三極管，全稱半(ban)導(dao)體(ti)(ti)(ti)三極(ji)管，也稱雙極(ji)型晶體(ti)(ti)(ti)管、晶體(ti)(ti)(ti)三極(ji)管，是一種(zhong)控制電(dian)流的半(ban)導(dao)體(ti)(ti)(ti)器件其作(zuo)用是把微弱(ruo)信號放大(da)(da)成幅度(du)值較大(da)(da)的電(dian)信號， 也用作(zuo)無觸點開關。
三極管，是半導體基本元器件之一，具有電流放(fang)大作用，是電子電路(lu)的(de)核心元件(jian)。三(san)極管是在一塊半導體基(ji)片上制作兩(liang)個相距很近的(de)PN結(jie)，兩(liang)個PN結(jie)把整塊半導體分成三(san)部(bu)分，中(zhong)間部(bu)分是基(ji)區(qu)，兩(liang)側部(bu)分是發(fa)射(she)區(qu)和(he)集(ji)電區(qu)，排列方(fang)式(shi)有PNP和(he)NPN兩(liang)種(zhong)。
發射區(qu)(qu)(qu)和(he)基區(qu)(qu)(qu)之間的(de)PN結(jie)(jie)叫發射結(jie)(jie)，集(ji)(ji)電(dian)(dian)(dian)(dian)區(qu)(qu)(qu)和(he)基區(qu)(qu)(qu)之間的(de)PN結(jie)(jie)叫集(ji)(ji)電(dian)(dian)(dian)(dian)結(jie)(jie)。基區(qu)(qu)(qu)很薄，而發射區(qu)(qu)(qu)較(jiao)厚(hou)，雜質濃度大，PNP型(xing)(xing)三(san)極(ji)(ji)(ji)(ji)管(guan)發射區(qu)(qu)(qu)"發射"的(de)是(shi)(shi)空穴(xue)，其(qi)移(yi)(yi)動(dong)方(fang)向與電(dian)(dian)(dian)(dian)流方(fang)向一致，故發射極(ji)(ji)(ji)(ji)箭(jian)頭向里；NPN型(xing)(xing)三(san)極(ji)(ji)(ji)(ji)管(guan)發射區(qu)(qu)(qu)"發射"的(de)是(shi)(shi)自由(you)電(dian)(dian)(dian)(dian)子，其(qi)移(yi)(yi)動(dong)方(fang)向與電(dian)(dian)(dian)(dian)流方(fang)向相(xiang)反(fan)，故發射極(ji)(ji)(ji)(ji)箭(jian)頭向外。發射極(ji)(ji)(ji)(ji)箭(jian)頭指向也是(shi)(shi)PN結(jie)(jie)在正向電(dian)(dian)(dian)(dian)壓下的(de)導通方(fang)向。硅(gui)晶(jing)體(ti)三(san)極(ji)(ji)(ji)(ji)管(guan)和(he)鍺晶(jing)體(ti)三(san)極(ji)(ji)(ji)(ji)管(guan)都有PNP型(xing)(xing)和(he)NPN型(xing)(xing)兩種類型(xing)(xing)。從三(san)個區(qu)(qu)(qu)引出相(xiang)應的(de)電(dian)(dian)(dian)(dian)極(ji)(ji)(ji)(ji)，分別為基極(ji)(ji)(ji)(ji)b發射極(ji)(ji)(ji)(ji)e和(he)集(ji)(ji)電(dian)(dian)(dian)(dian)極(ji)(ji)(ji)(ji)c。
NPN型三極管(guan)
在制造(zao)三極管時，有(you)意(yi)識地使發射(she)區(qu)(qu)的(de)多數載流(liu)子(zi)(zi)(zi)濃度(du)大于基區(qu)(qu)的(de)，同時基區(qu)(qu)做得很(hen)薄，而且(qie)，要嚴格控制雜質含量，這樣，一旦接通(tong)電(dian)(dian)(dian)源(yuan)后(hou)，由于發射(she)結正偏(pian)，發射(she)區(qu)(qu)的(de)多數載流(liu)子(zi)(zi)(zi)（電(dian)(dian)(dian)子(zi)(zi)(zi)）及基區(qu)(qu)的(de)多數載流(liu)子(zi)(zi)(zi)（空(kong)穴）很(hen)容易(yi)地越過發射(she)結互相向對方擴散(san)，但因前(qian)者(zhe)的(de)濃度(du)基大于后(hou)者(zhe)，所以通(tong)過發射(she)結的(de)電(dian)(dian)(dian)流(liu)基本上是電(dian)(dian)(dian)子(zi)(zi)(zi)流(liu)，這股電(dian)(dian)(dian)子(zi)(zi)(zi)流(liu)稱為(wei)發射(she)極電(dian)(dian)(dian)流(liu)子(zi)(zi)(zi)。
三極(ji)(ji)管(guan)按材料分有(you)兩(liang)種：硅(gui)管(guan)和鍺管(guan)。而每一種又(you)有(you)NPN和PNP兩(liang)種結構形(xing)式，但使(shi)用最多(duo)的(de)是硅(gui)NPN和鍺PNP兩(liang)種三極(ji)(ji)管(guan)，（其中(zhong)，N表示在高純度硅(gui)中(zhong)加(jia)入磷(lin)，取(qu)代一些硅(gui)原(yuan)子(zi)，在電壓刺激下產(chan)生自由(you)電子(zi)導電，而p是加(jia)入硼取(qu)代硅(gui)，產(chan)生大量空穴利(li)于導電）；兩(liang)者除(chu)了電源極(ji)(ji)性不同外，其工作原(yuan)理都是相同的(de)，下面僅介紹NPN硅(gui)管(guan)的(de)電流放大原(yuan)理。
對于NPN管，它是由2塊N型半導(dao)體(ti)中間(jian)夾(jia)著一塊P型半導(dao)體(ti)所組(zu)成(cheng)，發射(she)區與基(ji)區之間(jian)形(xing)成(cheng)的PN結(jie)(jie)稱為發射(she)結(jie)(jie),而集電區與基(ji)區形(xing)成(cheng)的PN結(jie)(jie)稱為集電結(jie)(jie),三條引線分別(bie)稱為發射(she)極e （Emitter）、基(ji)極b (Base)和集電極c (Collector)。
當b點(dian)(dian)電(dian)位高于(yu)e點(dian)(dian)電(dian)位零點(dian)(dian)幾伏時(shi)，發射結處于(yu)正偏狀(zhuang)態，而C點(dian)(dian)電(dian)位高于(yu)b點(dian)(dian)電(dian)位幾伏時(shi)，集電(dian)結處于(yu)反偏狀(zhuang)態，集電(dian)極電(dian)源(yuan)Ec要(yao)高于(yu)基極電(dian)源(yuan)Eb。
我們把從(cong)基(ji)極(ji)(ji)B流(liu)(liu)至發射(she)(she)(she)極(ji)(ji)E的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)叫做基(ji)極(ji)(ji)電(dian)(dian)(dian)(dian)流(liu)(liu)Ib；把從(cong)集(ji)電(dian)(dian)(dian)(dian)極(ji)(ji)C流(liu)(liu)至發射(she)(she)(she)極(ji)(ji)E的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)叫做集(ji)電(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)流(liu)(liu) Ic。這兩(liang)個(ge)電(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)方向都是流(liu)(liu)出(chu)發射(she)(she)(she)極(ji)(ji)的(de)(de)(de)，所(suo)以發射(she)(she)(she)極(ji)(ji)E上就(jiu)用了(le)一(yi)個(ge)箭頭(tou)來表示電(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)方向。
三極(ji)(ji)(ji)管(guan)是一種控制(zhi)(zhi)元件(jian)，主(zhu)要用來(lai)控制(zhi)(zhi)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的大小(xiao)，以(yi)共發射極(ji)(ji)(ji)接法為(wei)例（信(xin)號從基(ji)極(ji)(ji)(ji)輸入，從集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)輸出，發射極(ji)(ji)(ji)接地），當(dang)基(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)壓UB有(you)一個(ge)微小(xiao)的變(bian)化(hua)(hua)時，基(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)IB也會(hui)隨之(zhi)有(you)一小(xiao)的變(bian)化(hua)(hua)，受基(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)IB的控制(zhi)(zhi)，集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)IC會(hui)有(you)一個(ge)很大的變(bian)化(hua)(hua)，基(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)IB越大，集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)IC也越大，反(fan)之(zhi)，基(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)越小(xiao)，集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)也越小(xiao)，即(ji)基(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)控制(zhi)(zhi)集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的變(bian)化(hua)(hua)。但是集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的變(bian)化(hua)(hua)比基(ji)極(ji)(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的變(bian)化(hua)(hua)大得多，這就是三極(ji)(ji)(ji)管(guan)的放大作用。IC 的變(bian)化(hua)(hua)量與IB變(bian)化(hua)(hua)量之(zhi)比叫做三極(ji)(ji)(ji)管(guan)的放大倍(bei)數β（β=ΔIC/ΔIB, Δ表示變(bian)化(hua)(hua)量。），三極(ji)(ji)(ji)管(guan)的放大倍(bei)數β一般在幾十到幾百(bai)倍(bei)。
由(you)于基(ji)區(qu)很薄,加上(shang)集電(dian)(dian)結的(de)(de)(de)反偏，注入基(ji)區(qu)的(de)(de)(de)電(dian)(dian)子大部分越過集電(dian)(dian)結進(jin)(jin)入集電(dian)(dian)區(qu)而形成(cheng)集電(dian)(dian)極電(dian)(dian)流(liu)(liu)Ic，只剩(sheng)下很少（1-10%）的(de)(de)(de)電(dian)(dian)子在(zai)基(ji)區(qu)的(de)(de)(de)空(kong)穴進(jin)(jin)行復(fu)(fu)合(he)，被復(fu)(fu)合(he)掉的(de)(de)(de)基(ji)區(qu)空(kong)穴由(you)基(ji)極電(dian)(dian)源Eb重新補給，從而形成(cheng)了基(ji)極電(dian)(dian)流(liu)(liu)Ib。根據電(dian)(dian)流(liu)(liu)連續性原理得：
Ie=Ib+Ic
這(zhe)就是(shi)說，在基極補(bu)充一(yi)個很(hen)小(xiao)的(de)(de)Ib，就可以在集電(dian)極上(shang)得到(dao)一(yi)個較(jiao)大的(de)(de)Ic，這(zhe)就是(shi)所謂電(dian)流放大作用，Ic與Ib是(shi)維持一(yi)定(ding)的(de)(de)比例關系，即(ji)：
β1=Ic/Ib
式中：β1--稱(cheng)為直流放大(da)倍數，
集電極電流(liu)的變(bian)化(hua)量△Ic與基極電流(liu)的變(bian)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(shu)，由于(yu)低頻(pin)時(shi)β1和β的數(shu)值(zhi)相(xiang)差不(bu)大，所以有(you)時(shi)為了方便(bian)起見，對兩者不(bu)作(zuo)嚴格區分，β值(zhi)約為幾(ji)(ji)十至幾(ji)(ji)百。
α1=Ic/Ie(Ic與Ie是直流(liu)通(tong)路中的電流(liu)大小)
式中：α1也稱為直流放大倍數，一般在(zai)共(gong)基極(ji)(ji)(ji)組態(tai)放大電(dian)路中使用，描述了發射極(ji)(ji)(ji)電(dian)流與集電(dian)極(ji)(ji)(ji)電(dian)流的(de)關系。
α =△Ic/△Ie
表達(da)式中的(de)α為交(jiao)流共基極電流放大倍數(shu)。同理(li)α與(yu)α1在小(xiao)信號輸入時相差也不大。
對于(yu)兩個描述電流關(guan)(guan)系的放大倍數有(you)以下關(guan)(guan)系β=a/（1-a）。
三極(ji)管的(de)(de)放(fang)大(da)作用就(jiu)是：集(ji)(ji)(ji)(ji)電(dian)(dian)極(ji)電(dian)(dian)流(liu)(liu)受基極(ji)電(dian)(dian)流(liu)(liu)的(de)(de)控(kong)制（假設電(dian)(dian)源 能夠提供給集(ji)(ji)(ji)(ji)電(dian)(dian)極(ji)足夠大(da)的(de)(de)電(dian)(dian)流(liu)(liu)的(de)(de)話），并且(qie)基極(ji)電(dian)(dian)流(liu)(liu)很小(xiao)的(de)(de)變(bian)化(hua)，會引起集(ji)(ji)(ji)(ji)電(dian)(dian)極(ji)電(dian)(dian)流(liu)(liu)很大(da)的(de)(de)變(bian)化(hua)，且(qie)變(bian)化(hua)滿足一定的(de)(de)比例(li)(li)關系：集(ji)(ji)(ji)(ji)電(dian)(dian)極(ji)電(dian)(dian)流(liu)(liu)的(de)(de)變(bian)化(hua)量是基極(ji)電(dian)(dian)流(liu)(liu)變(bian) 化(hua)量的(de)(de)β倍，即(ji)電(dian)(dian)流(liu)(liu)變(bian)化(hua)被放(fang)大(da)了β倍，所以我們(men)把β叫做三極(ji)管的(de)(de)放(fang)大(da)倍數（β一般遠大(da)于1，例(li)(li)如幾(ji)十(shi)，幾(ji)百）。
