Research Of Key Technology Of Multi-Mode PSR Flyback Controller With High-Efficiency

With the extensive use of portable electronic devices in our daily life,the power management ICs used in small and medium-power power supply is becoming larger and larger.The function of portable electronic devices is becoming more and more complex as the volume is becoming more and more compactable.For the application of multi-mode primary-side controlled flyback converter,the efficiency and the power of the system is improved,the cost of the system is reduced further.However,the accuracy of constant voltage(CV)/constant current(CC)output for multi-mode AC-DC converter has a great impact on the life of electronic device.As the new energy efficiency requirements for power supply is put forward by European Union and the United States,it is of great significance to reduce the excessive loss of electric energy in the standby and to improve the efficiency of converter.This dissertation focuses on improving the accuracy of output current and reducing the power consumption of the system based on the multi-mode PSR(Primary Side Regulator)flyback converters.The study mainly containing:1.The output current is regulated through sampling the peak current of primary side inductor for PSR flyback converter.Traditional sampling control circuit is only suitable for one single working mode.An average current sampling control circuit is put forward based on the Miller platform of the power switch during switching on and off period,which is suitable for multi-mode PSR flyback converter in this dissertation.A controller is fabricated based on the process of 0.18μm BCD with the proposed method and the layout area is 1.313mm×0.741mm.To verify the feasibility of the proposed method,a controller for charging application is fabricated.Hardware experimental results show that the control system can properly operate in multimode.The accuracy of constant output current is ± 1%and the line regulation of the system is 1.6%under the input line voltage ranges from 85 to 265 Vac.It is obvious,with the proposed method the CC feature is well improved.2.Due to the inner control relationship of traditional flyback converter,LSP is easily to be occurred during startup and over-power protection.A high-precision over current protection(OCP)circuit is proposed for eliminating the noise caused by long and short waveform(LSP)of the traditional flyback converter and improving the stability of the system.To verify the feasibility and performance,the proposed scheme has been implemented in 0.18μm BCD process which occupies an area of 1.12×0.71 mm2.Experimental results show that the LSP is eliminated during startup and over-power protection.The accuracy of output current can be as high as ± 1.04%.With the proposed control strategy,the converter can be adapted to a smaller bulk input capacitance which can reduce the volume and cost easily.3.Detailed formula derivation and analysis are carried out for the resonance period after the demagnetization period of the flyback converter.A quasi-resonant(QR)valley locking control scheme is proposed in this dissertation according to the insufficient in traditional QR valley locking control scheme.With the proposed method,a double points of period limitation are adopted to instead the single period limitation.So,the hopping is avoided with audible noise disappeared.The zero pole and stability of the system are analyzed by small signal model circuit,and verified by Simulink in MATLAB.Based on 0.18μm BCD process,a controller chip has been fabricated to verify the feasibility and performance,which occupies an area of 1.313mm×0.741mm.Under different test load conditions,the maximum efficiency of flyback converter can be as high as 89.67%,and the average efficiency is as high as 88.85%.The experimental result shows that there is no valley hopping happens in different steady loads and dynamic loads.So,the audio noise caused by the frequency hopping is eliminated with the maximum efficiency and average efficiency improves significantly.4.The pre shutdown technology is adopted in multi-mode synchronous rectifier technology.However,the parasitic diode starts to conduct after the pre shutdown,which caused additional power losses.A dynamic pre shutdown synchronous rectification driving circuit is proposed.A turn off threshold(Vsr_thoff)is set to compare with the Drian souse voltage(VDS)of SR MOS under DCM.As soon as VDS is detected to be larger than Vsr_thoff,the SR MOS is switched off after the false turn-off is not triggered.In CCM mode,the system presets a turn-off time and continuously corrects the pre turn off time of rectifier MOS to reduce the rectifier loss of parasitic diode.To verify the feasibility and performance,the proposed scheme has been implemented in 0.18μm BCD process which occupies an area of 585μm*520μm.Under different load and input voltages,the maximum efficiency is as high as 88%.5.A negative threshold voltage(Vth_off)is set to turned off SR MOS in advance before the secondary current drops to zero,which is not suitable for CCM.A fast turn off driving circuit is proposed for synchronous rectification.Based on the proposed method,the secondary side current is detected to adjust the driving voltage VDRI for multi-mode synchronous rectification control.A controller is fabricated based on the process of 0.35μm HV CMOS with the proposed method and the layout area is 1.027mm*0.807mm.Under the test condition of 220 Vac,the load changes from 1A to 5A.With the fast turn-off synchronous rectifier circuit proposed in this paper,the overall efficiency of the converter is improved by 3.5%,and the overall efficiency of the converter is up to 92.72%.