Design of a flyback transformer using a stress annealed Finemet nanocrystalline alloy

This paper presents experimental results obtained in a flyback converter whose transformer is realized with a stress annealed nanocrystalline (Finemet) material developed by the authors' laboratory. This new original process results in providing a low value of relative permeability (around 200), allowing to store large energy. So, a flyback transformer without an air gap has been tested in order to evaluate the performances of this material. Very satisfying results have been measured. Because of the low magnetic losses of the material at high induction level (up to 0.6 T) and high frequency switching (up to 50 kHz), low transformer losses and low temperature rise have been obtained. Some comparison measurements with a ferrite transformer are given in the study. Discussions are proposed in order to show the benefit brought by this technology and what improvements can be carried out.