Low-power flyback converter with synchronous rectification for a system with AC power distribution

The design of efficient, isolated low output voltage converters is a major concern due to their widespread use. One of the preferred methods used to maximize their efficiency is synchronous rectification, i.e. the replacement of the secondary side diodes with MOSFETs to decrease conduction losses. However, depending on the topology being used, synchronous rectification might not provide the required efficiency improvement or even be easily implemented. This paper presents a novel synchronous rectification system that can be applied to converters with symmetrically-driven transformers and to converters from the Flyback family; in both cases, the proposed system adaptively generates a control signal that controls a synchronous rectifier MOSFET placed in paralell with each diode, turning it on during the conduction intervals of the diodes. The proposed system uses only information from the secondary side, thus avoiding breaking the isolation barrier; it can be built using a few low cost analog components, it is reliable and simple, and could be easily implemented in an integrated circuit. Up to a 3 % improvement is demonstrated in a 3.3-5 V, 120 W Push-Pull converter and up to a 2.5 % improvement is obtained in a 5 V, 50 W Flyback converter, both of them designed for telecom applications.

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“…The time when the voltage ramp V − equals V + determines the lenght of the control pulse, t VAR . Using (6) and (8):…”

Section: Implementation Of the Adaptive Off-timementioning

confidence: 99%