晶體管特性文獻(xiàn)翻譯

1、黃河科技學(xué)院畢業(yè)設(shè)計(jì)（文獻(xiàn)翻譯） 第 18 頁(yè) 晶體管特性第一章中已經(jīng)指出，晶體管能夠放大電流。因此，晶體管在電子線路中應(yīng)用很廣，例如音頻放大器，助聽(tīng)器，擴(kuò)音機(jī)放大器，無(wú)線電接收機(jī)和電視接收機(jī)，測(cè)量?jī)x表和工業(yè)控制。另外，晶體管也可以用作“電子開(kāi)關(guān)”，它可使電流通路或者呈現(xiàn)高電阻或者呈現(xiàn)低電阻。這就是晶體管有可能在計(jì)算機(jī)電路和控制系統(tǒng)中獲得廣泛應(yīng)用。對(duì)每一項(xiàng)應(yīng)用都必須進(jìn)行細(xì)致的電路設(shè)計(jì)，在能夠系統(tǒng)地進(jìn)行設(shè)計(jì)工作之前，應(yīng)對(duì)晶體管這一電路元件的特性有個(gè)詳盡的了解，知道什么是最佳工作電壓和電流，對(duì)信號(hào)的阻抗有多大，晶體管的放大倍數(shù)有多大，什么是晶體管輸出端內(nèi)阻抗等等。這些特性資料可從各類晶體管有關(guān)數(shù)據(jù)

2、中獲得，這些數(shù)據(jù)由制造廠商提供，印成“數(shù)據(jù)表”發(fā)行，使晶體管使用者能根據(jù)此進(jìn)行初步設(shè)計(jì)，而不必自行量測(cè)。首要的問(wèn)題是取得晶體管電壓電流關(guān)系曲線。通常要提供出兩組曲線；發(fā)射結(jié)正向電壓電流特性曲線，通常稱為發(fā)射極特性曲線或輸入特性曲線；以及集電結(jié)反向電壓電流曲線，通常稱為集電極特性曲線或輸出特性曲線。1 基特性曲線首先研究共基極電路，圖1所示為發(fā)射極基極正向特性曲線，它描述了發(fā)射極電流如何隨發(fā)射極基極電壓從零正向增高而增大。圖上所示的特性曲線是小型鍺管的典型曲線。由圖可看出，最初電流隨電壓增高而增加，但增加的幅度很小。在這期間，外加電壓逐漸克服pn結(jié)的勢(shì)壘。勢(shì)壘一旦被中和，電流就迅速增加。圖1 發(fā)

3、射極基極正向特性曲線現(xiàn)在來(lái)研究發(fā)射極電流變化時(shí)集電極電路出現(xiàn)的情況。首先，發(fā)射極電流為零時(shí)集電極基極特性如圖2中IE=0的曲線所示。它和前面圖所示的pn結(jié)反向特性曲線相似。圖中的小股電流稱為集電結(jié)的漏電流?，F(xiàn)在使發(fā)射結(jié)電流增加到1毫安（圖1中的A點(diǎn)），并使之維持不變。我們看到，幾乎全部發(fā)射極電流都傳送到集電極，通過(guò)集電極的電流量與集電極電壓的高低無(wú)關(guān)。這樣，集電極電壓電流特性曲線就成了圖2中IE=2,3,4和5毫安時(shí)的集電極曲線B,C,D和E。集電極特性曲線幾乎處于水平位置這一性質(zhì)突出了高輸出電阻這一特性，因而集電極電壓發(fā)生大幅度變化時(shí)，電流變化很小。 圖2 集電極基極特性由圖中可以看出，甚至

4、在集電極電壓為零時(shí)仍然存在集電極電流。這是因?yàn)榛鶚O電流在通過(guò)基區(qū)電阻時(shí)在集電極基極回路中產(chǎn)生一小電勢(shì)差，從而在集電極兩端形成很小的反向偏壓。要使集電極電流減為零，就需要外加一很小的正向集電極電壓，如圖2所示。圖2中集電極特性曲線畫(huà)在第三象限，以使人們注意到集電極反向偏置?，F(xiàn)在一般把它畫(huà)在第一象限，如圖3所示，這在某種程度上是由于熱離子管的輸出特性曲線本身就是這樣處理的。圖3 集電極特性曲線 2 共基極放大器的相位關(guān)系基極發(fā)射極回路是正向偏置。以pnp晶體管為例，它的發(fā)射極與基極相比為正。信號(hào)正向半周與Vee串聯(lián)連接時(shí)，發(fā)射極比以前更正，使發(fā)射極基極電流增大。在晶體管中，發(fā)射極基極電流的增大使集

5、電極電流相應(yīng)增加。由于RL中的電流方向朝上，此電阻器上端與它的下端相比較就比以前更正了。因此，正向半周輸入信號(hào)引出正向半周輸出信號(hào)。這就是說(shuō)共基極晶體管放大器沒(méi)有倒相問(wèn)題。圖4 共基極放大器的倒位關(guān)系在許多類型的多級(jí)放大器、振蕩器和電視用視頻放大器中，相位關(guān)系是考慮的重要問(wèn)題。對(duì)今后的應(yīng)用來(lái)說(shuō)，重要的是要記住我們?nèi)绾闻袛嗟瓜嗯c否的方法。 3 單電源共基極電路 圖5 單電池共基極電路共基極電路的設(shè)計(jì)通常避免使用發(fā)射極電池Vee。要做到這一點(diǎn)，只需加上一基極電阻（Rb），并使此電阻的低端成為輸入和輸出回路兩者的公共端。此電路除了省去發(fā)射極電池外，還使一個(gè)輸入端和一個(gè)輸出端處于低電位。這樣，輸入和輸

6、出兩個(gè)回路現(xiàn)在都有一個(gè)公共的參考電位（低電位）。流過(guò)Rb的小股電流Ico和地連接，它相對(duì)于基極是負(fù)的（這是npn晶體管）。因而不用電池就獲得了較小的正向偏壓。偏置電阻Rb可以旁路，這樣在可能出現(xiàn)交流信號(hào)時(shí)Rb的電壓降仍保持不變。4 共發(fā)射極特性曲線共發(fā)射極連接時(shí)可得出與共基極連接時(shí)相類似的特性曲線。首先是輸入特性曲線，它表明基極電流隨發(fā)射極基極結(jié)兩端電壓正向升高而變化的情況，如圖6所示；其次是輸出特性曲線，它表明集電極電流隨不同基極電流下的集電極電壓變化已定的情況下，基極電流變化比發(fā)射極電流變化小。圖7的輸出特性曲線和共基極特性曲線很相似，只是電流曲線有明顯的坡度，即電流隨電壓而增大。這說(shuō)明它

7、的輸出電阻比基極電路低，但它仍然是相當(dāng)高的。此外，集電極電壓為零時(shí)集電極電流也為零，這是因?yàn)榛鶚O電流所形成的電勢(shì)并沒(méi)有出現(xiàn)在集電極反射極回路。圖6 共發(fā)射極特性曲線圖7 2N78輸出特性曲線5 集電極曲線的應(yīng)用當(dāng)你觀察集電極曲線時(shí)，首先映入眼中使你感興趣的是電流并不隨集電極電壓的變化而急劇增大。它是一組十分近似于水平的直線，特別在基極電流很低的區(qū)域；即使在基極電流較高的區(qū)域，坡度也很平緩的。我們可以說(shuō)：在制造廠商所推薦的區(qū)域范圍內(nèi)，晶體管的集電極電流相對(duì)獨(dú)立于集電極電壓。圖8 IbIc曲線與之相反，在集電極電勢(shì)恒定的條件下，基極電流稍有變化就可使用集電極電流發(fā)生較大的變化?；鶚O電流作等值增長(zhǎng)時(shí)

8、，集電極電流是否相應(yīng)地等值上升呢？為了弄清這一點(diǎn)，我們選定一集電極電勢(shì)，譬如說(shuō)5伏，然后沿這條5伏線上升。注意觀察基極電流每增加25毫安時(shí)集電極電流的變化情況。為幫助你估算集電極電流的變化量，我們繪制了集電極電勢(shì)為5伏的IbIc曲線。雖然這條曲線并不完全是一條直線，但它確實(shí)很近似于直線，如果晶體管用于例如音頻放大電路，我們就可以說(shuō)：如果Ib的變化局限在相當(dāng)小的范圍內(nèi)，集電極電流就隨Ib作線性變化。這一提法可進(jìn)一步解釋如下：如饋入基極的輸入電流是弱音頻電流，則集電極回路的電流變化比輸入電流的變化大，但其波形保持不變。這樣，我們得到一種度量我們對(duì)這類晶體管所能要求的保真度的方法，或者反過(guò)來(lái)說(shuō)，度量

9、晶體管固有畸變的方法。圖9 晶體管畸變曲線只要IbIc曲線是條直線，其固有畸變就為零。曲線的曲率越大，晶體管本身所造成的畸變?cè)絿?yán)重。前面所有討論的前提是，電路元件選擇恰當(dāng)，才能使所用的晶體管產(chǎn)生正常的偏壓。不然，就可能出現(xiàn)與晶體管固有特性無(wú)關(guān)的畸變。圖10 Ic的改變影響Ib的改變我們可利用集電極特性曲線或者IbIc曲線在幾秒鐘內(nèi)即可估算出晶體管的值。晶體管集電極特性一般可在制造廠商的參數(shù)表中取得。讓我們利用它來(lái)校核晶體管2N78的ß值，即常說(shuō)的所謂的基極電流增益。晶體管2N78通常在5伏集電極電位下工作，我們先找出5伏線，然后沿此線選出基極電流變化的一般區(qū)域范圍內(nèi)，例如從100微安

10、到125微安。利用我們已經(jīng)知道的等式=IC/Ib，取Ib從100微安到125微安的變化為Ib，它等于25微安。然后，我們可注意到在Ib的變換范圍內(nèi)Ic從2.9毫安變?yōu)?.5毫安。將這些值代入等式就得到：=246 單電池共發(fā)射極電路關(guān)于這個(gè)電路，讓我們先回顧第三節(jié)雙電池共基極放大器改成單電池電路的部分。你可能會(huì)發(fā)現(xiàn)，為了提供所需要的偏置電位，需要在基極回路上外加一電阻和電容。電阻Rb使基極相對(duì)于發(fā)射極（正向偏置）和集電極（反向偏置）都具有正確的極性。如果我們進(jìn)一步分析雙電池共基極電路，顯然可知，需要外加偏壓元件的原因在于發(fā)發(fā)射極和集電極電流的流動(dòng)方向。我們用pnp晶體管為例，可知Ie和IC在接向

11、基極的公共引線中流動(dòng)方向相反。由于用一個(gè)電池，不論放在電路的哪個(gè)部分，要在一個(gè)元件中產(chǎn)生兩股方向相反的電流是決不可能的，所以為了建立正常的偏置電位，借助于人為的輔助元件即偏置電阻是完全必要的。圖11 雙電池共發(fā)射極電路現(xiàn)在我們來(lái)分析雙電池共發(fā)射極電路。Vee使電子流向通過(guò)Ri(或通過(guò)信號(hào)源本身，假設(shè)信號(hào)源是連續(xù)直流的)和基極到發(fā)射極，再向下經(jīng)過(guò)公共導(dǎo)線回到電池的正端，如深色箭頭所示。Vee使電子流向通過(guò)RL和集電極到發(fā)射極，再向下經(jīng)過(guò)公共連接線回到電池的正端，如淺色箭頭所示。由此可知，從發(fā)射極到兩組電池正極結(jié)點(diǎn)的公共導(dǎo)線中電流的流向相同。這就很容易用一組電池來(lái)完成原來(lái)兩組電池的工作。不管我們把

12、電池接到那里，一定要記住，pnp晶體管的基極相對(duì)于發(fā)射極應(yīng)是負(fù)的，但負(fù)的程度不如集電極。 圖12 發(fā)射極和集電極電流的流動(dòng)同向圖13 單電池基極發(fā)射極放大電路實(shí)際上去掉第二組電池很容易，這不能不使我們感到奇怪，為什么在共發(fā)射極電路中曾經(jīng)使用過(guò)兩組電池。我們只注意到Vee和Vcc相對(duì)于發(fā)射極都是負(fù)的。全面檢查線路的連接，我們很快就可看出，集電極電流的通路與過(guò)去完全相同；從電池的負(fù)端通過(guò)集電極，離開(kāi)發(fā)射極，又回到正端。與此同時(shí)，同一電池按深色箭頭指示的方向把電流（雖然可能很小）送入基極回路。這股電流的流動(dòng)和采用兩組電池時(shí)的情況完全相同。剩下要作的只是選擇適當(dāng)?shù)碾娮柚?，使基極電壓大小合適。由于Ri阻

13、值大小在很大程度上取決于晶體管類型、Vcc的電勢(shì)和環(huán)境溫度，所以我們無(wú)法提供某一定值。晶體管2N78在標(biāo)準(zhǔn)中頻電路室溫下的Ri典型阻值為10,000歐姆左右。 來(lái)自晶體管原理附：英文原文Transistor CharacteristicsIt has been shown in the previous chapter that the transistor is cable of amplifying electric currents. As a result, it can be used for many applications in electronic circuits, suc

14、h as audio amplifiers, hearing aids, pubic address amplifiers, radio and television receivers, instrumentation and industrial control. Also, the transistor can be used as an "electronic switch ", that is it can present either a high or a low resistance to the passage of current. This opens

15、 up the possibility of wide use in computer circuits and control systems.For each application careful circuit design work must be carried out. Before this can be done systematically, it is necessary to have detailed knowledge of the characteristics of the characteristics of the transistor as a circu

16、it element, that is, to know what is the best operating voltage and current, what impedance is presented to the signal, what amplification the transistor will give, what is the internal impedance of the transistor at the output, and so on. Data from which information of this nature can be obtained i

17、s prepared by the manufacturer on each type of transistor and published as “data sheets” so that the user can carry out his preliminary design without having to make measurements himself. First, it is important to derive groups of voltage-current relationships for the transistor. Two sets of curves

18、are normally presented, the forward voltage-current characteristics of the emitter junction, referred to as the emitter characteristics curves of the collector junction, called the collector characteristics or the output characteristics.1 Common Base CharacteristicsConsidering first the common base

19、arrangement, Fig. 1 shows the emitter to base forward characteristic, that is, how the emitter current increaser as the emitter to base voltage is increased positively from zero. The characteristic shown is typical of a small germanium transistor. It will be seen that at first the current increases

20、only very slightly as the voltage is increased. During this region the applied voltage is overcoming the potential barrier of the junction. Once the barrier has been neutralized, the current increases rapidly.Now consider what happens in the collector circuit when the emitter current is varied. At f

21、irst, with zero emitter current, the collector to base characteristic is shown as the cure for in Fig. 2. This is similar to the reverse characteristic of a pn junction shown previously in Fig. The small current is known as the leakage current of the collector junction. Now let the emitter current b

22、e increased to 1 mApoint A in Fig. 1 and held constant at that value. We have seen that nearly all of the emitter current passes to the collector, the amount of current crossing the collector junction not being dependent on the collector voltage. Thus the collector voltage current characteristic wil

23、l now be curve A for IE=1 in Fig. 2.Similarly, as the emitter current is increased in further steps collector curves B,C,D and E are obtained for emitter current IE=2,3,4 and 5 mA. The almost horizontal nature of the collector characteristics emphasizes the high output resistance, a large change of

24、collector voltage producing only a very small change of current.It will be seen that the collector current is maintained even at zero collector voltage. This is because the base current, in flowing out through the resistance of the base region, sets up a small potential which appears in the collecto

25、r-base circuit, and constitutes a small reverse bias across the collector junction. To reduce the collector current to zero it is necessary to apply a small forward collector voltage as shown in Fig. 2.In Fig. 2 the collector characteristics have been shown in the third quadrant as a reminder that t

26、he collector junction is biased in the reverse direction. It is now customary to present them in the first quadrant as shown in Fig. 3, to some extent because the output characteristics of thermionic valves were always drawn in this way.2 Hase Relations in a Common-Base AmplifierThe base-emitter cir

27、cuit is forward-biased. In the case of the pnp transistor used as an example, this means that the emitter is more positive than the base. When a positive-going half-cycle is now inserted in series with Vee ,the emitter becomes more positive than before, increasing the emitter-base current. In a tran

28、sistor, an increase of emitter-base current produces a corresponding increase of collector current. Since the direction of current flow is upward in RL, the top terminal of this resistor must become more positive than it was before with respect to the bottom terminal. Hence a positive-going input ha

29、lf-cycle gives rise to a positive-going output half-cycle. This means that there is no phase inversion in the common base transistor amplifier.Phase relations are important considerations in many types of multistage amplifiers. In oscillators, and in video amplifiers for television. It is important

30、to remember how we determine whether phase inversion does or does not occur for future use.3 Single-battery Common-base Circuit A common-base circuit is normally designed to do away with the need for an emitter battery Vee. To do this we need merely add a base resistor(Rb) and make the lower termina

31、l of this resistor common to both input and output circuits. In addition to doing away with the emitter battery, this circuit makes it possible to maintain one input and one output terminal at ground potential . There is now a common reference potential(ground) for both input and output. The small l

32、eakage current ICO flowing through Rb places the base at a slightly higher positive potential than ground. Since the emitter is connected to ground through Re, this element must be negative with respect to the base(this is an npn transistor). Thus, the small amount of for-ward-bias is obtained witho

33、ut the need for a battery. The bias resistor Rb may be bypassed to maintain the voltage drop across it constant, despite the possible presence of alternating signal currents.4 Common Emitter CharacteristicsWith the common emitter connection, similar characteristics can be prepared. First, the input

34、characteristic, which shows how the base current varies as the voltage across the emitter-base junction is increased in the forward direction, as shown in Fig. 7. It will be seen from Fig. 6 that the input resistance is higher than for the common base arrangement, the change of base current being sm

35、aller than the change of emitter current for a given change of emitter to base voltage .The output characteristics in Fig. 7 are similar to the common base characteristics except that there is now a noticeable slope on the current lines, the current increasing with voltage. This indicates that the o

36、utput resistance is lower than in the common base arrangement; but nevertheless it is still high. Also, the collector current is now zero for zero collector voltage since the potential produced by the base current does not appear in the collector to emitter circuit.5 Using the Collector CurvesOne of

37、 the first interesting things that strikes you as you look at the collector curves is that the current does not rise very rapidly with changes of collector voltage. Notice how horizontal the graph lines are, especially when the base current is low. Even for higher base currents, the slopes are very

38、shallow. We can say it this way: over the range recommended by the manufacturer, the collector current of a transistor is relatively independent of the collector voltage.On the other hand, a small change of base current always produces a relatively large change in collector current, if the collector

39、 potential is maintained constant. Does the collector current rise in equal steps for equal increments of base current? To see this, choose a certain collector potential, say 5 volts, then follow the 5-volt line upward and note how the current changes, we have drawn IbIc curve for a collector potent

40、ial of 5 volts.Although this curve is not a perfect straight line, it certainly does approach it closely. Of the transistor is used in an audio amplifier circuit, for example, we might then say: If the range of variation of Ib is held within reasonably small limits, the collector current varies line

41、arly with it.This may be interpreted as follows: if the input current to the base is a weak audio current, the current variations in the collector circuit will be large but will have the same waveform. Thus, we arrive at a measure of the fidelity or, conversely, the inherent distortion that we may e

42、xpect from a transistor of this type. As long as the IbIc curve is a straight line, the inherent distortion will be zero. The greater the curvature of the graph, the greater will be the distortion that can be attributed to the transistor itself.All of the foregoing presupposes that the circuit compo

43、nents have been selected to produce the proper bias for the specific transistor used. If this is not the case, distortion may occur that has no connection with the inherent characteristics of the transistor.Either the collector characteristic curves or the IbIc curve may be used to estimate the beta

44、 of a transistor in just a few seconds. Since the collector characteristics are those generally found in manufacturers' rating sheets, suppose we use these to check the beta, or base current gain as it is often called, of the 2N78.Since this transistor normally operates at a collector potential

45、of 5 volts, we first locate the 5-volt line. Then we select an average region of base current change along this line, say from 100 microamperes to 125 microamperes. Using our knowledge that beta =Ic/Ib ,we can take the change of Ib from 100A to 125A for a total of Ib=25A . We then note that Ic goes

46、from 2.9 ma to 3.5 ma over this range of Ib .Substituting these values in the equation we have:=246 The Single-Battery Common-Emitter CircuitAt this point, let us refer back to where we converted the two-battery common-base amplifier into a single-battery circuit. You will find that it was necessary

47、 to add a special resistance and capacitor in the base circuit to provide the required biasing potentials. That is, Rb permits the base to have the correct polarity with respect to the emitter(forward bias) and with respect to the collector (reverse bias).If we analyze the two-battery common-base ci

48、rcuit further, it is apparent that the reason for the need of an extra biasing component lies in the directions of flow of the emitter and collector currents. Using a pnp transistor as an example (the npn is analyzed the same way except that all current directions are reversed), we see that Ie and I

49、c flow in opposite directions in the common lead going to the base. Since one battery, placed anywhere at all in the circuit, could never produce two oppositely-directed currents in a common element, it is necessary to create the correct bias potentials by means of an artificial aid -the bias resistor.Now let us analyze the two-battery common-emitter circuit. Vee forces current up through Ri (or through the signal source itself if the source has d-c continuity), through the base to the emitter, then downward through the common lead back to the positive terminal of