A new method to drive synchronous rectifiers in forward converter topologies for extended input voltage applications

Conventional voltage-based self-driven synchronous rectifier circuits for forward converters traditionally suffer from large variations of driving voltage which, further, restrict them from wide input voltage applications. The origin of this problem comes from the use of forward and reset transformer voltage as single components from which the driving voltage is derived. The proposed method uses the sum of transformer forward and reset voltages to derive an efficient driving voltage waveforms and allows for extended input voltage range, e.g. 4:1. The phenomenon of "a small relative change of the sum of forward and reset transformer voltages" is explained and used effectively. Computer simulation and experimental results are attached.