三(san)極管，全(quan)稱半(ban)導體三極(ji)管(guan)，也稱雙極(ji)型晶(jing)體管(guan)、晶(jing)體三極(ji)管(guan)，是(shi)一種控制(zhi)電流的半(ban)導體器件其作(zuo)用是(shi)把微(wei)弱信(xin)號(hao)放(fang)大(da)成幅度值較大(da)的電信(xin)號(hao)， 也用作(zuo)無觸點開關。
三極管，是半導體基本元器件(jian)之一(yi)，具有電流(liu)放大作用，是電子電路的(de)核心元件。三極管是(shi)在一(yi)塊半(ban)導(dao)(dao)體基片上制作兩(liang)個(ge)相距很近的(de)PN結(jie)，兩(liang)個(ge)PN結(jie)把整塊半(ban)導(dao)(dao)體分(fen)成三部分(fen)，中間部分(fen)是(shi)基區，兩(liang)側部分(fen)是(shi)發(fa)射區和(he)集電區，排列(lie)方式有PNP和(he)NPN兩(liang)種。
發射區(qu)和(he)基區(qu)之(zhi)間(jian)的(de)PN結(jie)叫(jiao)發射結(jie)，集電(dian)區(qu)和(he)基區(qu)之(zhi)間(jian)的(de)PN結(jie)叫(jiao)集電(dian)結(jie)。基區(qu)很薄，而發射區(qu)較厚，雜質濃度(du)大，PNP型三(san)(san)極(ji)(ji)管發射區(qu)"發射"的(de)是空穴，其移動方向(xiang)(xiang)與(yu)電(dian)流(liu)方向(xiang)(xiang)一(yi)致，故發射極(ji)(ji)箭頭向(xiang)(xiang)里(li)；NPN型三(san)(san)極(ji)(ji)管發射區(qu)"發射"的(de)是自由電(dian)子(zi)，其移動方向(xiang)(xiang)與(yu)電(dian)流(liu)方向(xiang)(xiang)相反(fan)，故發射極(ji)(ji)箭頭向(xiang)(xiang)外。發射極(ji)(ji)箭頭指向(xiang)(xiang)也是PN結(jie)在正向(xiang)(xiang)電(dian)壓下的(de)導(dao)通(tong)方向(xiang)(xiang)。硅(gui)晶(jing)體(ti)三(san)(san)極(ji)(ji)管和(he)鍺(zang)晶(jing)體(ti)三(san)(san)極(ji)(ji)管都有PNP型和(he)NPN型兩種類(lei)型。從三(san)(san)個區(qu)引出相應的(de)電(dian)極(ji)(ji)，分別為基極(ji)(ji)b發射極(ji)(ji)e和(he)集電(dian)極(ji)(ji)c。
NPN型三極(ji)管
在制造三極(ji)管時(shi)，有(you)意識地使發(fa)(fa)射區的(de)(de)多(duo)數(shu)載(zai)(zai)(zai)流子(zi)(zi)濃(nong)度(du)(du)大于基(ji)區的(de)(de)，同時(shi)基(ji)區做得很薄，而且，要嚴格控制雜質含量，這樣，一旦接(jie)通(tong)電(dian)(dian)(dian)源后，由(you)于發(fa)(fa)射結(jie)正偏，發(fa)(fa)射區的(de)(de)多(duo)數(shu)載(zai)(zai)(zai)流子(zi)(zi)（電(dian)(dian)(dian)子(zi)(zi)）及基(ji)區的(de)(de)多(duo)數(shu)載(zai)(zai)(zai)流子(zi)(zi)（空穴）很容易地越過發(fa)(fa)射結(jie)互相向對(dui)方擴(kuo)散，但(dan)因(yin)前(qian)者(zhe)的(de)(de)濃(nong)度(du)(du)基(ji)大于后者(zhe)，所以(yi)通(tong)過發(fa)(fa)射結(jie)的(de)(de)電(dian)(dian)(dian)流基(ji)本上是電(dian)(dian)(dian)子(zi)(zi)流，這股電(dian)(dian)(dian)子(zi)(zi)流稱為發(fa)(fa)射極(ji)電(dian)(dian)(dian)流子(zi)(zi)。
三極管(guan)按材料分(fen)有(you)兩種：硅(gui)(gui)管(guan)和鍺(zang)管(guan)。而(er)每一(yi)種又有(you)NPN和PNP兩種結構形(xing)式(shi)，但使用最多(duo)的(de)是(shi)硅(gui)(gui)NPN和鍺(zang)PNP兩種三極管(guan)，（其(qi)中，N表(biao)示(shi)在高純(chun)度硅(gui)(gui)中加入磷，取代一(yi)些硅(gui)(gui)原(yuan)(yuan)子，在電(dian)(dian)壓刺(ci)激下產生(sheng)自(zi)由電(dian)(dian)子導電(dian)(dian)，而(er)p是(shi)加入硼取代硅(gui)(gui)，產生(sheng)大量(liang)空穴(xue)利(li)于導電(dian)(dian)）；兩者(zhe)除(chu)了電(dian)(dian)源極性不同外，其(qi)工(gong)作(zuo)原(yuan)(yuan)理都是(shi)相同的(de)，下面僅介(jie)紹NPN硅(gui)(gui)管(guan)的(de)電(dian)(dian)流放(fang)大原(yuan)(yuan)理。
對于NPN管，它是由2塊N型半導體中(zhong)間夾著一(yi)塊P型半導體所(suo)組成(cheng)，發射區與基(ji)區之間形成(cheng)的PN結稱(cheng)(cheng)(cheng)為(wei)發射結,而集電區與基(ji)區形成(cheng)的PN結稱(cheng)(cheng)(cheng)為(wei)集電結,三條引(yin)線分別稱(cheng)(cheng)(cheng)為(wei)發射極(ji)(ji)(ji)e （Emitter）、基(ji)極(ji)(ji)(ji)b (Base)和集電極(ji)(ji)(ji)c (Collector)。
當(dang)b點(dian)(dian)電(dian)(dian)位高(gao)于(yu)e點(dian)(dian)電(dian)(dian)位零(ling)點(dian)(dian)幾(ji)伏時，發射結處(chu)于(yu)正(zheng)偏狀態，而C點(dian)(dian)電(dian)(dian)位高(gao)于(yu)b點(dian)(dian)電(dian)(dian)位幾(ji)伏時，集電(dian)(dian)結處(chu)于(yu)反(fan)偏狀態，集電(dian)(dian)極電(dian)(dian)源Ec要(yao)高(gao)于(yu)基(ji)極電(dian)(dian)源Eb。
我們把(ba)從基極(ji)(ji)(ji)B流(liu)(liu)(liu)至發射(she)極(ji)(ji)(ji)E的電(dian)(dian)(dian)流(liu)(liu)(liu)叫(jiao)做基極(ji)(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)Ib；把(ba)從集電(dian)(dian)(dian)極(ji)(ji)(ji)C流(liu)(liu)(liu)至發射(she)極(ji)(ji)(ji)E的電(dian)(dian)(dian)流(liu)(liu)(liu)叫(jiao)做集電(dian)(dian)(dian)極(ji)(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu) Ic。這兩個電(dian)(dian)(dian)流(liu)(liu)(liu)的方向都是(shi)流(liu)(liu)(liu)出發射(she)極(ji)(ji)(ji)的，所以發射(she)極(ji)(ji)(ji)E上(shang)就用了一(yi)個箭頭來表示電(dian)(dian)(dian)流(liu)(liu)(liu)的方向。
三極(ji)(ji)管是一(yi)種控(kong)(kong)(kong)制(zhi)元(yuan)件，主要用(yong)來控(kong)(kong)(kong)制(zhi)電(dian)(dian)(dian)流(liu)(liu)(liu)的(de)(de)(de)大(da)(da)小(xiao)，以共發(fa)射(she)極(ji)(ji)接法(fa)為例（信號(hao)從基(ji)極(ji)(ji)輸入，從集(ji)電(dian)(dian)(dian)極(ji)(ji)輸出，發(fa)射(she)極(ji)(ji)接地），當基(ji)極(ji)(ji)電(dian)(dian)(dian)壓UB有(you)(you)一(yi)個(ge)微(wei)小(xiao)的(de)(de)(de)變(bian)(bian)(bian)(bian)(bian)化(hua)(hua)時(shi)，基(ji)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)IB也會(hui)隨之(zhi)有(you)(you)一(yi)小(xiao)的(de)(de)(de)變(bian)(bian)(bian)(bian)(bian)化(hua)(hua)，受基(ji)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)IB的(de)(de)(de)控(kong)(kong)(kong)制(zhi)，集(ji)電(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)IC會(hui)有(you)(you)一(yi)個(ge)很大(da)(da)的(de)(de)(de)變(bian)(bian)(bian)(bian)(bian)化(hua)(hua)，基(ji)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)IB越大(da)(da)，集(ji)電(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)IC也越大(da)(da)，反之(zhi)，基(ji)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)越小(xiao)，集(ji)電(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)也越小(xiao)，即(ji)基(ji)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)控(kong)(kong)(kong)制(zhi)集(ji)電(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)的(de)(de)(de)變(bian)(bian)(bian)(bian)(bian)化(hua)(hua)。但是集(ji)電(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)的(de)(de)(de)變(bian)(bian)(bian)(bian)(bian)化(hua)(hua)比(bi)基(ji)極(ji)(ji)電(dian)(dian)(dian)流(liu)(liu)(liu)的(de)(de)(de)變(bian)(bian)(bian)(bian)(bian)化(hua)(hua)大(da)(da)得多，這就是三極(ji)(ji)管的(de)(de)(de)放(fang)大(da)(da)作用(yong)。IC 的(de)(de)(de)變(bian)(bian)(bian)(bian)(bian)化(hua)(hua)量與IB變(bian)(bian)(bian)(bian)(bian)化(hua)(hua)量之(zhi)比(bi)叫做三極(ji)(ji)管的(de)(de)(de)放(fang)大(da)(da)倍(bei)數β（β=ΔIC/ΔIB, Δ表示變(bian)(bian)(bian)(bian)(bian)化(hua)(hua)量。），三極(ji)(ji)管的(de)(de)(de)放(fang)大(da)(da)倍(bei)數β一(yi)般在幾(ji)十到幾(ji)百倍(bei)。
由(you)于基(ji)區很薄(bo),加上集電(dian)(dian)結的(de)反(fan)偏，注入(ru)基(ji)區的(de)電(dian)(dian)子大部分越過集電(dian)(dian)結進入(ru)集電(dian)(dian)區而(er)形(xing)成集電(dian)(dian)極電(dian)(dian)流Ic，只剩下(xia)很少（1-10%）的(de)電(dian)(dian)子在(zai)基(ji)區的(de)空穴(xue)進行復(fu)合(he)，被(bei)復(fu)合(he)掉的(de)基(ji)區空穴(xue)由(you)基(ji)極電(dian)(dian)源Eb重(zhong)新補給，從而(er)形(xing)成了基(ji)極電(dian)(dian)流Ib。根據電(dian)(dian)流連續性(xing)原(yuan)理得：
Ie=Ib+Ic
這就是說，在基極補充一個(ge)很小的Ib，就可(ke)以在集電極上得到(dao)一個(ge)較大的Ic，這就是所(suo)謂電流放(fang)大作用(yong)，Ic與Ib是維持(chi)一定的比例關系，即：
β1=Ic/Ib
式中：β1--稱為直流(liu)放(fang)大倍數，
集(ji)電(dian)(dian)極(ji)(ji)電(dian)(dian)流的變(bian)化量(liang)△Ic與基極(ji)(ji)電(dian)(dian)流的變(bian)化量(liang)△Ib之比為(wei)：
β= △Ic/△Ib
式中β--稱(cheng)為交(jiao)流電(dian)流放大(da)倍數，由于低頻時β1和(he)β的數值相(xiang)差不大(da)，所以有(you)時為了方便起見，對兩(liang)者不作嚴格區分，β值約為幾十(shi)至幾百。
α1=Ic/Ie(Ic與Ie是直流通路中的電(dian)流大小(xiao))
式中：α1也(ye)稱為(wei)直(zhi)流(liu)放(fang)大倍數，一般在共基極(ji)組態放(fang)大電路(lu)中使用，描述(shu)了發射極(ji)電流(liu)與集電極(ji)電流(liu)的關系(xi)。
α =△Ic/△Ie
表達(da)式中的α為交流(liu)共基極電(dian)流(liu)放大倍數(shu)。同理α與α1在小信號輸(shu)入時相(xiang)差也(ye)不大。
對于兩個(ge)描述電(dian)流(liu)關系的放大倍數有(you)以下關系β=a/（1-a）。
三(san)極(ji)(ji)管的(de)(de)放(fang)(fang)大(da)作用就(jiu)是：集電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)受基極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)控制(zhi)（假設電(dian)(dian)(dian)(dian)(dian)源 能(neng)夠提供給(gei)集電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)足(zu)夠大(da)的(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)話），并且(qie)基極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)很小的(de)(de)變化(hua)(hua)(hua)，會引起集電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)很大(da)的(de)(de)變化(hua)(hua)(hua)，且(qie)變化(hua)(hua)(hua)滿(man)足(zu)一定的(de)(de)比例(li)關系：集電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)變化(hua)(hua)(hua)量是基極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)流(liu)變 化(hua)(hua)(hua)量的(de)(de)β倍，即電(dian)(dian)(dian)(dian)(dian)流(liu)變化(hua)(hua)(hua)被放(fang)(fang)大(da)了β倍，所以我們把β叫做三(san)極(ji)(ji)管的(de)(de)放(fang)(fang)大(da)倍數(shu)（β一般(ban)遠大(da)于1，例(li)如幾十，幾百）。
