New 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 SR (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 a new SDSR system that keeps the rectifiers on even during the dead times. Thus, it can be used to obtain very low output voltages, such as 1.5 V, with quite good efficiency. Moreover, it can be used over a wide input voltage range. The new system is implemented in a prototype in order to measure the real efficiency that can be achieved with the proposed scheme.