Soft Switching on Center Driven Piezoelectric Transformer Based Inverters

摘要

A new center-driven piezoelectric transformer vibrating at 3/2 λ mode is proposed in this paper. The modal electrode can provide full modal filtering effect for rectified input voltage. Both the theoretical results and the experimental verification are presented in this paper. From the two output sections of the center-driven piezoelectric transformer, which was polarized in opposite directions, out-of-phase output voltages at the designed third resonance frequency were output. Two center-driven piezoelectric transformer configurations were used to light CCFL. The first configuration connects two CCFLs (cold cathode fluorescent lamps) to the two output sections of the piezoelectric transformer and shows that the two CCFLs can be lit in sequence or simultaneously. The other one is that a single extra-long CCFL for large size LCD TV backlight can be connected between the two output electrode and the floating connection configuration can provide doubled driving voltage to light the extra long CCFL. Soft switching techniques were adopted to reduce the switching loss and to lower the wasste heat. The switching dead time between the on and off states was adjusted to make the end voltages of MOSFETs being charged and discharged to reach zero voltage right before switching, i.e., to drive the MOSFET in the so-called zero voltage switching (ZVS) condition. The modal filtering electrodes were also adopted to filter out the higher order harmonics while keeping the driving efficiency high. By combining the techniques mentioned above, an innovative piezoelectric transformer based inverter is completed and found to possess performance higher than traditional inverters.