A new method to design piezoelectric transformer used in MOSFET and IGBT gate drive circuits

Abstract

This paper is situated in the continuity of our works focused on the use of piezoelectric transformer (PT) in MOSFET/IGBT gate drives. In this paper, a new design method for a gate drive PT is presented. We have previously demonstrated that this kind of transformer can be successfully used in insulated MOSFETs/IGBT's gate drive circuits. An optimized multi-layered PT working in the second thickness mode has been studied for transmitting signal and energy in a gate drive circuit. Based on an analytical Mason model, the design method gives the minimal size of the multi-layer PT. Thickness of the PT is given by its mechanical resonance frequency and by maximum electrical field in the material. This method takes into account mechanical losses and heating of the piezoelectric material. Area of the PT is calculated considering the required secondary power P/sub 2/ and heating of the material. This analytical design method can be extended to predict the characteristics of the PT: gain, transmitted power, efficiency and heating of piezoelectric materials according to load resistance. A prototype of a PT based on this design process was fabricated and tested experimentally. Piezoelectric material used for primary and secondary layers is lead titanate, PbTiO/sub 3/, polarized along the thickness. Insulation between the primary and the secondary is achieved by a 300 /spl mu/m thickness layer of alumina, Al/sub 2/O/sub 3/. All calculated characteristics have been confirmed by measurements.