Novel Quadratic Isolated Step-Down Converter With Concise Configuration and Alternating Flux Balance Derived From Double-Ended Forward-Buck Converter

This paper presents a novel quadratic isolated step-down converter (NQISC) that integrates a double-ended forward converter with a buck circuit to achieve a quadratic step-down feature and continuous output current with a concise structure. NQISC only requires two switches, which can be operated independently. Moreover, partial resonance is incorporated into the converter design to accomplish alternating operation of the isolation transformer, balance the magnetic flux, and extend the duty cycle beyond 0.5. The converter operation and theoretical analysis are comprehensively discussed. A 240-W prototype operating with an input voltage from 200 V to 600 V and 24-V output is implemented to validate the NQISC and verify the mathematical derivations. The measured peak efficiency is 92.98%, and the full-load efficiency is 92.28%.