恒流源電氣類外文翻譯

1、<p>　　CURRENT SOURCE</p><p>　　A current source is an electrical or electronic device that delivers or absorbs electric current. A current source is the dual of a voltage source. The term constant-curren

2、t sink is sometimes used for sources fed from a negative voltage supply. Figure 1 shows a schematic for an ideal current source driving a resistor load.</p><p><b>　　Figure 1</b></p><p&

3、gt;　　Ideal current sources</p><p>　　In circuit theory, an ideal current source is a circuit element where the current through it is independent of the voltage across it. It is a mathematical model, which rea

4、l devices can only approach in performance. If the current through an ideal current source can be specified independently of any other variable in a circuit, it is called an independent current source. Conversely, if the

5、 current through an ideal current source is determined by some other voltage or current in a circuit, it is c</p><p><b>　　Figure 2</b></p><p>　　An independent current source with zer

6、o current is identical to an ideal open circuit. For this reason, the internal resistance of an ideal current source is infinite. The voltage across an ideal current source is completely determined by the circuit it is c

7、onnected to. When connected to a short circuit, there is zero voltage and thus zero power delivered. When connected to a load resistance, the voltage across the source approaches infinity as the load resistance approache

8、s infinity (an open ci</p><p>　　No real current source is ideal (no unlimited energy sources exist) and all have a finite internal resistance (none can supply unlimited voltage). However, the internal resist

9、ance of a physical current source is effectively modeled in circuit analysis by combining a non-zero resistance in parallel with an ideal current source (the Norton equivalent circuit).</p><p>　　Resistor cur

10、rent source</p><p>　　The simplest current source consists of a voltage source in series with a resistor. The current available from such a source is given by the ratio of the voltage across the voltage sourc

11、e to the resistance of the resistor. For a nearly ideal current source, the value of this resistor should be very large but this implies that, for a specified current, the voltage source must be very large. Thus, efficie

12、ncy is low (due to power loss in the resistor) and it is usually impractical to construct a 'g</p><p>　　Active current sources </p><p>　　Active current sources have many important applicatio

13、ns in electronic circuits. Current sources (current-stable resistors) are often used in place of ohmic resistors in analog integrated circuits to generate a current without causing attenuation at a point in the signal pa

14、th to which the current source is attached. The collector of a bipolar transistor, the drain of a field effect transistor, or the plate of a vacuum tube naturally behave as current sources (or sinks) when properly connec

15、ted to </p><p>　　JFET and N-FET current source</p><p>　　A JFET can be made to act as a current source by tying its gate to its source. The current then flowing is the IDSS of the FET. These can

16、be purchased with this connection already made and in this case the devices are called current regulator diodes or constant current diodes or current limiting diodes (CLD). An enhancement mode N channel MOSFET can be use

17、d in the circuits listed below.</p><p>　　Simple transistor current source</p><p>　　Figure 3 shows a typical constant current source (CCS). DZ1 is a zener diode which, when reverse biased (as sho

18、wn in the circuit) has a constant voltage drop across it irrespective of the current flowing through it. Thus, as long as the zener current (IZ) is above a certain level (called holding current), the voltage across the z

19、ener diode (VZ) will be constant. Resistor R1 supplies the zener current and the base current (IB) of NPN transistor (Q1). The constant zener voltage is applied across t</p><p>　　Voltage across R2 (VR2) is g

20、iven by VZ - VBE, where VBE is the base-emitter drop of Q1. The emitter current of Q1 which is also the current through R2 is given by.</p><p><b>　　Figure 3</b></p><p>　　Since VZ is

21、constant and VBE is also (approximately) constant for a given temperature, it follows that VR2 is constant and hence IE is also constant. Due to transistor action, emitter current IE is very nearly equal to the collector

22、 current IC of the transistor (which in turn, is the current through the load). Thus, the load current is constant (neglecting the output resistance of the transistor due to the Early effect) and the circuit operates as

23、a constant current source. As long as the temper</p><p>　　A more common current source in integrated circuits is the current mirror.</p><p>　　Simple transistor current source with diode compensa

24、tion</p><p>　　Temperature changes will change the output current delivered by the circuit of Figure 3 because VBE is sensitive to temperature. Temperature dependence can be compensated using the circuit of F

25、igure 4 that includes a standard diode D (of the same semiconductor material as the transistor) in series with the Zener diode as shown in the image on the left. The diode drop (VD) tracks the VBE changes due to temperat

26、ure and thus significantly counteracts temperature dependence of the CCS.</p><p>　　Resistance R2 is now calculated as</p><p>　　Since VD = VBE = 0.65 V,</p><p>　　Therefore, .</p&g

27、t;<p><b>　　Figure 4</b></p><p>　　This method is most effective for Zener diodes rated at 5.6 V or more. For breakdown diodes of less than 5.6 V, the compensating diode is usually not requi

28、red because the breakdown mechanism is not as temperature dependent as it is in breakdown diodes above this voltage.</p><p>　　Simple transistor current source with LED</p><p>　　Another method is

29、 to replace the Zener diode with a light-emitting diode LED1 as shown in Figure 5. The LED voltage drop (VD) is now used to derive the constant voltage and also has the additional advantage of tracking (compensating) VBE

30、 changes due to temperature. R2 is calculated as ,and R1 as , where ID is the LED current.</p><p>　　Figure 5 Figure 6</p><p>　　Another common method is to use feedback

31、to set the current and remove the dependence on the Vbe of the transistor. Figure 6 shows a very common approach using an op amp with the non-inverting input connected to a voltage source (such as the Zener in an above e

32、xample) and the inverting input connected to the same node as the resistor and emitter of the transistor. This way the generated voltage is across the resistor, rather than both the resistor and transistor. (For details,

33、 see the article on</p><p>　　Other practical sources</p><p>　　In the case of opamp circuits sometimes it is desired to inject a precisely known current to the inverting input (as an offset of si

34、gnal input for instance) and a resistor connected between the source voltage and the inverting input will approximate an ideal current source with value V/R.</p><p>　　Inductor type current source</p>

35、<p>　　Amongst other applications, the circuit of Figure 7 using the LM317 voltage regulator is used to present a source of constant current in Class E (switching) electronic amplifiers.</p><p><b>

36、　　Figure 7</b></p><p>　　Current and voltage source comparison</p><p>　　Most sources of electrical energy (mains electricity, a battery, ...) are best modeled as voltage sources. Such sourc

37、es provide constant voltage, which means that as long as the amount of current drawn from the source is within the source's capabilities, its output voltage stays constant. An ideal voltage source provides no energy

38、when it is loaded by an open circuit (i.e. an infinite impedance), but approaches infinite power and current when the load resistance approaches zero (a short circuit)</p><p>　　Conversely, a current source p

39、rovides a constant current, as long as the load connected to the source terminals has sufficiently low impedance. An ideal current source would provide no energy to a short circuit and approach infinite energy and voltag

40、e as the load resistance approaches infinity (an open circuit). An ideal current source has an infinite output impedance in parallel with the source. A real-world current source has a very high, but finite output impedan

41、ce. In the case of transistor </p><p>　　An ideal current source cannot be connected to an ideal open circuit because this would create the paradox of running a constant, non-zero current (from the current so

42、urce) through an element with a defined zero current (the open circuit). Nor can an ideal voltage source be connected to an ideal short circuit (R=0), since this would result a similar paradox of finite non zero voltage

43、across an element with defined zero voltage (the short circuit). Because no ideal sources of either variety exist</p><p><b>　　恒流源</b></p><p>　　電流源是電氣或電子裝置，可提供或吸收電流。一個電流源是一個電壓源雙。術(shù)語恒流源

44、有時用來從一個負(fù)電壓電源饋來源。圖1顯示了一個理想的電流源驅(qū)動的電阻負(fù)載的原理圖。</p><p><b>　　圖1理想電流源</b></p><p><b>　　1、理想電流源</b></p><p>　　在電路理論，理想電流源電路元件的電流通過時與其兩端的電壓無關(guān)。這是一個數(shù)學(xué)模型。如果通過一個理想的電流源電流可以指定

45、獨(dú)立于任何其他變量的電路，它被稱為一個獨(dú)立的電流源。相反，如果其他一些電壓或電路中的電流通過一個理想電流源的電流決定，它被稱為從屬或控制的電流源。這些源符號，如圖2所示。</p><p><b>　　圖2各種電流源符號</b></p><p>　　一個獨(dú)立的電流源與零電流是相同的理想開路?；谶@個原因，一個理想電流源內(nèi)阻是無限的。在一個理想的電流源的電壓是完全取決于它

46、的連接電路。當(dāng)連接到短路，存在零電壓，從而零功率交付。當(dāng)連接到負(fù)載電阻兩端的電壓接近源的負(fù)載電阻接近無窮大（開路）。因此，一個理想的電流源可提供無限的能量將代表無限的能源來源。連接的理想開路理想非零電流源是無效的，在電路的電路方程分析將是自相矛盾的。</p><p>　　沒有真正的電流源是理想的（不存在無限的能源），并且所有的有限的內(nèi)部電阻（沒有人能提供無限的電壓）。然而，內(nèi)部電阻電流源建模的有效結(jié)合電路分析與理

47、想電流源非零并聯(lián)電阻（諾頓等效電路）。</p><p><b>　　2、電阻電流源</b></p><p>　　最簡單的電流源包括一個與一個電阻器系列電壓源。目前從這樣的來源可以是由兩端的電壓源電壓比電阻器的電阻提供。對于一個幾近完美的電流源，這個電阻值應(yīng)該是非常大的，但是這意味著，在規(guī)定的電流，電壓源必須是非常大的。因此，效率低（由于功率的電阻損耗），它通常是不切實(shí)

48、際的建好這樣的電流源。盡管如此，在很多情況下，這種電路將提供足夠的性能時指定的電流和負(fù)載電阻小。例如，與一個4.7K的歐姆電阻器系列5V的電壓源將提供一個大約1mA的恒定電流（± 5％），以在50至450歐姆負(fù)載電阻范圍。 3、主動電流源</p><p>　　主動電流源在電子電路中的許多重要的應(yīng)用。 （電流）穩(wěn)定電阻電流源通常用于在模擬集成電路的歐姆電阻的地方產(chǎn)生的電流而不會導(dǎo)致一個在信號路徑的電流源

49、連接點(diǎn)的衰減。一個雙極晶體管的集電極，一個場效應(yīng)晶體管，或一個真空管自然表現(xiàn)為（或匯漏電流源盤）當(dāng)正確連接到外部的能源來源（如電力供應(yīng)），因?yàn)檩敵鲞@些設(shè)備的高阻抗，自然是當(dāng)電流源配置中使用。 4、結(jié)型場效應(yīng)管和N - FET電流源</p><p>　　一款JFET可作為一所捆綁的大門，它的源電流源。目前則是流動的FET的IDSS的。這些就可以買到這個已經(jīng)在此設(shè)備被稱為電流穩(wěn)壓二極管或恒定電流二極管或限流二極管（

50、CLD）的案件有關(guān)。一個增強(qiáng)型N溝道MOSFET，可用于下列電路</p><p>　　5、簡單晶體管電流源</p><p>　　圖3顯示了一個典型的恒定電流源（CCS）的。 DZ1是一個齊納二極管，當(dāng)這種反向偏置（所示電路），它有一個恒定的電壓上，不論是流經(jīng)它的電流下降。因此，只要齊納電流（輸出型）超過一定水平（稱為維持電流），對面的齊納二極管（VZ）的電壓將保持不變。電阻R1用品齊納電流

51、和基極電流（IB）的的NPN晶體管（Q1）。恒定納電壓是適用于整個Q1和發(fā)射極電阻R2基地。電路的操作如下：R2的（VR2）電壓由下式給出VE- VBE中，在VBE中是Q1基地發(fā)射極下降。Q1的發(fā)射極電流，也是經(jīng)過R2的電流由下式給出</p><p><b>　　圖3典型恒流源</b></p><p>　　由于VE不變，VBE中也（大約）某一溫度恒定，可以得出VR2

52、是恒定的，所以IE也不變。由于晶體管的作用，發(fā)射極電流IE是非常接近等于集電極電流的晶體管集成電路（反過來，是當(dāng)前通過負(fù)載）。因此，負(fù)載電流為常數(shù)（忽略了晶體管，由于早期的效果輸出電阻）和電路作為一個恒定電流源的運(yùn)作。只要溫度保持不變（或變化不大），負(fù)載電流將是電源電壓，R1和晶體管的增益無關(guān)。 R2的允許負(fù)載電流在任何可取的值集，并計(jì)算或,由于VBE中通常是0.65 V的硅器件（IR2也是發(fā)射極電流，并假設(shè)作為收藏家或負(fù)載所需的電流，

53、同時提供HFE的足夠大）。阻力在電阻，其中，K= 1.2到2（使R1是足夠低，以確保有足夠的IB）， 是最低的，特別是可以接受的類型正在使用的晶體管的電流增益。6、簡單晶體管電流源與二極管補(bǔ)償</p><p>　　溫度的變化會改變輸出電流由圖3電路交付因?yàn)閂BE對溫度很敏感。溫度補(bǔ)償?shù)囊蕾嚳梢杂脠D4電路，包括一個標(biāo)準(zhǔn)（作為晶體管的半導(dǎo)體材料相同）與齊納二極管系列二極管D為在圖像顯示在左側(cè)。該二極管壓降（VD）的

54、追蹤VBE中由于溫度變化和溫度，從而大大抵消了對CCS的依賴。</p><p><b>　　電阻,</b></p><p>　　由于VD= VBE中= 0.65V，因此， ,</p><p><b>　　R1的計(jì)算方法</b></p><p><b>　　圖4補(bǔ)償電路</b>&

55、lt;/p><p>　　這種方法是最有效的齊納二極管，在5.6 V或以上評級。對于小于5.6 V時，補(bǔ)償二極管故障二極管通常不是必需的，因?yàn)閾舸C(jī)理是溫度依賴并不像它在上述這個電壓擊穿二極管的。</p><p>　　7、簡單晶體管電流源與LED</p><p>　　另一種方法是取代輕齊納二極管的發(fā)光二極管LED1，如圖5。 LED的電壓降（VD）現(xiàn)在用于推導(dǎo)恒壓，也有額

56、外的跟蹤優(yōu)勢（補(bǔ)償）VBE中溫度引起的變化。 R2的計(jì)算公式為, R1的計(jì)算公式為,其中ID是LED電流。</p><p>　　圖5 LED1代替DZ1 圖6反饋電路</p><p>　　另一種常見的方法是使用反饋來設(shè)置當(dāng)前和消除對晶體管的VBE中的依賴。圖6顯示了一個非常普遍的使用方法與非反相在上面的例子中輸入連接到一個電壓源和反相輸入端連接到的

57、電阻和晶體管的發(fā)射極相同的節(jié)點(diǎn)。這種方式產(chǎn)生的電壓是電阻兩端，而不是兩個電阻器和晶體管。 （詳見上的理想運(yùn)算放大器的文章 - 在零器。）電流鏡上的文章討論的另一個這些所謂的收益，例如，提高了電流鏡。反饋也被用于兩個晶體管發(fā)射極電流鏡變性。反饋是在某些電流鏡使用諸如維德拉電流源和威爾遜電流源，多晶體管的基本特征。8、其他實(shí)際來源</p><p>　　在運(yùn)放電路的情況下，有時候是理想的注入電流精確已知的反相輸入（

58、作為一個信號，例如輸入偏移量）和源之間的電壓和反相輸入端連接一個電阻將接近理想值為電流源V/R。</p><p><b>　　9、電感式電流源</b></p><p>　　除其他應(yīng)用中，圖7電路采用LM317穩(wěn)壓器是用來向一個不斷在E級電流（開關(guān)源）的電子放大器。 </p><p><b>　　圖7電感式電流源</b>&l

59、t;/p><p>　　10、當(dāng)前及電壓源比較 </p><p>　　大部分的電能的來源（主要電力，電池，...）是最好的建模為電壓源。這種來源提供恒定的電壓，這意味著只要當(dāng)前從源頭上得出的數(shù)額在源的能力，但是它的輸出電壓保持不變。一個理想的電壓源規(guī)定，如果是由開路加載沒有能源（即一個無限阻抗），但方法無限的功率和電流時，負(fù)載電阻趨近于零（短路）。這種理論的設(shè)備將有一個與源系列零歐姆的輸出阻抗。

60、一個真正的世界電壓源具有非常低的，但不為零輸出阻抗：通常遠(yuǎn)小于1歐姆。 相反，電流源提供恒定電流，只要負(fù)載連接到源碼頭已經(jīng)足夠低的阻抗。一個理想的電流源將提供沒有力氣短路和方法無限的能源和負(fù)載電阻接近無窮大電壓（開路）。一個理想的電流源具有同時與源無限輸出阻抗。一個真正的世界電流源具有非常高，但有限的輸出阻抗。在晶體管電流源情況下，一（在直流）數(shù)兆歐阻抗典型。</p><p>　　一個理想電流源不能被連接到一個