Re: A question about SSTC tuning

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

Original poster: "K. C. Herrick by way of Terry Fritz <twftesla-at-qwest-dot-net>" <kchdlh-at-juno-dot-com>

Jan (& all)-

Comments interspersed...

On Mon, 05 Aug 2002 08:18:41 -0600 "Tesla list" <tesla-at-pupman-dot-com>
writes:
> Original poster: "Jan Wagner by way of Terry Fritz 
> <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>
> 
> Hi Ken and all,
> 
> > For the amplification, I am just using several 5V CMOS inverting 
> logic
> > gates daisy-chained, capacitively coupled and "linearized" using 
> input-
> > and feedback-resistors.  The output of the last one of those is
> > essentially a rail-to-rail square wave and that then feeds to 
> several
> > additional logic gates for phase selection, on-off gating and 
> MOSFET
> > drive-generation.
> 
> Just as a side note: another one which works quite well is the 
> single
> 74HC4046 based signal-square-up trick which Gary Johnson presents in 
> his
> brilliant Tesla coiling papers at
>  http://www.eece.ksu.edu/~gjohnson/
>  (chapter 7, tesla coil driver, page 16, stuff around IC U3, and
>   also see description of the circuit)
> 
> Anyway it probably doesn't matter what method you use. 

You need a scheme that will keep the duty cycle close to 50%--so that, if
you are using some kind of a push-pull primary-driving circuit, the
transistors each stay on 50% of the time (less dead-time).  I'd
downloaded Gary's paper; not much description of the 4046 application,
the FSC data sheet on that item is pretty impenetrable--and Gary's Fig. 6
schematic is surely as daunting as some that I used to draw, in my more
productive days.

> Propagation delay  is likely to be the same anyways and <50ns. :o)
> (That's if you don't want to modulate the TC. Otherwise I'd use a
> manually tuned VCO with the audio signal injected into the control
> voltage.)

I tried to modulate my coil and apparently caused myself a whole pile of
grief.  I think it's because I was cutting the MOSFETs off in mid-cycle,
i.e., asynchronously with the secondary's excitation, & thus causing
alternate-phase MOSFETs to turn on together.  I've given that up
completely & am now trying to get the coil up & running again.

> 
> But - a controllable signal delay would be nice, to get proper 
> phase.
>   http://www.maxim-ic-dot-com/appnotes.cfm/appnote_number/559
> 
> That's something I'm trying to figure out right now, i.e. a maximum 
> power
> follower which could be added to this simple feedback scheme. 
> Something
> that would use a digital (or analog) controlled, automatically 
> adjusting
> phase shift which leads to maximum output power! :-)~

As I recall, I had made rough comparisons, from time to time, of spark
output as to my self-exciting scheme vs. just using a VFO for input
instead of the signal from the secondary.  I didn't notice any
improvement in the case of being able to tune through resonance, so
concluded that my phasing is close enough to optimum.
> 
> If someone already has done this, it'd be interesting to hear your
> experiences on how well it works! And how you did it! :)
> (or maybe I should buy a copy of Ken's patent? :o) )

My patent is just for the scheme of connecting the power transistors &
power supplies together into daisy-chained current loops so as to
constitute the primary.  It does not cover any transistor-driving
arrangement.

As far as the patent itself is concerned, anyone can use it, of course,
but if they want to use it in commerce in the U.S., then they must get my
agreement.  Otherwise, it's merely my license to sue them--nothing more. 
And I'm not likely to do that: the last defendant to be sued (another
invention) owes me $200K and counting, and they've been highly skilled,
so far, at concealing their assets.  Happens all the time...

Ken Herrick