VERY SMALL COIL-LESS ELECTRIC POWER SUPPLIES USING PIEZOELECTRIC CERAMICS FOR MOBILE ELECTRONIC INSTRUMENT

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This study aimed to realize the very small AC-DC converter and DC-DC converter by using the piezoelectric transformer. Following terms and results have been obtained through the four years'investigations.1.Higher electric power density can be achieved by using the higher mode resonance in the piezoelectric transformer. These facts have been found and confirmed.From these results, the second Radial vibration and the fifth Width Extensional vibration have been selected.2.Design method for the piezoelectric transformer has been established. In the method, the high power characteristics of the piezoelectric ceramic materials have been adopted, which were measured by us.3.Second Radial mode piezoelectric transformer has been investigated as a high power density transformer. High efficiency of 95% has been achieved, and the multilayered type transformer has been made.4.Fifth Width Extensional mode piezoelectric transformer has been investigated as a much higher power density transformer. Also in this transformer, high efficiency of about 90% has been achieved.5.Losses of the piezoelectric material have been measured separately by the automatic measurement system.These experimental values of losses can be used to evaluate the transformer efficiency precisely. The measurement system were developed and improved by us.6.Stable and high efficiency driving and rectifying cicuit have been investigated. In the driving circuit, PLL automatic tracking system has been adopted.