毕业设计与论文(基于TL494的电动车充电器设计)(7)

change ton (GM) and the second is the frequency modulation, ton unchanged, change Ts (easily interference). Their specific circuit from the following categories: (1) Buck circuit - buck chopper, the average output voltage U0 less than the input voltage Ui, the same polarity. (2) Boost circuit - Boost chopper, the average output voltage U0 greater than the input voltage Ui, the same polarity. (3) Buck-Boost circuit - buck or boost chopper, U0 average output voltage greater than or less than the input voltage Ui, polar opposite,

inductance transmission. (4) Cuk circuit - buck or boost chopper, its average output power U0 pressure greater than or less than the input voltage Ui, polar opposite, capacitance transmission. Today's technology allows soft switching DC / DC has undergone a

qualitative leap forward, the United States VICOR companies design and manufacture of a variety of ECI soft-switching DC / DC converters, the largest of its power output is 300 W, 600W, 800W, the power density of the corresponding (6.2 , 10,17) W/cm3, efficiency (80 to 90)%. Japan's latest NemicLambda launched a soft-switch technology using

high-frequency switching power supply module RM Series, the switches at (200 ~ 300) kHz, the power density has reached 27 W/cm3, using synchronous rectifier (MOS ? FET replace SCHOTT - Diode), the efficiency of the entire circuit to 90 percent.

2 AC/DC transform

AC / DC transformation is to transform exchange for DC, its power can be a two-way flow, the flow of power flow from the power load known as the \flow from the load to return to power as \importation of AC 50/60 Hz, due to the rectification, filtering, the relatively large size of the filter capacitor is essential, because encountered safety standards (such as UL, CCEE) and EMC Directive Restrictions (such as IEC,, FCC, CSA), AC input side and EMC filter must meet safety standards and the use of the components, such restrictions on the AC / DC power of the small size of the addition, since the internal high-frequency, high-pressure, big Current switching action, made the resolution of EMC difficult to electromagnetic compatibility problems, will install the internal high-density circuit design to the high demand for the same reason, high-voltage, high current power switches make greater loss of work, limiting the AC / DC converter modular process, it must be in power system

design methods to optimize the efficiency of its work reaches a certain level of satisfaction. AC / DC transform the circuit can be divided into the connection mode, half-wave circuit, full-wave circuit. By the power of a few can be divided into, single-phase,

three-phase, multi-phase. Circuit work on a quadrant can be divided into quadrants, the quadrant, the three-quadrant, the four quadrants. Selection of switching power supply

3 Switching power supply

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In the importation of anti-jamming performance, as its own circuit of the characteristics of (multi-level series), the general importation of interference such as a surge through the difficult, in the output voltage stability of the technology indicators compared with the

linear power Have greater advantages, its output voltage stability up (0.5 to 1)%. Switching power modules as a power electronic device integration, the choice should note the

following: Because of the high efficiency switching power supply, can usually more than 80 percent, it was their choice of output current, accurate measurement of electrical equipment or calculating the maximum absorption current, so that was the choice of switching power supply has a high cost performance, Output is usually calculated as follows: Is = KIf

Type in: Is-switching power supply is rated output current;

If-the largest electrical equipment absorb current; K-margin coefficient, from 1.5 to 1.8 in general;

4 grounding

Linear power than the power switch will generate more interference, the common mode interference sensitive electrical equipment, grounding and shielding should take measures, according to ICE1000, EN61000, FCC restrictions, such as EMC, switching power supply are taking measures EMC EMC, Switching power supply should normally with EMC EMC filter. If lied Huafu technology HA series switching power supply, its FG terminal users access to the land or the case in order to meet the electromagnetic compatibility requirements.

protection circuit In switching power supply design must have a flow of overheating, such as short-circuit protection, it should be preferred in the design of the protection of the

full-featured switch power modules, and its protection circuit with the technical parameters of the work of electrical equipment matched to Avoid damage to electrical equipment or switching power supply. Switching power supply technology development trends

Switching Power Supply is the direction of development of high-frequency, high reliability, low consumption, low noise, interference and modular. Since switching power supply light, small, thin is the key technology of high-frequency, switching power supply major foreign manufacturers are committed to synchronize the development of new high-intelligent devices, particularly in the second rectifier of the loss and iron in power Oxygen-(Mn ? Zn) materials to increase the scientific and technological innovation, to enhance the

high-frequency and larger magnetic flux density (Bs) under high magnetic properties, and the small capacitor is also a key technology. SMT technology applications makes switching power supply has made considerable progress, both sides of the circuit board layout components, to ensure that the light switch power, small, thin. The high-frequency 第 32 页

switching power supply is bound to the tradition of the PWM switching technology

innovation and achieve ZVS, ZCS the soft-switch technology has become the mainstream of switching power supply technology and a substantial increase in the switching power supply efficiency. For high-reliability indicators, the U.S. switching power supply

manufacturers by reducing operating current, lower junction temperature devices, and other measures to reduce the stress, increased reliability greatly improved. Modular Switching Power Supply is the general trend of development, can be used modular power components distributed power systems, designed to N +1 redundant power systems, and parallel way to achieve the capacity expansion. Power switching operation for this big noise shortcomings, if the individual pursuit of its high-frequency noise will also increase with, and the use of the resonance conversion circuit technology, in theory, can achieve the high-frequency noise can be reduced, but some Resonant conversion of the practical application of

technology there are still technical problems in this area is still a great deal of work to make the technology to practical use.Power electronics technology innovation, switching power supply industry has broad development prospects. China's switch to accelerate the pace of development of power industry, we must walk the road of technological innovation, out of production, study and research with Chinese characteristics, the joint development, for the rapid development of China's national economy to contribute.

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微机开关电源的含义

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MOSFET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，这一点称为成本反转点。随着电力电子技术的发展和创新，使得开关电源技术也在不断地创新，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阔的发展空间。

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。开关电源的分类人们在开关电源技术领域是边开发相关电力电子器件，边开发开关变频技术，两者相互促进推动着开关电源每年以超过两位数字的增长率向着轻、小、薄、低噪声、高可靠、抗干扰的方向发展。开关电源可分为AC/DC和DC/DC两大类，DC/DC变换器现已实现模块化，且设计技术及生产工艺在国内外均已成熟和标准化，并已得到用户的认可，但AC/DC的模块化，因其自身的特性使得在模块化的进程中，遇到较为复杂的技术和工艺制造问题。以下分别对两类开关电源的结构和特性作以阐述。 1.DC/DC

变换 DC/DC变换是将固定的直流电压变换成可变的直流电压，也称为直流斩波。斩波器的工作方式有两种，一是脉宽调制方式Ts不变，改变ton(通用)，二是频率调制方式，ton不变，改变Ts（易产生干扰）。其具体的电路由以下几类： （1）Buck电路——降压斩波器，其输出平均电压U0小于输入电压Ui，极性相同。（2）Boost电路——升压斩波器，其输出平均电压 U0大于输入电压Ui，极性相同。 （3）Buck－Boost电路——降压或升压斩波器，其 输出平均电压U0大于或小于输入电压Ui，极性相反，电感传输。 （4）Cuk电路——降压或升压斩波器，其输出平均电压U0大于或小于输入电压Ui，极性相反，电容传输。当今软开关技术使得DC/DC发生了质的飞跃，美国VICOR公司设计制造的多种ECI软开关DC/DC变换器，其最大输出功率有300W、600W、800W等，相应的功率密度为(6.2、10、17)W/cm3，效率为（80～90）％。日本NemicLambda公司最新推出的一种采用软开关技术的高频开关电源模块RM系列，其开关频率为（200～300)kHz，功率密度已达到27W/cm3，采用同步整流器（MOS?FET代替肖特基二极管），使整个电路效率提高到90％。 2.AC/DC变换

AC/DC变换是将交流变换为直流，其功率流向可以是双向的，功率流由电源流向负载的称为“整流”，功率流由负载返回电源的称为“有源逆变”。AC/DC变换器输入为50/60Hz的交流电，因必须经整流、滤波，因此体积相对较大的滤波电容器是必不 第 34 页

可少的，同时因遇到安全标准（如UL、CCEE等）及EMC指令的限制（如IEC、、FCC、CSA），交流输入侧必须加EMC滤波及使用符合安全标准的元件，这样就限制AC/DC电源体积的小型化，另外，由于内部的高频、高压、大电流开关动作，使得解决EMC电磁兼容问题难度加大，也就对内部高密度安装电路设计提出了很高的要求，由于同样的原因，高电压、大电流开关使得电源工作损耗增大，限制了AC/DC变换器模块化的进程，因此必须采用电源系统优化设计方法才能使其工作效率达到一定的满意程度。AC/DC变换按电路的接线方式可分为，半波电路、全波电路。按电源相数可分为，单相、三相、多相。按电路工作象限又可分为一象限、二象限、三象限、四象限。开关电源的选用开关电源在输入抗干扰性能上，由于其自身电路结构的特点（多级串联），一般的输入干扰如浪涌电压很难通过，在输出电压稳定度这一技术指标上与线性电源相比具有较大的优势，其输出电压稳定度可达(0.5～1）％。开关电源模块作为一种电力电子集成器件，在选用中应注意以下几点： 3.输出电流的选择

因开关电源工作效率高，一般可达到80％以上，故在其输出电流的选择上，应准确测量或计算用电设备的最大吸收电流，以使被选用的开关电源具有高的性能价格比，通常输出计算公式为： Is=KIf式中：Is—开关电源的额定输出电流； If—用电设备的最大吸收电流； K—裕量系数，一般取1.5～1.8； 4.接地

开关电源比线性电源会产生更多的干扰，对共模干扰敏感的用电设备，应采取接地和屏蔽措施，按ICE1000、EN61000、FCC等EMC限制，开关电源均采取EMC电磁兼容措施，因此开关电源一般应带有EMC电磁兼容滤波器。如利德华福技术的HA系列开关电源，将其FG端子接大地或接用户机壳，方能满足上述电磁兼容的要求。3.3保护电路开关电源在设计中必须具有过流、过热、短路等保护功能，故在设计时应首选保护功能齐备的开关电源模块，并且其保护电路的技术参数应与用电设备的工作特性相匹配，以避免损坏用电设备或开关电源。开关电源技术的发展动向开关电源的发展方向是高频、高可靠、低耗、低噪声、抗干扰和模块化。由于开关电源轻、小、薄的关键技术是高频化，因此国外各大开关电源制造商都致力于同步开发新型高智能化的元器件，特别是改善二次整流器件的损耗，并在功率铁氧体（Mn?Zn)材料上加大科技创新，以提高在高频率和较大磁通密度（Bs)下获得高的磁性能，而电容器的小型化也是一项关键技术。SMT技术的应用使得开关电源取得了长足的进展，在电路板两面布置元器件，以确保开关电源的轻、小、薄。开关电源的高频化就必然对传统的PWM开关技术进行创新，实现ZVS、ZCS的软开关技术已成为开关电源的主流技术，并大幅提高了开关电源的工作效率。对于高可靠性指标，美国的开关电源生产商通过降低运行电流，降低结温等措施以减少器件的应力，使得产品的可靠性大大提高。模块化是开关电源发展的总体趋势，可以采用模块化电源组成分布式电源系统，可以设计成N＋1冗余电源系统，并实现并联方式的容量扩展。针对开关电源运行噪声大这一缺点，若单独追求高频化其噪声也必将随着增大，而采用部分谐振转换电路技术，在理论上即可实现高频化又可降低噪声，但部分谐振转换技术的实际应用仍存在着技术问题，故仍需在这一领域开展大量的 第 35 页

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