Comparative Analysis on Minimum Output Impedance of Fixed-Ratio Hybrid Switched Capacitor Converters

Abstract

Hybrid switched capacitor (SC) converters have gained popularity as they showcase promising performance in high- and fixed-ratio applications. Hybrid SCs are able to achieve minimum output impedance at lower switching frequency compared to conventional SC converters; yet, the minimum achievable output impedance of hybrid SCs operating under resonant or soft-charging conditions may be higher than. This work evaluates and analyzes the performance of conventional SC and hybrid converters through the output impedance. Hence, the output impedance of various SC topologies are characterized with different inductors placement, i.e single inductor at the output v.s. distributed inductors in series with each flying capacitor, for performance comparison. It is found that the deviation of duty ratio from 50% yields differences in minimum output impedance between conventional SCs and those hybrid SCs with a single inductor at their outputs. In order to compare between topologies, three types of optimization approaches that result in minimum output impedance are evaluated with the design constraints of switch rated voltage and conductance. If both constraints are available for fully customization on switches, the Dickson topology would have the lowest minimum output impedance. In contrast, if only switch conductance or minimal number of switches is considered (in low-voltage applications where voltage rating is no longer a constraint), other topologies showcase promising performances.