Fabrication and characteristics of PDA LCD backlight driving circuits using piezoelectric transformer

In this paper, to apply piezoelectric transformer for personal digital assistants (PDA) liquid crystal display (LCD) backlight driving circuits, piezoelectric transformer using 0.3 wt.% Nb 2O 5 added PNW-PMN-PZT ceramics was fabricated as Rosen-type one with the size of 1 mm×16 mm×5 mm, and their electrical characteristics were investigated with the variations of load resistance and driving frequency. Then, the PDA LCD backlight driving circuits was manufactured using piezoelectric transformer, two MOSFET connected in series, voltage control oscillator (VCO) and one-chip microprocessor. After driving LCD backlight for 25 min using the proposed circuit, at driving frequency of 214.4 kHz, input voltage of 31.78 V and input current of 21.1 mA were measured at the input part of piezoelectric transformer. Then, output voltage of 293.2 V and output current of 2.2 mA were shown at the output part of piezoelectric transformer. At the same time, efficiency of 96.2% and temperature rise of 3.6 °C were appeared at the piezoelectric transformer.