T17.6 - A Novel Isolated Flying-Capacitor DC-DC Converter with Integrated Magnetics and Hysteretic Capacitor-Balancing Control

In recent years, the demand for isolated converters with high efficiency, high power density and low cost has increased. The Single-Active-Bridge (SAB) converter is an attractive option, as it can theoretically operate with a single magnetic component by using the transformer leakage inductance. However, the large series inductance required hinders magnetic integration. To address this, a new topology is proposed by combining the SAB with a flying-capacitor stage, adding only two capacitors. The converter reduces the required series inductance, halves the primary-side MOSFET voltage stress, achieves ZVS for all primary switches and ZCS for the secondary diodes, and regulates the output at constant switching frequency. These benefits rely on proper flying-capacitor voltage balancing, ensured through a hysteresis-based controller. The topology also avoids transformer core saturation and achieves soft charging and discharging of the flying capacitor. A 150 W, 300 V–36 V prototype operating at 100 kHz demonstrates a peak efficiency of 94% and 92.6% at full load.