Switched-capacitor-based DC-to-DC converter with improved input current waveform

A new type of DC-to-DC converter is proposed by using dual basic quasi-switched-capacitor (QSC) converter cells. The prominent feature of this converter is its improved input current waveform, which can highly reduce the electromagnetic interference due to the conducted emissions as compared to the classical PWM-type and SC-based converters. The concept of energy transfer is realized by two symmetrical converter cells, operating in two cyclical phases. The d.c. voltage conversion ratio is determined by the voltage applied to the quasi-switch in each cell for controlling the charging trajectory of the capacitors in order to maintain a constant output voltage for a wide range of load and supply voltage. As the converter does not contain any inductive element, it makes the converter be small size, light weight, high power density and be possible to be fabricated in IC form. The small-signal frequency response shows that the designed converter has good operation stability. A prototype of 36W, 12V/9V, step-down DC-to-DC converter has been built, giving an overall efficiency of 73% with power density of 20W/in³.