Optimisation of a self-driven synchronous rectification system for converters with a symmetrically driven transformer

Synchronous rectification (SR) is mandatory to achieve good efficiencies with low output voltages. If the transformer is driven asymmetrically without dead times, self-driven synchronous rectification (SDSR) is a very interesting solution. However, if the transformer is driven symmetrically, the synchronous rectifiers are off during the dead times and, as a consequence, the efficiency is lowered. This paper deals with the optimisation of a SDSR system that keeps the rectifiers on even during the dead times. Hence, the most important parameters have been studied in order to obtain the highest possible efficiency. This system is very interesting because it can be used in any topology with a symmetrically driven transformer independently of the output voltage level and for a wide input voltage range. The system has been implemented in a prototype in order to measure the real efficiency that can be achieved with the proposed scheme and compared with the efficiency of the same prototype without SDSR.