| HOW THE ROYER CIRCUIT WORKS |
| Mazzilli Vladimiro described in an e-mail how this circuit works: The Royer circuit is a push pull, current fed, zero voltage resonant converter. At starting T1 go in conduction for first through the 820 ohms resistor at point B. The conduction of T1 through D1 keep low the gate voltage of T2 that remains open. The current flowing through L1-L2-C cause an excitation in the tank circuit L1+L2 - C that is a parallel resonant dipole at frequency that is f = 1/ {2 * pi * sqrt [(L1+L2) * C ]} which is fixed and depend only from Ltot = L1+L2 and C. On L2 and on T2 we have half sine of the frequency f , but L1 is reversed respect (tight push pull topology) L2 and in this inductance the wave is reversed and from maximum value goes to zero naturally. The diode D2 can switch off T1 and consequently unlock the gate of T2 through D1, now the other 820 ohms resistor force in conduction T2, etc. The inductance at center of trafo/ inductor is an AF impedance that to do not disturb the running of the tank circuit, limits the ripple current and must not saturate because continuous current flowing into it. It is also a constant current generator at running frequency. The advantages of this topology is that the voltage decay naturally and the switching occurs with zero voltage, so the comutation losses are decreased and the soft switching make possible standard IGBT to go over 100 kHz, while in the hard switching is difficult to reach 20 kHz. The disadvantage is that the collector peak reach pi*Vcc-in, but differently from MOSFET the IGBTs at 1200 volts are normal production and also 1700 volts |
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