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

Original poster: "Steve Conner" <steve.conner@xxxxxxxxxxx>

>I think this is a Phase Locked Loop or external oscillator timed system
>issue...  If I have the IGBT timing run off an oscillator and the primary
>frequency suddenly shifts 180 degrees without the oscillator shifting as
>well....  It blows up!!

Yes it is mostly relevant to PLL and VCO operation. There does seem to be a
limit to how fast the frequency can shift due to the primary Q, unless
reversals happen. (those double length cycles that your circuit produces)

>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 :(

>Steve Conner's PLL circuit is very >capable!!

It's probably too capable, it just confuses things. I am thinking of going
to a plain self-resonant circuit but maybe with something that keeps it off
the harmonics (not sure what yet)

>No. I think the two pole system will always dance between the two >frequencies. I don't think you can stop that unless you give up zero >current crossing as in the case of secondary feedback.

I think it is possible to stay on one frequency (or at least get rid of the
reversals) by tuning right, but the way you put it, there doesn't really
seem to be any point unless you are trying to "tame" the system to match a

Steve C.