三極管，全稱半導體(ti)三(san)極(ji)(ji)管(guan)，也稱雙極(ji)(ji)型(xing)晶體(ti)管(guan)、晶體(ti)三(san)極(ji)(ji)管(guan)，是一種(zhong)控制電流的半導體(ti)器(qi)件其作用是把微弱(ruo)信號放大成幅度值較大的電信號， 也用作無觸(chu)點開關。
三(san)極管，是半導(dao)體基本元器(qi)件之一，具有電流(liu)放大作用，是電(dian)子(zi)電(dian)(dian)路的核心元件。三極管(guan)是(shi)在(zai)一塊半導(dao)體基片(pian)上制(zhi)作兩(liang)個相(xiang)距很近的PN結，兩(liang)個PN結把(ba)整塊半導(dao)體分成(cheng)三部分，中間部分是(shi)基區，兩(liang)側部分是(shi)發射(she)區和集電(dian)(dian)區，排(pai)列方式(shi)有PNP和NPN兩(liang)種。
發(fa)(fa)(fa)射(she)(she)區(qu)(qu)(qu)和(he)(he)(he)基(ji)(ji)區(qu)(qu)(qu)之間的(de)(de)(de)PN結叫發(fa)(fa)(fa)射(she)(she)結，集電(dian)區(qu)(qu)(qu)和(he)(he)(he)基(ji)(ji)區(qu)(qu)(qu)之間的(de)(de)(de)PN結叫集電(dian)結。基(ji)(ji)區(qu)(qu)(qu)很薄(bo)，而發(fa)(fa)(fa)射(she)(she)區(qu)(qu)(qu)較厚，雜(za)質濃度大，PNP型(xing)(xing)(xing)三極(ji)(ji)(ji)管發(fa)(fa)(fa)射(she)(she)區(qu)(qu)(qu)"發(fa)(fa)(fa)射(she)(she)"的(de)(de)(de)是(shi)空穴，其移動方向(xiang)與電(dian)流方向(xiang)一致，故發(fa)(fa)(fa)射(she)(she)極(ji)(ji)(ji)箭(jian)頭向(xiang)里；NPN型(xing)(xing)(xing)三極(ji)(ji)(ji)管發(fa)(fa)(fa)射(she)(she)區(qu)(qu)(qu)"發(fa)(fa)(fa)射(she)(she)"的(de)(de)(de)是(shi)自由電(dian)子，其移動方向(xiang)與電(dian)流方向(xiang)相反(fan)，故發(fa)(fa)(fa)射(she)(she)極(ji)(ji)(ji)箭(jian)頭向(xiang)外。發(fa)(fa)(fa)射(she)(she)極(ji)(ji)(ji)箭(jian)頭指(zhi)向(xiang)也是(shi)PN結在正向(xiang)電(dian)壓下的(de)(de)(de)導通方向(xiang)。硅(gui)晶體(ti)三極(ji)(ji)(ji)管和(he)(he)(he)鍺晶體(ti)三極(ji)(ji)(ji)管都(dou)有PNP型(xing)(xing)(xing)和(he)(he)(he)NPN型(xing)(xing)(xing)兩種類型(xing)(xing)(xing)。從三個區(qu)(qu)(qu)引(yin)出相應的(de)(de)(de)電(dian)極(ji)(ji)(ji)，分別為基(ji)(ji)極(ji)(ji)(ji)b發(fa)(fa)(fa)射(she)(she)極(ji)(ji)(ji)e和(he)(he)(he)集電(dian)極(ji)(ji)(ji)c。
NPN型三(san)極管
在(zai)制(zhi)造三(san)極管時(shi)(shi)，有(you)意識地使發(fa)射區(qu)的(de)(de)(de)多數載流(liu)子(zi)(zi)(zi)濃度大(da)于基區(qu)的(de)(de)(de)，同時(shi)(shi)基區(qu)做(zuo)得很薄，而且，要嚴格控制(zhi)雜質含量(liang)，這(zhe)樣，一旦(dan)接通電(dian)(dian)(dian)源后，由于發(fa)射結(jie)正(zheng)偏，發(fa)射區(qu)的(de)(de)(de)多數載流(liu)子(zi)(zi)(zi)（電(dian)(dian)(dian)子(zi)(zi)(zi)）及基區(qu)的(de)(de)(de)多數載流(liu)子(zi)(zi)(zi)（空穴）很容易地越過(guo)發(fa)射結(jie)互相向對方擴散，但因前者的(de)(de)(de)濃度基大(da)于后者，所(suo)以通過(guo)發(fa)射結(jie)的(de)(de)(de)電(dian)(dian)(dian)流(liu)基本上是(shi)電(dian)(dian)(dian)子(zi)(zi)(zi)流(liu)，這(zhe)股電(dian)(dian)(dian)子(zi)(zi)(zi)流(liu)稱為發(fa)射極電(dian)(dian)(dian)流(liu)子(zi)(zi)(zi)。
三(san)極(ji)管按材料分有兩(liang)種(zhong)：硅(gui)管和鍺管。而每(mei)一種(zhong)又有NPN和PNP兩(liang)種(zhong)結構形(xing)式，但使用最多的是硅(gui)NPN和鍺PNP兩(liang)種(zhong)三(san)極(ji)管，（其中，N表示在(zai)高(gao)純度硅(gui)中加入磷(lin)，取(qu)代(dai)一些硅(gui)原(yuan)子，在(zai)電(dian)(dian)壓刺激下產(chan)生自(zi)由電(dian)(dian)子導電(dian)(dian)，而p是加入硼取(qu)代(dai)硅(gui)，產(chan)生大量空穴利于(yu)導電(dian)(dian)）；兩(liang)者除了電(dian)(dian)源(yuan)極(ji)性不(bu)同(tong)(tong)外，其工(gong)作原(yuan)理都是相同(tong)(tong)的，下面僅(jin)介(jie)紹NPN硅(gui)管的電(dian)(dian)流放大原(yuan)理。
對于NPN管，它是由2塊(kuai)N型半(ban)導體中間(jian)夾著一塊(kuai)P型半(ban)導體所組成，發(fa)射區與基區之間(jian)形成的PN結(jie)稱(cheng)為發(fa)射結(jie),而集(ji)(ji)電區與基區形成的PN結(jie)稱(cheng)為集(ji)(ji)電結(jie),三條引(yin)線分別稱(cheng)為發(fa)射極e （Emitter）、基極b (Base)和集(ji)(ji)電極c (Collector)。
當(dang)b點(dian)電(dian)(dian)位(wei)(wei)高(gao)于(yu)(yu)e點(dian)電(dian)(dian)位(wei)(wei)零點(dian)幾伏(fu)(fu)時，發射(she)結處(chu)于(yu)(yu)正(zheng)偏狀(zhuang)態，而C點(dian)電(dian)(dian)位(wei)(wei)高(gao)于(yu)(yu)b點(dian)電(dian)(dian)位(wei)(wei)幾伏(fu)(fu)時，集電(dian)(dian)結處(chu)于(yu)(yu)反(fan)偏狀(zhuang)態，集電(dian)(dian)極電(dian)(dian)源(yuan)Ec要(yao)高(gao)于(yu)(yu)基(ji)極電(dian)(dian)源(yuan)Eb。
我們(men)把(ba)從基(ji)極(ji)(ji)B流(liu)(liu)(liu)至發射極(ji)(ji)E的電(dian)流(liu)(liu)(liu)叫做(zuo)基(ji)極(ji)(ji)電(dian)流(liu)(liu)(liu)Ib；把(ba)從集電(dian)極(ji)(ji)C流(liu)(liu)(liu)至發射極(ji)(ji)E的電(dian)流(liu)(liu)(liu)叫做(zuo)集電(dian)極(ji)(ji)電(dian)流(liu)(liu)(liu) Ic。這兩個電(dian)流(liu)(liu)(liu)的方向都是流(liu)(liu)(liu)出發射極(ji)(ji)的，所以發射極(ji)(ji)E上就(jiu)用了一個箭頭(tou)來表示(shi)電(dian)流(liu)(liu)(liu)的方向。
三(san)極(ji)(ji)(ji)(ji)管是(shi)一(yi)(yi)種控(kong)制(zhi)元件，主要用(yong)來控(kong)制(zhi)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)的(de)大(da)(da)小(xiao)(xiao)，以共(gong)發(fa)射極(ji)(ji)(ji)(ji)接(jie)法(fa)為例（信號從基(ji)極(ji)(ji)(ji)(ji)輸入，從集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)(ji)輸出，發(fa)射極(ji)(ji)(ji)(ji)接(jie)地(di)），當基(ji)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)壓UB有(you)一(yi)(yi)個微小(xiao)(xiao)的(de)變(bian)化(hua)時，基(ji)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)IB也(ye)會(hui)(hui)隨之有(you)一(yi)(yi)小(xiao)(xiao)的(de)變(bian)化(hua)，受基(ji)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)IB的(de)控(kong)制(zhi)，集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)IC會(hui)(hui)有(you)一(yi)(yi)個很大(da)(da)的(de)變(bian)化(hua)，基(ji)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)IB越大(da)(da)，集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)IC也(ye)越大(da)(da)，反之，基(ji)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)越小(xiao)(xiao)，集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)也(ye)越小(xiao)(xiao)，即基(ji)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)控(kong)制(zhi)集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)的(de)變(bian)化(hua)。但是(shi)集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)的(de)變(bian)化(hua)比基(ji)極(ji)(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)的(de)變(bian)化(hua)大(da)(da)得多，這就是(shi)三(san)極(ji)(ji)(ji)(ji)管的(de)放大(da)(da)作用(yong)。IC 的(de)變(bian)化(hua)量與IB變(bian)化(hua)量之比叫(jiao)做三(san)極(ji)(ji)(ji)(ji)管的(de)放大(da)(da)倍(bei)數(shu)β（β=ΔIC/ΔIB, Δ表示變(bian)化(hua)量。），三(san)極(ji)(ji)(ji)(ji)管的(de)放大(da)(da)倍(bei)數(shu)β一(yi)(yi)般在幾十到幾百倍(bei)。
由于基區(qu)很薄,加上集(ji)電(dian)(dian)(dian)(dian)(dian)結的(de)(de)反(fan)偏，注(zhu)入基區(qu)的(de)(de)電(dian)(dian)(dian)(dian)(dian)子大部分越過集(ji)電(dian)(dian)(dian)(dian)(dian)結進入集(ji)電(dian)(dian)(dian)(dian)(dian)區(qu)而形成(cheng)集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)Ic，只(zhi)剩下很少（1-10%）的(de)(de)電(dian)(dian)(dian)(dian)(dian)子在基區(qu)的(de)(de)空(kong)穴進行復合(he)，被復合(he)掉(diao)的(de)(de)基區(qu)空(kong)穴由基極(ji)電(dian)(dian)(dian)(dian)(dian)源Eb重新(xin)補給，從而形成(cheng)了(le)基極(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)Ib。根據(ju)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)連續性原理得：
Ie=Ib+Ic
這(zhe)就是說，在(zai)基極(ji)補(bu)充一個很小的(de)Ib，就可以在(zai)集電極(ji)上得到(dao)一個較大(da)的(de)Ic，這(zhe)就是所謂電流(liu)放大(da)作用，Ic與(yu)Ib是維持(chi)一定(ding)的(de)比例關系，即：
β1=Ic/Ib
式(shi)中：β1--稱為直流(liu)放大倍數，
集電極(ji)電流的變化(hua)量△Ic與(yu)基極(ji)電流的變化(hua)量△Ib之(zhi)比為：
β= △Ic/△Ib
式中β--稱為交(jiao)流電流放大倍數，由于低頻時β1和β的數值(zhi)(zhi)相差(cha)不大，所以(yi)有(you)時為了方便起見(jian)，對兩(liang)者不作嚴格區(qu)分(fen)，β值(zhi)(zhi)約為幾(ji)十至幾(ji)百(bai)。
α1=Ic/Ie(Ic與(yu)Ie是(shi)直流通(tong)路中的(de)電流大小)
式中：α1也稱為直流(liu)(liu)放大(da)倍數，一般(ban)在共基極組態放大(da)電路中使(shi)用，描述(shu)了發射極電流(liu)(liu)與集電極電流(liu)(liu)的(de)關系。
α =△Ic/△Ie
表(biao)達式中的α為(wei)交(jiao)流共基極電流放大倍數。同(tong)理α與α1在小(xiao)信號輸入(ru)時(shi)相差(cha)也不大。
對于兩個(ge)描述電流關系(xi)的(de)放(fang)大倍數有以下關系(xi)β=a/（1-a）。
三極(ji)(ji)管(guan)的(de)(de)放大(da)作(zuo)用(yong)就是(shi)：集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)受(shou)基(ji)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的(de)(de)控(kong)制(zhi)（假設(she)電(dian)(dian)(dian)(dian)(dian)源 能夠提(ti)供給集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)足(zu)夠大(da)的(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的(de)(de)話(hua)），并(bing)且基(ji)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)很小的(de)(de)變(bian)(bian)(bian)化，會引起集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)很大(da)的(de)(de)變(bian)(bian)(bian)化，且變(bian)(bian)(bian)化滿足(zu)一(yi)定的(de)(de)比(bi)例關系：集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的(de)(de)變(bian)(bian)(bian)化量(liang)是(shi)基(ji)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)變(bian)(bian)(bian) 化量(liang)的(de)(de)β倍(bei)，即電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)變(bian)(bian)(bian)化被放大(da)了β倍(bei)，所(suo)以(yi)我們把(ba)β叫做三極(ji)(ji)管(guan)的(de)(de)放大(da)倍(bei)數(shu)（β一(yi)般遠大(da)于1，例如幾十，幾百(bai)）。
