《模擬電子線路》第一章半導(dǎo)體二極管及其應(yīng)用

1、1模擬電子線路2電子電路數(shù)字電路模擬電路低頻電路（處理低頻信號）高頻電路（處理高頻信號）電子電路分類電子電路數(shù)字電路模擬電路線性電路（處理小信號）非線性電路（處理大信號）3內(nèi)容簡介第一章 晶體二極管及其基本電路第二章 雙極型晶體管及其放大電路第三章 場效應(yīng)管及其基本電路第五章 集成運(yùn)算放大器電路第六章 反饋第四章 頻率響應(yīng)第七章 集成運(yùn)放的應(yīng)用第八章 功率放大電路第九章 直流穩(wěn)壓電源4課程地位與課程體系 是重要的學(xué)科基礎(chǔ)課 是電子信息類專業(yè)的主干課程 是強(qiáng)調(diào)硬件應(yīng)用能力的工程類課程 是工程師訓(xùn)練的基本入門課程 是很多重點(diǎn)大學(xué)的考研課程很重要!5掌握硬件本領(lǐng)當(dāng)前社會對于硬件工程師（特別是具有設(shè)計

2、開發(fā)能力的工程師）需求量很大。培養(yǎng)硬件工程師比較困難。學(xué)好并掌握硬件本領(lǐng)將使你基礎(chǔ)實(shí)，起點(diǎn)高，發(fā)展大，受益無窮！很有用!6這門課的特點(diǎn) 涉及相關(guān)知識較多：高等數(shù)學(xué)、電路分析、信號與系統(tǒng)等 曾有人戲稱模擬電子電路為“魔鬼電路”，簡稱“魔電”。很難學(xué)!7學(xué)習(xí)方法“過四關(guān)”基本器件關(guān)電路構(gòu)成工程近似關(guān)分析方法EDA應(yīng)用關(guān)設(shè)計能力實(shí)驗(yàn)動手關(guān)實(shí)踐應(yīng)用8 以電阻串、并聯(lián)為例來進(jìn)行說明 a 若兩電阻R1 、R2 串聯(lián)，如果R1 R2（一般R1大十倍以上即可），則可忽略R2 。即：R=R1+ R2R1 。、近似計算（估算） 9b、若兩電阻R1 、R2 并聯(lián)，如果R1 R2（R1大十倍以上即可），則可忽略R1

3、。即：R=R1|R2R2 。10、交、直流源同時出現(xiàn)在電路中時，采用疊加原理vO=vo2+VO1求vo2的過程稱為動態(tài)分析求VO1的過程稱為靜態(tài)分析最后利用疊加原理得直流等效電路交流等效電路11例一：電路如下圖，求vOvo =vo1 +vo2 = es第一步：靜態(tài)分析vo2= es畫直流等效電路，求vo1vo1=0V第二步：動態(tài)分析畫交流等效電路，求vo212例二：電路如下圖，求VO1 、VO2第一步：靜態(tài)分析畫直流等效電路，求Vo1、Vo2第二步：動態(tài)分析畫交流等效電路，求vo2、vo213、非線性元件有條件的線性化?？蓪⒎蔷€性電路化為線性電路。 二極管的特性 三極管的特性IC VCE I

4、V 14考試成績評定平時 30%期末 70%151 孫肖子 等編, 模擬電子技術(shù)基礎(chǔ),西安:西安電子科技大學(xué)出版社,2001.2 康華光主編電子技術(shù)基礎(chǔ)（模擬部分，第四版），北京：高等教育出版社，19883 謝嘉奎主編電子線路（線性部分，第四版），北京：高等教育出版社，1999參考書16第一章 晶體二極管及其基本電路1-1 半導(dǎo)體物理基礎(chǔ)知識導(dǎo)體 104s/cm半導(dǎo)體 在10-9104s/cm間絕緣體 7V時為雪崩擊穿； UBR 5V時為齊納擊穿； UBR介于57V時，兩種擊穿都有。 68擊穿的可逆性電擊穿是 可逆的（可恢復(fù)，當(dāng)有限流電阻時）。電擊穿后如無限流措施，將發(fā)生熱擊穿現(xiàn)象。熱擊穿會破

5、壞PN結(jié)結(jié)構(gòu)（燒壞）熱擊穿是 不可逆 的。691-2-4 PN結(jié)的電容特性 PN 結(jié)的耗盡區(qū)與平板電容器相似，外加電壓變化，耗盡區(qū)的寬度變化，則耗盡區(qū)中的正負(fù)離子數(shù)目變化，即存儲的電荷量變化。一、 勢壘電容CT70多子擴(kuò)散在對方區(qū)形成非平衡少子的濃度分布曲線偏置電壓變化分布曲線變化非平衡少子變化電荷變化。二、擴(kuò)散電容CD71圖112 P區(qū)少子濃度分布曲線 72結(jié)電容Cj= CT + CD結(jié) 論因?yàn)镃T和CD并不大，所以在高頻工作時，才考慮它們的影響。正偏時以擴(kuò)散電容CD為主， Cj CD ，其值通常為幾十至幾百pF；反偏時以勢壘電容CT為主， Cj CT,其值通常為幾至幾十pF。（如：變?nèi)荻O

6、管）731-3 晶體二極管及其基本電路PN結(jié)加上電極引線和管殼就形成晶體二極管。圖1-13 晶體二極管結(jié)構(gòu)示意圖及電路符號 P區(qū)N區(qū)正極負(fù)極（a）結(jié)構(gòu)示意圖（b）電路符號PN正極負(fù)極741-3-1 二極管特性曲線二極管特性曲線與PN結(jié)基本相同，略有差異。圖1-14 二極管伏安特性曲線 i /mAu/V(A)0102030-5-10-0.50.5硅 二 極 管75一、正向特性硅: UD(on) = 0.7V；1.導(dǎo)通電壓或死區(qū)電壓2. 曲線分段：鍺: UD(on) = 0.3V。3. 小功率二極管正常工作的電流范圍內(nèi)，管壓降變化比較小。指數(shù)段（小電流時）、直線段（大電流時）。一般硅：0.60.8

7、V，鍺：0.10.3V。 i /mAu/V(A)0102030-5-10-0.50.5硅 二 極 管76二、反向特性2.小功率二極管的反向電流很小。一般硅管0.1A，鍺管幾十微安。1.反向電壓加大時，反向電流也略有增大。 i /mAu/V(A)0102030-5-10-0.50.5硅 二 極 管771-3-2 二極管的主要參數(shù)一、直流電阻 圖1-15 二極管電阻的幾何意義IDUDQ1RD=UD / IDRD 的幾何意義：iu0Q2(a)直流電阻RDQ點(diǎn)到原點(diǎn)直線斜率的倒數(shù)。RD不是恒定的，正向的RD隨工作電流增大而減小，反向的RD隨反向電壓的增大而增大。781.正向電阻：幾百歐姆；反向電阻：幾

8、百千歐姆；2.Q點(diǎn)不同，測出的電阻也不同；結(jié) 論 因此，PN結(jié)具有單向?qū)щ娞匦浴?9二 、交流電阻二極管在其工作狀態(tài)(I DQ, UDQ)下的電壓微變量與電流微變量之比。iu0Qiu(b)交流電阻rDrD 的幾何意義:Q(IDQ, UDQ)點(diǎn)處切線斜率的倒數(shù)。80與IDQ成反比，并與溫度有關(guān)。81例：已知D為Si二極管，流過D的直流電流ID=10mA，交流電壓有效值U=10mV，求室溫下流過D的交流電流有效值I=?10VDR0.93KUID解：交流電阻交流電流有效值為：82三、最大整流電流 I F四、最大反向工作電壓 URM五、反向電流IR允許通過的最大正向平均電流。通常取U(BR)的一半，超

9、過U(BR)容易發(fā)生反向擊穿。未擊穿時的反向電流。 IR越小，單向?qū)щ娦阅茉胶谩?3六、最高工作頻率 f M 需要指出，手冊中給出的一般為典型值，需要時應(yīng)通過實(shí)際測量得到準(zhǔn)確值。工作頻率超過 f M時，二極管的單向?qū)щ娦阅茏儔摹?84對電子線路進(jìn)行分析(定量分析)時,電路中的實(shí)際器件必須用相應(yīng)的電路模型來等效表示，這稱為：“建?！?。計算機(jī)輔助分析計算要使用管子的模型。 一、二極管的大信號等效電路1-3-3 晶體二極管模型85由于二極管的非線性特性，當(dāng)電路加入二極管時，便成為非線性電路。實(shí)際應(yīng)用時可根據(jù)二極管的應(yīng)用條件作合理近似，得到相應(yīng)的等效電路，化為線性電路非線性近似線性 i /mAu/V(

10、A)0102030-5-10-0.50.5硅 二 極 管86圖1-16 二極管特性的折線近似及電路模型硅管：UD(on). 7 V 鍺管：UD(on). 3 ViA1uBUD(on)C0（a) 折線近似特性UUD(on)UUD(on)12UD(on)rD(on)（b) 近似電路模型87圖1-16 二極管特性的折線近似及電路模型iAuBUD(on)C0（a) 折線近似特性UUD(on)UUD(on)12UD(on)（c) 簡化電路模型88圖1-16 二極管特性的折線近似及電路模型iA2uB0C0（a) 折線近似特性U0U012（d) 理想電路模型89二極管大信號模型以上三種電路模型(近似、簡化、

11、理想)均為二極管線性化模型。對不同電路模型可在不同需求時采用。90一、二極管整流電路 把交流電轉(zhuǎn)變?yōu)橹绷麟姺Q為“整流”。 反之稱為“逆變”。 整流 交流電 直流電 逆變1-3-4 二極管基本應(yīng)用電路91圖1-17 二極管半波整流電路及波形tui0 uot0(b)輸入、輸出波形關(guān)系VRLuiuo(a)電路 二極管近似為理想模型 思考：二極管近似為簡化模型的電路輸出？92uit010V0.7V93二、二極管限幅電路又稱為：“削波電路”。能夠把輸入電壓變化范圍加以限制，常用于波形變換和整形。94圖1-20 二極管上限幅電路及波形 (b) 輸入、輸出波形關(guān)系t0 uo/V2.7-5t ui/V0-55

12、(a)電路E2VVRuiuo 二極管近似為簡化模型95判別原則：ui-EUD(ON) 時, V 導(dǎo)通，否則截止。 當(dāng)u i 2.7V, V導(dǎo)通，uo=E+0.7=2.7 V 當(dāng)u i 2.7V時, V截止，即開路，uo = u i 。即：E2VVRuiuo96三、二極管電平選擇電路能夠從多路輸入信號中選出最低電平或最高電平的電路稱為電平選擇電路。97輸入數(shù)字量時為與邏輯。5V981. 穩(wěn)壓二極管的正向特性、反向特性與普通二極管基本相同，區(qū)別僅在于反向擊穿時，特性曲線更加陡峭。2. 穩(wěn)壓管在反向擊穿后，能通過調(diào)節(jié)自身電流， 實(shí)現(xiàn)穩(wěn)定電壓的功能。電壓幾乎不變，為-UZ。即當(dāng)一、穩(wěn)壓二極管的特性1-

13、3-5 穩(wěn)壓二極管及穩(wěn)壓電路99圖1-21 穩(wěn)壓二極管及其特性曲線(a) 電路符號i/mAu/V IZmax0-UZ IZmin(b) 伏安特性曲線100二、穩(wěn)壓二極管主要參數(shù)穩(wěn)壓電壓 UZ額定功耗 Pz穩(wěn)定電流 Iz動態(tài)電阻 rz溫度系數(shù) 101穩(wěn)壓電壓UZ指管子長期穩(wěn)定時的工作電壓值。102額定功耗Pz 與材料、結(jié)構(gòu)、工藝有關(guān)。使用時不允許超過此值。103穩(wěn)定電流Iz穩(wěn)壓二極管正常工作時的參考電流。IZminIZIZmax,如果電流小于IZmin時，不能穩(wěn)壓，大于IZmax時，容易燒壞管子。i/mAu/V IZmax0-UZ IZmin(b) 伏安特性曲線104動態(tài)電阻 rz是在擊穿狀態(tài)下

14、,管子兩端電壓變化量與電流變化量的比值。反映在特性曲線上，是工作點(diǎn)處切線斜率的倒數(shù)。 一般為幾歐姆到幾十歐姆（越小越好）。i/mAu/V IZmax0-UZ IZmin(b) 伏安特性曲線105溫度系數(shù)指管子穩(wěn)定電壓受溫度影響的程度。7V是正溫系數(shù)(雪崩擊穿)；5V是負(fù)溫系數(shù)(齊納擊穿)；57V溫度系數(shù)最小。106所謂穩(wěn)壓指當(dāng)Ui、RL變化時，UO保持恒定。圖1-22 穩(wěn)壓二極管穩(wěn)壓電路R ILIZVZ RLUiUo三、穩(wěn)壓二極管穩(wěn)壓電路穩(wěn)壓原理：若Ui不變，RLIzILUO基本不變；若RL不變，UiIzURUO基本不變 107限流電阻R的選擇： 選擇R的限制條件：當(dāng)Ui、RL變化時，Iz應(yīng)滿

15、足IzminIzIzmax 設(shè)外界條件為:UiminUiUimax；RLminRLRLmax 圖1-22 穩(wěn)壓二極管穩(wěn)壓電路R ILIZVZ RLUiUo108圖1-22 穩(wěn)壓二極管穩(wěn)壓電路R ILIZVZ RLUiUo分析過程：根據(jù)電路：Iz何時取最大值？ui=Uimax，RL=RLmax109圖1-22 穩(wěn)壓二極管穩(wěn)壓電路R ILIZVZ RLUiUo110圖1-22 穩(wěn)壓二極管穩(wěn)壓電路R ILIZVZ RLUiUoIz何時取最小值？ui=Uimin，RL=RLmin111Rmin R 0Vapplied 0 the diode is in forward bias and is acti

16、ng like a perfect conductor so: ID = VA/RS = 5 V / 50 = 100 mAb) With VA 0 the diode is in forward bias and is acting like a perfect conductor so write a KVL equation to find ID:0 = VA IDRS - V ID = VA - V = 4.7 V = 94 mA RS 50 V+V+134Diode Circuit ModelsThe Ideal Diode with Barrier Potential and Li

17、near Forward Resistance This model is the most accurate of the three. It includes a linear forward resistance that is calculated from the slope of the linear portion of the transconductance curve. However, this is usually not necessary since the RF (forward resistance) value is pretty constant. For

18、low-power germanium and silicon diodes the RF value is usually in the 2 to 5 ohms range, while higher power diodes have a RF value closer to 1 ohm.Linear Portion of transconductance curveVDIDVDIDRF = VD IDKristin Ackerson, Virginia Tech EESpring 2002+VRF135Diode Circuit ModelsThe Ideal Diode with Ba

19、rrier Potential and Linear Forward Resistance Kristin Ackerson, Virginia Tech EESpring 2002Example: Assume the diode is a low-power diode with a forward resistance value of 5 ohms. The barrier potential voltage is still: V = 0.3 volts (typical for a germanium diode) Determine the value of ID if VA =

20、 5 volts.+_VAIDRS = 50 V+RFOnce again, write a KVL equation for the circuit:0 = VA IDRS - V - IDRFID = VA - V = 5 0.3 = 85.5 mA RS + RF 50 + 5136Diode Circuit ModelsKristin Ackerson, Virginia Tech EESpring 2002Values of ID for the Three Different Diode Circuit ModelsIdeal Diode ModelIdeal Diode Mode

21、l with Barrier Potential VoltageIdeal Diode Model with Barrier Potential and Linear Forward ResistanceID100 mA94 mA85.5 mAThese are the values found in the examples on previous slides where the applied voltage was 5 volts, the barrier potential was 0.3 volts and the linear forward resistance value w

22、as assumed to be 5 ohms.137The Q PointKristin Ackerson, Virginia Tech EESpring 2002The operating point or Q point of the diode is the quiescent or no-signal condition. The Q point is obtained graphically and is really only needed when the applied voltage is very close to the diodes barrier potential

23、 voltage. The example 3 below that is continued on the next slide, shows how the Q point is determined using the transconductance curve and the load line.+_VA= 6VIDRS = 1000 V+First the load line is found by substituting in different values of V into the equation for ID using the ideal diode with ba

24、rrier potential model for the diode. With RS at 1000 ohms the value of RF wouldnt have much impact on the results.ID = VA V RSUsing V values of 0 volts and 1.4 volts we obtain ID values of 6 mA and 4.6 mA respectively. Next we will draw the line connecting these two points on the graph with the tran

25、sconductance curve. This line is the load line.138The Q PointID (mA)VD (Volts)246810120.20.40.60.81.01.21.4The transconductance curve below is for a Silicon diode. The Q point in this example is located at 0.7 V and 5.3 mA.4.6Kristin Ackerson, Virginia Tech EESpring 20020.75.3Q Point: The intersecti

26、on of the load line and the transconductance curve.139Capacitance and Voltage of PN JunctionsDiode Operation AnimationWebpage Link140Dynamic ResistanceKristin Ackerson, Virginia Tech EESpring 2002The dynamic resistance of the diode is mathematically determined as the inverse of the slope of the tran

27、sconductance curve. Therefore, the equation for dynamic resistance is:rF = VT IDThe dynamic resistance is used in determining the voltage drop across the diode in the situation where a voltage source is supplying a sinusoidal signal with a dc offset.The ac component of the diode voltage is found usi

28、ng the following equation:vF = vac rF rF + RSThe voltage drop through the diode is a combination of the ac and dc components and is equal to:VD = V + vF141Dynamic ResistanceKristin Ackerson, Virginia Tech EESpring 2002Example: Use the same circuit used for the Q point example but change the voltage

29、source so it is an ac source with a dc offset. The source voltage is now, vin = 6 + sin(wt) Volts. It is a silicon diode so the barrier potential voltage is still 0.7 volts.+vinIDRS = 1000 V+The DC component of the circuit is the same as the previous example and therefore ID = 6V 0.7 V = 5.2 mA 1000

30、 rF = VT = 1 * 26 mV = 4.9 ID 5.3 mA = 1 is a good approximation if the dc current is greater than 1 mA as it is in this example.vF = vac rF = sin(wt) V 4.9 = 4.88 sin(wt) mV rF + RS 4.9 + 1000 Therefore, VD = 700 + 4.9 sin (wt) mV (the voltage drop across the diode)142Kristin Ackerson, Virginia Tec

31、h EESpring 2002Types of Diodes and Their UsesPN Junction Diodes:Are used to allow current to flow in one direction while blocking current flow in the opposite direction. The pn junction diode is the typical diode that has been used in the previous circuits.AKSchematic Symbol for a PN Junction DiodeP

32、nRepresentative Structure for a PN Junction DiodeZener Diodes:Are specifically designed to operate under reverse breakdown conditions. These diodes have a very accurate and specific reverse breakdown voltage.AKSchematic Symbol for a Zener Diode143Types of Diodes and Their UsesKristin Ackerson, Virgi

33、nia Tech EESpring 2002Schottky Diodes:These diodes are designed to have a very fast switching time which makes them a great diode for digital circuit applications. They are very common in computers because of their ability to be switched on and off so quickly. AKSchematic Symbol for a Schottky Diode

34、Shockley Diodes:The Shockley diode is a four-layer diode while other diodes are normally made with only two layers. These types of diodes are generally used to control the average power delivered to a load. AKSchematic Symbol for a four-layer Shockley Diode144Types of Diodes and Their UsesKristin Ac

35、kerson, Virginia Tech EESpring 2002Light-Emitting Diodes:Light-emitting diodes are designed with a very large bandgap so movement of carriers across their depletion region emits photons of light energy. Lower bandgap LEDs (Light-Emitting Diodes) emit infrared radiation, while LEDs with higher bandga

36、p energy emit visible light. Many stop lights are now starting to use LEDs because they are extremely bright and last longer than regular bulbs for a relatively low cost. AKSchematic Symbol for a Light-Emitting DiodeThe arrows in the LED representation indicate emitted light.145Types of Diodes and T

37、heir UsesKristin Ackerson, Virginia Tech EESpring 2002Photodiodes:While LEDs emit light, Photodiodes are sensitive to received light. They are constructed so their pn junction can be exposed to the outside through a clear window or lens.In Photoconductive mode the saturation current increases in pro

38、portion to the intensity of the received light. This type of diode is used in CD players.In Photovoltaic mode, when the pn junction is exposed to a certain wavelength of light, the diode generates voltage and can be used as an energy source. This type of diode is used in the production of solar powe

39、r.AKAKSchematic Symbols for Photodiodes 146SourcesDailey, Denton. Electronic Devices and Circuits, Discrete and Integrated. Prentice Hall, New Jersey: 2001. (pp 2-37, 752-753)2 Figure 1.10. The diode transconductance curve, pg. 7Figure 1.15. Determination of the average forward resistance of a diode

40、, pg 113 Example from pages 13-14Liou, J.J. and Yuan, J.S. Semiconductor Device Physics and Simulation. Plenum Press, New York: 1998.Neamen, Donald. Semiconductor Physics & Devices. Basic Principles. McGraw-Hill, Boston: 1997. (pp 1-15, 211-234)1 Figure 6.2. The space charge region, the electric fie

41、ld, and the forces acting on the charged carriers, pg 213.Kristin Ackerson, Virginia Tech EESpring 2002147Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.Chapter 1: Semiconductor Diodes148Slide 1 Robert BoylestadDigi

42、tal ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.DiodesSimplest Semiconductor DeviceIt is a 2-terminal device149Slide 2Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All ri

43、ghts reserved.Basic operationIdeally it conducts current in only one directionand acts like an open in the opposite direction150Slide 3Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.Characteristics of an ideal diode

44、: Conduction RegionLook at the vertical line!In the conduction region, ideally the voltage across the diode is 0V, the current is , the forward resistance (RF) is defined as RF = VF/IF, the diode acts like a short.151Slide 4Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.

45、Upper Saddle River, New Jersey 07458All rights reserved.Characteristics of an ideal diode: Non-Conduction RegionLook at the horizontal line!In the non-conduction region, ideally all of the voltage is across the diode, the current is 0A, the reverse resistance (RR) is defined as RR = VR/IR, the diode

46、 acts like open.152Slide 5Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.Semiconductor MaterialsCommon materials used in the development of semiconductor devices: Silicon (Si) Germanium (Ge)153Slide 6Robert Boylesta

47、dDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.DopingThe electrical characteristics of Silicon and Germanium are improved by adding materials in a process called doping.The additional materials are in two types: n-type p-type154Sl

48、ide 7Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.n-type materials make the Silicon (or Germanium) atoms more negative.p-type materials make the Silicon (or Germanium) atoms more positive.Join n-type and p-type do

49、ped Silicon (or Germanium) to form a p-n junction.n-type versus p-type155Slide 8Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.p-n junctionWhen the materials are joined, the negatively charged atoms of the n-type do

50、ped side are attracted to the positively charged atoms of the p-type doped side.The electrons in the n-type material migrate across the junction to the p-type material (electron flow). Or you could say the holes in the p-type material migrate across the junction to the n-type material (conventional

51、current flow).The result is the formation of a depletion layer around the junction.depletion layerpn156Slide 9Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.Operating Conditions No Bias Forward Bias Reverse Bias157S

52、lide 10Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.No external voltage is applied: VD = 0V and no current is flowing ID = 0A.Only a modest depletion layer exists.No Bias Condition158Slide 11Robert BoylestadDigita

53、l ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.Reverse Bias ConditionExternal voltage is applied across the p-n junction in the opposite polarity of the p- and n-type materials.This causes the depletion layer to widen. The electrons in t

54、he n-type material are attracted towards the positive terminal and the holes in the p-type material are attracted towards the negative terminal.159Slide 12Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.Forward Bias

55、ConditionExternal voltage is applied across the p-n junction in the same polarity of the p- and n-type materials.The depletion layer is narrow. The electrons from the n-type material and holes from the p-type material have sufficient energy to cross the junction.160Slide 13Robert BoylestadDigital El

56、ectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.Actual Diode CharacteristicsNote the regions for No Bias, Reverse Bias, and Forward Bias conditions.Look closely at the scale for each of these conditions!161Slide 14Robert BoylestadDigital Elec

57、tronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.A diode, as any semiconductor device is not perfect! There are two sets of currents: Majority CarriersThe electrons in the n-type and holes in the p-type materialare the source of the majority of

58、the current flow in a diode. Minority CarriersElectrons in the p-type and holes in the n-type materialare rebel currents. They produce a small amount of opposing current.Majority and Minority Carriers in Diode162Slide 15Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Uppe

59、r Saddle River, New Jersey 07458All rights reserved.Another detail about the diode is the useful Zener region.The diode is in the reverse bias condition. At some point the reverse bias voltage is so large the diode breaks down. The reverse current increases dramatically. This maximum voltage is call

60、ed avalanche breakdown voltage and the current is called avalanche current.Zener Region163Slide 16Robert BoylestadDigital ElectronicsCopyright 2002 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.The point at which the diode changes from No Bias condition to Forward