The optimal bus voltage study for 12 V two-stage VR based on an accurate analytical loss model

Today's single stage VR directly converter 12 V input to around 1.3 V. The extremely small duty cycle dramatically impacts the performance and limits VR's switching frequency. In this paper, two-stage approach for 12 V VR (Yuancheng Ren, et al., 2004) is briefly introduced first. Compared with the conventional single stage approach, the two-stage approach shows much better performance at high frequency application. But, how to choose the bus voltage is still not clear. In order to identify the optimal bus voltage of two-stage approach, an accurate analytical loss model is built, which considers the parasitic inductors and the non-linear capacitors of the devices and shows much better accuracy than conventional loss model. Based on this model, many factors, such as the switching frequency, the devices, output voltage and parasitic components are investigated. The conclusion is that 5 V is the optimal bus voltage for high frequency application. A prototype is built to verify the analysis results.