This letter proposes a self-driven gate driver solely composed of passive components for synchronous rectification (SR). It utilizes the energy of the converter itself, automatically considers component tolerances and temperature variations of critical design parameters, and tunes the SRs on-time. Furthermore, no microcontroller, auxiliary power supply or current-sensing/voltage-sensing components is required. A great amount of cost is therefore saved. The proposed gate driver is preferable to be used to any resonant converters operating as DC transformers. This letter presents its practical implementation in an LLC resonant converter. Experiment results illustrate that the body diodes conduction and reverse recovery are eliminated.