Light-Load Switching-Loss Elimination Utilizing Pulse Density Modulation for Switched-Capacitor-Based Resonant Converters

This paper proposed the operation of switched-capacitor-based resonant converters with pulse-density modulation. The pulse density modulation inserts an interval periodically where a zero-average free-oscillating resonant current flows. The free-oscillating current ensures all MOSFETs operate with ZVS transition, and the interval reduces the equivalent switching frequency. Thus, it is possible to operate the SCRC with a negligibly small switching power loss and to reduce the resonant inductor core loss. The capability of maintaining ZVS transition distinguishes pulse-density modulation from the well-known burst-mode control method. The burst-mode operation always suffers from the unavoidable turn-on switching losses to stop and restart the resonance. The experimental results using a 3-kW prototype compares the performance of these two control methods. The pulse-density modulation is capable of reducing the loss of as much as 40% compared with burst-mode control and exhibits an efficiency over 99% in a wide range starting from 14% of the rated power.