Abstract: The arrival of the 5G era has put forward higher requirements for the power system，that is，the

converter is required to have high efficiency，high power density，and rapid dynamic response. In response to this

problem，the third generation of wide bandgap semiconductor device gallium nitride（GaN）transistors was used. A new type of fractional turn structure was adopted to optimized transformer structure. The DSP digital control method was used to design a 400 V to 12 V，and the output power is 500Whigh efficiency，high power density LLC resonance converter. Through theoretical analysis of the influence of actual LLC circuit parameters under high frequency conditions，the system optimization direction was determined，and the structure of fractional turns transformer was improved by combining finite element simulation software. Finally，a physical platform was built to verify the feasibility of the theory.

      Key words: LLC resonant converter；gallium nitride（GaN）；fractional turn transformer；high efficiency and

high power density