A modal actuator-based single-layer piezoelectric transformer for coilless soft switching inverters

In this paper, we propose a coilless backlight inverter for LCD TVs. To simplify the manufacturing procedures of the inverter, a single-layer piezoelectric transformer was used as the basis for the development. Traditionally, the input capacitance of a single-layer piezoelectric transformer prevents us from identifying a proper inductor to achieve LC resonance. Without the presence of LC resonance, high-frequency noise within the output signal can be found. The zero-voltage switching technique can be used to adjust the rectified input voltage to become a trapezoidal voltage waveform and thus reduce some of the high-frequency voltage signals amplified from the input voltage waveform. As the presence of this high-frequency voltage waveform will influence the vibration of the Rosen-type piezoelectric transformer, which can lead to a lower energy transfer efficiency and higher temperature rise on the MOSFET, a solution is needed to further enhance the performance of the piezoelectric transformer-based inverter. It can be shown that the above problems can be solved using a quasi-modal surface electrode adopted onto the surface of a piezoelectric transformer. More specifically, modal filtering provided by the surface electrode of the piezoelectric transformer can be shown to facilitate the removal of the inductor and to eliminate the high-frequency noise that cannot be eliminated by a soft switching technique. In addition, the temperature rise of the MOSFET within the driving circuitry can be shown to be improved significantly. The experimental results were found to match well with the theoretical predictions. © IOP Publishing Ltd.