A Stage-by-Stage Soft Start-up Strategy for Multiple-Modes Resonant Switched Capacitor Converter

A safe and rapid soft start-up mechanism is critical and essential for enhancing the reliability of resonant switched capacitor converter. This paper proposes a soft start-up strategy for a resonant switched capacitor converter with two-stage resonant tanks and multiple operating modes. Based on the principle of establishing the capacitor voltage with maximum possible rate, the state trajectories of the first-stage and secondstage resonant tanks are sequentially designed within the resonant current limiting band. After that, the output voltage is built up with optimal switching frequency. The proposed strategy is elaborated in detail under one of the operating modes. On this basis, a generalized soft start-up procedure applicable to all operating modes is designed. Furthermore, the comparison with hard start-up and the impact of component tolerances are investigated. The proposed strategy enables rapid and sequential establishment of capacitor voltages across three stages, while ensuring that there is no inrush currents or voltage spikes on components. The correctness of the proposed strategy is verified by soft starting a 48V/100W converter prototype under two different operating modes.