A step-down switched-capacitor AC-DC converter with double conversion topology

Abstract

In the field of portable electronic devices, a small and light AC-DC converter or AC adapter has been required in these last few decades. To meet such demands, a switched-capacitor (SC) AC-DC converter draws many researchers’ attentions in recent years. It is known that the SC AC-DC converter can realize smaller size and lighter weight than transformer-based AC-DC converters, because no magnetic component is required to design the SC AC-DC converter. In previous studies, several AC-DC converters succeeded in downsizing and light-weighting by using SC techniques. However, the power efficiency of conventional SC AC-DC converters is still low, and their control method is complicated. To overcome these problems, a step-down SC AC-DC converter with double conversion topology is proposed in this paper. The proposed converter consists of a full waveform rectifier with a big capacitor and two converter blocks. In each converter block, the 1/3 × step-down conversion is performed by connecting three capacitors in series, where electric charges stored in these capacitors are averaged by using series-connected flying capacitor. By connecting these converter blocks in series, the 1/9 × step-down conversion is realized by controlling power switches by non-overlapped two-phase clock pulses. Therefore, unlike the conventional converters using multiphase clock pulses, the proposed converter can achieve not only simple circuit control but also small ripple noise. Furthermore, the reduction of output ripple leads to the improvement of power efficiency. To help readers’ understanding for the proposed converter, first, a simple four equivalent circuit of the proposed converter is derived theoretically. The characteristics of the proposed converter are clarified by the theoretical analysis. Then, in order to demonstrate the effectiveness of the proposed converter, the proposed converter is implemented by simulated program with integrated circuit emphasis (SPICE) simulator. The validity of the theoretical results is confirmed by the SPICE simulation. Finally, the feasibility of the proposed converter is confirmed by experiments implemented on a breadboard.