三極管，全(quan)稱半導(dao)體(ti)三極(ji)管，也(ye)稱雙極(ji)型晶(jing)體(ti)管、晶(jing)體(ti)三極(ji)管，是一種控制電流的半導(dao)體(ti)器件其作用是把微(wei)弱信號放(fang)大(da)成幅度值較大(da)的電信號， 也(ye)用作無觸點(dian)開關。
三極管，是半(ban)導體基本元(yuan)器件之一，具有電流放大作用，是電子(zi)電路的核(he)心元(yuan)件。三極管是(shi)在一塊半(ban)導(dao)(dao)體基片(pian)上制作兩個相(xiang)距很近的PN結(jie)，兩個PN結(jie)把整塊半(ban)導(dao)(dao)體分(fen)成(cheng)三部(bu)分(fen)，中間部(bu)分(fen)是(shi)基區(qu)，兩側部(bu)分(fen)是(shi)發射區(qu)和集電區(qu)，排列(lie)方式有PNP和NPN兩種(zhong)。
發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)區(qu)和(he)基(ji)區(qu)之間(jian)(jian)的(de)PN結叫發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)結，集電(dian)(dian)區(qu)和(he)基(ji)區(qu)之間(jian)(jian)的(de)PN結叫集電(dian)(dian)結。基(ji)區(qu)很薄，而發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)區(qu)較厚(hou)，雜質濃度大，PNP型(xing)三極(ji)管(guan)發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)區(qu)"發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)"的(de)是空穴，其(qi)移動(dong)方向與電(dian)(dian)流(liu)方向一致(zhi)，故發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)極(ji)箭頭向里；NPN型(xing)三極(ji)管(guan)發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)區(qu)"發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)"的(de)是自由電(dian)(dian)子，其(qi)移動(dong)方向與電(dian)(dian)流(liu)方向相(xiang)(xiang)反，故發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)極(ji)箭頭向外。發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)極(ji)箭頭指向也是PN結在(zai)正向電(dian)(dian)壓下的(de)導通方向。硅晶(jing)體三極(ji)管(guan)和(he)鍺晶(jing)體三極(ji)管(guan)都(dou)有PNP型(xing)和(he)NPN型(xing)兩(liang)種類型(xing)。從三個區(qu)引出(chu)相(xiang)(xiang)應的(de)電(dian)(dian)極(ji)，分別為基(ji)極(ji)b發(fa)(fa)(fa)(fa)(fa)(fa)(fa)射(she)(she)(she)(she)極(ji)e和(he)集電(dian)(dian)極(ji)c。
NPN型三極管
在制造三極管(guan)時(shi)，有意識地使發(fa)射(she)(she)區(qu)的(de)(de)多(duo)(duo)數載(zai)流子(zi)(zi)濃(nong)度(du)大于基(ji)(ji)區(qu)的(de)(de)，同時(shi)基(ji)(ji)區(qu)做(zuo)得很薄，而且，要(yao)嚴格(ge)控(kong)制雜質含量(liang)，這(zhe)樣，一旦接通(tong)電(dian)(dian)源后，由于發(fa)射(she)(she)結(jie)正偏，發(fa)射(she)(she)區(qu)的(de)(de)多(duo)(duo)數載(zai)流子(zi)(zi)（電(dian)(dian)子(zi)(zi)）及(ji)基(ji)(ji)區(qu)的(de)(de)多(duo)(duo)數載(zai)流子(zi)(zi)（空穴）很容(rong)易(yi)地越(yue)過發(fa)射(she)(she)結(jie)互相向對方擴散，但因前者的(de)(de)濃(nong)度(du)基(ji)(ji)大于后者，所(suo)以通(tong)過發(fa)射(she)(she)結(jie)的(de)(de)電(dian)(dian)流基(ji)(ji)本上是(shi)電(dian)(dian)子(zi)(zi)流，這(zhe)股(gu)電(dian)(dian)子(zi)(zi)流稱為發(fa)射(she)(she)極電(dian)(dian)流子(zi)(zi)。
三極(ji)管按材料(liao)分有兩(liang)(liang)種：硅(gui)(gui)管和鍺管。而(er)每(mei)一種又有NPN和PNP兩(liang)(liang)種結構(gou)形式(shi)，但使(shi)用最多的(de)是硅(gui)(gui)NPN和鍺PNP兩(liang)(liang)種三極(ji)管，（其(qi)中(zhong)，N表示在高純度硅(gui)(gui)中(zhong)加入磷(lin)，取(qu)代(dai)一些硅(gui)(gui)原子(zi)，在電(dian)壓刺激下產(chan)生自(zi)由(you)電(dian)子(zi)導電(dian)，而(er)p是加入硼取(qu)代(dai)硅(gui)(gui)，產(chan)生大量空穴利于導電(dian)）；兩(liang)(liang)者除了電(dian)源極(ji)性不同(tong)外(wai)，其(qi)工作原理(li)都是相同(tong)的(de)，下面(mian)僅(jin)介紹NPN硅(gui)(gui)管的(de)電(dian)流放大原理(li)。
對于NPN管，它是由2塊N型半導體(ti)中間夾著一塊P型半導體(ti)所組成(cheng)，發(fa)射區(qu)與基(ji)區(qu)之間形(xing)成(cheng)的(de)PN結(jie)稱(cheng)(cheng)為(wei)(wei)發(fa)射結(jie),而集電(dian)區(qu)與基(ji)區(qu)形(xing)成(cheng)的(de)PN結(jie)稱(cheng)(cheng)為(wei)(wei)集電(dian)結(jie),三條引線分別稱(cheng)(cheng)為(wei)(wei)發(fa)射極(ji)e （Emitter）、基(ji)極(ji)b (Base)和集電(dian)極(ji)c (Collector)。
當b點電(dian)(dian)(dian)位高(gao)(gao)于e點電(dian)(dian)(dian)位零點幾伏(fu)時，發射結處于正偏(pian)狀態，而C點電(dian)(dian)(dian)位高(gao)(gao)于b點電(dian)(dian)(dian)位幾伏(fu)時，集電(dian)(dian)(dian)結處于反偏(pian)狀態，集電(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)源(yuan)Ec要高(gao)(gao)于基極(ji)(ji)電(dian)(dian)(dian)源(yuan)Eb。
我們把從基極(ji)B流(liu)(liu)至(zhi)發射(she)(she)極(ji)E的(de)電流(liu)(liu)叫做基極(ji)電流(liu)(liu)Ib；把從集電極(ji)C流(liu)(liu)至(zhi)發射(she)(she)極(ji)E的(de)電流(liu)(liu)叫做集電極(ji)電流(liu)(liu) Ic。這兩個(ge)電流(liu)(liu)的(de)方(fang)向都是(shi)流(liu)(liu)出發射(she)(she)極(ji)的(de)，所(suo)以發射(she)(she)極(ji)E上(shang)就用了一個(ge)箭(jian)頭來表(biao)示電流(liu)(liu)的(de)方(fang)向。
三(san)(san)極(ji)(ji)(ji)管(guan)(guan)是一種控制(zhi)元件(jian)，主要用來控制(zhi)電(dian)(dian)(dian)(dian)流的(de)(de)(de)大小(xiao)(xiao)，以共發射極(ji)(ji)(ji)接法為例（信(xin)號從基(ji)(ji)極(ji)(ji)(ji)輸(shu)入，從集(ji)電(dian)(dian)(dian)(dian)極(ji)(ji)(ji)輸(shu)出(chu)，發射極(ji)(ji)(ji)接地），當(dang)基(ji)(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)壓UB有一個(ge)微小(xiao)(xiao)的(de)(de)(de)變(bian)(bian)化(hua)時(shi)，基(ji)(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流IB也會隨之有一小(xiao)(xiao)的(de)(de)(de)變(bian)(bian)化(hua)，受基(ji)(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流IB的(de)(de)(de)控制(zhi)，集(ji)電(dian)(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流IC會有一個(ge)很(hen)大的(de)(de)(de)變(bian)(bian)化(hua)，基(ji)(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流IB越大，集(ji)電(dian)(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流IC也越大，反(fan)之，基(ji)(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流越小(xiao)(xiao)，集(ji)電(dian)(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流也越小(xiao)(xiao)，即(ji)基(ji)(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流控制(zhi)集(ji)電(dian)(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流的(de)(de)(de)變(bian)(bian)化(hua)。但是集(ji)電(dian)(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流的(de)(de)(de)變(bian)(bian)化(hua)比基(ji)(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)流的(de)(de)(de)變(bian)(bian)化(hua)大得(de)多(duo)，這就(jiu)是三(san)(san)極(ji)(ji)(ji)管(guan)(guan)的(de)(de)(de)放大作用。IC 的(de)(de)(de)變(bian)(bian)化(hua)量與IB變(bian)(bian)化(hua)量之比叫做(zuo)三(san)(san)極(ji)(ji)(ji)管(guan)(guan)的(de)(de)(de)放大倍數(shu)β（β=ΔIC/ΔIB, Δ表示變(bian)(bian)化(hua)量。），三(san)(san)極(ji)(ji)(ji)管(guan)(guan)的(de)(de)(de)放大倍數(shu)β一般在幾十到幾百倍。
由于基(ji)區(qu)(qu)很薄,加上集電(dian)(dian)(dian)結的反偏，注入基(ji)區(qu)(qu)的電(dian)(dian)(dian)子(zi)大部(bu)分越過集電(dian)(dian)(dian)結進入集電(dian)(dian)(dian)區(qu)(qu)而形成(cheng)集電(dian)(dian)(dian)極電(dian)(dian)(dian)流Ic，只剩下很少（1-10%）的電(dian)(dian)(dian)子(zi)在基(ji)區(qu)(qu)的空穴(xue)進行(xing)復合，被復合掉的基(ji)區(qu)(qu)空穴(xue)由基(ji)極電(dian)(dian)(dian)源Eb重新(xin)補給，從而形成(cheng)了(le)基(ji)極電(dian)(dian)(dian)流Ib。根據電(dian)(dian)(dian)流連續(xu)性原理得(de)：
Ie=Ib+Ic
這(zhe)就(jiu)是說，在(zai)基極補充一個很小的(de)Ib，就(jiu)可以在(zai)集電極上得到一個較大的(de)Ic，這(zhe)就(jiu)是所(suo)謂(wei)電流放大作用(yong)，Ic與Ib是維持一定的(de)比例關系，即：
β1=Ic/Ib
式中：β1--稱(cheng)為直流放(fang)大倍數，
集(ji)電(dian)極電(dian)流的變化量△Ic與基極電(dian)流的變化量△Ib之比為：
β= △Ic/△Ib
式中β--稱為(wei)交流(liu)電流(liu)放大倍數，由于(yu)低頻時β1和β的數值相差不大，所以有(you)時為(wei)了方便起(qi)見，對兩者不作(zuo)嚴格(ge)區(qu)分，β值約為(wei)幾十(shi)至幾百。
α1=Ic/Ie(Ic與Ie是直(zhi)流通路中的電流大小)
式中(zhong)：α1也(ye)稱為直流(liu)放(fang)(fang)大倍數，一般在共(gong)基極組態放(fang)(fang)大電路中(zhong)使用，描述(shu)了發射極電流(liu)與集(ji)電極電流(liu)的關系。
α =△Ic/△Ie
表達式中的α為交流共基極電流放大(da)倍數。同理α與α1在小信(xin)號輸入(ru)時(shi)相(xiang)差也不大(da)。
對于兩個描述(shu)電流關系的(de)放(fang)大倍數有(you)以下關系β=a/（1-a）。
三極(ji)管(guan)的(de)放(fang)大(da)(da)作(zuo)用(yong)就是：集電(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)受基(ji)極(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)控制（假(jia)設(she)電(dian)(dian)(dian)(dian)(dian)源 能夠提供給集電(dian)(dian)(dian)(dian)(dian)極(ji)足夠大(da)(da)的(de)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)話），并且基(ji)極(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)很小的(de)變化(hua)(hua)(hua)，會(hui)引起集電(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)很大(da)(da)的(de)變化(hua)(hua)(hua)，且變化(hua)(hua)(hua)滿足一(yi)定的(de)比例(li)關系：集電(dian)(dian)(dian)(dian)(dian)極(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)變化(hua)(hua)(hua)量是基(ji)極(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)變 化(hua)(hua)(hua)量的(de)β倍，即電(dian)(dian)(dian)(dian)(dian)流(liu)變化(hua)(hua)(hua)被放(fang)大(da)(da)了β倍，所以我們把(ba)β叫做三極(ji)管(guan)的(de)放(fang)大(da)(da)倍數（β一(yi)般遠大(da)(da)于1，例(li)如(ru)幾十(shi)，幾百）。
