A Performance of the Soft-Charging Operation in Series of Step-Up Power Switched-Capacitor Converters

Due to their high power density and appropriateness for small circuits integration, switched-capacitor (SC) converters have gotten more interests. Applying the soft-charging technique effectively eliminates the current transient that results in a higher power density and a higher fundamental efficiency. Achieving the complete soft-charging operation is impossible by using the conventional control diagram for any SC converter topology. In this paper, we proposed a split-phase control to achieve the complete soft-charging operation in a power switched-capacitor (PSC) converter. The proposed control diagram was designed for a 1-to-4 PSC converter (two-level of the PSC converter). The implemented split-phase diagram successfully controls eight switches to exhibit eight modes of operation. In addition to the current transient elimination, the complete soft-charging allows us to reduce capacitor sizes. However, reducing capacitor size negatively increases the output voltage ripple; hence, an output LC filter is needed. The complete soft-charging achievement accomplishes a 96% efficiency due to the lower output impedance and the dead time switching. LT-Spice software has been used to verify the proposed control and the results were compared with hard-charging and incomplete soft-charging operations.