Input Parallel-Output Series Connection of Radial Mode disk-type Piezoelectric Transformer for Thermal Balance Improvement

Nowadays the piezoelectric transformer (PT) is used widely in power applications. However the amount of power that a PT can handle is limited and the parallel connection of PTs is needed to overcome this limit. In the parallel connection, the thermal imbalance between PTs should be prevented to avoid the thermal runaway of one of the parallel connected PTs. The mechanical resonant frequency of the radial mode disk-type PT becomes larger as the temperature increases. Because this thermal characteristic operates as the positive feedback in the conventional parallel-parallel connection, it is difficult to achieve the thermal balance. This paper introduces the parallel-series connection of the radial mode disk-type PT to improve thermal balance. The main idea is that the parallel-series connection uses the inherent thermal characteristics as the negative feedback. It is verified that the thermal balance between the PTs is improved in the proposed connection method by testing it with a constructed 40 W adapter system