Self‐oscillating isolated‐buck (fly‐buck) converter

Abstract

Abstract This study presents a self‐oscillating fly‐buck converter. The primary objective of this research is to lower the final bill of materials cost of a fly‐buck converter. The fly‐buck converter is based on a relaxation self‐oscillation circuit. The main transformer is updated with two additional auxiliary windings for positive feedback implementation. The turn ratios of these windings are estimated, and criteria for a stable oscillation mode are developed. A switching frequency formula is also provided. Furthermore, an example start‐up circuit is proposed and calculated. Output voltage stabilisation is implemented and demonstrated to work with ±10% variations in input voltage. The experimental data and design procedure are presented along with a comparison of the proposed fly‐buck converter against conventional fly‐buck converters. The converter is optimised for maximum efficiency, with an efficiency of >85% demonstrated at 20 W output power. The proposed self‐oscillating circuit can also be implemented in a conventional synchronous buck converter. The Maxima software code for automated calculation of the converter is supplied as supplemental active media content.

Keywords

• Power electronics, supply and supervisory circuits
• Transformers and reactors
• Power convertors and power supplies to apparatus
• Control of electric power systems