LLC resonant converters are popular in high-frequency and high-power-density applications with the advantage of excellent soft switching characteristics. Nevertheless

voltage regulation capability is constrained

and additional power losses will be introduced in a wide operating range. A partial-power LLC resonant converter for a wide input range is presented in this article. Two LLC converters are both designed at the open-loop state

performing as a DC transformer (DCX) to realize a constant transformation ratio. System input power is divided into two parts by a series connection of the two DCXs

which is helpful to reduce component ratings. A synchronous Buck-Boost is cascaded with DCX2 to achieve system closed-loop control by pulse width modulation. Most system power is transmitted by DCX1

and a small portion is processed by DCX2

so less power loss will be generated by Buck-Boost. Working principle

parameters optimization

and integration design of magnetic components are introduced in detail in this paper. A 200W 280 V-400 V/48 V experimental prototype with 1-MHz is established to demonstrate the correctness of the theoretical analysis. Peak test efficiency is up to 95.8%

which is improved compared with the conventional two-stage scheme under the same working conditions.