Loss Model of High-Frequency Planar Transformer for High-Voltage Resonant DC/DC Converter

The increasing demands towards the power density and miniaturization on the power converters make the transformer become the bottleneck. For the traditional transformer, the copper wire is fixed on magnetic core by using the plastic bobbin, which may lead to a bulky size. The planar transformer adopts the multi-layer printed circuit board (PCB) as the winding structure and also uses the planar core, thus to remarkably reduce the size, especially the height. For the DC/DC converter with a high step-up ratio, the transformer with a high turn ratio and the Cockcroft-Walton voltage multiplier are normally employed to achieve the high voltage gain. Since this converter normally works in the zero-voltage-switching (ZVS) mode with relatively low output power, the power dissipation of transformer becomes a key issue. This work demonstrates the loss model of a planar transformer, which is used in the 24-V/1.8-kW resonant DC/DC converter with 20-W peak output power. The loss analysis is compared with the experimental results and a good agreement achieved. It is found that the winding loss is the dominating factor of the total loss.