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

Abstract

In this paper, we propose a coilless backlight inverter for LCD TVs. To simplify themanufacturing procedures of the inverter, a single-layer piezoelectric transformer was usedas the basis for the development. Traditionally, the input capacitance of a single-layerpiezoelectric transformer prevents us from identifying a proper inductor to achieveLC resonance. Withoutthe presence of LC resonance, high-frequency noise within the output signal can be found. The zero-voltageswitching technique can be used to adjust the rectified input voltage to become atrapezoidal voltage waveform and thus reduce some of the high-frequency voltage signalsamplified from the input voltage waveform. As the presence of this high-frequency voltagewaveform will influence the vibration of the Rosen-type piezoelectric transformer, whichcan lead to a lower energy transfer efficiency and higher temperature rise on theMOSFET, a solution is needed to further enhance the performance of the piezoelectrictransformer-based inverter. It can be shown that the above problems can be solved using aquasi-modal surface electrode adopted onto the surface of a piezoelectric transformer. Morespecifically, modal filtering provided by the surface electrode of the piezoelectrictransformer can be shown to facilitate the removal of the inductor and to eliminate thehigh-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 beimproved significantly. The experimental results were found to match well with thetheoretical predictions.