In this paper, an efficient algorithm strategy for synchronous rectification (SR) used in LLC resonant converters is proposed. The output voltage and the primary resonant inductor current of LLC converter are combined together to produce suitable drive signals for SR in the below resonance mode. In the other resonance modes, the drive signals for SR are synchronous with the drive signals of corresponding primary switches. In order to validate the feasibility of the proposed algorithm strategy, a 300W prototype with 100V input voltage, 25V output voltage is implemented using field-programmable gate array (FPGA). The measured maximum efficiency is 92.1% and the overall efficiency is higher than the one with conventional drive method for SR.