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In this paper, a short circuit phenomenon when dc-dc modules with self-driven synchronous rectifier (SR) run in parallel is described. Three existing driving schemes are analyzed and compared. A novel driving scheme for SR maintains the performance of SR as a self-driven scheme, while solving the problem of a short circuit when modules run in parallel. In addition, the amplitude of an SR driving voltage can be adjusted by using the proposed scheme. Therefore, the scheme is more attractive in the applications of comparatively high-voltage output. The principle of operation and the characteristics of the scheme are analyzed and verified on a 36-75 V input 1.8-V/60-A output experimental prototype, whose size is 1/4 brick and efficiency is above 90% under rating conditions. Index Terms--In parallel, self-driven scheme, synchronous rectifier (SR).

Paper presents a three-level soft switching LLC series resonant dc/dc converter. Zero-voltage switching (ZVS) is achieved for each main switch without any auxiliary circuit. Voltage stress of each main switch is half of input voltage. Zero-current-switching (ZCS) is achieved for rectifier diodes. Wide input/output range can be achieved under low frequency range because of two-stage resonance. Only one magnetic component is required in this converter. Efficiency is higher in high line input, so this converter is a preferable candidate for power products with the requirement of hold up time. For design convenience, relationship between dc gain and switching frequency, load resistance is deduced. Its open load characteristic and short load characteristic are exposed to provide theory basis for no load operation and over current protection. Design consideration of four dead times is presented to assure that voltage stress for main switches is within half of input voltage and ZVS for each main switch is achieved. Finally the principle of operation and the characteristics of the presented converter are verified on a 500 V-700 V input 54 V/10 A output experimental prototype, whose efficiency reaches 94.7 % under rating condition. Index Terms--Hold-up time, resonant converter, three-level.