Abstract: LLC converter is widely used because of its soft switching characteristics of zero voltage switching turn-on on the primary side and zero current switching turn-off on the secondary side in the full load range, but it has the defects of excessively wide switching frequency range and reduced efficiency in wide voltage range applications. In response to this defect, this paper proposed a circuit topology that adapted to a wide output voltage and its modulation method of mode-switching. The principle of topology was discussed first. Then mode switching modulation strategy to reduce the frequency adjustment range was analyzed in detail, and modes analysis was carried out for the low-voltage mode and the high-voltage mode. This paper analyzed the design considerations of LLC circuit for 200~900V wide output voltage, built a 2000W experimental prototype, and verified the feasibility of the proposed topology and mode switching modulation strategy.