Piezoelectric Transformer Efficiency Tests in a Digitally Controlled Converter Circuit

The paper discusses efficiency issues of piezoelectric transformers in a step-down DC/DC converter application. With the development of piezoelectric technology, these compact non-magnetic devices are becoming an interesting alternative to traditional transformers in a wide range of electronic equipment. Despite high declared efficiency (above 90%), heat effects resulting from energy loss are still a great concern. A prototype of ring-shaped piezoelectric transformer specially suited for step-down applications was tested in an experimental converter circuit, driven by a programmable digital control system of the authors' own design, described in the paper. The influence of input voltage, frequency, duty factor and other conditions on the power transformation efficiency was investigated. The safe operation area for the device under test is determined and compared with its declared ratings. The correlation between efficiency and thermal behavior of the transformer is discussed.