Research And Improvement Of A Boost Converter Based On Constant Off-time Control Mode

With the guidance of customer markets and the rapid development of integrated-circuits technology,electronic products put forward higher requirements about the power management chip.The power management technology is becoming more and more efficient,DC-DC converter with small volume and low power dissipation has become research and development priorities of power management chip.In order to meet the development demands of emerging green energy,many research institutes start to study DC-DC boost converter with step-up function and make an optimal design in the aspects of its high stability,fast transient response and high efficiency.This paper firstly discusses the research background of DC-DC converter and the current status on the system stability,quasi constant frequency and high conversion efficiency.Based on the research on operating principle and efficiency loss factors of boost converter,this paper makes a detailed analysis about the constant off time(CFT)current mode control.The research shows that the switch frequency of boost converter changes with input and output voltage.Furthermore,the switch frequency gets higher as the load becomes smaller at light load,which lead to the increased switching and driving loss.For this problem,this paper designs a nonlinear variable frequency control by utilizing the trend of error signal changing with load,which is applicable to operation at light load for boost converter.It is based on CFT current mode control architecture.And at heavy load quasi constant frequency is realized by adopting adaptive off time control(AFT).Through the loop analysis and small-signal modeling for the boost converter system,a suitable compensation network is designed in this paper,and the accuracy of output voltage is improved.In this paper,the Simulink software is used to model the conveter system,and the validation and analysis for Simulink behavior level model are carried out.The analytical results show that the switching frequency and output ripple voltage of DC-DC boost converter are in relation to the charging coefficient when boost converter is working with the nonlinear variable frequency control technology at light load.The larger the charging coefficient,the larger the switching frequency and the smaller the ripple voltage.Under other constant conditions,on state resistance of the power transistor is greater,which leads to a decrease in the switching frequency of boost converter.At the same time,the study shows that the cut-off frequency and phase margin of the system loop are affected by load,the sampling coefficient of inductance current and peripheral parameters.Based on the eastern 0.18 μm BCD process,this paper designs a off-timer for light load condition,and builds the control circuit modules through the use of Cadence simulation software.The performance parameters of the converter system are simulated on Spectre simulation platform.The simulation results show that the ripple voltage is less than 50 mV within the output voltage range of 3 to 5 V,and the peak efficiency is up to 93.1%.It is known that the converter achieves high convert efficiency in full load range.Finally,this paper gives a conversion efficiency comparison of this design,CFT control,AFT control and pulse width modulation(PWM)through simulation.It shows that the nonlinear variable frequency control has a increase by 8.9% in efficiency compared with the original CFT control,when the input voltage is 4 V at light load.This research work for improving the performance of boost converters based on constant off-time control mode has a certain reference value.