A Two-stage Converter with a Coupled-Inductor

In this paper, a novel multi-stage converter with a coupled-inductor is presented in order to reduce the ripple currents in the switches and the output capacitor. The operating principle is described in detail and the steady state analysis is performed for a 12 V to 1.5 V prototype buck converter. From the experiments, it is confirmed that ripple currents in switches are greatly reduced and power efficiency is improved compared with the conventional multiphase converter. Furthermore, from the small signal analysis, it is found that the transfer function of the duty ratio of the first stage to the output voltage of the second stage becomes nearly quadratic similar to the single buck converter even though composed of two cascaded stages, so the converter with feedback circuit is inherently stable.