An Integrated 6.78-MHz Class Φ2 Converter Using Bifurcation Phenomenon of Resonance Between the Isolation Transformer

Class Φ
₂
(or Class EF
₂
) reduces the voltage stress of a Class E conver
t
er by adding an additional
LC
branch, which increases the complexity of the circuit. This letter proposes an integrated Class Φ
₂
converter that uses the bifurcation phenomenon of the impedance matching network of the isolation transformer to eliminate the additional
LC
of a typical Class Φ
₂
(or Class EF
₂
) converter. With bifurcation between the isolation transformer, the resonant circuit can be tuned simultaneously at the first, second, and third harmonics, hence achieving a similar quasi-square voltage waveform. Since fewer components are employed, the additional
LC
can be removed, reducing complexity in comparison to the typical Class Φ
₂
(or Class EF
₂
) converter. A mathematical model has been developed to illustrate the frequency response under the bifurcation status. A 6.78 MHz prototype system has been built to verify the correctness of the mathematical analysis. The experiment demonstrates a lower switch voltage stress similar to the typical Class Φ
₂
converter but without using the additional
LC
.  The system has a high efficiency of 90.5% for a megahertz low-power system and exhibits zero-voltage switching independency over the power output range from 3 W to rated 30 W.