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Re: DRSSTC driver tests- Dual resonance disaster

Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>

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

> I also managed to test some of Antonio's tunings. I discovered if I reversed
> the feedback connections I could get the PLL to sit midway between the two
> poles in pulsed mode. I got waveforms that looked just like Antonio and
> Jimmy H's simulations, I'll post some screenshots tomorrow.
> I tried detuning the secondary in various ways and I was surprised how
> robust these tunings were. I tried a heavy simulated streamer load of a ~200
> ohm light bulb in series with 52nF (the secondary capacitance is also 52nF)
> and it hardly changed the frequency needed for soft switching. Shorting the
> secondary altogether didn't change the frequency much either.

These values, 200 Ohms and 52 nF, look quite strange for streamer load.

> I saw things that suggested these tunings could be used with longer burst
> lengths. When I added the load, the beats disappeared leaving a decent
> steady state response. The one problem would be- if using longer burst
> lengths the coil must break out during the first beat or it goes completely
> nuts. I think the sign of the feedback reverses or something.

The tunings turn in almost perfect impedance matching networks when load
is added. But when using feedback from the double resonator, some care
must be taken about from where it is taken.

Look at these simulated waveforms (mode 17:19:21, Ca=30 nF, La=15.67 uH,
Lb=30 mH, Cb=15 pF, squared sine drive at 238580 Hz):
a) No load. Note the reversal of the input current after complete energy
transfer. The same waveforms appear if the driver is turned off at the
maximum output voltage. The free-wheeling diodes create the input
In this case, however, the cycle doesn't repeat.
b) Light load (800 kOhms). Still some reversal.
c) Heavier load (400 kOhms). No reversal.
So, feedback can´t be from the input current. Can be from the output
voltage, or from the secondary current, with a 90 degrees phase shift.

Antonio Carlos M. de Queiroz