This paper describes an optimized sensorless synchronous rectification (SR) method for LLC resonant converter to improve its efficiency in wide output voltage range. In LLC resonant converters, SR, which replaces the secondary side diodes with switches, is mainly mentioned to enhance efficiency. Among SR methods, the sensorless method has gained significant attention because it does not require additional circuits. However, conventional sensorless methods cannot be applied for the wide output voltage range due to the inaccuracy of model analysis. Furthermore, these methods might cause an early turn-ON of SR in the step-down region, resulting in the inversion current that reduces efficiency and stability. To solve these problems, the proposed SR method utilizes a time-domain model, which obtains high SR accuracy in entire range. Moreover, it prevents the inversion current by introducing an accurate turn-ON of SR. Therefore, the proposed SR method can achieve high efficiency in wide output voltage range with high stability.
