RE: Terry's DRSSTC actually hooked to a coil now >:-))

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jan Wagner <jwagner@xxxxxxxxx>

Hi Steve,

On Wed, 2 Feb 2005, Tesla list wrote:
> Original poster: "Steve Conner" <steve.conner@xxxxxxxxxxx>
> > My driver has no predetermined
> > frequencies so the drive frequency is totally up to what every the coil
> > system wants whenever and however it wants it.
>
> The only problem is if it asks for something stupidly high. With primary
> feedback there's nothing stopping it jumping to a harmonic of the resonator
> when ground arcs happen, so it could go to 3x or 5x the frequency you
> started with. The result is racing sparks and maybe burnt IGBTs. That is why
> I chose to use the PLL, so I could put a limit on the frequency range. But
> it seems to bring a lot of drawbacks too :(

About drawbacks: instead of a PLL you could plug in a small DSP like free 
samples of TI's TMS320LF2401A (32-pin, 40mips) or Motorola/Freescale 
56f8122 etc series (48-pin, 40mips, free devel tools).

The task doesn't require any special ADC, just a good square wave input to 
a digital input pin like the "real" digital PLL chips. You can then program 
it to set upper and lower limits to the output (driving) pulse lenghts, how 
fast the 'PLL' should slide towards the input (feedback) pulse lenghts, and 
what the phase difference between output and average input should be, and 
then add some further intelligence to the 'PLL' behaviour (scan start at 
previously known good freq, avoid harmonics, select a particular one of the 
freqs around f_res, etc).

A microcontroller could work, too, if it's a real fast one (clock + cycles 
per instruction), but a tiny DSP is better.
It doesn't require much components, basically just the DSP, xtal, 3.3v(?) 
regulator, and some protection for input and output lines going to business 
end section of the TC. The shielding against electronic interference must 
be similarly good as for the PLL circuit.
Just an idea! ;-))

cheers,
 - Jan

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