A realization of low‐power supplies using switched‐capacitor transformers and its analysis

A switched‐capacitor transformer is a coil‐less transformer in which stepping‐up and ‐down of voltage is handled by switching the connections between capacitors alternately into series and parallel. This paper demonstrates that a low‐power coil‐less power supply can be created with these transformers. the proposed circuit has the following features: (1) High efficiency, comparable to that of a switching regulator, can be obtained easily. (2) Because of its coil‐less construction, it can be made small and light. Hybrid integration is also possible. (3) Coil‐less construction significantly reduces generation of magnetic fields. the operating principle is first shown for the circuit with ideal elements. State equations are then derived in which the on‐resistance of the switch element is considered, and these are numerically analyzed. an SC transformer with a transformer ratio of 1/2 and an SC dc‐dc converter with an output voltage regulator already have been constructed with discrete components. Results of the average output voltage and efficiency have been confirmed numerically by experiments on constructed circuits. A comparison of the above two circuits demonstrates that although the latter has an efficiency of about 80% (which is lower than that of the former), both have less than ±0.06% in input‐output variation. the voltage variation is at most ‐0.16% for the temperature variation of −20° ∼ 80°.