Re: phase locked loop SSTC

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

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?

Regards,
--
Paul Nicholson,
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