A Comparison of DC and AC Output Inductors in Tunable Piezoelectric Transformer Based DC/DC Converters

Tunable piezoelectric transformer (TPT) is a recently developed piezoelectric transformer with three ports: input, output and control ports. It can be treated as the integration of an LCC resonant tank and a transformer, where the series resonant capacitance can be tuned by the control port. There are two methods to design the output LC filter in TPT based converters. The traditional method is to place the output inductor after the rectifier. Such inductor is denoted by DC output inductor since it has a non-zero average current. The proposed method in this paper is to place output inductor before the rectifier. Such output inductor operates with zero average current and is denoted by AC output inductor. The regulation limitation caused by the DC output inductor is analyzed. This can be improved by the new resonance characteristic induced by the AC output inductor. The performance of TPT based converters with these two types of output inductors are compared. Experimental results show that the TPT based DC/DC converter with AC output inductor requires smaller output inductance and control capacitance than the one with DC output inductor. Also, the one with AC output inductor has better regulation and light load efficiency but worse full load efficiency.