Piezoelectric transformers (PTs) allow the design of promising power supply applications, increasing efficiency, reducing size, facilitating the achievement of high transformation ratio, besides providing high immunity against electromagnetic noise. Due to the electrical equivalent model having resonant characteristics, some resonant topologies are used to build these power supplies, i.e. the Class-E converter. In order to make easier the analysis of high order converters, it's possible to use a normalized analysis method. The control of the Class-E converter using PTs is implemented through the switching frequency and duty cycle variation. The static gain is achieved though the switching frequency variation, while the duty cycle is adjusted with the purpose of achieving soft switching for different frequencies and loads. This paper shows a normalized analysis of this process, including a normalized frequency and load variation, without the need of design parameters. Experimental results for a 3W step-down converter are shown for a universal 85-260VAC input and out put voltage 6 V DC, to validate the proposed method.
Power enhancement of piezoelectric transformers for power supplies