Abstract
The main purpose of this paper is based on a push-pull DC/DC SG3525 switching power supply, can be transformed into DC10~35V, DC360V, rated power reaches 500W. Can be used in high pressure and low pressure rotor device, especially suitable for low voltage inverter power input before voltage etc..
Through the comparative study, design the main topology of push-pull DC/DC switching power supply based on SG3525, the low voltage DC power stage through transformer step-up, output filtered bridge rectifier and LC, 360V DC high voltage. MOSFET drain source using RC snubber circuit, peak voltage of transformer leakage generated by absorption. Isolation by TL431 and PC817 combined with the feedback sampling voltage, electrical isolation between the before and after class. Comparison of terminal voltage feedback signal is sent to SG3525, compared with the internal triangular wave SG3525, can get the PWM duty cycle waveform changes, to achieve closed-loop control of output voltage.
Through the work of the main circuit principle analysis and parameter calculation, completed the hardware circuit design, the power electronic simulation software SABER to verify the circuit, the input voltage can achieve the full range output voltage 360V, output power reaches the rated circuit requirements, stable performance, fast response speed.
Key words：SG3525 push-pull DC/DC SABER simulation
目 录
第1章 绪 论 ······································································································· 1
1.1 课题研究的目的意义 ···················································································· 1 1.2 国内外研究现状 ·························································································· 1 1.3 论文研究内容 ····························································································· 2 第2章 课题设计要求及方案 ····················································································· 3
2.1 设计要求 ··································································································· 3 2.2 设计方案 ··································································································· 3 第3章 系统主要元器件介绍 ····················································································· 5
3.1 SG3525芯片介绍 ························································································· 5
3.1.1 引脚功能说明 ······················································································ 6 3.1.2 SG3525的工作原理················································································ 7 3.2 TL431工作原理介绍 ···················································································· 9 3.3 PC817性能介绍 ························································································ 11 3.4 高频变压器 ······························································································ 12 第4章 硬件电路设计 ····························································································· 14
4.1 推挽电路原理及设计 ·················································································· 14 4.2 SG3525控制电路设计················································································· 17 4.3 TL431和PC817反馈电路设计 ····································································· 18 4.4 高频变压器设计 ························································································ 19 第5章 saber仿真验证 ···························································································· 22
5.1 仿真软件介绍 ··························································································· 22 5.2 系统仿真电路图 ························································································ 23 5.3 仿真结果 ································································································· 23 第6章 结 论 ····································································································· 27 参考文献 ·············································································································· 28 致 谢 ················································································································· 29 附 录 ················································································································· 30
附录A 外文资料 ···························································································· 30 附录B 电路原理图 ························································································· 47
石家庄铁道大学四方学院毕业设计
第1章 绪 论
1.1 课题研究的目的意义
随着电力电子技术的高速发展，电力电子设备与人们的工作、生活的关系日益密切，而电子设备都离不开可靠的电源，进入80年代计算机电源全面实现了开关电源化，率先完成计算机的电源换代，进入90年代开关电源相继进入各种电子、电器设备领域，程控交换机、通讯、电子检测设备电源、控制设备电源等都已广泛地使用了开关电源，更促进了开关电源技术的迅速发展[1]。
开关电源是利用现代电力电子技术，控制开关晶体管开通和关断的时间比率，维持稳定输出电压的一种电源，开关电源一般由脉冲宽度调制（PWM）控制IC和开关器件（MOSFET、BJT等）构成。开关电源和线性电源相比，二者的成本都随着输出功率的增加而增长，但二者增长速率各异。线性电源成本在某一输出功率点上，反而高于开关电源。随着电力电子技术的发展和创新，使得开关电源技术在不断地创新，这一成本反转点日益向低输出电力端移动，这为开关电源提供了广泛的发展空间[2]。
开关电源高频化是其发展的方向，高频化使开关电源小型化，并使开关电源进入更广泛的应用领域，特别是在高新技术领域的应用，推动了高新技术产品的小型化、轻便化。另外开关电源的发展与应用在节约能源、节约资源及保护环境方面都具有重要的意义[3]。
1.2 国内外研究现状
自20世纪50年代，美国宇航局以小型化重量轻为目标而为搭载火箭开发首个开关电源以来，在半个多世纪的发展中，开关电源逐步取代了传统技术制造的相控稳压电源，并广泛应用于电子整机设备中。随着集成电路的发展，开关电源逐渐向集成化方向发展，趋于小型化和模块化。近20年来，集成开关电源沿两个方向发展。第一个方向是对开关电源的控制电路实现集成化[4]。1977年国外首先研制成脉宽调制(PWM)控制器集成电路，美国Motorola公司、Silicon General公司、Unitrode公司等相继推出一系列PWM芯片。近些年来，国外研制出开关频率达1MHz的高速PWM、PFM芯片。第二个方向是实现中、小功率开关电源单片集成化。1994年，美国电源集成公司(Power Integrations)在世界上率先研制成功三端隔离式PWM型单片开关电源，其属于AC/DC电源变换器。之后相继推出TOPSwitch、TOPSwitch-II、
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石家庄铁道大学四方学院毕业设计
TOPSwitch-Fx、TOPSwitch-GX、PeakSwitch、LinkSwitch等系列产品。意-法半导体公司最近也开发出VIPer100、VIPer100A、VIPer100B等中、小功率单片电源系列产品，并得到广泛应用。目前，单片开关电源已形成了几十个系列、数百种产品。单片开关电源自问世以来便显示出强大的生命力，其作为一项颇具发展前景和影响力的新产品，引起了国内外电源界的普遍关注。[5]单片开关电源具有高集成度、高性价比、最简外围电路、最佳性能指标等特点，现己成为开发中小功率开关电源、精密开关电源及开关电源模块的优选集成电路。
与国外开关电源技术相比，国内从1977年才开始进入初步发展期，起步较晚、技术相对落后。目前国内DC/DC模块电源市场主要被国外品牌所占据，它们覆盖了大功率模块电源的大部分以及中小功率模块电源一半的市场。但是，随着国内技术的进步和生产规模的扩大，进口中小功率模块电源正在快速被国产DC/DC产品所代替。开关电源的发展从来都是与半导体器件及磁性元件等的发展休戚相关的。高频化的实现，需要相应的高速半导体器件和性能优良的高频电磁元件。发展功率MOSFET、IGBT等新型高速器件，开发高频用的低损磁性材料，改进磁元件的结构及设计方法，提高滤波电容的介电常数及降低其等效串联电阻等，对于开关电源小型化始终产生着巨大的推动作用[6]。
1.3 论文研究内容
本文旨在研究和设计一款基于SG3525的推挽式DC/DC开关电源，可以用于低压到高压的转换，特别是适用于低压输入的逆变电源的前级，比如车载逆变器和家用逆变器的前级升压。主要研究内容包括：
(1)提出设计参数要求，并设计系统的硬件电路方案和软件仿真验证方案。 (2)对系统中用到的主要原件进行说明和原理介绍。包括SG3525的电气参数介绍以及工作原理和结构特性；TL431构成反馈电路的工作原理介绍；PC817的主要性能介绍；高频变压器的工作原理。
(3)对系统的硬件电路进行分模块设计。包括推挽主电路的设计和推挽电路工作原理分析；SG3525控制电路的设计，以及SG3525的工作频率和死区时间的选定；TL431和PC817构成的反馈电路的参数设计；高频变压器的设计和制作。
(4)选择SABER仿真软件对系统进行建模仿真。并且对仿真得到的波形进行分析，判断电路设计的正确性和性能。
(5)对本设计进行总结，给出改进意见。
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石家庄铁道大学四方学院毕业设计
第2章 课题设计要求及方案
2.1 设计要求
设计一个基于SG3525可调占空比的推挽式DC/DC开关电源，输入的电压为DC 10—35V，输入额定电压为12V，输出为360V，额定功率为500W。电路以SG3525为控制芯片，使电源工作性能稳定，电源效率高。给出系统的电路设计方法以及主要单元电路的参数计算，选择符合设计要求的元器件，最后用saber进行仿真。
2.2 设计方案
设计方案主要包括硬件设计和仿真分析两部分。其中硬件系统主要由SG3525控制电路、推挽电路、TL431和PC817反馈电路几部分组成。系统框图如图2-1所示。
+DC10~35V推挽电路360V-负载驱动信号SG3525控制电路TL431+PC817反馈电路
图2-1 系统框图
直流电压输入范围是10~35V，额定状态下为12V，作为推挽电路的直流供电。推挽电路将低压直流斩波成高频交流信号，再通过变压器耦合、升压，次级通过快速恢复二极管构成的整流桥整流，经过LC滤波器滤波后得到高压直流，给负载供电。TL431和PC817构成的反馈电路可以采集高压直流信号，并跟基准电压比较，通过补偿器的调节，再将反馈信号送入SG3525的比较端。SG3525控制电路把反馈电路送入的反馈电压信号与内部的三角波进行比较，就可以得到占空比变化的PWM波
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