Research On Control Strategy And Circuit Of BUCK Converter With Wide Application Range

With the rapid development of electronic information technology,how to provide efficient and stable power supply for various electronic components has become a common problem faced by the industry.DC-DC converters have become a frequently-used power topology with high energy conversion efficiency and small volume.Due to the continuous emergence of application scenarios such as automotive electronics and industrial control,Buck converters need to operate under a wide range of input and output voltage,load current,frequency applications.In order to meet the above requirements,wide application range Buck converter came into being.To design this kind of Buck converter,it is necessary to select appropriate control strategy and build up the implementation circuit that meets the requirements.In order to find an appropriate control strategy,this thesis summarizes the performance requirements of control strategy for wide application range Buck converter and establishes the deduction idea of DC/DC loop stability by analyzing the sideband effect.This thesis makes accurate small signal modeling for three common control modes: peak current mode,COT current mode and RBCOT.Based on the modeling results,the model parameter variation and frequency compensation strategies of these control modes are analyzed and validated in a wide range of applications.Considering various factors,the peak current mode has become the final choice because of strong anti-noise ability and easy control of switching frequency.Based on PCM control mode and corresponding frequency compensation strategy,an asynchronous rectifier with high reliability circuit is designed in this thesis.For the purpose of achieving internal power supply integrated in the chip,this thesis sets up multiple separate power rails inside the circuit.The power supply of the system is accomplished by using multiple LDOs and pseudo LDO circuits.A high precision reference circuit is used to generate a zero temperature coefficient reference voltage and bias current.Circuits such as high-speed SenseFET current sampling and frequency-dependent slope compensation circuits enable loop control over a wide range of applications.The above implementation scheme has tape-out based on 0.35μm 60 V BCD process.The test results show that the proposed scheme can achieve good adjustment effect under the wide application range of 4.5-36 V,200k-1.5MHz and 0-2A.The experimental results meet the design specifications.Based on the work of asynchronous circuit,this thesis also designs a synchronous rectifier to meet a wider range of applications,focusing on several key issues in the circuit design.A high energy conversion efficiency LDO and a bootstrap charging circuit based on LDMOS are proposed to meet the system power supply requirements under low voltage and high frequency condition.In addition,this thesis proposes a novel current sampling architecture for high frequency applications.This thesis also designs a low-side power transistor’s current detection module for synchronous rectifier circuit.The simulation results show that the controller chip based on the above scheme can adjust the output voltage well in the application range of 3.6-42 V,200k-3MHz and 0-3A.