利盈娱乐(中国)创新平台有限公司

MOS场效应(ying)晶体管通常简称为场效应管，是一种应用场效应原理工作的半导体器件，外形如图4-2，所示。和普通双极型晶体管相比拟，场效应管具有输入阻抗高、噪声低、动态范围大、功耗小、易于集成等特性，得到了越来越普遍的应用.

绝缘栅场效应(ying)管也叫做(zuo)金属氧化(hua)物半导体场效应(ying)管，简称为MOS场效应(ying)管，分为耗尽型MOS管和增强型MOS管。

1，MOS管种类和结构
MOSFET管(guan)(guan)(guan)(guan)(guan)(guan)是(shi)FET的(de)(de)(de)(de)一种(zhong)（另一种(zhong)是(shi)JFET），可以(yi)被制(zhi)构成增强(qiang)(qiang)(qiang)型(xing)或(huo)耗(hao)尽型(xing)，P沟道或(huo)N沟道共4种(zhong)类型(xing)，但理(li)(li)论应用的(de)(de)(de)(de)只(zhi)需增强(qiang)(qiang)(qiang)型(xing)的(de)(de)(de)(de)N沟道MOS管(guan)(guan)(guan)(guan)(guan)(guan)和增强(qiang)(qiang)(qiang)型(xing)的(de)(de)(de)(de)P沟道MOS管(guan)(guan)(guan)(guan)(guan)(guan)，所以(yi)通(tong)常提到(dao)NMOS，或(huo)者(zhe)PMOS指的(de)(de)(de)(de)就(jiu)是(shi)这(zhei)(zhei)两种(zhong)。至于为什么不(bu)运(yun)用耗(hao)尽型(xing)的(de)(de)(de)(de)MOS管(guan)(guan)(guan)(guan)(guan)(guan)，不(bu)建议(yi)寻根究(jiu)底。关于这(zhei)(zhei)两种(zhong)增强(qiang)(qiang)(qiang)型(xing)MOS管(guan)(guan)(guan)(guan)(guan)(guan)，比较(jiao)常用的(de)(de)(de)(de)是(shi)NMOS。缘由是(shi)导(dao)通(tong)电(dian)阻小，且容易(yi)制(zhi)造。所以(yi)开关电(dian)源和马达驱(qu)动的(de)(de)(de)(de)应用中(zhong)，普通(tong)都用NMOS。下(xia)面的(de)(de)(de)(de)引见中(zhong)，也多以(yi)NMOS为主。 MOS管(guan)(guan)(guan)(guan)(guan)(guan)的(de)(de)(de)(de)三个(ge)管(guan)(guan)(guan)(guan)(guan)(guan)脚之间有(you)寄生电(dian)容存在(zai)(zai)(zai)(zai)，这(zhei)(zhei)不(bu)是(shi)我们需求的(de)(de)(de)(de)，而是(shi)由于制(zhi)造工艺限制(zhi)产生的(de)(de)(de)(de)。寄生电(dian)容的(de)(de)(de)(de)存在(zai)(zai)(zai)(zai)使得在(zai)(zai)(zai)(zai)设计(ji)或(huo)选择驱(qu)动电(dian)路的(de)(de)(de)(de)时分要省事一些，但没有(you)办法避免，后边再细致引见。在(zai)(zai)(zai)(zai)MOS管(guan)(guan)(guan)(guan)(guan)(guan)原理(li)(li)图上可以(yi)看(kan)到(dao)，漏极和源极之间有(you)一个(ge)寄生二极管(guan)(guan)(guan)(guan)(guan)(guan)。这(zhei)(zhei)个(ge)叫体二极管(guan)(guan)(guan)(guan)(guan)(guan)，在(zai)(zai)(zai)(zai)驱(qu)动理(li)(li)性(xing)负载，这(zhei)(zhei)个(ge)二极管(guan)(guan)(guan)(guan)(guan)(guan)很重要。顺(shun)便说(shuo)一句(ju)，体二极管(guan)(guan)(guan)(guan)(guan)(guan)只(zhi)在(zai)(zai)(zai)(zai)单个(ge)的(de)(de)(de)(de)MOS管(guan)(guan)(guan)(guan)(guan)(guan)中(zhong)存在(zai)(zai)(zai)(zai)，在(zai)(zai)(zai)(zai)集(ji)成电(dian)路芯片内部通(tong)常是(shi)没有(you)的(de)(de)(de)(de)。

2，MOS管导通特性

导(dao)通(tong)的(de)意(yi)义(yi)是(shi)作为开关(guan)，相当(dang)于(yu)开关(guan)闭(bi)合。NMOS的(de)特性，Vgs大于(yu)一定的(de)值就会(hui)导(dao)通(tong)，适(shi)宜用(yong)于(yu)源极接地(di)时的(de)情况(kuang)（低端驱动(dong)），只需(xu)栅(zha)极电压抵达(da)4V或10V就可以(yi)了(le)。PMOS的(de)特性，Vgs小(xiao)于(yu)一定的(de)值就会(hui)导(dao)通(tong)，适(shi)宜用(yong)于(yu)源极接VCC时的(de)情况(kuang)（高(gao)(gao)端驱动(dong)）。但是(shi)，固然PMOS可以(yi)很便(bian)当(dang)地(di)用(yong)作高(gao)(gao)端驱动(dong)，但由(you)于(yu)导(dao)通(tong)电阻大，价钱贵，交流种类少等(deng)缘由(you)，在高(gao)(gao)端驱动(dong)中，通(tong)常还是(shi)运用(yong)NMOS。

3，MOS开关管
损(sun)(sun)(sun)失(shi)(shi)(shi)(shi)不(bu)管(guan)是(shi)NMOS还是(shi)PMOS，导(dao)通(tong)(tong)(tong)后都有(you)导(dao)通(tong)(tong)(tong)电(dian)阻(zu)存在(zai)，这(zhei)(zhei)样电(dian)流就会在(zai)这(zhei)(zhei)个电(dian)阻(zu)上(shang)消(xiao)耗能量(liang)，这(zhei)(zhei)部分消(xiao)耗的(de)(de)(de)能量(liang)叫做(zuo)导(dao)通(tong)(tong)(tong)损(sun)(sun)(sun)耗。选(xuan)择(ze)导(dao)通(tong)(tong)(tong)电(dian)阻(zu)小的(de)(de)(de)MOS管(guan)会减(jian)(jian)小导(dao)通(tong)(tong)(tong)损(sun)(sun)(sun)耗。往(wang)常的(de)(de)(de)小功(gong)率(lv)MOS管(guan)导(dao)通(tong)(tong)(tong)电(dian)阻(zu)普(pu)通(tong)(tong)(tong)在(zai)几十毫欧左右(you)，几毫欧的(de)(de)(de)也有(you)。MOS在(zai)导(dao)通(tong)(tong)(tong)和截止的(de)(de)(de)时分，一(yi)定不(bu)是(shi)在(zai)瞬(shun)间(jian)完成(cheng)的(de)(de)(de)。MOS两端的(de)(de)(de)电(dian)压(ya)(ya)有(you)一(yi)个降(jiang)落(luo)的(de)(de)(de)过(guo)程，流过(guo)的(de)(de)(de)电(dian)流有(you)一(yi)个上(shang)升(sheng)的(de)(de)(de)过(guo)程，在(zai)这(zhei)(zhei)段时间(jian)内(nei)，MOS管(guan)的(de)(de)(de)损(sun)(sun)(sun)失(shi)(shi)(shi)(shi)是(shi)电(dian)压(ya)(ya)和电(dian)流的(de)(de)(de)乘积(ji)，叫做(zuo)开(kai)(kai)关(guan)(guan)(guan)损(sun)(sun)(sun)失(shi)(shi)(shi)(shi)。通(tong)(tong)(tong)常开(kai)(kai)关(guan)(guan)(guan)损(sun)(sun)(sun)失(shi)(shi)(shi)(shi)比导(dao)通(tong)(tong)(tong)损(sun)(sun)(sun)失(shi)(shi)(shi)(shi)大(da)得多(duo)，而(er)且开(kai)(kai)关(guan)(guan)(guan)频(pin)率(lv)越(yue)快，损(sun)(sun)(sun)失(shi)(shi)(shi)(shi)也越(yue)大(da)。导(dao)通(tong)(tong)(tong)瞬(shun)间(jian)电(dian)压(ya)(ya)和电(dian)流的(de)(de)(de)乘积(ji)很(hen)(hen)大(da)，构成(cheng)的(de)(de)(de)损(sun)(sun)(sun)失(shi)(shi)(shi)(shi)也就很(hen)(hen)大(da)。缩短开(kai)(kai)关(guan)(guan)(guan)时间(jian)，可以减(jian)(jian)小每次(ci)导(dao)通(tong)(tong)(tong)时的(de)(de)(de)损(sun)(sun)(sun)失(shi)(shi)(shi)(shi)；降(jiang)低开(kai)(kai)关(guan)(guan)(guan)频(pin)率(lv)，可以减(jian)(jian)小单位时间(jian)内(nei)的(de)(de)(de)开(kai)(kai)关(guan)(guan)(guan)次(ci)数。这(zhei)(zhei)两种办法都可以减(jian)(jian)小开(kai)(kai)关(guan)(guan)(guan)损(sun)(sun)(sun)失(shi)(shi)(shi)(shi)。mos管(guan)

4，MOS管驱动
跟双极(ji)性晶体管(guan)相比(bi)，普通(tong)(tong)以(yi)(yi)(yi)(yi)为使MOS管(guan)导(dao)通(tong)(tong)不(bu)需(xu)(xu)求电(dian)(dian)(dian)(dian)(dian)流(liu)，只需(xu)(xu)GS电(dian)(dian)(dian)(dian)(dian)压(ya)高于一(yi)定(ding)的(de)(de)(de)(de)(de)(de)值，就(jiu)可(ke)以(yi)(yi)(yi)(yi)了。这个很(hen)容(rong)易做到(dao)(dao)，但是(shi)，我(wo)们还需(xu)(xu)求速度。在(zai)MOS管(guan)的(de)(de)(de)(de)(de)(de)结构中(zhong)可(ke)以(yi)(yi)(yi)(yi)看到(dao)(dao)，在(zai)GS，GD之间存(cun)在(zai)寄生电(dian)(dian)(dian)(dian)(dian)容(rong)，而(er)(er)MOS管(guan)的(de)(de)(de)(de)(de)(de)驱(qu)(qu)动(dong)(dong)(dong)，理论上就(jiu)是(shi)对(dui)电(dian)(dian)(dian)(dian)(dian)容(rong)的(de)(de)(de)(de)(de)(de)充(chong)放(fang)电(dian)(dian)(dian)(dian)(dian)。对(dui)电(dian)(dian)(dian)(dian)(dian)容(rong)的(de)(de)(de)(de)(de)(de)充(chong)电(dian)(dian)(dian)(dian)(dian)需(xu)(xu)求一(yi)个电(dian)(dian)(dian)(dian)(dian)流(liu)，由于对(dui)电(dian)(dian)(dian)(dian)(dian)容(rong)充(chong)电(dian)(dian)(dian)(dian)(dian)瞬(shun)(shun)间可(ke)以(yi)(yi)(yi)(yi)把(ba)电(dian)(dian)(dian)(dian)(dian)容(rong)看成(cheng)短路(lu)，所(suo)以(yi)(yi)(yi)(yi)瞬(shun)(shun)间电(dian)(dian)(dian)(dian)(dian)流(liu)会比(bi)较大(da)(da)(da)。选(xuan)择/设计(ji)MOS管(guan)驱(qu)(qu)动(dong)(dong)(dong)时(shi)第一(yi)要(yao)留(liu)意的(de)(de)(de)(de)(de)(de)是(shi)可(ke)提供(gong)瞬(shun)(shun)间短路(lu)电(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)(de)(de)大(da)(da)(da)小(xiao)。第二留(liu)意的(de)(de)(de)(de)(de)(de)是(shi)，普遍用(yong)于高端驱(qu)(qu)动(dong)(dong)(dong)的(de)(de)(de)(de)(de)(de)NMOS，导(dao)通(tong)(tong)时(shi)需(xu)(xu)求是(shi)栅极(ji)电(dian)(dian)(dian)(dian)(dian)压(ya)大(da)(da)(da)于源极(ji)电(dian)(dian)(dian)(dian)(dian)压(ya)。而(er)(er)高端驱(qu)(qu)动(dong)(dong)(dong)的(de)(de)(de)(de)(de)(de)MOS管(guan)导(dao)通(tong)(tong)时(shi)源极(ji)电(dian)(dian)(dian)(dian)(dian)压(ya)与漏极(ji)电(dian)(dian)(dian)(dian)(dian)压(ya)（VCC）相同，所(suo)以(yi)(yi)(yi)(yi)这时(shi)栅极(ji)电(dian)(dian)(dian)(dian)(dian)压(ya)要(yao)比(bi)VCC大(da)(da)(da)4V或10V。假(jia)设在(zai)同一(yi)个系(xi)统里，要(yao)得到(dao)(dao)比(bi)VCC大(da)(da)(da)的(de)(de)(de)(de)(de)(de)电(dian)(dian)(dian)(dian)(dian)压(ya)，就(jiu)要(yao)特地的(de)(de)(de)(de)(de)(de)升压(ya)电(dian)(dian)(dian)(dian)(dian)路(lu)了。很(hen)多(duo)马(ma)达驱(qu)(qu)动(dong)(dong)(dong)器都集成(cheng)了电(dian)(dian)(dian)(dian)(dian)荷泵，要(yao)留(liu)意的(de)(de)(de)(de)(de)(de)是(shi)应该选(xuan)择适(shi)合的(de)(de)(de)(de)(de)(de)外接电(dian)(dian)(dian)(dian)(dian)容(rong)，以(yi)(yi)(yi)(yi)得到(dao)(dao)足够的(de)(de)(de)(de)(de)(de)短路(lu)电(dian)(dian)(dian)(dian)(dian)流(liu)去驱(qu)(qu)动(dong)(dong)(dong)MOS管(guan)。上边(bian)说的(de)(de)(de)(de)(de)(de)4V或10V是(shi)常用(yong)的(de)(de)(de)(de)(de)(de)MOS管(guan)的(de)(de)(de)(de)(de)(de)导(dao)通(tong)(tong)电(dian)(dian)(dian)(dian)(dian)压(ya)，设计(ji)时(shi)当(dang)然需(xu)(xu)求有(you)一(yi)定(ding)的(de)(de)(de)(de)(de)(de)余量。而(er)(er)且电(dian)(dian)(dian)(dian)(dian)压(ya)越高，导(dao)通(tong)(tong)速度越快(kuai)，导(dao)通(tong)(tong)电(dian)(dian)(dian)(dian)(dian)阻(zu)也越小(xiao)。往常也有(you)导(dao)通(tong)(tong)电(dian)(dian)(dian)(dian)(dian)压(ya)更小(xiao)的(de)(de)(de)(de)(de)(de)MOS管(guan)用(yong)在(zai)不(bu)同的(de)(de)(de)(de)(de)(de)范畴里，但在(zai)12V汽车电(dian)(dian)(dian)(dian)(dian)子系(xi)统里，普通(tong)(tong)4V导(dao)通(tong)(tong)就(jiu)够用(yong)了。

MOS管(guan)主要参数(shu)如(ru)下(xia)：

1. 栅(zha)源击穿电(dian)(dian)压BVGS-在增加(jia)栅(zha)源电(dian)(dian)压过程(cheng)中，使(shi)栅(zha)极电(dian)(dian)流(liu)IG由零开端剧增时的VGS，称为栅(zha)源击穿电(dian)(dian)压BVGS。

2.开启电(dian)压(ya)VT-开启电(dian)压(ya)（又称阈值(zhi)电(dian)压(ya)）：使得源极(ji)(ji)S和(he)漏极(ji)(ji)D之间开端构(gou)成导电(dian)沟道(dao)(dao)所需(xu)的栅极(ji)(ji)电(dian)压(ya)；-规范的N沟道(dao)(dao)MOS管(guan)，VT约为3～6V；-经过工艺上的改(gai)良(liang)，能够使MOS管(guan)的VT值(zhi)降到2～3V。

3. 漏源击穿电压BVDS-在VGS=0（加强型）的条件下 ，在增加漏源电压过程中使ID开端剧增时的VDS称为漏源击穿电压BVDS-ID剧增的缘由有下列两个方面：
（1）漏极左近耗尽层的雪崩击穿
（2）漏(lou)(lou)源(yuan)(yuan)极间(jian)(jian)的穿(chuan)通击穿(chuan)-有些MOS管中，其沟(gou)道(dao)长(zhang)度较短(duan)，不(bu)时(shi)增加VDS会(hui)使漏(lou)(lou)区(qu)(qu)的耗(hao)尽层不(bu)时(shi)扩展到源(yuan)(yuan)区(qu)(qu)，使沟(gou)道(dao)长(zhang)度为零，即产生漏(lou)(lou)源(yuan)(yuan)间(jian)(jian)的穿(chuan)通，穿(chuan)通后(hou)，源(yuan)(yuan)区(qu)(qu)中的多数载流(liu)子，将直承受耗(hao)尽层电场的吸收，抵达(da)漏(lou)(lou)区(qu)(qu)，产生大的ID。

4. 直流(liu)(liu)(liu)输(shu)入电(dian)阻(zu)RGS-即(ji)在栅(zha)(zha)源极之间加的(de)电(dian)压与栅(zha)(zha)极电(dian)流(liu)(liu)(liu)之比-这一(yi)特性有时以流(liu)(liu)(liu)过栅(zha)(zha)极的(de)栅(zha)(zha)流(liu)(liu)(liu)表示-MOS管的(de)RGS能够很容易地超越1010Ω。

5. 低频跨导gm-在(zai)VDS为(wei)某一固定数值的(de)(de)条件下 ，漏(lou)极电(dian)流的(de)(de)微变(bian)量和惹起这个变(bian)化的(de)(de)栅源电(dian)压(ya)微变(bian)量之比称为(wei)跨导-gm反映了栅源电(dian)压(ya)对漏(lou)极电(dian)流的(de)(de)控(kong)制才干(gan)-是表征MOS管放大(da)才干(gan)的(de)(de)一个重要(yao)参数-普通在(zai)非常之几至几mA/V的(de)(de)范围内(nei)。

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