400V-to-48V GaN Modular LLC Resonant Converter with Planar Transformers

This paper presents a 400V-to-48V GaN modular unregulated LLC resonant converter with integrated planar transformer. Four identical MHz full-bridge 100V-to-48V GaN LLC resonant converter modules are connected in series on the input side and in parallel on the output side. In each module, this modular LLC resonant converter has only a 2-to-1 turns ratio which can have the simplest interleaved winding structure. Since the total power is divided into four modules, the PCB winding loss and the PCB manufacture cost are significantly reduced. In addition, the parasitic capacitance is also reduced since the multiple planar transformers are horizontally distributed. The power density is further improved due to the more distributed thermal stress. This modular LLC converter can extend the input voltage range by more modules in series on the input side, and extend the output current by more modules in parallel on the output side. In this paper, a 3kW 400V-to-48V prototype using 150V and 80V GaN power devices is developed and tested with a 98.6% peak efficiency and 522W/in ³ power density.