Research And Design Of A Wide Range And High Efficiency Four-switch Buck-Boost Converter

With the rapid advancement of technology,electronic products play an indispensable role in all aspects of people’s life and work.As the power supply module of any electronic device,the power management chip directly affects the entire system and can be called the "heart" of the electronic device.As an important classification in power management,switching power supply chips are widely used in many application fields due to their high efficiency,wide voltage regulation range,buck-boost and high reliability,etc.And continue to develop towards the trend of high frequency,high efficiency,intelligence and digitization.In some applications where the output voltage falls within the input voltage range,a non-isolated DC-DC converter with Buck-Boost capability is required,and in order to prolong the operating time of the battery in the electronic equipment.In this thesis,a four-switch Buck-Boost（FSBB）converter with wide voltage range and high efficiency is designed.The main contributions of this thesis are as follows（1）An input voltage feedforward circuit based on divider is proposed when the converter works in the voltage mode Buck state,which eliminates the dependence of the power stage on the input voltage in the system,and makes the transfer function of the system no longer affected by the input voltage,Enhanced linear transient performance when the system is in Buck mode,compared with the traditional circuit,the proposed divider structure has the advantages of simple structure and wide input current range.（2）The designed converter has a total of four operating modes,among which the two modes located in the middle of the buck and boost modes reduce the power loss of the switch when the input voltage and output voltage of the converter are similar;The introduction of Burst mode improves the conversion efficiency of the converter at light load,making the conversion efficiency of the converter better in the entire load range.（3）The internal power supply voltage module is used to convert the input high voltage into a low voltage that can be used by the core circuit.When the input voltage is higher,the converter can still work normally,which expanding the working voltage range of it.Based on the DB Hi Tek’s 0.18μm BCD（Bipolar CMOS DMOS）process,this thesis uses simulation software to verify the designed circuit.The simulation results show that the converter can work normally in the entire input voltage range and load current range,as well as in different operating modes.At the same time,it can switch smoothly between different modes,and in the Buck mode after adding feed-forward,the input voltage jumps from 24 V to 12 V,the output undershoot voltage is reduced from the previous 310.67 m V to only 25.77 m V,and the recovery time is reduced from the original time of more than 500μs to 33.5μs;the overshoot voltage is reduced from 387 m V to91.31 m V,and the recovery time is reduced from more than 500μs to about 99.17μs.The maximum conversion efficiency of the designed circuit can reach 95%,and when the load current is lower than 100 m A,that is,when the load is light,the conversion efficiency can reach up to 87%.