A 48 V-1 V Auxiliary-Assisted Hybrid DC-DC Converter With Flying-Capacitor-Based Virtual Bus for Fast Transient Response

The focus of this work is an auxiliary-assisted 4:1 dual-inductor hybrid (DIH) converter for fast transient response in 48 V PoL applications. The flying capacitor of the DIH converter is utilized as the energy buffer for the auxiliary stage, which is a low-cost, GaN-based bidirectional buck converter. The main DIH converter delivers the dc load power from the 48 V bus using an average-current-mode-control scheme, while the auxiliary stage regulates the output voltage with an output-capacitor-current (OCC) sensing scheme. The proposed architecture operates with a virtual auxiliary voltage bus with minimal auxiliary capacitance, C_\text{AUX}, due to the OCC-sensing scheme. A 40 W prototype has been fabricated to validate the proposed architecture with the virtual bus concept. The prototype achieves a peak efficiency of 93.8% and regulates the output voltage of 1 V within \pm50 mV during 20 A load transients with an output capacitance of only 800 µF. Experimental results validate the operation of the virtual bus with C_\text{AUX} = 0.47 µF during 20 A load transients while observing a deviation of 4.7 V on the 12 V auxiliary virtual bus voltage, V_\text{AUX}.