電力電子外文翻譯---電路與功率半導(dǎo)體器件

1、<p>　　畢業(yè)設(shè)計(jì)（外文翻譯）</p><p>　　題 目 電路與功率二極管器件 </p><p>　　系 （院） 自動(dòng)化系 </p><p>　　專 業(yè) 電氣工程與自動(dòng)化 </p><p>　　學(xué)生姓名 陳芬 </p

2、><p>　　學(xué) 號(hào) 2007090403 </p><p>　　指導(dǎo)教師 劉應(yīng)乾 </p><p>　　職 稱 助 教 </p><p>　　2011年 6月15日</p><p>　　Electr

3、ical Networks and Power Semiconductor Devices</p><p>　　Electrical Networks</p><p>　　An electrical circuit or network is composed of elements such as resistors, inductors, and capacitors connecte

4、d together in some manner. If the network contains no energy sources, such as batteries or electrical generators, it is known as a passive network. On the other hand, if one or more energy sources are present, the result

5、ant combination is an active network. In studying the behavior of an electrical network, we are interested in determining the voltages and currents that exist within the </p><p>　　In the case of a resistor,

6、the voltage-current relationship is given by Ohm’s law, which states that the voltage across the resistor is equal to the current though the resistor multiplied by the value of the resistance. Mathematically, this is exp

7、ressed as</p><p>　　(1-1A-1) </p><p>　　where u=voltage,V; i=current, A; R=resistance, Ω.</p><p>　　The voltage across a pure inductor is defined by Faraday’s law, which states tha

8、t the voltage across the inductor is proportional to the rate of change with time of the current through the inductor. Thus we have</p><p><b>　　(1-1A-2)</b></p><p>　　Where =rate of c

9、hange of current, ; L=inductance, H.</p><p>　　The voltage developed across a capacitor is proportional to the electric change q accumulating on the plates of the capacitor. Since the accumulation of charge m

10、ay be expressed as the summation, or integral, of the charge increments dq, we have the equation</p><p><b>　　(1-1A-3)</b></p><p>　　where the capacitance C is the proportionality cons

11、tant relating voltage and charge. By definition, current equals the rate of change of charge with time and is expressed as i= . Thus an increment of charge dq is equal to the current multiplied by the corresponding time

12、increment, or dq=idt. Eq.(1-1A-3) may then be written as</p><p><b>　　(1-1A-4)</b></p><p>　　where C= capacitance, F.</p><p>　　Active electrical devices involve the conver

13、sion of energy to electrical form. For example, the electrical energy in a battery is derived from its stored chemical energy. The electrical energy of a generator is a result of the mechanical energy of the rotating arm

14、ature.</p><p>　　Active electrical elements occur in two basic forms: voltage sources and current sources. In their ideal form, voltage sources generate a constant voltage independent of the current drawn fro

15、m the source. The aforementioned battery and generator are regarded as voltage sources since their voltage is essentially constant with load. On the other hand, current sources produce a current whose magnitude is indepe

16、ndent of the load connected to the source. Although current sources are not as familiar i</p><p>　　A common method of analyzing an electrical network is mesh or loop analysis. The fundamental law that is app

17、lied in this method is Kirchhoff’s first law, which states that the algebraic sum of the voltages around a closed loop is 0, or, in any closed loop, the sum of the voltage rises must equal the sum of the voltage drops. M

18、esh analysis consists of assuming that currents-termed loop currents-flow in each loop of a network, algebraically summing the voltage drops around each loop, and setting e</p><p>　　Power Semiconductor Devic

19、es</p><p>　　Power semiconductor devices constitute the heart of modern power electronic appartus. They are used in power electronic converters in the form of a matrix of on-off switches. And the switching mo

20、de power conversion gives high efficiency.</p><p>　　Today’s power semiconductor devices are almost exclusively based on silicon material and can be classified as follow:</p><p><b>　　Diode&

21、lt;/b></p><p>　　Thyristor or silicon-controlled rectifier (SCR)</p><p><b>　　Triac</b></p><p>　　Gate turn-off thyristor (GTO)</p><p>　　Bipolar junction tr

22、ansistor (BJT or BPT)</p><p>　　Power MOSFET</p><p>　　Static induction transistor (SIT)</p><p>　　Insulated gate bipolar transistor (IGBT)</p><p>　　MOS-controlled thyrist

23、or (MCT)</p><p>　　Integrated gate-commutated thyristor (IGCT)</p><p><b>　　Diodes</b></p><p>　　Power diodes provide uncontrolled rectification of power and are used in ap

24、plications such as electroplating, anodizing, battery charging, welding, power supplies (DC and AC), and variable-frequency drives. They are also used in feedback and the freewheeling functions of converters and snubbers

25、. A typical power diode has P-I-N stucture, thatis, it is a P-N junction with a near intrinsic semiconductor layer (I-layer) in the middle to sustain reverse voltage.</p><p>　　In the forward-biased condition

26、, the diode can be represented by a junction offset drop and a series-equivalent resistance.The typical forward conduction drop is 1.0V. This drop will cause conduction loss,and the device must be cooled by the appropria

27、te heat sink to limit the junction temperature. In the reverse-biased condition, a small leakage urrent flows due to minority carries, which gradually increase with voltage. If the reverse voltage exceeds a threshold val

28、ue, called the breakdown volt</p><p>　　Power diodes can be classified as follows:</p><p>　　Standard or slow-recovery diode </p><p>　　Fast-recovery diode</p><p>　　Schott

29、ky diode</p><p>　　Thyristors</p><p>　　Thyristors, or silicon-controlled rectifiers (SCRs) have been the traditional workhorses for bulk power conversion and control in industry. The modern era o

30、f solid-state power electronics started due to the intorduction of this device in the late 1950s. The term ”thyristor” camefrom its gas tube equivalent, thyratron. Often, it is a family name that includes SCR,taiac, GTO,

31、MCT, and IGCT. Thyristors can be classified as standard, or slow phase-control-type and fast-switching,voltage-fed inverter-</p><p>　　Basically, it is a three-junction P-N-P-N device, where P-N-P and N-P-N c

32、omponent transistors are connected in regenerative feedback mode. The device blocks volgate in both the forward and reverse direction (symmetric blocking). When the anode is positive, the device can be trggered into cond

33、uction by a short positive gate current pulse; but once the device is conducting, the gate loses its control to turnoff the device. A thyristor can also turn on by excessive anode voltage, its rate of rise (</p>&

34、lt;p>　　At gate current IG = 0, if forward voltage is applied on the device, there will be a leakage current due to blocking of the middle junction. If the voltage exceeds a critical limit (breakover voltage), the devi

35、ce switchs into conduction. With increasing magnitude of IG, the forward breakover voltage is reduced, and eventually at IG3, the device behaves like a diode with the entire forward bloking region removed. The device wil

36、l turn on successfully if a minimum current, called a latching current</p><p><b>　　Triacs</b></p><p>　　A triac has a complex multiple-junction structure, but functionally, it is an i

37、ntergration of a pair of phase-controlled thyristors connected in inverse-parallel on the same chip. A triac is more economical than a pair of thyristors in anti-parallel and its control is simpler, but its integrated co

38、nstuction has some disadvantages. The gate current sensitivity of a triac is poorer and the turn-off time is longer due to the minority carrier storage effect. For the same reason, the reapplied ratin</p><p&g

39、t;<b>　　GTOs</b></p><p>　　A gate turn-off thyristor (GTO), as the name indicates, is basically a thyristor-type device that can be turned on by a small positive gate current pulse, but in addition

40、, has the capability of being turned off by a negative gate current pulse. The turn-off capability of a GTO is due to the diversion of P-N-P collector current by the gate, thus breaking the P-N-P / N-P-N regenerative fee

41、dback effect. GTOs are available with asymmetric and symmetric voltage-blocking capabilities, which are used i</p><p>　　Power MOSFETs</p><p>　　Unlike the devices discussed so far, a power MOSFET

42、 (metal-oxide semiconductor field-effect transistor) is a unipolar, majority carrier, “zero junction”, voltage-controlled device.IF the gate voltage is positive and beyond a threshold value, an N-type conducting channel

43、will be induced that permit current flow by majority carrier (electrons) betwwen the drain and the source. Although the gate impedance is extremely high at steady state, the effective gate-source capacitance will demand

44、a pulse c</p><p>　　While the conduction loss of a MOSFET is large for higher voltage devices, its turn-on and turn-off switching times are extremely small, causing low switching loss. The device does not hav

45、e the minority carrier storage delay problem associated with a bipolar device. Although a MOSFET can be controlled statically by a voltage source, it is normal practice to drive it by a current source dynamically followe

46、d by a voltage source to minimize switching delaya. MOSFETs are extremely popular in low-vol</p><p><b>　　IGBTs</b></p><p>　　The introduction of insulated gate bipolar transistors (IG

47、BTs) in the mid-1980s was an important milestone in the history of power semiconductor devices. They are extremely popular devices in power electronics up to medium power (a few kW to a few MW) range and are applied exte

48、nsively in DC/AC drives and power supply systems. They ousted BJTs in the ipper range, and are currently ousting GTOs in the lower power range. An IGBT is basically a hybrid MOS-gated turn-on/off bipolar transistor that

49、co</p><p><b>　　MCTs</b></p><p>　　An MOS-controlled thyristor (MCT), as the name indicates, is a thyristor-like, trigger-into-conduction hybrid device that can be turned on or off by

50、a short voltage pulse on the MOS gate. The device has a microcell construction, where thousand of microdevices are connected in parallel on the same chip. The cell structure is somewhat complex. The MCT is turned on by a

51、 negative voltage pulse at the gate with respect to the anode and is turned off by a positive voltage pulse. The MCT has a thyristo</p><p>　　The MCT was commercially introduced in 1992, and currently, medium

52、-power devices are available commercially. The future acceptance of the device remains uncertain at this point.</p><p><b>　　IGCTs</b></p><p>　　The integrated gate-commutated thyristo

53、r (IGCT) is the newest member of the power semiconductor family at this time, and was introduced by ABB in 1997. Basically, it is a high-voltage, high-power, hard-driven,asymmetric-blocking GTO with unity turn-off curren

54、tgain. This means that a 4,500V IGCT with a controllable anode current of 3,000A requires turn-off negative gate current of 3,000A. Such a gate current pulse of very short duration and very large di/dt has small energy c

55、ontent and can be sup</p><p>　　電路與功率半導(dǎo)體器件

56、

57、 </p><p><b>　　電路</b></p><p>　　電路或電網(wǎng)絡(luò)由以某種方式連接的電阻器、電感器和電容器等元件組成。如果網(wǎng)絡(luò)不包含能源，如電池或發(fā)電機(jī)

58、，那么就被作為無源網(wǎng)絡(luò)。換句話說，如果存在一個(gè)或多個(gè)能源，那么組合的結(jié)果為有源網(wǎng)絡(luò)。在研究電網(wǎng)絡(luò)的特性時(shí)，我們感興趣的是電路中的電壓和電流。因?yàn)榫W(wǎng)絡(luò)由無源電路元件組成，所以必須首先這些元件的電特性。</p><p>　　就電阻元件來說，電壓-電流的關(guān)系由歐姆定律給出，歐姆定律指出：電阻兩端的電壓等于電阻上流過的電流乘以電阻值。在數(shù)學(xué)上表達(dá)為：</p><p><b>　?。?-1

59、A-1）</b></p><p>　　式中 u=電壓，伏特；i=電流，安培；R=電阻，歐姆。</p><p>　　純電感電壓由法拉第定律定義，法拉第定律指出：電感兩端的電壓正比于流過電感的電流隨時(shí)間的變化率。因此可以以得到：</p><p><b>　?。?-1A-2）</b></p><p>　　式中di/

60、dt=電流變化率，安培/秒；L=感應(yīng)系數(shù)，亨利。</p><p>　　電容兩端建立的電壓正比于電容兩極板上積累的電荷q.因?yàn)殡姾傻姆e累可以表示為電荷增量dq的和或積分，因此得到的等式為：</p><p><b>　?。?-1A-3）</b></p><p>　　式中電容量C是與電壓和電荷相關(guān)的比例常數(shù)。有定義可知，電流等于電荷隨時(shí)間的變化率，可

61、表示為i = dq/dt。因此電荷增量dq等于電流乘以相應(yīng)的時(shí)間增量，或dq=idt，那么等式（1-1A-3）可寫為</p><p><b>　?。?-1A-4）</b></p><p>　　式中C=電容量，法拉。</p><p>　　有源電氣元件涉及其他能量轉(zhuǎn)換為電能，例如電池中的電能來自其儲(chǔ)存的化學(xué)能，發(fā)電機(jī)的電能是旋轉(zhuǎn)電樞機(jī)械能轉(zhuǎn)換的結(jié)果

62、。</p><p>　　有源電器元件存在兩種基本方式：電壓源和電流源。其理想狀態(tài)為：電壓源兩端的電壓恒定，與從電壓源中流出的電流無關(guān)。因?yàn)樨?fù)載變化時(shí)電壓基本恒定，所以上述電池和發(fā)電機(jī)被認(rèn)為是電壓源。另一方面，電流源產(chǎn)生電流，電流的大小與電源連接的負(fù)載無關(guān)。雖然電流源在實(shí)際中不常見，但其概念的確在表示借助于等值電路的放大器件，比如晶體管中具有廣泛應(yīng)用。</p><p>　　分析電網(wǎng)絡(luò)的方法是

63、網(wǎng)孔分析法或回路分析法。應(yīng)用于此方法的基本定律是基爾霍夫第一定律，基爾霍夫第一定律指出：一個(gè)閉合回路中的電壓代數(shù)和為0，換句話說，任一閉合回路中的電壓升等于電壓降。</p><p>　　網(wǎng)孔分析法指的是：假設(shè)有一個(gè)電流—即所謂的回路電流—流過電路中的每一個(gè)回路，求每一個(gè)回路電壓降的代數(shù)和，并令其為零。</p><p><b>　　功率半導(dǎo)體器件</b></p&g

64、t;<p>　　功率半導(dǎo)體器件構(gòu)成了現(xiàn)代電力電子設(shè)備的核心。他們以通-斷開關(guān)矩陣的方式被用于電力電子轉(zhuǎn)換器中。開關(guān)式功率變換的效率更高。</p><p>　　現(xiàn)今的功率半導(dǎo)體器件幾乎都是用硅材料制造，可分類如下：</p><p>　　* 二極管</p><p>　　* 晶閘管或可控硅</p><p>　　*

65、 雙向可控硅</p><p>　　* 門極可關(guān)斷晶閘管</p><p>　　* 雙集結(jié)型晶體管</p><p>　　* 電力金屬氧化物半導(dǎo)體場(chǎng)效應(yīng)晶體管</p><p>　　* 靜電感應(yīng)晶體管</p><p>　　* 絕緣柵雙極性晶體管</p>&

66、lt;p>　　* 金屬氧化物半導(dǎo)體控制的晶閘管</p><p>　　* 集成門極換向晶閘管</p><p><b>　　二極管</b></p><p>　　電力二極管提供不可控的整流電源，這些電源有很廣的應(yīng)用，如：電鍍、電極氧化、電池充電、焊接、交直流電源和變頻驅(qū)動(dòng)。它們也被應(yīng)用于變換器和緩沖器的回饋和慣性滑行功能。典

67、型的功率二極管具有P-N結(jié)構(gòu)，即它幾乎是純半導(dǎo)體層（本征層），位于P-N結(jié)的中部以阻斷反向電壓。二極管在正向偏置的條件下，可用一個(gè)結(jié)偏置壓降和連續(xù)變化的電阻來表示。典型的正向?qū)▔航禐?.0伏。導(dǎo)通壓降會(huì)引起導(dǎo)通損耗，必須用合適的吸熱設(shè)備對(duì)二極管進(jìn)行冷卻來限制結(jié)溫上升。在反向偏置條件下，由于少數(shù)載流子的存在，又很小的泄露電流流過，泄漏電流隨電壓逐漸增加。如果反向電壓超過了臨界值，叫做擊穿電壓，二極管的雪崩擊穿，雪崩擊穿指的是當(dāng)反向電流變

68、大時(shí)由于結(jié)功率損耗過大造成的熱擊穿。</p><p>　　電力二極管分類如下：</p><p>　　標(biāo)準(zhǔn)或慢速恢復(fù)二極管</p><p><b>　　快速恢復(fù)二極管</b></p><p><b>　　肖特基二極管</b></p><p><b>　　晶閘管<

69、/b></p><p>　　晶閘管或可控硅一直是工業(yè)上用于大功率和控制的傳統(tǒng)設(shè)備。50年代后期，這種裝置的投入使用開辟了現(xiàn)代固態(tài)電力電子技術(shù)。術(shù)語“晶閘管”來自與其相應(yīng)的充氣管等效應(yīng)裝置，閘流管。通常，晶閘管是個(gè)系列產(chǎn)品的總稱，包括可控硅、雙向可控硅、門極可關(guān)斷晶閘管、金對(duì)屬氧化物半導(dǎo)體控制的晶閘管、集成門極換向晶閘管。晶閘管可分成標(biāo)準(zhǔn)或慢速相控型，快速開關(guān)型，電壓回饋逆變器型。逆變器型現(xiàn)已淘汰。</

70、p><p>　　基本上，晶閘管是一個(gè)三結(jié)P-N-P器件，器件內(nèi)P-N-P和N-P-N兩個(gè)三極管按正反饋方式連接。晶閘管可阻斷正向和反向電壓（對(duì)稱阻斷）。當(dāng)陽極為正時(shí)，晶閘管可由一個(gè)短暫的正門極電流脈沖觸發(fā)導(dǎo)通；但晶閘管一旦導(dǎo)通，門極即失去控制晶閘管關(guān)斷的能力。晶閘管也可由陽極過電壓、陽極電壓的上升率（dv/dt）、結(jié)溫的上升、PN結(jié)上光照等產(chǎn)生誤導(dǎo)通。</p><p>　　在們電流IG=0時(shí)，

71、如果將正向電壓施加到晶閘管上，由于中間結(jié)的阻斷會(huì)產(chǎn)生漏電流；如果電壓超過臨界極限（轉(zhuǎn)折電壓），晶閘管進(jìn)入到通狀態(tài)。隨著門極控制電流IG的增加正向轉(zhuǎn)折電壓隨之減少，最后，當(dāng)門極控制電流IG=IG3時(shí)，整個(gè)正向阻斷區(qū)域消失，晶閘管的工作狀態(tài)就和二極管一樣了。在晶閘管的門極出現(xiàn)一個(gè)最小電流，即阻塞電流，晶閘管將成功導(dǎo)通。</p><p>　　在導(dǎo)通期間，如果門極電流是零并且陽極電流降到臨界極限值以下，稱作維持電流，晶閘

72、管轉(zhuǎn)換到正向阻斷狀態(tài)。相對(duì)反向電壓而言，晶閘管末端的P-N結(jié)處于反向偏置狀態(tài)?，F(xiàn)在的晶閘管具有大電壓（數(shù)千伏）、大電流（數(shù)千安）額定值。</p><p><b>　　雙向可控硅</b></p><p>　　雙向可控硅有復(fù)雜的復(fù)結(jié)結(jié)構(gòu)，但從功能上講，它是同一芯片上一對(duì)反并聯(lián)的相控晶閘管。</p><p>　　雙向可控硅比一對(duì)反并聯(lián)的晶閘管便宜和易

73、于控制，但它的集成結(jié)構(gòu)有一些缺點(diǎn)。由于少數(shù)載流子效應(yīng)，雙向可控硅的門極電流敏感性較差，關(guān)斷時(shí)間較長(zhǎng)。由于同樣的原因，重復(fù)施加的dv/dt額定值較低，因此用于感性負(fù)載比較困難。雙向可控硅電路必須有精心設(shè)計(jì)的RC緩沖器。雙向可控硅用于電燈的亮度調(diào)節(jié)、加熱控制、聯(lián)合型電機(jī)驅(qū)動(dòng)、50/60赫茲電源頻率的固態(tài)繼電器。</p><p><b>　　門極可關(guān)斷晶閘管</b></p><

74、p>　　門極可關(guān)斷晶閘管，顧名思義，是一種晶閘管類型的器件。同其他晶閘管一樣，它可以由一個(gè)小的正門極電流脈沖觸發(fā)，但除此之外，它還能被負(fù)門極電流脈沖關(guān)斷。GTO的關(guān)斷能力來自由門極轉(zhuǎn)移P-N-P集電極的電流，因此消除P-N-P/N-P-N的正反饋效應(yīng)。GTO有非對(duì)稱和稱電壓阻斷兩種類型，分別用于電壓回饋和電流回饋?zhàn)儔浩鳌TO的阻斷電流增益定義為陽極電流與阻斷所需的負(fù)門極電流之比，典型值為4或5，非常低。這意味著6000安培的GT

75、O需要1,500安培的門極電流脈沖。</p><p>　　但是，脈沖化的門極電流和與其相關(guān)的能量非常小，用低壓電力MOS場(chǎng)效應(yīng)晶體管提供非常容易。GTO被用于電機(jī)驅(qū)動(dòng)、靜態(tài)無功補(bǔ)償器和大容量AC/DC電源。大容量GTO的出現(xiàn)取代了強(qiáng)迫換流、電壓回饋的可控硅換流器。</p><p>　　電力MOS場(chǎng)效應(yīng)晶體管</p><p>　　與以前討論的器件不同，電力MOS場(chǎng)效應(yīng)

76、晶體管是一種單極、多載流子、“零結(jié)”、電壓控制器件。</p><p>　　如果柵極電壓為正并且超過它們的門限值，N型溝道將被感應(yīng)，允許在漏極和源極之間流過由多數(shù)載流子（電子）組成的電流。雖然柵極阻抗在穩(wěn)態(tài)非常高，有效地柵—源極電容在導(dǎo)通和關(guān)斷時(shí)會(huì)產(chǎn)生一個(gè)脈沖電流。MOS場(chǎng)效應(yīng)晶體管有不對(duì)稱的電壓阻斷能力，其內(nèi)部集成一個(gè)通過所有的反相電流的二極管。二極管具有慢速恢復(fù)特性，在高頻應(yīng)用場(chǎng)合下通常被一個(gè)外部連接的快恢復(fù)二

77、極管旁路。</p><p>　　雖然對(duì)較高的電壓器件來說，MOS場(chǎng)效應(yīng)晶體管處于導(dǎo)通時(shí)損耗較大，但他的導(dǎo)通和關(guān)斷時(shí)間非常小，因而開關(guān)損耗小。它確實(shí)沒有與雙極性器件相關(guān)的少數(shù)載流子存儲(chǔ)延遲問題。雖然在靜態(tài)MOS場(chǎng)效應(yīng)晶體管可由電壓源來控制，通常的做法是在動(dòng)態(tài)有電流源驅(qū)動(dòng)而后跟隨一個(gè)電壓源來減少開關(guān)延遲。</p><p>　　MOS場(chǎng)效應(yīng)晶體管在低壓、小功率和高頻（數(shù)十萬赫茲）開關(guān)應(yīng)用等領(lǐng)域得

78、到極其廣泛的應(yīng)用。譬如開關(guān)式電源、無刷直流電機(jī)、步進(jìn)電機(jī)驅(qū)動(dòng)和固態(tài)直流繼電器。</p><p><b>　　絕緣柵雙極型晶體管</b></p><p>　　在20世紀(jì)80年代中期出現(xiàn)的絕緣柵雙極型晶體管是功率半導(dǎo)體器件發(fā)展歷史上的一個(gè)重要的里程碑。它們?cè)谥械裙β剩〝?shù)千瓦到數(shù)兆瓦）的電力電子設(shè)備上處處可見，被廣泛用于直流/交流傳動(dòng)和電源系統(tǒng)。它們?cè)跀?shù)兆瓦功率級(jí)取代了雙極

79、結(jié)型晶體管，在數(shù)千瓦功率級(jí)正在取代門極可關(guān)斷晶閘管。IGBT基本上是混合的MOS門控通斷雙極型晶體管，它綜合了MOSFET和BJT的優(yōu)點(diǎn)。它的結(jié)構(gòu)基本上與MOSFET的結(jié)構(gòu)相似，只是在MOSFET的N+漏極層上的集電極加上了一個(gè)額外的P+層。</p><p>　　IGBT有MOSFET的高輸入阻抗和像BJT的導(dǎo)通特性。如果門極電壓相對(duì)于發(fā)射極為正，P區(qū)得N型溝道受到感應(yīng)。這個(gè)P-N-P晶體管正向偏置的基極—發(fā)射極

80、結(jié)使IGBT導(dǎo)通并引起N-區(qū)傳導(dǎo)性調(diào)制，這使得導(dǎo)通壓降大大低于MOSFET的導(dǎo)通壓降。在導(dǎo)通條件下，在IGBT的等效電路中，驅(qū)動(dòng)器MOSFET運(yùn)送大部分的端子電流。由寄生N-P-N晶體管引起的與晶閘管相似的阻塞作用通過有效地減少P+層電阻系數(shù)和通過MOSFET將大部分電流轉(zhuǎn)移而得到預(yù)防。</p><p>　　IGBT通過減小門極電壓到零或負(fù)電壓來關(guān)斷，這樣就切斷了P區(qū)得導(dǎo)通通道。IGBT比BJT或MOSFET有更

81、高的電流密度。IGBT的輸入電容比MOSFET的要小得多。還有，IGBT的門極—集電極電容與門極—發(fā)射極之比更低，給出了改善的密勒反饋效應(yīng)。</p><p>　　金屬氧化物半導(dǎo)體控制的晶閘管</p><p>　　金屬氧化物半導(dǎo)體控制的晶閘管（MCT），正像名字所說那樣，是一種類似于晶閘管，通過觸發(fā)進(jìn)入導(dǎo)通的混合器件，它可以通過在MOS門施加一個(gè)短暫的電壓脈沖來控制通斷。MCT具有微單元結(jié)構(gòu)

82、，在那里同一個(gè)芯片上數(shù)千個(gè)微器件并聯(lián)起來，單元結(jié)構(gòu)有點(diǎn)復(fù)雜。</p><p>　　MCT由一個(gè)相對(duì)于陽極的負(fù)電壓脈沖觸發(fā)導(dǎo)通，由一個(gè)相對(duì)于陽極的正電壓脈沖控制關(guān)斷。它具有類似晶閘管的P-N-P結(jié)構(gòu)，在那里P-N-P和N-P-N兩個(gè)晶體管部件連接成正反饋方式。但與晶閘管不同的是MCT只有單極（或不對(duì)稱）電壓阻斷能力。如果MCT的門極電壓相對(duì)于陽極為負(fù)，在P型場(chǎng)效應(yīng)晶體管中的P溝道受到感應(yīng)，使N-P-N晶體管正向偏置

83、。這也使P-N-P晶體管正向偏置，由正反饋效應(yīng)MCT進(jìn)入飽和狀態(tài)。在導(dǎo)通情況下，壓降為1伏左右（類似于晶閘管）。</p><p>　　如果MCT的門極電壓相對(duì)于陽極為正，N型場(chǎng)效應(yīng)晶體管飽和并將P-N-P晶體管的發(fā)射極-基極短路。這將打破晶體管工作的正反饋環(huán)，MCT關(guān)斷。關(guān)斷完全是由于再結(jié)合效應(yīng)，因而MCT關(guān)斷時(shí)間有點(diǎn)長(zhǎng)。MCT有限定的上升速率，因此在MCT變換器中必須加緩沖器電路。最近，MCT以用于“軟開關(guān)”變

84、換器中，在那不用限定上升速率。盡管電路結(jié)構(gòu)復(fù)雜，MCT的電流卻比電力MOSFET、BJT 和IGBT的大，因此它需要有一個(gè)較小的死區(qū)。1992年在市場(chǎng)上可見到MCT，現(xiàn)在可買到中等功率的MCT。MCT的發(fā)展前景尚未可知。</p><p><b>　　集成門極換向晶閘管</b></p><p>　　集成門極換向晶閘管是當(dāng)前電力半導(dǎo)體家族中的最新成員，有ABB在1997年

85、推出?；旧?，IGCT是一個(gè)具有單位關(guān)斷電流增益的高壓、大功率、應(yīng)驅(qū)動(dòng)不對(duì)稱阻塞的GTO。這表示具有可控3,000安培陽極電流的4,500VIGCT需要3,000安培負(fù)的門極關(guān)斷電流。這樣一個(gè)持續(xù)時(shí)間非常短、di/dt非常大、能量又較小的們極電流脈沖可以由多個(gè)并聯(lián)的MOSFET來提供，并且驅(qū)動(dòng)電路中的漏感要特別低。</p><p>　　門驅(qū)動(dòng)電路內(nèi)置在IGCT模塊內(nèi)。IGCT內(nèi)有一對(duì)單片集成的反并聯(lián)二極管。導(dǎo)通壓