Power improvement of piezoelectric transformer based DC/DC converter

In this paper a novel strategy to increase the power of piezoelectric transformer (PT) by using a cooling system is presented. A thermal pad is directly attached to a PT to dissipate the heat and enhance the power capacity. In a piezoelectric ceramic the heat increase quickly when the vibration velocity become too large. Therefore there is a limit in vibration velocity magnitude. To explain the relationship between the vibration velocity, the output current and the output power we propose a theoretical-phenomenological model based on nonlinear equivalent circuit. It will be shown that the vibration velocity and temperature influence the characteristics of the piezoelectric transformer significantly. A large vibration velocity may lead that the internally thermo-physical feedback loop of the PT enters into an unstable state. In this paper, a PT with the cooling system was implemented in a DC/DC converter. A zero voltage switching (ZVS) half-bridge is used to drive the PT and a full-wave rectifier is used to obtain the DC load voltage. As a result, the maximum power of the PT based DC/DC converter can be increased from 4.41 W to 10.2 W at specific temperature. The study comprises of a theoretical part and experimental proof-of-concept demonstration of the proposed system.