【場(chang)效(xiao)應管工作(zuo)原(yuan)理(li)】場(chang)效(xiao)應管的(de)工作(zuo)原(yuan)理(li)是什么(me) 場(chang)效(xiao)應管的(de)特點

場效應管的工作原理是什么

場效應管工作原理用一句話說，就(jiu)是(shi)“漏(lou)極(ji)(ji)(ji)(ji)-源(yuan)極(ji)(ji)(ji)(ji)間(jian)流經(jing)溝(gou)道的(de)ID，用以(yi)柵(zha)極(ji)(ji)(ji)(ji)與(yu)溝(gou)道間(jian)的(de)pn結形成(cheng)的(de)反偏的(de)柵(zha)極(ji)(ji)(ji)(ji)電(dian)壓控制(zhi)ID”。更(geng)正確地說，ID流經(jing)通路(lu)的(de)寬(kuan)度(du)，即溝(gou)道截面積，它(ta)是(shi)由pn結反偏的(de)變(bian)(bian)化(hua)，產生耗盡層擴展變(bian)(bian)化(hua)控制(zhi)的(de)緣故(gu)。在VGS=0的(de)非飽和區域，表示(shi)的(de)過渡(du)層的(de)擴展因為(wei)不(bu)很大，根據漏(lou)極(ji)(ji)(ji)(ji)-源(yuan)極(ji)(ji)(ji)(ji)間(jian)所(suo)加VDS的(de)電(dian)場，源(yuan)極(ji)(ji)(ji)(ji)區域的(de)某(mou)些電(dian)子被漏(lou)極(ji)(ji)(ji)(ji)拉(la)去，即從漏(lou)極(ji)(ji)(ji)(ji)向(xiang)源(yuan)極(ji)(ji)(ji)(ji)有電(dian)流ID流動(dong)。從門極(ji)(ji)(ji)(ji)向(xiang)漏(lou)極(ji)(ji)(ji)(ji)擴展的(de)過度(du)層將溝(gou)道的(de)一部(bu)分構成(cheng)堵塞型，ID飽和。將這(zhe)種狀態(tai)稱為(wei)夾斷。這(zhe)意味著過渡(du)層將溝(gou)道的(de)一部(bu)分阻擋，并不(bu)是(shi)電(dian)流被切斷。

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在過(guo)渡(du)(du)層由(you)(you)(you)于沒有電(dian)(dian)子(zi)、空穴的(de)(de)自由(you)(you)(you)移動，在理想狀(zhuang)態下幾乎具有絕緣(yuan)特性，通(tong)常電(dian)(dian)流(liu)也難(nan)流(liu)動。但是此時漏極-源極間的(de)(de)電(dian)(dian)場，實際上是兩(liang)個過(guo)渡(du)(du)層接觸(chu)漏極與門極下部(bu)附(fu)近，由(you)(you)(you)于漂(piao)移電(dian)(dian)場拉(la)去(qu)的(de)(de)高速電(dian)(dian)子(zi)通(tong)過(guo)過(guo)渡(du)(du)層。因漂(piao)移電(dian)(dian)場的(de)(de)強度幾乎不變(bian)產生ID的(de)(de)飽和現象(xiang)。其次，VGS向負的(de)(de)方向變(bian)化，讓VGS=VGS(off)，此時過(guo)渡(du)(du)層大致成為覆(fu)蓋全區(qu)域(yu)的(de)(de)狀(zhuang)態。而且VDS的(de)(de)電(dian)(dian)場大部(bu)分(fen)加到過(guo)渡(du)(du)層上，將電(dian)(dian)子(zi)拉(la)向漂(piao)移方向的(de)(de)電(dian)(dian)場，只(zhi)有靠近源極的(de)(de)很短部(bu)分(fen)，這更使(shi)電(dian)(dian)流(liu)不能流(liu)通(tong)。

MOS場效應管電源開關電路

MOS場效應管也(ye)(ye)被稱(cheng)為(wei)金屬氧(yang)化物半導(dao)體(ti)(ti)場(chang)(chang)效(xiao)(xiao)應管(guan)(MetalOxideSemiconductor FieldEffect Transistor, MOSFET)。它(ta)一般(ban)有(you)耗盡型和(he)增強型兩種(zhong)。增強型MOS場(chang)(chang)效(xiao)(xiao)應管(guan)可分(fen)為(wei)NPN型PNP型。NPN型通(tong)常稱(cheng)為(wei)N溝道(dao)型，PNP型也(ye)(ye)叫(jiao)P溝道(dao)型。對于N溝道(dao)的(de)(de)(de)場(chang)(chang)效(xiao)(xiao)應管(guan)其源極(ji)(ji)和(he)漏(lou)極(ji)(ji)接在(zai)N型半導(dao)體(ti)(ti)上，同(tong)(tong)樣對于P溝道(dao)的(de)(de)(de)場(chang)(chang)效(xiao)(xiao)應管(guan)其源極(ji)(ji)和(he)漏(lou)極(ji)(ji)則接在(zai)P型半導(dao)體(ti)(ti)上。場(chang)(chang)效(xiao)(xiao)應管(guan)的(de)(de)(de)輸出電流是(shi)由(you)輸入的(de)(de)(de)電壓（或(huo)稱(cheng)電場(chang)(chang)）控制，可以認(ren)為(wei)輸入電流極(ji)(ji)小或(huo)沒有(you)輸入電流，這使得該器(qi)件有(you)很高的(de)(de)(de)輸入阻抗，同(tong)(tong)時這也(ye)(ye)是(shi)我(wo)們稱(cheng)之為(wei)場(chang)(chang)效(xiao)(xiao)應管(guan)的(de)(de)(de)原因(yin)。

在(zai)(zai)二極(ji)(ji)管加上(shang)正向(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)（P端(duan)接正極(ji)(ji)，N端(duan)接負極(ji)(ji)）時(shi)(shi)，二極(ji)(ji)管導(dao)通(tong)，其PN結有電(dian)(dian)(dian)(dian)(dian)流通(tong)過(guo)。這是(shi)因為(wei)(wei)(wei)在(zai)(zai)P型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)端(duan)為(wei)(wei)(wei)正電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)時(shi)(shi)，N型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)內的(de)(de)(de)負電(dian)(dian)(dian)(dian)(dian)子(zi)被吸引(yin)而涌(yong)向(xiang)(xiang)加有正電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)(de)(de)P型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)端(duan)，而P型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)端(duan)內的(de)(de)(de)正電(dian)(dian)(dian)(dian)(dian)子(zi)則(ze)朝N型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)端(duan)運(yun)動，從而形成導(dao)通(tong)電(dian)(dian)(dian)(dian)(dian)流。同理，當(dang)二極(ji)(ji)管加上(shang)反(fan)向(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)（P端(duan)接負極(ji)(ji)，N端(duan)接正極(ji)(ji)）時(shi)(shi)，這時(shi)(shi)在(zai)(zai)P型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)端(duan)為(wei)(wei)(wei)負電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，正電(dian)(dian)(dian)(dian)(dian)子(zi)被聚(ju)集在(zai)(zai)P型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)端(duan)，負電(dian)(dian)(dian)(dian)(dian)子(zi)則(ze)聚(ju)集在(zai)(zai)N型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)端(duan)，電(dian)(dian)(dian)(dian)(dian)子(zi)不移動，其PN結沒(mei)有電(dian)(dian)(dian)(dian)(dian)流通(tong)過(guo)，二極(ji)(ji)管截(jie)止(zhi)(zhi)。在(zai)(zai)柵(zha)極(ji)(ji)沒(mei)有電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)時(shi)(shi)，由前(qian)面(mian)分析可(ke)知，在(zai)(zai)源(yuan)極(ji)(ji)與漏(lou)極(ji)(ji)之間(jian)(jian)(jian)不會(hui)有電(dian)(dian)(dian)(dian)(dian)流流過(guo)，此時(shi)(shi)場效應管處(chu)與截(jie)止(zhi)(zhi)狀態（圖7a）。當(dang)有一(yi)(yi)個正電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)加在(zai)(zai)N溝(gou)道(dao)的(de)(de)(de)MOS場效應管柵(zha)極(ji)(ji)上(shang)時(shi)(shi)，由于電(dian)(dian)(dian)(dian)(dian)場的(de)(de)(de)作用，此時(shi)(shi)N型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)的(de)(de)(de)源(yuan)極(ji)(ji)和(he)漏(lou)極(ji)(ji)的(de)(de)(de)負電(dian)(dian)(dian)(dian)(dian)子(zi)被吸引(yin)出來而涌(yong)向(xiang)(xiang)柵(zha)極(ji)(ji)，但由于氧(yang)化膜的(de)(de)(de)阻擋(dang)，使得電(dian)(dian)(dian)(dian)(dian)子(zi)聚(ju)集在(zai)(zai)兩(liang)個N溝(gou)道(dao)之間(jian)(jian)(jian)的(de)(de)(de)P型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)中（見圖7b），從而形成電(dian)(dian)(dian)(dian)(dian)流，使源(yuan)極(ji)(ji)和(he)漏(lou)極(ji)(ji)之間(jian)(jian)(jian)導(dao)通(tong)。可(ke)以想像為(wei)(wei)(wei)兩(liang)個N型(xing)(xing)半(ban)導(dao)體(ti)(ti)(ti)之間(jian)(jian)(jian)為(wei)(wei)(wei)一(yi)(yi)條溝(gou)，柵(zha)極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)(de)(de)建立相當(dang)于為(wei)(wei)(wei)它們(men)之間(jian)(jian)(jian)搭了(le)一(yi)(yi)座橋(qiao)梁，該橋(qiao)的(de)(de)(de)大小由柵(zha)壓(ya)(ya)(ya)的(de)(de)(de)大小決定。

C-MOS場效應管

電路將一個增強型P溝道MOS場效應管和一個增強型N溝道MOS場效應管組合在(zai)一起使用。當輸(shu)入(ru)端為低電(dian)平時(shi)，P溝(gou)(gou)道(dao)MOS場效應(ying)(ying)管導通(tong)，輸(shu)出(chu)端與(yu)電(dian)源(yuan)正極(ji)接(jie)通(tong)。當輸(shu)入(ru)端為高電(dian)平時(shi)，N溝(gou)(gou)道(dao)MOS場效應(ying)(ying)管導通(tong)，輸(shu)出(chu)端與(yu)電(dian)源(yuan)地接(jie)通(tong)。在(zai)該電(dian)路(lu)(lu)中，P溝(gou)(gou)道(dao)MOS場效應(ying)(ying)管和N溝(gou)(gou)道(dao)MOS場效應(ying)(ying)管總是在(zai)相反的(de)(de)狀態(tai)下工(gong)作，其相位(wei)輸(shu)入(ru)端和輸(shu)出(chu)端相反。通(tong)過這種(zhong)工(gong)作方式(shi)我們可以獲得較大(da)的(de)(de)電(dian)流(liu)輸(shu)出(chu)。同時(shi)由于漏電(dian)流(liu)的(de)(de)影響，使得柵壓(ya)在(zai)還(huan)沒有到0V，通(tong)常在(zai)柵極(ji)電(dian)壓(ya)小于1到2V時(shi)，MOS場效應(ying)(ying)管既被關斷。不(bu)同場效應(ying)(ying)管其關斷電(dian)壓(ya)略(lve)有不(bu)同。也正因(yin)為如此，使得該電(dian)路(lu)(lu)不(bu)會因(yin)為兩(liang)管同時(shi)導通(tong)而造成電(dian)源(yuan)短路(lu)(lu)。

場效應管的特點

（1）場效應管是電壓控(kong)制器(qi)件，它通過VGS(柵源電壓)來控(kong)制ID（漏(lou)極電流）；

（2）場效應管的控制輸入端電流(liu)極小，因(yin)此它的輸入電阻（107～1012Ω）很(hen)大。

（3）它是利(li)用多數載流子(zi)導電(dian)，因此它的溫度(du)穩定性較(jiao)好；

（4）它組成的放大電路(lu)的電壓放大系數要(yao)小于(yu)三(san)極管(guan)組成放大電路(lu)的電壓放大系數；

（5）場效應(ying)管的(de)抗輻射能力(li)強；

（6）由于它不存(cun)在雜亂運動的電子擴散(san)引起的散(san)粒(li)噪聲，所以噪聲低。