一种恒定导通时间控制模式Buck变换器的设计

发布时间：2018-09-18 10:30

【摘要】：近年来,随着科技的不断进步,智能手机和平板电脑等便携式电子产品逐渐成为人们日常生活中不可或缺的一部分。而电源作为此类电子产品的动力中枢,其续航能力直接决定着电子产品的使用寿命。要提高电子产品的性能,节约能源,关键是要解决电源的性能问题。电源在目前主要分为线性电源和开关电源,由于开关电源具有功耗小、变换效率高等优良性能,加上生产成本低,已经逐渐取代了变换效率低、不利于节能环保的线性电源,并在电子行业得以广泛使用。直流/直流(DC/DC)变换器作为开关电源领域的重要成员,能够对输入的直流电压进行降压、升压、升降压和极性反转等灵活转换。DC/DC变换器因功能强大而倍受追捧,被人们广泛地应用于各类便携式电子产品中。传统控制模式的DC/DC变换器可分为电流模式和电压模式,两种模式都采用误差放大器和环路补偿网络,这种做法会减小环路带宽,影响系统的瞬态响应。而恒定导通时间模式的电压变换器不需要采用误差放大器,把输出电压纹波信号作为PWM控制信号输入到开环的环路比较器,因此相比传统控制模式具有系统架构简单、瞬态响应快的优点。本文设计了一种采用恒定导通时间控制模式(COT)的降压DC/DC变换器。该变换器存在电流连续导通(Continuous Conduction Mode,CCM)和电流非连续导通(Discontinuous Conduction Mode,DCM)两种不同的工作模式供其根据负载电流的大小进行选择,即重载时选择CCM模式,轻载时则选择DCM模式。该变换器的输入电压范围宽,最低为4.2V,而最高可达16V;其输出电压由于可以使用外围元件进行设置,范围达到0.8V~13V,在重载状态下变换效率最高达到95%以上,同时由于采用了恒定导通时间模式,在轻载状态下变换效率也高于82%。芯片还集成了一系列保护电路,使其避免过压、短路、过温以及过流等问题,以达到安全工作的目的。本论文介绍开关电源的发展过程,介绍了DC/DC变换器的理论基础,就本文所设计DC/DC变换器的功能特点、系统架构和系统整体性能进行了进一步的讨论,后面重点讨论二阶温度补偿的带隙基准电路、二阶温度补偿的偏置电流电路、过温保护电路几个子模块的分析与设计。使用Hspice等软件对相应电路进行仿真验证,如果在0.6μm HVCD工艺基础上子电路指标得以满足,则进一步仿真验证整体电路。从仿真结果可以看出,该变换器具有很好的瞬态响应能力和较高的变换效率。
[Abstract]:In recent years, with the development of technology, portable electronic products such as smart phones and tablets have gradually become an indispensable part of people's daily life. As the power center of this kind of electronic products, the power supply has a direct impact on the service life of electronic products. To improve the performance of electronic products and save energy, the key is to solve the problem of power performance. At present, the power supply is mainly divided into linear power supply and switching power supply. Due to the good performance of switching power supply, such as low power consumption, high conversion efficiency and low production cost, it has gradually replaced the low conversion efficiency, which is not conducive to energy saving and environmental protection. And in the electronics industry can be widely used. As an important member in the field of switching power supply, DC / DC converters are popular for their powerful functions, such as lowering DC voltage, lowering voltage and reversing polarity, etc. It is widely used in portable electronic products. The conventional control mode of DC/DC converter can be divided into current mode and voltage mode. The error amplifier and loop compensation network are used in both modes, which can reduce the loop bandwidth and affect the transient response of the system. The constant on-time mode voltage converter does not need to use an error amplifier, and the output voltage ripple signal is input to the open-loop comparator as the PWM control signal. Therefore, compared with the traditional control mode, the system structure is simple. The advantage of fast transient response. In this paper, a step-down DC/DC converter with constant on-time control mode (COT) is designed. The converter has two different operating modes: current continuous on-on (Continuous Conduction Mode,CCM) and current discontinuous on-( Discontinuous Conduction Mode,DCM (Discontinuous Conduction Mode,DCM), which can be selected according to the magnitude of load current, that is, CCM mode is chosen when heavy load is loaded and DCM mode is selected when light load is used. The input voltage range of the converter is wide, the lowest is 4.2 V, and the maximum is 16 V. the output voltage of the converter can be set by peripheral components, and the range reaches 0.8V ~ (13) V, and the conversion efficiency is up to 95% under heavy load. At the same time, the conversion efficiency under light load is higher than that of 822 because of the constant on-time mode. The chip also integrates a series of protective circuits to avoid the problems of overvoltage, short circuit, overtemperature and overcurrent, so as to achieve the purpose of safe operation. This paper introduces the development process of switching power supply, introduces the theoretical basis of DC/DC converter, and further discusses the functional characteristics, system architecture and overall performance of the DC/DC converter designed in this paper. The second order temperature compensation bandgap reference circuit, the second order temperature compensation bias current circuit, the over-temperature protection circuit several sub-modules analysis and design. The corresponding circuits are simulated and verified by using Hspice and other software. If the sub-circuit index is satisfied on the basis of 0.6 渭 m HVCD process, the whole circuit is further simulated and verified. The simulation results show that the converter has good transient response ability and high conversion efficiency.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM46

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