RE: Full bridge with current and voltage switching?

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

Original poster: "Jan Wagner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>

Hi,

 > Original poster: "Jolyon Vater Cox by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
 >
 > Is it possible to have a full-bridge output stage where the
 > switching devices in one branch of the bridge are driven
 > signals in phase with the voltage, and in the other branch
 > in phase with the current, to obtain a dead-time effect
 > between  current reversal in the respective transistors?
 >
 > I am thinking of having a current transformer to switch the
 > transistors in the second branch, the transistors in the
 > first branch being switched by the squarewave from an astable.

Sounds like an interesting idea though i think you'll have to manually tune
the astable to f_res, which means it's not a self-oscillating setup.

 > Since current lags voltage n an inductor by up to 90 degrees
 > apart won't the transistors in the second (current-gated)
 > branch start to switch over up to a quarter-cycle after the
 > transistors in the first branch have switched over?

At least looking from the ideal transformer model (well-coupled for a SSTC),
on the pri side you've the transformed secondary impedance in series with
the rather small uncoupled/leakage inductance. The phase shift is less than
90deg... Ideally with unity coupling it would be 0deg. (or pls correct
me...)

But you can find a somewhat similar approach in a SSTC by Mazzilli
Vladimiro,
  http://www.pupman-dot-com/current/vladi2/mosfet.pdf
Maybe it gives you some ideas.

As what regards current transformers and phase shift - xfmr works with
current in, current out. Minimal phase shift. The output current is
transformed into a voltage by using a small resistive load, so no extra
phase shift there.


 > And, more relevant to the subject Tesla coils, would it be
 > possible to
 > derive the voltage signal from a winding inductively coupled
 > to the TC
 > primary (effectively in parallel with the primary)
 > and the current signal from a current transformer in series
 > with the primary? This way would it not be simple to design a
 > self-oscillating driver?

I know that at least the current transformer setup works, tried and tested
it in a switch mode welding supply, not much different to a SSTC... And
Mazzilli's SSTC shows it works for TCs too.

The old style Royer oscillator works too:
http://laptops.home.att-dot-net/Inverter-info.htm Actually, IIRC, Mazilli has
built one of these too. Maybe if you search the list archives you can find
some info...

cheers,
  - Jan

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