High Frequency Isolated Bus Converter with Gallium Nitride Transistors and Integrated Transformer

Fig. 1.
(a) Traditional single core design.
(b) Original matrix transformer design.
(c) Core simplification combining to single EI core.
(d) Winding rearrangement to cancel AC flux in center leg.
(e) FEA simulation with AC flux cancellation.
(f) FEA simulation without AC flux cancellation.

The trend in isolated DC/DC converters is increasing output power demands and higher op-erating frequencies. Improved topologies combined with gallium nitride (GaN) transistors can allow for lower loss at higher frequencies. A major barrier to further improvement is the trans-former design. With high current levels and high frequency effects the transformers can become the major loss component in the circuit. This paper will study the impact of increased switching frequencies on transformer size, the ability of GaN transistors to increase switching frequency in high frequency resonant topologies, and propose an improved integrated transformer design that can decrease core loss and further improve the performance of traditional matrix transformers. The final demonstration being a Vin=48V, Vo=12V, Io=30A, 1.6MHz GaN converter with an improved integrated transformer offering a power density of 900W/in³.

Fig. 2.
(a) Integrated single core matrix structure with flux cancellation in center leg.
(b) Integrated single core matrix transformer without center leg.