Research On The Key Techniques Of High Performance AC-DC Converter IC

With the development of portable devices,the market of power management ICs becomes larger and larger.In this thesis,after introducing basic theories of AC-DC flyback converter ICs and system,the current design techniques are compared from the direction of feedback method,control mode and circuit implementation way.The digital control is more appropriate to implement the complex control strategy for improving the system performance than analog control.Now the digital control technique has been widely used in buck,boot topology and so on.However,there is not too much research on the system model and design method of digital control flyback system.And there are many papers for the modeling of regular mode control such as voltage mode control and current mode control.But there are not so many references for the variable frequency system.In this thesis,the modeling procedure should be done step by step for the variable frequency system.In addition,the accuracy of the output voltage and current will directly affect the life-time of the load battrery,so how to improve the accuracy is an important design goal.The system efficiency and standby power consumption have been the important design requirements for the power products.How to improve the efficiency and reduce the standby power consumption is the very important direction for research.This thesis focuses on the above key techniques and the innovation points are shown as below.1?A system diagram with digital power techniques applied in flyback topology is proposed in this thesis.A discrete system of flyback topology is simulated in Simulink to verify the analysis.From the simulation results,it can be seen when the limiting-cycle resonant phenomenon will occur.At the same time,the dynamic response performance is compared with the traditional analog system,the results show that the way to design a discrete system is suitable and the close loop model is accurate.2?A novel digital control technique is proposed to improve the accuracy of the output current in this thesis.FPGA is the testing platform for the adaptive technique of loop delay compensation technique.Using 7w LED as the load and set 350mA as the goal of output current,the system can achieve 1%accuracy of the output current and the peak-peak current is +/-1.7%.Compare with the system without compensation,the accuracy of output current is improved by 3.4%.And the compensation result is more obviously when the imput voltage becomes larger.3?A multi-mode frequency-folded control strategy is proposed to improve the efficiency in this thesis.The modeling method is used to analyze the stability of the system.A dual-sampling method is introduced to eliminate the sampling mismatch phenomenon which will occur during the mode switch in the multi-mode control strategy.The results of behavior simulation show that the system can maintain stability with the mode switch when the load changes.4?A strategy for reducing the system power consumption under standby condition is proposed in this thesis.The voltage mode control is used instead of peak current mode control under the standby condition.In this way,the pulse width of the driving signal can be smaller to reduce the power stage consumption.For the control IC consumption,the unnecessary block can be power off under standby condition to reduce the power consumption.Based on the researchs have done including AC-DC switching power system working principle,modeling of system,constant voltage output control,constant current output control and standby power consumption,a high performance AC-DC converter charger IC is designed.After finish the circuits and layout design of the AC-DC converter charger IC with the constant voltage/constant current output functions,the parasitics parameters are extracted to do the post-simulation.Compare with the products in the market,the results show that the average efficiency of the system is improved by 3.6%with the multi-mode frequency-folded strategy.And the standby power consumption can be reduced from 30mW to 10mW which is much lower than the strictest requirement of the charger application.