Consideration for Abnormal Phenomenon in Common-Source type Active-clamped Forward Converter with Self-driven Synchronous Rectifier

Many switching converters use soft-switching techniques with an active-clamp snubber so as to reduce switching surge and common-mode noise. In particular, the common-source type active-clamped forward converter is known as an effective circuit topology for common-mode noise reduction. On the other hand, replacing the output rectifying diodes with synchronous rectifier circuits, the power efficiency can be improved in the DC-DC converter with low-voltage and large-current output. Furthermore, the self-driven synchronous-rectifier circuits are generally used because of isolation and simple structure of their gate-driving circuits. However, for this common-source type active-clamped forward converter with self-driven synchronous rectifiers, it has been recently noticed that an abnormal phenomenon such as the inductor-current oscillation and the acoustic noise generation in the transformer occur in some conditions. This paper discusses the above-mentioned abnormal phenomenon. The cause of the abnormal phenomenon is examined and its occurrence condition is clarified