Control Technique Of Single-inductor Dual-output Buck Converter In Hybrid Conduction Mode

Portable devices and light emitting diodes(LED)lighting with different voltages pose challenges for the multi-output converters.Single-inductor multiple-output(SIMO)switching converters which have been widely used in such applications require only one inductor which can decrease the volume and cost,and each output branch can be controlled independently.Thus,the research on SIMO switching converters is of great significance.In this thesis,a V~2 controlled pseudo-continuous conduction mode(PCCM)single-inductor dual-output(SIDO)buck converter is presented and its operation principle is analyzed.Then,the expression of load of PCCM SIDO buck converter is derived.Based on it,the cross-regulation and the load range are analyzed.Besides,the expression of the freewheel time is derived which reveals the efficiency characteristic of the converter.Through the experiments and theoretical analysis,a conclusion can be drawn that comparing to the voltage-mode controlled PCCM SIDO buck converter,the V~2 controlled PCCM SIDO buck converter improves the transient response and cross-regulation.However,whether V~2controlled PCCM SIDO buck converter or the voltage-mode controlled PCCM SIDO buck converter,the load range is limited and the efficiency is decreased under light load.To increase the efficiency of V~2 controlled PCCM SIDO buck converter under light load,a V~2 controlled SIDO buck converter in hybrid conduction mode(HCM)is presented.The operation principle of the converter is analyzed,and the expressions of key parameters such as the freewheel current and switching period are derived.Then,the load range and the cross-regulation of the converter are discussed based on these expressions.Furthermore,considering parasitic parameters of the converter and based on its state equations,efficiency expressions of V~2 controlled SIDO buck converters in PCCM or HCM are derived.The comparison of the efficiency is presented with the variation of the load.Through the experiments and theoretical analysis,a conclusion can be drawn that compared to the V~2controlled PCCM SIDO buck converter,the V~2 controlled HCM SIDO buck converter can improve the efficiency in wide load range while maintain the low cross regulation and fast transient response.The discrete-map model of the V~2 controlled HCM SIDO buck converter whose voltage outer loop is constant is established to analyze the stability of this system.On the basis of it,the bifurcation map of inductor current can be drawn which reveals the variation of stability of the system with the change of circuit parameters.Then,a V~2 controlled HCM SIDO buck converter with ramp compensation is put forward to improve the stability.The principle and the stability of the system are analyzed in detail.The results show that,with the decrease of the constant fall time,the reference voltage and load of one output branch which operates in continuous conduction mode,or the increase of output capacitance and its equivalent series resistance of the two output branches,input voltage and the coefficient of ramp compensation,the state of the system varies from unstable to stable.Besides,the ramp compensation can improve the stability of the system.The experiment results validate the correctness of theoretical analysis.