High-powered backlight inverter for LCD-TVs using piezoelectric transformers

In this study, an innovative design of a high-voltage, high-powered, low-cost backlight inverter based on piezoelectric transformer technology for lighting long cold cathode fluorescent lamps (CCFLs) on large size LCD-TVs is presented. Three innovative design thoughts are introduced here. First, the quasi-modal electrode is used as the input electrode of the piezoelectric transformer. It is shown that a full modal filtering effect is achieved. In other words, all unwanted vibration modes of the structure are suppressed, which eliminates all higher harmonics of the input voltage. The second one is an innovative rigid support design which can enhance the modal filtering effect, which can also be used to replace thin input wiring and lead to lower contact resistance. The third innovative design uses direct switching on the rectified voltage from the power line (110/220V). With direct line voltage input, a single layer Rosen-type piezoelectric transformer (PT) can have enough gain to generate a high voltage to light long length CCFLs instead of using high cost multilayered PTs. A piezoelectric transformer-based inverter based on the above design considerations is built and verified in this study.