利盈娱乐(中国)创新平台有限公司

一、场效应管是什么

场效应管是场效应晶体管（Field Effect Transistor缩写(FET)）的简称。主要有两种类型（junction FET—JFET)和金属 - 氧化物半导体场效应管（metal-oxide semiconductor FET，简称MOS-FET）。由多数载流子参与导电，也称为单极型晶体管。它属于电压控制型半导体器件。具有输入电阻高（107～1015Ω）、噪声小、功耗低、动态范围大、易于集成、没有二次击穿现象、安全工作区域宽等优点，现已成为双极型晶体管和功率晶体管的强大竞争者。

二、场效应管工作原理

场(chang)效应管(guan)工作原(yuan)理(li)用(yong)一句话说，就是(shi)“漏极(ji)(ji)(ji)-源(yuan)极(ji)(ji)(ji)间流经沟(gou)(gou)道(dao)的(de)ID，用(yong)以栅极(ji)(ji)(ji)与沟(gou)(gou)道(dao)间的(de)pn结形(xing)成的(de)反(fan)偏的(de)栅极(ji)(ji)(ji)电(dian)压控制ID”。更正确地说，ID流经通路(lu)的(de)宽度(du)，即沟(gou)(gou)道(dao)截(jie)面积，它(ta)是(shi)由pn结反(fan)偏的(de)变(bian)化(hua)，产生耗(hao)尽层(ceng)(ceng)扩展(zhan)(zhan)变(bian)化(hua)控制的(de)缘故(gu)。在VGS=0的(de)非饱和(he)(he)区(qu)域(yu)，表示的(de)过(guo)渡层(ceng)(ceng)的(de)扩展(zhan)(zhan)因为不很大，根据漏极(ji)(ji)(ji)-源(yuan)极(ji)(ji)(ji)间所加(jia)VDS的(de)电(dian)场(chang)，源(yuan)极(ji)(ji)(ji)区(qu)域(yu)的(de)某(mou)些电(dian)子(zi)被漏极(ji)(ji)(ji)拉去，即从(cong)漏极(ji)(ji)(ji)向(xiang)源(yuan)极(ji)(ji)(ji)有电(dian)流ID流动。从(cong)门极(ji)(ji)(ji)向(xiang)漏极(ji)(ji)(ji)扩展(zhan)(zhan)的(de)过(guo)度(du)层(ceng)(ceng)将沟(gou)(gou)道(dao)的(de)一部分(fen)构成堵塞型，ID饱和(he)(he)。将这种状态称(cheng)为夹断(duan)。这意味着过(guo)渡层(ceng)(ceng)将沟(gou)(gou)道(dao)的(de)一部分(fen)阻(zu)挡，并不是(shi)电(dian)流被切断(duan)。

 在(zai)过(guo)渡(du)层由(you)于(yu)没有(you)电(dian)(dian)子(zi)、空穴的(de)自由(you)移动(dong)，在(zai)理想状态下(xia)(xia)几乎具有(you)绝(jue)缘特性，通(tong)常电(dian)(dian)流(liu)也难流(liu)动(dong)。但是此时(shi)漏(lou)(lou)极-源极间的(de)电(dian)(dian)场(chang)，实际上是两个过(guo)渡(du)层接触(chu)漏(lou)(lou)极与(yu)门极下(xia)(xia)部附(fu)近，由(you)于(yu)漂(piao)(piao)移电(dian)(dian)场(chang)拉去的(de)高速电(dian)(dian)子(zi)通(tong)过(guo)过(guo)渡(du)层。因漂(piao)(piao)移电(dian)(dian)场(chang)的(de)强度几乎不变产生ID的(de)饱(bao)和现象。其次，VGS向(xiang)负的(de)方向(xiang)变化，让VGS=VGS(off)，此时(shi)过(guo)渡(du)层大致(zhi)成为覆盖(gai)全区域的(de)状态。而且VDS的(de)电(dian)(dian)场(chang)大部分加到过(guo)渡(du)层上，将电(dian)(dian)子(zi)拉向(xiang)漂(piao)(piao)移方向(xiang)的(de)电(dian)(dian)场(chang)，只有(you)靠近源极的(de)很短部分，这更使电(dian)(dian)流(liu)不能(neng)流(liu)通(tong)。

1、MOS场效应管电源开关电路

MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)也被称(cheng)(cheng)为金属氧化物半(ban)导(dao)体场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)(MetalOxideSemiconductor   FieldEffectTransistor,MOSFET)。它(ta)一般有耗(hao)尽型(xing)(xing)(xing)(xing)(xing)和(he)增(zeng)强型(xing)(xing)(xing)(xing)(xing)两种。增(zeng)强型(xing)(xing)(xing)(xing)(xing)MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)可(ke)分为NPN型(xing)(xing)(xing)(xing)(xing)PNP型(xing)(xing)(xing)(xing)(xing)。NPN型(xing)(xing)(xing)(xing)(xing)通常称(cheng)(cheng)为N沟(gou)道(dao)型(xing)(xing)(xing)(xing)(xing)，PNP型(xing)(xing)(xing)(xing)(xing)也叫P沟(gou)道(dao)型(xing)(xing)(xing)(xing)(xing)。对于N沟(gou)道(dao)的(de)场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)其(qi)源极和(he)漏极接(jie)在N型(xing)(xing)(xing)(xing)(xing)半(ban)导(dao)体上，同样(yang)对于P沟(gou)道(dao)的(de)场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)其(qi)源极和(he)漏极则接(jie)在P型(xing)(xing)(xing)(xing)(xing)半(ban)导(dao)体上。场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)的(de)输(shu)出电(dian)流是(shi)由输(shu)入(ru)的(de)电(dian)压（或(huo)称(cheng)(cheng)电(dian)场(chang)(chang)）控制(zhi)，可(ke)以认为输(shu)入(ru)电(dian)流极小或(huo)没有输(shu)入(ru)电(dian)流，这使得(de)该器件有很(hen)高的(de)输(shu)入(ru)阻(zu)抗，同时(shi)这也是(shi)我们称(cheng)(cheng)之为场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)的(de)原因。

在二(er)极(ji)(ji)(ji)(ji)(ji)(ji)管(guan)加上正(zheng)(zheng)(zheng)向(xiang)电(dian)(dian)(dian)(dian)(dian)压（P端(duan)(duan)接正(zheng)(zheng)(zheng)极(ji)(ji)(ji)(ji)(ji)(ji)，N端(duan)(duan)接负(fu)极(ji)(ji)(ji)(ji)(ji)(ji)）时(shi)(shi)，二(er)极(ji)(ji)(ji)(ji)(ji)(ji)管(guan)导(dao)(dao)(dao)(dao)通(tong)(tong)(tong)，其PN结有电(dian)(dian)(dian)(dian)(dian)流通(tong)(tong)(tong)过。这(zhei)是(shi)因为在P型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)端(duan)(duan)为正(zheng)(zheng)(zheng)电(dian)(dian)(dian)(dian)(dian)压时(shi)(shi)，N型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)内的(de)负(fu)电(dian)(dian)(dian)(dian)(dian)子(zi)(zi)被(bei)吸(xi)引而(er)涌向(xiang)加有正(zheng)(zheng)(zheng)电(dian)(dian)(dian)(dian)(dian)压的(de)P型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)端(duan)(duan)，而(er)P型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)端(duan)(duan)内的(de)正(zheng)(zheng)(zheng)电(dian)(dian)(dian)(dian)(dian)子(zi)(zi)则(ze)朝N型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)端(duan)(duan)运动(dong)，从(cong)(cong)而(er)形成导(dao)(dao)(dao)(dao)通(tong)(tong)(tong)电(dian)(dian)(dian)(dian)(dian)流。同理，当(dang)(dang)二(er)极(ji)(ji)(ji)(ji)(ji)(ji)管(guan)加上反向(xiang)电(dian)(dian)(dian)(dian)(dian)压（P端(duan)(duan)接负(fu)极(ji)(ji)(ji)(ji)(ji)(ji)，N端(duan)(duan)接正(zheng)(zheng)(zheng)极(ji)(ji)(ji)(ji)(ji)(ji)）时(shi)(shi)，这(zhei)时(shi)(shi)在P型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)端(duan)(duan)为负(fu)电(dian)(dian)(dian)(dian)(dian)压，正(zheng)(zheng)(zheng)电(dian)(dian)(dian)(dian)(dian)子(zi)(zi)被(bei)聚(ju)集(ji)(ji)在P型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)端(duan)(duan)，负(fu)电(dian)(dian)(dian)(dian)(dian)子(zi)(zi)则(ze)聚(ju)集(ji)(ji)在N型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)端(duan)(duan)，电(dian)(dian)(dian)(dian)(dian)子(zi)(zi)不(bu)移动(dong)，其PN结没(mei)有电(dian)(dian)(dian)(dian)(dian)流通(tong)(tong)(tong)过，二(er)极(ji)(ji)(ji)(ji)(ji)(ji)管(guan)截止。在栅(zha)(zha)极(ji)(ji)(ji)(ji)(ji)(ji)没(mei)有电(dian)(dian)(dian)(dian)(dian)压时(shi)(shi)，由(you)前面分析可知，在源(yuan)极(ji)(ji)(ji)(ji)(ji)(ji)与漏极(ji)(ji)(ji)(ji)(ji)(ji)之(zhi)间不(bu)会(hui)有电(dian)(dian)(dian)(dian)(dian)流流过，此时(shi)(shi)场效应(ying)管(guan)处与截止状态（图(tu)7a）。当(dang)(dang)有一个(ge)正(zheng)(zheng)(zheng)电(dian)(dian)(dian)(dian)(dian)压加在N沟(gou)道的(de)MOS场效应(ying)管(guan)栅(zha)(zha)极(ji)(ji)(ji)(ji)(ji)(ji)上时(shi)(shi)，由(you)于电(dian)(dian)(dian)(dian)(dian)场的(de)作用(yong)，此时(shi)(shi)N型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)的(de)源(yuan)极(ji)(ji)(ji)(ji)(ji)(ji)和漏极(ji)(ji)(ji)(ji)(ji)(ji)的(de)负(fu)电(dian)(dian)(dian)(dian)(dian)子(zi)(zi)被(bei)吸(xi)引出来而(er)涌向(xiang)栅(zha)(zha)极(ji)(ji)(ji)(ji)(ji)(ji)，但(dan)由(you)于氧(yang)化膜的(de)阻挡，使得电(dian)(dian)(dian)(dian)(dian)子(zi)(zi)聚(ju)集(ji)(ji)在两(liang)个(ge)N沟(gou)道之(zhi)间的(de)P型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)中（见图(tu)7b），从(cong)(cong)而(er)形成电(dian)(dian)(dian)(dian)(dian)流，使源(yuan)极(ji)(ji)(ji)(ji)(ji)(ji)和漏极(ji)(ji)(ji)(ji)(ji)(ji)之(zhi)间导(dao)(dao)(dao)(dao)通(tong)(tong)(tong)。可以想像(xiang)为两(liang)个(ge)N型(xing)(xing)半(ban)(ban)导(dao)(dao)(dao)(dao)体(ti)之(zhi)间为一条沟(gou)，栅(zha)(zha)极(ji)(ji)(ji)(ji)(ji)(ji)电(dian)(dian)(dian)(dian)(dian)压的(de)建立相当(dang)(dang)于为它们(men)之(zhi)间搭了一座桥(qiao)梁(liang)，该桥(qiao)的(de)大(da)小由(you)栅(zha)(zha)压的(de)大(da)小决定。

2、C-MOS场效应管（增强型MOS场效应管）

电(dian)(dian)(dian)路将一个(ge)增(zeng)强(qiang)型P沟道MOS场(chang)效(xiao)(xiao)(xiao)应(ying)(ying)管和一个(ge)增(zeng)强(qiang)型N沟道MOS场(chang)效(xiao)(xiao)(xiao)应(ying)(ying)管组合在(zai)(zai)一起使(shi)用。当输(shu)(shu)(shu)入端(duan)为(wei)低电(dian)(dian)(dian)平时，P沟道MOS场(chang)效(xiao)(xiao)(xiao)应(ying)(ying)管导通，输(shu)(shu)(shu)出(chu)端(duan)与电(dian)(dian)(dian)源(yuan)(yuan)正极接通。当输(shu)(shu)(shu)入端(duan)为(wei)高(gao)电(dian)(dian)(dian)平时，N沟道MOS场(chang)效(xiao)(xiao)(xiao)应(ying)(ying)管导通，输(shu)(shu)(shu)出(chu)端(duan)与电(dian)(dian)(dian)源(yuan)(yuan)地接通。在(zai)(zai)该电(dian)(dian)(dian)路中，P沟道MOS场(chang)效(xiao)(xiao)(xiao)应(ying)(ying)管和N沟道MOS场(chang)效(xiao)(xiao)(xiao)应(ying)(ying)管总是在(zai)(zai)相反的(de)状(zhuang)态下工作(zuo)，其相位输(shu)(shu)(shu)入端(duan)和输(shu)(shu)(shu)出(chu)端(duan)相反。通过这种工作(zuo)方(fang)式我(wo)们可(ke)以(yi)获(huo)得(de)(de)较大的(de)电(dian)(dian)(dian)流输(shu)(shu)(shu)出(chu)。同(tong)(tong)时由于漏电(dian)(dian)(dian)流的(de)影(ying)响，使(shi)得(de)(de)栅压(ya)在(zai)(zai)还没有到(dao)(dao)0V，通常在(zai)(zai)栅极电(dian)(dian)(dian)压(ya)小于1到(dao)(dao)2V时，MOS场(chang)效(xiao)(xiao)(xiao)应(ying)(ying)管既被关(guan)断。不(bu)同(tong)(tong)场(chang)效(xiao)(xiao)(xiao)应(ying)(ying)管其关(guan)断电(dian)(dian)(dian)压(ya)略有不(bu)同(tong)(tong)。也正因为(wei)如(ru)此，使(shi)得(de)(de)该电(dian)(dian)(dian)路不(bu)会因为(wei)两(liang)管同(tong)(tong)时导通而造成(cheng)电(dian)(dian)(dian)源(yuan)(yuan)短路。

三、场效应管的作用

1、场效(xiao)应(ying)管(guan)可(ke)应(ying)用于(yu)放(fang)大(da)。由于(yu)场效(xiao)应(ying)管(guan)放(fang)大(da)器的输入阻抗很高，因此(ci)耦(ou)合电(dian)容(rong)可(ke)以容(rong)量较小，不必使用电(dian)解(jie)电(dian)容(rong)器。

2、场效应管很高的输(shu)入阻抗非常(chang)适合作阻抗变换。常(chang)用于多级(ji)放大器的输(shu)入级(ji)作阻抗变换。

3、场(chang)效应管可以(yi)用作可变电阻。

4、场效应管可以方(fang)便地用作恒(heng)流(liu)源。

5、场(chang)效应管可以用作(zuo)电子(zi)开关。

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