New Fixed-Frequency Digital Control to Improve the Light-Load Efficiency of an Isolated Regulated Converter

With the development of environmental and economic requirements, the light-load efficiency of DC/DC converters is increasingly important. However, many isolated regulated converters still use fixed-frequency control, which has low light-load efficiency. This paper proposes a new digital control method to improve the light-load efficiency under fixed-frequency control. On the one hand, new gate-drive timing control is proposed to achieve the soft-switching of the primary switch. On the other, the software voltage-second balance method realizes the synchronous rectification in the discontinuous conduction mode, which reduces the conduction loss. The diagram and workflow of the proposed control scheme are demonstrated at length. A 100-Watt prototype was designed, and the test results show that synchronous rectification and quasi-zero-voltage-switching are realized in the whole operating range at the light load. The light-load efficiency is 81% to 87%, which improves by 5% to 10% in comparison to the traditional forward converter. The prototype also functions well under the load transient. The proposed control scheme is implemented in one digital controller without additional components, and the circuit is low loss and low cost.