英文文獻 科技類 原文及翻譯 （電子 電氣 自動化 通信…） 8

《英文文獻 科技類 原文及翻譯 （電子 電氣 自動化 通信…） 8》由會員分享，可在線閱讀，更多相關《英文文獻 科技類 原文及翻譯 （電子 電氣 自動化 通信…） 8（18頁珍藏版）》請在裝配圖網(wǎng)上搜索。

1、Switching Power Supply 目 錄 1 Switching Power Supply 2 Linear versus Switching Power Supplies 2 Basic Converters 3 1.2.1Forward-Mode Converter Fundamentals 3 1.2.3 Flyback or Boost-mode Converter Fundamentals 4 1.3 Topologies 6 1 開關電源 8 1.1 線性電源和開關電源之比擬 8 根本轉換器 8 1.2.1 前向模式轉換器根

2、底 8 12.2 增壓模式轉換器根底 9 1.3 拓撲結構 10 2 Operational Amplifiers 11 2 放 大 器 15 1 Switching Power Supply Every new electronic product , except those that battery powered, requires converting off-line 115V ac or 230V ac power to some dc voltage for powering

3、the electronics. Efficient conversion of electrical power is becoming a primary concern to companies and to society as a whole. Switching power supplies offer not only higher efficiencies but also offer greater flexibility to the designer. Recent advances in semiconductor, magnetic and passive tech

4、nologies make the switching power supply an ever more popular choice in the power conversion arena today. 1.1 Linear versus Switching Power Supplies Historically, the linear regulator was the primary method of creating a regulated output voltage. It operates by reducing a higher input volta

5、ge down to the lower output voltage by linearly controlling the conductivity of a series pass power device in response to changes in its load. This results in a large voltage being placed across the pass unit with the load current flowing through it. This headroom loss causes the linear regulator

6、to only be 30 to 50 percent efficient. That means that for each watt delivered to the load , at least a watt has to be dissipated in heat. The cost of the heatsink actually makes the linear regulator uneconomical above 10watts for small applications. Below that point, however, they are cost effectiv

7、e in step-down applications. The switching regulator operates the power devices in the full-on and cutoff states. This then results in either large currents being passed through the power devices with a low“on〞voltage or no current flowing with high voltage across the device. This results in a much

8、 lower power being dissipated within the supply. The average switching power-supply exhibits efficiencies of between 70 to 90 percent, regardless of the input voltage. Higher levers of integration have driven the cost of switching power supplies downward which makes in an attractive choice for out

9、put powers greater than 10 watts or where multiple outputs are desired. 1.2 Basic Converters Forward-Mode Converter Fundamentals The most elementary forward-mode converter is the Buck or Step-down Converter which can be seen in Figure 3.1. Its operation can be seen as having two distinct time

10、 periods which occur when the series power switch is on and off. When the power switch is on ,the input voltage is connected to the input of the inductor .The output of switch of inductor is the output voltage, and the rectifier is back-biased. During this period, since there is a constant voltage s

11、ource connected across the inductor, the inductor current begins to linearly ramp upward which is described by: During the “on〞 period , energy is being stored within the core material of the inductor in the form of flux. There is sufficient energy stored to carry the requirements of the load dur

12、ing the next off period. The next period is the “off〞 period of the power switch .When the power switch turns off, the input voltage of the inductor flies below ground and is clamped at one diode drop below ground by the catch diode. Current now begins to flow through the catch diode thus maintai

13、ning the load current loop. This remove the stored energy from the inductor, The inductor. The inductor current during this time is: This period ends when the power switch is once again turned on. Regulation is accomplished by varying the on-to-off duty cycle of the

14、power switch. The relationship which approximately describes its operation is: Where is the duty cycle (). The buck converter is capable of kilowatts of output power, but suffers from one serious shortcoming which would occur if the power switch were to fail short-circuited, the input power sou

15、rce is connected directly to the load circuitry with usually produces catastrophic results. To avoid this situation, a crowbar is placed across the output. A crowbar is a latching SCR which is fired when the output is sensed as entering an overvoltage condition. The buck converter should only be use

16、d for board-level regulation. Flyback or Boost-mode Converter Fundamentals The most elementary flyback-mode converter is the boost or Step-up Converter. Its schematic can be seen in Figure3.2. Its operation can also be broken into two distinct periods where the power switch is on or off. When

17、 power switch turns on, the input voltage source is placed directly across the inductor. This causes the current to begin linearly ramping upwards from zero and is described by: Once again, energy is being stored during each cycle times the frequency of operation must b higher than the power dem

18、ands of the load or, The power switch then turns off and the inductor voltage flies back above the input voltage and is clamped and is clamed by the rectifier at the output voltage .The current then begins to linearly ramp downward until the until the energy within the core is completely depleted

19、. Its waveform which is shown in Figure 3.3 is determined by: The boost converter should also be only used for board-level regulation. 1.3 Topologies A topology is the arrangement of the power devices and their magnetic elements. Each topology has its own merits within ce

20、rtain applications. Some of the factors which determine the suitability of a particular topology to a certain application are: 1) Is the topology electrically isolated from the input to the output or not. 2) How much of the input voltage is placed across the inductor or transformer. 3) What is th

21、e peakcurrent flowing through the power semiconductors. 4) Are multiple outputs required. 5) How much voltage appears across the power semiconductors. The first choice that faces the designer is whether to have input to output transformer isolation. Non-isolated switching power supplies are typi

22、cally used for board-level regulation where a dielectric barrier is provided elsewhere within the system. Non-isolated topologies should also be used where the possibility of a failure does not connect the input power source to the fragile load circuitry. Transformer isolation should be used in all

23、other situations. Associated with that is the need for multiple output voltages. Transformers provide an easy method for adding additional output voltage to the switching power supply. The companies building their own power systems are leaning toward transformer isolation in as many power supplies a

24、s possible since it prevents a domino effect during failure conditions. 1 開關電源 除了那些用電池做電源的電子產(chǎn)品外，每個新型電子產(chǎn)品都需要將115V或者230V的交流電源轉換為直流電源，為電路供電。電功率的轉換率正在成為是、公司和整個社會關注的重點。 開關電源不僅提供了較高的轉換效率，而且為設計者提供為設計提供了更大的靈活性，半導體技術、磁器件和無源器件技術的進步，使得開關電源在今天功率轉換的舞臺成為日

25、益流行的選擇。 1.1 線性電源和開關電源之比擬 在歷史上，線性穩(wěn)壓器曾是產(chǎn)生穩(wěn)壓輸出電壓的主要方法。通過對級聯(lián)功率通過對器件的掉電性進行線性控制以響應負載變化，線性穩(wěn)壓器可以將輸入高電壓降為輸出地電壓。這種方法導致在負載電流流經(jīng)的通過單元兩端出現(xiàn)一個大電壓。 這個功率損耗使得線性穩(wěn)壓電源的效率只有30%～50%。這意味著每向負載輸出1瓦特的功率，就會有至少1瓦特功率以熱能形式消耗了。對于這一些功率超過10瓦特的小型應用而言，散熱裝置的本錢就導致使用線性穩(wěn)壓電源不合算。 開關電源中的功率器件工作在全開和截止狀態(tài)。這樣，要么在大電流流經(jīng)功率器件時，導通電壓很低；要么在大電壓時，沒有電流通

26、過器件。因此，電源內(nèi)部消耗的功率就很少，。開關電源的平均效率為70%～90%，而且和輸入電壓無關。 集成度的提高推動開關電源本錢的下降，這使得它在輸出功率超過10瓦特及多輸出應用中成為具有吸引力的選擇。 根本轉換器 前向模式轉換器根底 最根本的前向轉換器是如圖3.1所示的降壓轉換器。其工作過程可視為兩個不同的時間周期，它們分別出現(xiàn)在串聯(lián)功率開關處于“接通〞和“斷開〞的狀態(tài)。當功率開關接通時，輸入電壓連接到電感的輸入端。電感的輸出電壓就是轉換器的輸出電壓，整流器處于反偏置。在這個期間，由于在電感兩端存在一個恒定電壓源，所以電感電流開始按照如下公式線性增加： 在“接通〞周期，能量以

27、磁通的形式存儲在電感的鐵心材料中。存儲的能量足以滿足負載在下一個“斷開〞周期的需求。 下一個周期就是功率開關的“斷開〞周期。當功率開關斷開時，電感輸入電壓被捕捉二極管鉗位在地電位下一個二極管電壓降。電流開始流過捕獲二極管以維護如在環(huán)路電流。存儲在電感中的能量被移走。這段時間內(nèi)的電感電流可表示為： 當功率二極管再次接通時，這個周期就結束了。 電壓調(diào)節(jié)是通過改變功率的“接通——斷開〞的占空比來實現(xiàn)的。下面的關系式近似描述這個工作過程： 式中是占空比。 該轉換器可以輸出千瓦級功率，但它卻有一個嚴重缺點——假設功率開關非正常短路

28、，輸入電源就會直接連接到負載電路，這通常會造成災難性后果。為了防止出現(xiàn)這種情況，在輸出端跨置一個短路器。斷路器是一個閉塞的半導體可控整流器。當輸出進入過電壓狀態(tài)時，就會激發(fā)這個整流器。降壓轉換器僅用于板級電源管理。 12.2 增壓模式轉換器根底 最根本的增壓模式轉換器是升壓穩(wěn)壓器。其原理圖見圖3.2。其工作過程也可以分為兩個不同的周期，分別對應著功率開關的“導通〞和“斷開〞狀態(tài)。當功率開關導通時，輸入電壓源接到電感兩端。電流從零開始按照如下公式增加： 能量被存儲在鐵心材料中。 每個周期存儲的能量和工作頻率的乘積必須大于負載的功率需求，即滿足下式：

29、 然后，功率開關斷開，電感電壓超過輸入電壓并被整流器鉗位在輸出電壓上。電流開始線性下降直至鐵心中的能量全部耗盡。如圖3.3所示，其電流波形由下式?jīng)Q定： 升壓變換器也僅用于板級電壓管理。 拓撲結構 拓撲結構是指功率器件和磁元件的布局。每種拓撲結構在特定應用中都有各自的優(yōu)點。決定一種拓撲結構是否是適于某個特定應用的因素如下： 1） 該拓撲結構的輸入輸出之間是否實現(xiàn)了電氣隔離? 2） 有多少輸入電壓加在電感或者變壓器兩端？ 3） 流經(jīng)功率半導體器件的峰值電流為多少？ 4） 是否需要多個電壓輸出？ 5） 功率半導體器件兩端出現(xiàn)的電壓有多大? 設計者面臨的第一選擇

30、是：是否采用輸入和輸出之間的變壓器格力。非隔離開電源的典型應用是為具備絕緣隔板的系統(tǒng)提供板級電壓調(diào)理。非隔離拓撲結構還可用于這種情況：當出現(xiàn)故障時，輸入電源不會連接到易損負載電路。對于所有其他情況，應該使用變壓器隔離。與變壓器隔離相關的是對多電壓輸出的需求。變壓器為開關電源增加附加輸出提供了一種易于實現(xiàn)的方法。制造自己系統(tǒng)電源的公司傾向于在盡可能多的電源中采用變壓器隔離，因為這種隔離防止了故障出現(xiàn)時將產(chǎn)生的連鎖反響。 2 Operational Amplifiers In 1943 Harry Black commuted from his

31、 home in New York City at Bell Labs in New Jersey by way of a ferry. The ferry ride relaxed Harry enabling him to do some conceptual thinking. Harry had a tough problem to solve; when phone lines were extended long distance, they needed amplifiers, and undependable amplifiers limited phone service.

32、First, initial tolerances on the gain were poor, but that problem was quickly solved wuth an adjustment. Second, even when an amplifier was adjusted correctly at the factory, the gain drifted so much during field operation that the volume was too low or the incoming speech was distorted. Many attem

33、pts had been made to make a stable amplifier, but temperature changes and power supply voltage extremes experienced on phone lines caused uncontrollable gain drift. Passive components had much better drift characteristics than active components had, thus if an amplifier’s gain could be made dependen

34、t on passive components, the problem would be solve. During one of his ferry trips, Harry’s fertile brain conceived a novel solution for the amplifier problem, and he documented the solution while riding on the ferry. The solution was to first build an amplifier that had more gain than the applica

35、tion required. Then some of the amplifier output signal was fed back to the input in a manner that makes the circuit gain (circuit is the amplifier and feedback components) dependent on the feedback circuit rather than the amplifier gain. Now the circuit gain is dependent on the passive feedback com

36、ponents rather than the active amplifier. This is called negative feedback, and it is the underlying operating principle for all modern day opamps. Harry had documented the first intentional feedback circuit had been built prior to that time ,but the designers ignored the effect. I can hear the squ

37、eals of anguish coming from the manager and amplifier designers. I imagine that they said something like this, “it is hard enough to achieve 30kHz gainbandwidth (GBW), and now this fool wants me to design an amplifier with 3MHz GBW. But ,he is still going to get a circuit gain GBW of 30kHz .〞 Well,

38、 time has proven Harry right ,but there is a minor problem. It seems that circuit designed with large pen loop gains sometimes oscillate when the loop is closed. A lot of people investigated the instability effect, and it was pretty well understood in the 1940s, but solving stability problems involv

39、ed long, tedious, and intricate calculations. Years passed without anybody making the problem solution simpler or more understandable. In 1945 H. W. Bode presented a system for analyzing the stability of feedback system by using graphical methods. Until this time, feedback analysis was done by mult

40、iplication and division, so calculation of transfer functions was a time consuming and laborious task. Remember, engineers did not have calculators or computers until the ‘70s, Bode presented a log technique that transformed the intensely mathematical process of calculating a feedback system’s stabi

41、lity into graphical analysis that was simple and perceptive. Feedback system design was still complicated, but it no longer was an art dominated by a few electrical engineers kept in a small dark room. Any electrical engineer could use Bode’s methods to find the stability of a feedback circuit, so t

42、he application of feedback to machines began to grow. There really wasn’t much call for electrical feedback design until computers and transducers become of age. The first real-time computer was the analog computer! This computer used preprogrammed equations and input data to calculate control acti

43、ons. The programming was hard wired with a series of circuit that performed math operations on the data, and the hard wiring limitation eventually caused the declining popularity of the analog computer. The heart of the analog computer was a device called an operational amplifier because it could be

44、 configured to perform many mathematical operations such as multiplication, addition, subtraction, division, integration, and differentiation on the input signals. The name was shortened to the familiar op amp, as we have come to know and love them. The op amp used an amplifier with a large open loo

45、p gain, and when the loop was closed, the amplifier performed the mathematical operations dictated by the external passive components. This amplifier was very large because it was built with vacuum tubes and it required a high-voltage power supply,but it was the heart of the analog computer, thus it

46、s large size and huge power requirements were accepted. Many early op amps were designed for analog computers, an it was soon found out the op amps had other uses and were handy to have around the physics lab . At this time general-purpose analog computers were found in universities and large compa

47、ny laboratories because they were critical to the research work done there. There was a parallel requirement for transducer signal conditioning in lab experiments, and op amps found their way into signal conditioning applications. As the signal conditioning applications expanded, the demand for op a

48、mps grew beyond the analog computer requirements , and even when the analog computers lost favor to digital computers, the op amps survived because of its importance in universal analog applications. Eventually digital computes replaced the analog computers, but the demand for op amps increased as m

49、easurement applications increased. The first signal conditioning op amps were constructed with vacuum tubes prior to the introduction of transistors, so they were large and bulky. During the’50s, miniature vacuum tubes that worked from lower voltage power supplies enabled the manufacture of op amps

50、 that shrunk to the size lf a brick used in house construction, so the op amp modules were nick named bricks. Vacuum tube size and component size decreased until an op amp was shrunk to the size of a single octal vacuum tube. Transistors were commercially developed in the ‘60s, and they further redu

51、ced op amp size to several cubic inches. Most of these early op amps were made for specific applications, so they were not necessarily general purpose. The early op amps served a specific purpose, but each manufacturer had different specifications and packages; hence, there was little second sourcin

52、g among the early op amps. ICs were developed during the late 1950s and early 1960s, but it wasn’t till the middle 1960s that Fairchild released the μA709. This was the first commercially successful IC op am. TheμA709 had its share of problems, bur any competent analog engineer could use it, and it

53、 served in many different analog applications. The major drawback of theμA709 was stability; it required external compensation and a competent analog engineer to apply it. Also, theμA709 was quite sensitive because it had a habit of self-destruction under any adverse condition. TheμA741 followed the

54、μA709, and it is an internally compensated op amp that does not require external compensation if operated under data sheet conditions. There has been a never-ending series of new op amps released each year since then, and their performance and reliability had improved to the point where present day

55、op amps can be used for analog applications by anybody. The IC op amp is here to stay; the latest generation op amps cover the frequency spectrum from 5kHz GBW to beyond 1GHz GBW. The supply voltage ranges from guaranteed operation at 0.9V to absolute maximum voltage ratings of 1000V. The input cur

56、rent and input offset voltage has fallen so low that customers have problems verifying the specifications during incoming inspection. The op amp has truly become the universal analog IC because it performs all analog tasks. It can function as a line driver, comparator (one bit A/D), amplifier, level

57、 shifter, oscillator, filter, signal conditioner, actuator driver, current source, voltage source, and etc. The designer’s problem is how to rapidly select the correct circuit /op amp combination and then, how to calculate the passive component values that yield the desired transfer function in the

58、circuit. The op amp will continue to be a vital component of analog design because it is such a fundamental component. Each generation of electronic equipment integrates more functions on silicon and takes more of the analog circuit inside the IC. As digital applications increase, analog applicatio

59、ns also increase because the predominant supply of data and interface applications are in the real world, and the real world is an analog world. Thus , each new generation of electronic equipment creates requirements for new analog circuit; hence, new generations of op amps are required to fulfill t

60、hese requirements. Analog design, and op amp design, is a fundamental skill that will be required far into the future. 2 放 大 器 1943年，哈利·布萊克乘火車或渡船從位于紐約市的家去新澤西州的貝爾實驗室上班。在上班途中，哈利能夠送下來，思考一些概念上的問題。哈利需要解決一個很棘手的問題： 線在用于長途傳輸時就需要放大器，而性能不可靠的放大器限制了 業(yè)務的擴展。首先，增益容差性能很差；但是，通過使用調(diào)節(jié)

61、器，這個問題很快就解決了。第二，即使放大器在工廠里被調(diào)節(jié)正確，但在現(xiàn)場工作是增益還是漂移地很厲害，以至于音量太低或輸入語音發(fā)生畸變。 為了制造出穩(wěn)定的放大器，哈利已經(jīng)進行了屢次嘗試；但是，溫度變化和 線上出現(xiàn)的供電電壓極限使得增益漂移無法控制。無源器件比有源器件具有好得多漂移特性；假設能使放大器增益僅由無源器件決定的話，那么這個問題就會解決。在乘渡船上下班途中，哈利設想一個新穎的、解決放大器問題的方法，并在途中將它記錄下來。 這個解決方案是這樣的：首先設計一個增益比實際需求高的放大器，然后，將放大器輸出信號的一局部反響輸入端，這使得電路增益〔這里的電路由放大器和反響器件組成〕由反響電路

62、決定，而不是放大器增益決定，這樣的話，電路增益就取決于無源反響器件，而不是有源放大器。這個方案被稱為“負反響“，它是現(xiàn)代運算放大器的根本工作原理。哈利在乘坐渡船途中記錄了第一個有意參加反響的電路。此前，也一定有人無意中使用過反響電路，但設計者無視了這種作用！ 管理者和放大器設計者可能會發(fā)生痛苦的抱怨。他們可能會說：“獲得30kHz的增益帶寬就夠難了，現(xiàn)在這個傻瓜要我設計增益帶寬為30MHz的放大器，而他還是想得到一個增益帶寬為30kHz電路〞。然而，時間已經(jīng)證明哈利是正確，但有一個小問題哈利沒有詳細討論——振蕩問題。在環(huán)路閉合時候，開環(huán)增益設計得很大的電路有時會發(fā)生振蕩。很多人都研究了這個不

63、穩(wěn)定現(xiàn)象，在20世紀40年代人們對它有了清晰的認識；不過，解決穩(wěn)定問題需要長時間單調(diào)復雜的計算。許多年過去了，沒有人能將解法簡化或使之易于理解。 1945年，波特用圖形化方法展示了一個用于分析反響系統(tǒng)穩(wěn)定性的系統(tǒng)。那時，反響分析是用乘法和除法完成的。因此，計算傳輸函數(shù)是一件耗時費力的工作。需要知道的是：直到20世紀70年代，工程師才有了計算器和計算機。波特采用了一種對數(shù)方法——將分析反響系統(tǒng)穩(wěn)定的數(shù)學過程轉換為容易的、好理解的圖形化分析。雖然反響系統(tǒng)的設計依然很復雜，但它再也不是一件只有少數(shù)電氣工程師掌握的技術。任何電氣工程師都可以使用波特的方法確定反響電路的穩(wěn)定性，并越來越多地將反響應用到

64、機器設計當中。直到計算機和傳感出現(xiàn)后，才產(chǎn)生了對電子反響設計的真正迫切需要。 第一臺實時計算機是模擬計算機。這臺計算機使用預先編程的數(shù)學公式和輸入數(shù)據(jù)來計算控制動作。編程是對一系列能完成對輸入數(shù)據(jù)進行數(shù)學操作電腦進行硬連線，硬連線的限制最終導致模擬計算機沒有普及。模擬計算機的心臟是運算放大器；通過配置，它可以對輸入數(shù)據(jù)進行多種數(shù)學運算，如乘法、除法、加法、減法、積分和微分。隨著人們逐步了解并喜歡運算放大器，它們名字就簡化成了大家熟知“op amp〞〔運放〕。運放使用具有一個很大開環(huán)增益的放大器，當電路形成閉合環(huán)路時，放大器就會執(zhí)行由外部無源元件控制的數(shù)學運算。這個放大器體積很大，因為它是用真

65、空管 做的，而且需要一個大電壓電源。但由于他是模擬計算機的心臟，所以人們還是接受了它這種大體積和大電壓。許多早期運放是為模擬計算機設計的，人們很快就發(fā)現(xiàn)運放還有其他用途，在屋里實驗室也很容易得到運放。 那個時候，在大學和大型公司的實驗室里就能夠看到通用模擬計算機；因為對那里進行的研究工作而言，計算機是至關重要的。同時，在實驗室中也需要對傳感器信號進行調(diào)理，運放在信號調(diào)理方面也找到用武之地。隨著信號調(diào)理應用范圍的拓展，其對運放需要的增長超過了模擬計算機。甚至在模擬計算機遜色于數(shù)字計算機之后，運放因其在通用模擬應用中的重要性而并未受到冷落。數(shù)字計算機最終代替了模擬計算機，但是運放的需求量卻隨著測

66、量應用的增長而增長了。 在晶體管出現(xiàn)之前，第一個用于信號調(diào)理的運放是用真空管構建的，因此它體積很大。20世紀50年代，低電壓工作的小型真空管使運放的體積縮小到一塊磚的大小，因此運放模塊有了一個“磚塊“的綽號。真空管和組件的體積不斷地縮小，直至運放縮至一只八角真空管的大小。在60年代，晶體管實現(xiàn)了商業(yè)開發(fā)，這進一步將運放的體積減至幾個立方英寸。大多數(shù)早期運放是為特定應用而制造的，所以它們不一定通用；早期運放是為某種特定應用效勞的，但每個生產(chǎn)商的技術上指標和封裝都不同。 50年代末60年代初，集成電路開發(fā)出來了。但直到60年代中期，仙童公司才發(fā)布了μA709。它是首片取得商業(yè)成功的集成運放。雖然μA709有自身的問題，然而任何一位稱職的模擬工程師都能使用它，在許多不同的模塊應用中都可以使用它。μA709的主要缺陷在穩(wěn)定性，他需要外部補償。μA709也很敏感；一旦不利條件出現(xiàn)，他就容易自毀。在μA709之后出現(xiàn)了內(nèi)部補償μA741；當在數(shù)據(jù)手冊要求的條件下工作時，μA741是不需要外部補償?shù)?。從那以后，新系列的運放就不斷出現(xiàn)；今天，運放的功能和可靠性已經(jīng)提高到了這種程度——任何人都能在模