| With the continuous development of semiconductor technology,the technology of switching power supply is also increasing.At the same time,the emergence of various electronic devices also puts forward more technical requirements for the power supply module,and the power factor is one of the important indicators to measure the performance of the power supply.At the same time,it is necessary to pay attention to its nonlinear behavior in order to design stable and reliable switching power supply.In this thesis,a discrete mapping model is constructed for the main extension complement structure of the flyback PFC converter,and the periodic iteration model of the switch power system is set up from the state equation of the circuit.The intermittent nonlinearity caused by the switching between the continuous conduction mode(CCM)and the intermittent conduction mode(DCM)is studied under the peak current control mode.Based on the study of the nonlinear behavior of the flyback PFC converter,a fixed time control scheme for the critical conduction mode is proposed in this thesis,which ensures that the system works in the critical conduction mode and avoids the intermittent nonlinearity of the flyback PFC converter.Based on the control scheme,the discrete mapping model is established for the control scheme,and the recurrence formula of the control scheme's conduction time is derived.The convergence of the recursive formula obtained in this paper proves that the control scheme is nonlinear under certain parameter conditions due to the limitation of the actual circuit.This thesis focuses on the influence of the reciprocal Kr,which is put forward in this paper,of the slope voltage slope on the nonlinear control scheme,and gives the range of the parameter Kr of the control scheme and designs the key parameters of the control circuit(charging current and capacitance)according to the value of the parameter Kr.At the same time,based on the study of the nonlinear behavior of the system,a flyback PFC control chip is designed on the basis of the value of the circuit parameters obtained under the stable working conditions.In this thesis,the power factor correction is realized by the fixed time control mode.Through the related circuit,the switch tube has the same conduction time in each cycle.Then the peak of the input current is followed by the input voltage,thus the input current and the input voltage phase are followed,thus the power factor of the system is improved.Meanwhile,the output current of the switch tube is controlled by the constant current control circuit,and the output current is a constant value.At the same time,the design details of the circuit modules and the layout are given in this paper.The control chip designed in this thesis has been fabricated in NEC 1?m 5V/40 V HVCMOS process.The test results show that when the input condition range from 85 V to 265 V,and the frequency of AC input is 50~60Hz.The output current is 1500 mA,the maximum power factor can reach 0.995,the system static power consumption is 470 mW,and the starting time of the system is 100 ms,the retention time is 8ms,the constant current output precision is ±2.6%,the constant current linear adjustment rate is ±2.4%,the constant current load adjustment rate is ±3.4%,and the maximum efficiency of the system can reach 80.85%.It can be seen that the control chip designed in this thesis accords with the design index proposed in this paper,and has a good application prospect. |
PDF Full Text Request