基于BUCK拓扑DC-DC充电芯片的稳定性分析

发布时间：2018-01-12 19:15

本文关键词：基于BUCK拓扑DC-DC充电芯片的稳定性分析　出处：《西安电子科技大学》2014年硕士论文　论文类型：学位论文

更多相关文章： BUCK 平均电流模 PWM 建模 稳定性 仿真

【摘要】：现代社会中随着便携式电子设备的迅猛发展,DC/DC开关转换器凭借其自身优良的特性已经在各类电子设备中得到越来越多的应用。目前应用于电池充电中的开关电源转换器逐渐成为主流。本文主要对基于BUCK拓扑的单环平均电流模充电芯片的工作原理和稳定性进行研究。首先对系统的工作原理做了详细介绍。第二,对系统进行建模,分别计算出环路中各个模块的小信号传输函数,然后依据系统的稳定性条件,完成了误差放大器以及补偿网络的设计,并且利用MATLAB软件对系统稳定性进行了仿真验证,仿真结果显示系统开环直流增益为76dB,带宽为87KHz,相位裕度是56度,因此整个环路满足闭环稳定工作的条件;同时系统具有比较高的电源抑制比,直流情况下电源抑制比为75dB,在开关频率处系统的电源抑制比为49dB,因而系统可以稳定工作。第三,对影响稳定性的主要模块电路进行了设计,最终利用HSPICE软件对模块电路以及整个系统完成了仿真。该充电芯片采用三段式充电法:涓流、恒流、恒压充电模式,提高了充电效率,同时能够增加电池的寿命。其中在涓流和恒流充电过程中系统采用单环平均电流模PWM(Pulse Width Modulation脉冲宽度调制)控制方式,并且系统处于闭环工作,因而在充电过程中会存在环路稳定性问题,所以需要对整个系统的环路进行精心设计,本文主要对采样放大模块,误差放大器,PWM比较器的设计做了详细介绍。其中误差放大器作为调节系统稳定性的一个关键模块,它的性能直接影响着系统稳定工作与否,文中采用的误差放大器为折叠共源共栅结构的跨导型放大器,它具有比较宽的共模输入范围,高输出阻抗、高增益,同时具有较快的响应速度,满足系统的稳定性要求;在恒压充电过程中,系统处于开环工作状态,然而恒压过程很短暂,从而保证了充电截止电压的精度要求。在5V输入电压,800KHz的开关频率,0.1欧姆的采样电阻,涓流充电管脚接地条件下,对芯片进行整体仿真,电池电压在2.9V以下时,充电电流为0.1A;电池电压上升到2.9V以上时,充电电流是1A,并且充电电流精度高,可以实现稳定充电;当电池电压上升到4.2V时,系统进入恒压充电模式,电感的磁路不平衡,电感消磁大于充磁,因而电感电流开始下降,直到充电电流下降到0.1A时,延迟一段时间(本文中设置为1.8ms),芯片充电使能信号关断,整个充电过程结束。
[Abstract]:With the rapid development of portable electronic devices in modern society. DC/DC switch converters have been more and more used in various electronic devices by virtue of their excellent characteristics. At present, switching power converters used in battery charging are becoming the mainstream. The working principle and stability of single-ring average current mode charging chip based on BUCK topology are studied. Firstly, the working principle of the system is introduced in detail. Second. The system is modeled and the small signal transfer functions of each module in the loop are calculated respectively. Then the error amplifier and compensation network are designed according to the stability conditions of the system. The simulation results show that the open-loop DC gain is 76db, the bandwidth is 87kHz, and the phase margin is 56 degrees. Therefore, the whole loop meets the conditions of closed-loop stability. At the same time, the system has a relatively high power supply rejection ratio, DC power rejection ratio is 75 dB, at the switching frequency of the system power supply rejection ratio is 49 dB, so the system can work stably. Third. The main module circuit which affects the stability is designed. Finally, the module circuit and the whole system are simulated by HSPICE software. The charging chip adopts three-stage charging method: trickle current, constant current. Constant voltage charging mode improves charging efficiency. At the same time, the battery life can be increased. Single loop average current mode PWM(Pulse Width Modulation pulse width modulation is used in trickle current and constant current charging process. Control mode. And the system is in the closed-loop operation, so there will be loop stability in the charging process, so the loop of the whole system needs to be carefully designed. In this paper, the sampling amplifier module, error amplifier. The design of PWM comparator is introduced in detail, in which error amplifier is a key module to adjust the stability of the system, and its performance directly affects the stability of the system. The error amplifier used in this paper is a transconductance amplifier with folded common-gate structure, which has a wide common-mode input range, high output impedance, high gain and high response speed. Meet the stability requirements of the system; In the process of constant voltage charging, the system is in an open loop state, but the constant voltage process is very short, thus ensuring the accuracy of charging cut-off voltage. The switching frequency of 800kHz at 5V input voltage is ensured. The sampling resistance of 0.1 ohms, the whole simulation of the chip under the condition of trickle charging pin grounding, when the battery voltage is below 2.9 V, the charging current is 0.1 A. When the voltage of the battery rises above 2.9 V, the charging current is 1A, and the accuracy of charging current is high, which can realize stable charging. When the battery voltage rises to 4.2 V, the system enters the constant voltage charging mode, the magnetic circuit of the inductor is unbalanced, the inductance demagnetization is larger than the magnetization, so the inductance current begins to decrease until the charging current drops to 0.1A. Delay for a period of time (1.8ms in this paper, chip charging enable signal turned off, the entire charging process is over.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM46

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