generous to explain in simple term
why can't you use a feedback loop like the grid loop in VTTC or
the feedback loop used in simple flyback ( 2* 2N3055 circuit )
for driving a half bridge mosfet.

I ask this question in many occasion in the last 2 years and I
never get an answer. Each time I try to rephrase the question
because I know my english could be ambiguous sometime but whit
out success.

Cheers,

Luc Benard

Tesla list wrote:
> 
> Original poster: "Malcolm Watts by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
> 
> Hi Paul,
> 
> On 27 Dec 2001, at 7:49, Tesla list wrote:
> 
> > Original poster: "Paul Nicholson by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
> >
> > John Tomacic wrote:
> >
> > > 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.
> >
> > I wrote:
> >
> > > John, can you help me understand just how the vco is tuned with
> > > this arrangement?  I don't see how, with only amplitude info
> > > from the sensor, the vco can 'know' which direction to tune, ie up
> > > or down?
> >
> > Malcolm wrote:
> >
> > > A digital approach can pull a "direction" out of the signal (a D FF
> > > is all it takes).
> >
> > Malcolm,
> >
> > Well, I don't understand this. John doesn't seem to be giving any
> > hints, maybe you can explain?  How can you tune the VCO with just an
> > amplitude feedback and a comparator?
> 
> If you apply one signal to the "D" input and the other to the clock
> input, Q will be high or low depending on relative phasing of the two
> signals. I realize that because the frequencies are different, the
> phase will slide from lagging to leading (or vice-versa) but if the
> difference is not too great, the direction indication should last for
> long enough to enable locking. An XOR gate fed from the same signals
> gives the degree of difference.
>       Kind of handwaving stuff from the digital realm but I thought
> it might be useful or applicable to the problem.
> 
> Regards,
> Malcolm