Energy Efficient Stepwise Charging of a Capacitor Using a DC-DC Converter With Consecutive Changes of its Duty Ratio. - Shunji Nakata; Hiroshi Makino; Junpei Hosokawa; Tsutomu Yoshimura; Shuhei Iwade; Yoshio Matsuda (IEEE Trans. Circuits Syst. I Regul. Pap., 2014)