OK thanks for summing that up guys 
Peterae, here is what follows, I have not had the time to post my reply to your previous post:
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Ex when you search for the principle of operation regarding these induction cookers why do the documents mention series resonance and use resonant capacitors in series with the coil.
I mean are you saying these are not resonant.
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"Resonance" is just a word. If Q=0.5 or Q=10
11, "resonance" doesn't say the difference. We must know what we are talking about.
If the capacitor made the coil resonant in a significant manner, we should observe a sine signal.
You can observe (
http://jnaudin.free.fr/gegene/images/gegene13cCURa.jpg) that the positive voltage is about twice the negative. The mean voltage being 0 because we have AC, this means that the negative pulses are larger than the positives ones. The signal is not sine => spectrum is not a single resonant frequency.
Then there is almost no significant overvoltage (
http://jnaudin.free.fr/gegene/images/gegene13cVTGa.jpg). The reason is that the IGBTs are switching components, they don't control a sine wave. When one is ON and the other OFF, the primary coil voltage is imposed, deleting the building of a resonant energy. So I think that the Q is much less than 1, perhaps not even 0.5 which doesn't prevent an oscillator to run.
Surely the capacitor is favouring the switching frequency and its role is essentially to avoid a too high or an unstable switching frequency that otherwise would occur, by lack of well defined time constant.
Compare the resonance here with that one of a mechanical oscillator (Q= 5=>10), a bad LC oscillators (Q=10), LC or lines oscillators (20=>100), high-Q active inductor (500=>3000), RF cavity (some thousands), quartz crystal oscillator (5000=>30000), single-crystal silicon micromechanical oscillator (10 000=>100 000), supermirror (10
11).
If one still really want to speak of resonance, formally one may, but the effect here is not significant.
Note that in your schematics the serial LC circuit using the 940nF should enhance a little the resonance but in most of the schematics that I saw here and there, there is not this circuit but only the primary coil connected to the IGBTs.
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Topic: Naudin's Gegene (Read 214400 times)
