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4hv.org :: Forums :: Tesla Coils
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Gate signals while interrupter is off

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Crow187
Sat May 28 2011, 12:34PM Print
Crow187 Registered Member #795 Joined: Mon May 21 2007, 06:04PM
Location: Bocholt, Germany
Posts: 35
Hi everyone.

I am thinking about creating a DRSSTC without a GDT, so I have the ability to leave all gates as long high as I want. Nearly every circuit I was able to have a look at switched all gates low while the interrupter is switching the coil off. Is there a meaning by that? You could just leave highside 1 and lowside 2 switched on, right? I know that IGBTs can not conduct reverse current (FETs can), but the diodes would. I see one advantage: the primary cap is charged to bus-voltage when the first switching cycle begins, doubling the "first sine" current, maybe than it is easier to feedback the phase?

I made a Spice simulation, everything seems to work great!

What did I miss, or is it practicable? Thank you for your thoughts!

Crow187 (Lukas)
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MRacerxdl
Sat May 28 2011, 02:41PM
MRacerxdl Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
I think the only problem to get the Two H-bridges conducting is that for some time, it will be injecting energy at primary circuit. As it already oscillating, this can be dangerous. I'm not sure about that.

I never had any problem with feedback (only when the I put it at wrong side), because the Input Schmitt Triggers are very sensitive to voltage (As I know, 1V and up is On Signal) and even the smallest signal for DRSSTC is about a few amps of peak. Sufficient to generate that signal on output.

Other thing, the first pulse is created by the interrupter, and the primary circuit only starts to work when the interrupter switches off. (The ringing starts when the voltage shuts and the current still flowing through the inductor) So it *maybe* made that effect you said even with a normal circuit.

I'm not sure about that, but I gaving my opinion from what I learned.
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Antonio
Sat May 28 2011, 06:10PM
Antonio Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
A DRSSTC can be tuned to produce an output voltage similar to what appears in a Tesla coil if the signal generated by the driver is a sinusoid, or, in a good approximation, a symmetrical square wave, applied to the system with no energy on it. The driver shall then be switched off when the output voltage is maximum. In a conventional Tesla coil all the energy is in the primary capacitor, that is switched to the rest of the circuit by a spark gap or equivalent switch. What you propose is equivalent to a superposition of the two systems, with the square wave driver and an initial charge in the primary capacitor. May work, but I think that not perfectly, since the ideal tunings for a DRSSTC and a Tesla coil are slightly different.
Leaving the bridge switched on after the burst is equivalent to recharge the primary capacitor, causing another energy transfer (smaller) after the burst, it seems.
Anyway, the energy delivered by the driver is much greater than the initial energy stored in the primary capacitor, so no great difference is expected.
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