Study On The Cross-Regulation Of Single-Inductor Dual-Output CCM Buck Converter

By using only one inductor, Single-Inductor Dual-Output (SIDO) DC-DC converter can generate two independently controlled outputs, and provide a good solution for smart phones, tablet computers and other portable devices which need power sources with two or more outputs. Due to the advantages of small volume, high efficiency, low cost and so on, SIDO DC-DC converter is widely studied.In this paper, the SIDO Buck converter is studied. According to the relative size of the duty cycle, the operation principle of the converter with three operation timing sequences are introduced. By using the timing average equivalent circuit method, the DC steady-state equivalent circuit is established to analysis the relationship between output current and operation timing sequence. Based on AC small signal equivalent circuit, the control to output transfer function, cross-coupled transfer function, impedance transfer function and cross-regulation transfer function of system are derived, thus, the small signal model of SIDO CCM Buck converter is obtained. Based on this, the small signal model of voltage controlled SIDO CCM Buck converter is established and the output cross-regulation is analyzed with load changed. The research results show that if one sub-converter of voltage controlled SIDO CCM Buck converter operates in light load, greater cross-regulation to another sub-converter and smaller cross-regulation to own sub-converter will be produced. And if the voltage controlled SIDO CCM Buck converter operates in heavy load, the conclusion is oppsite. Simulation and experiment results are given to verify the analysis results.In order to reduce the output cross-regulation of SIDO CCM Buck converter, small signal model of capacitive current controlled SIDO CCM Buck converter is established based on small signal model of voltage controlled SIDO CCM Buck converter. Comparing analysis their output cross-regulation, the comparitions show that capacitive current controlled SIDO CCM Buck converter has reduced the output cross-regulation. Frequeny domain and time domain simuation results are given to verify the analysis results. In addition, the output cross-regulation of capacitive current controlled SIDO CCM Buck converter with load changed is analyzed, the analysis results are same as voltage controlled SIDO CCM Buck converter.To further reduce the output cross-regulation of SIDO CCM Buck converter, the output current controlled SIDO CCM Buck converter is proposed and its small signal model is established. Compared with capacitive current controlled SIDO CCM Buck converter, the comparitions show that output current controlled SIDO CCM Buck converter has further reduced the output cross-regulation. Frequeny domain and time domain simuation results are given to verify the analysis results. As same as, the output cross-regulation of output current controlled SIDO CCM Buck converter with load changed is analyzed, the simulation results show that the theoretical analysis is reliability.