大功率(lv)(lv)MOS管工作原理及构(gou)造(zao)详解(jie)-大功率(lv)(lv)MOS管检测与代(dai)换-KIA MOS管
信息来源：本站 日期：2018-07-03
MOS管(guan)(guan)的英文全(quan)称叫MOSFET(Metal Oxide Semiconductor Field Effect Transistor)，即(ji)金属氧化物半导(dao)体型场效应管(guan)(guan)，属于场效应管(guan)(guan)中的绝(jue)缘栅(zha)(zha)型。因(yin)此，MOS管(guan)(guan)有(you)时被(bei)称为绝(jue)缘栅(zha)(zha)场效应管(guan)(guan)。在一(yi)般电(dian)(dian)子电(dian)(dian)路(lu)中，MOS管(guan)(guan)通常被(bei)用于放大电(dian)(dian)路(lu)或开关电(dian)(dian)路(lu)。
在一(yi)块掺(chan)杂浓度(du)较(jiao)低的(de)(de)P型(xing)半(ban)(ban)导(dao)体(ti)硅(gui)衬底(di)上，用半(ban)(ban)导(dao)体(ti)光刻、扩散(san)工艺制作(zuo)两个(ge)高(gao)掺(chan)杂浓度(du)的(de)(de)N+区，并用金属铝(lv)(lv)引(yin)出(chu)两个(ge)电(dian)极(ji)，分别作(zuo)为(wei)漏极(ji)D和(he)(he)源极(ji)S。然(ran)后在漏极(ji)和(he)(he)源极(ji)之间(jian)的(de)(de)P型(xing)半(ban)(ban)导(dao)体(ti)表(biao)面复盖一(yi)层(ceng)(ceng)很薄的(de)(de)二氧化(hua)硅(gui)（Si02）绝(jue)缘层(ceng)(ceng)膜(mo)，在再(zai)这(zhei)个(ge)绝(jue)缘层(ceng)(ceng)膜(mo)上装上一(yi)个(ge)铝(lv)(lv)电(dian)极(ji)，作(zuo)为(wei)栅极(ji)G。这(zhei)就构(gou)成了一(yi)个(ge)N沟道（NPN型(xing)）增强型(xing)MOS管。显然(ran)它的(de)(de)栅极(ji)和(he)(he)其它电(dian)极(ji)间(jian)是绝(jue)缘的(de)(de)。图1-1所示 A 、B分别是它的(de)(de)结构(gou)图和(he)(he)代表(biao)符号。
同样用上述(shu)相同的(de)方法在一(yi)块掺杂(za)浓度(du)(du)较低的(de)N型半(ban)导体(ti)硅衬底上，用半(ban)导体(ti)光刻、扩散工(gong)艺制作两个(ge)高掺杂(za)浓度(du)(du)的(de)P+区，及上述(shu)相同的(de)栅极制作过程，就制成为(wei)一(yi)个(ge)P沟(gou)道（PNP型）增强型MOS管。图1-2所示(shi)A 、B分(fen)别是P沟(gou)道MOS管道结构图和代表符号。
从图1-3-A可以看(kan)出(chu)，增(zeng)强型MOS管(guan)的(de)漏(lou)极D和源(yuan)极S之间有两(liang)个背靠背的(de)PN结。当栅-源(yuan)电压VGS=0时，即使加上漏(lou)-源(yuan)电压VDS，总有一(yi)个PN结处于(yu)反偏状态(tai)，漏(lou)-源(yuan)极间没(mei)有导(dao)电沟道（没(mei)有电流流过），所(suo)以这时漏(lou)极电流ID=0。
此时若在栅-源(yuan)(yuan)(yuan)极(ji)间(jian)加(jia)上正向电(dian)(dian)(dian)压(ya)，图1-3-B所示，即VGS＞0，则栅极(ji)和硅衬底之(zhi)(zhi)间(jian)的SiO2绝缘层(ceng)(ceng)中便(bian)产生一(yi)个(ge)(ge)(ge)栅极(ji)指向P型硅衬底的电(dian)(dian)(dian)场，由于氧化物层(ceng)(ceng)是(shi)绝缘的，栅极(ji)所加(jia)电(dian)(dian)(dian)压(ya)VGS无法形成电(dian)(dian)(dian)流(liu)(liu)，氧化物层(ceng)(ceng)的两(liang)边就(jiu)形成了(le)(le)一(yi)个(ge)(ge)(ge)电(dian)(dian)(dian)容，VGS等(deng)效是(shi)对这个(ge)(ge)(ge)电(dian)(dian)(dian)容充电(dian)(dian)(dian)，并形成一(yi)个(ge)(ge)(ge)电(dian)(dian)(dian)场，随着(zhe)VGS逐渐升高，受栅极(ji)正电(dian)(dian)(dian)压(ya)的吸引，在这个(ge)(ge)(ge)电(dian)(dian)(dian)容的另一(yi)边就(jiu)聚(ju)集大量的电(dian)(dian)(dian)子(zi)并形成了(le)(le)一(yi)个(ge)(ge)(ge)从漏极(ji)到(dao)(dao)源(yuan)(yuan)(yuan)极(ji)的N型导电(dian)(dian)(dian)沟(gou)道，当VGS大于管子(zi)的开启电(dian)(dian)(dian)压(ya)VT（一(yi)般约为(wei) 2V）时，N沟(gou)道管开始(shi)导通(tong)，形成漏极(ji)电(dian)(dian)(dian)流(liu)(liu)ID，我(wo)们把开始(shi)形成沟(gou)道时的栅-源(yuan)(yuan)(yuan)极(ji)电(dian)(dian)(dian)压(ya)称(cheng)为(wei)开启电(dian)(dian)(dian)压(ya)，一(yi)般用(yong)(yong)VT表示。控制栅极(ji)电(dian)(dian)(dian)压(ya)VGS的大小改(gai)变了(le)(le)电(dian)(dian)(dian)场的强弱，就(jiu)可以(yi)(yi)达(da)到(dao)(dao)控制漏极(ji)电(dian)(dian)(dian)流(liu)(liu)ID的大小的目(mu)的，这也是(shi)MOS管用(yong)(yong)电(dian)(dian)(dian)场来控制电(dian)(dian)(dian)流(liu)(liu)的一(yi)个(ge)(ge)(ge)重要特(te)点，所以(yi)(yi)也称(cheng)之(zhi)(zhi)为(wei)场效应管。
上述(shu)大功率(lv)MOS管工作原(yuan)理中可以(yi)看出，MOS管的(de)(de)栅极G和源(yuan)极S之间是(shi)绝(jue)缘的(de)(de)，由于Sio2绝(jue)缘层的(de)(de)存(cun)(cun)在(zai)，在(zai)栅极G和源(yuan)极S之间等效(xiao)是(shi)一(yi)个电(dian)(dian)容(rong)存(cun)(cun)在(zai)，电(dian)(dian)压(ya)VGS产(chan)生(sheng)电(dian)(dian)场从而导(dao)致源(yuan)极-漏(lou)极电(dian)(dian)流的(de)(de)产(chan)生(sheng)。此时的(de)(de)栅极电(dian)(dian)压(ya)VGS决定了漏(lou)极电(dian)(dian)流的(de)(de)大小(xiao)(xiao)，控(kong)制(zhi)栅极电(dian)(dian)压(ya)VGS的(de)(de)大小(xiao)(xiao)就(jiu)可以(yi)控(kong)制(zhi)漏(lou)极电(dian)(dian)流ID的(de)(de)大小(xiao)(xiao)。这就(jiu)可以(yi)得出如(ru)下结论：
1） MOS管是(shi)一(yi)个(ge)由(you)改(gai)变电(dian)压来控制电(dian)流的器件(jian)，所以(yi)是(shi)电(dian)压器件(jian)。
2） MOS管道(dao)输入(ru)特(te)性(xing)为(wei)容性(xing)特(te)性(xing)，所以输入(ru)阻抗极高。
图1-4-A 是(shi)N沟道(dao)MOS管的(de)符号(hao)，图中D是(shi)漏极(ji)(ji)，S是(shi)源极(ji)(ji)，G是(shi)栅极(ji)(ji)，中间的(de)箭头表(biao)示(shi)衬(chen)底，如果箭头向里表(biao)示(shi)是(shi)N沟道(dao)的(de)MOS管，箭头向外表(biao)示(shi)是(shi)P沟道(dao)的(de)MOS管。
在(zai)实际MOS管生产(chan)的过(guo)程中(zhong)衬底(di)在(zai)出厂前就(jiu)和源极(ji)连(lian)接(jie)，所以(yi)在(zai)符号的规(gui)则中(zhong)；表示衬底(di)的箭头也必须(xu)和源极(ji)相(xiang)连(lian)接(jie)，以(yi)区别漏(lou)极(ji)和源极(ji)。图1-5-A是P沟道MOS管的符号。
大功率MOS管(guan)(guan)应用(yong)电(dian)压(ya)的(de)极(ji)(ji)(ji)(ji)(ji)(ji)(ji)性和我(wo)们普通的(de)晶(jing)体三极(ji)(ji)(ji)(ji)(ji)(ji)(ji)管(guan)(guan)相(xiang)同(tong)(tong)，N沟(gou)(gou)道的(de)类(lei)似(si)NPN晶(jing)体三极(ji)(ji)(ji)(ji)(ji)(ji)(ji)管(guan)(guan)，漏极(ji)(ji)(ji)(ji)(ji)(ji)(ji)D接正极(ji)(ji)(ji)(ji)(ji)(ji)(ji)，源(yuan)极(ji)(ji)(ji)(ji)(ji)(ji)(ji)S接负(fu)极(ji)(ji)(ji)(ji)(ji)(ji)(ji)，栅极(ji)(ji)(ji)(ji)(ji)(ji)(ji)G正电(dian)压(ya)时导电(dian)沟(gou)(gou)道建立(li)，N沟(gou)(gou)道MOS管(guan)(guan)开始工作,如(ru)图1-4-B所示。同(tong)(tong)样(yang)P道的(de)类(lei)似(si)PNP晶(jing)体三极(ji)(ji)(ji)(ji)(ji)(ji)(ji)管(guan)(guan)，漏极(ji)(ji)(ji)(ji)(ji)(ji)(ji)D接负(fu)极(ji)(ji)(ji)(ji)(ji)(ji)(ji)，源(yuan)极(ji)(ji)(ji)(ji)(ji)(ji)(ji)S接正极(ji)(ji)(ji)(ji)(ji)(ji)(ji)，栅极(ji)(ji)(ji)(ji)(ji)(ji)(ji)G负(fu)电(dian)压(ya)时，导电(dian)沟(gou)(gou)道建立(li)，P沟(gou)(gou)道MOS管(guan)(guan)开始工作,如(ru)图1-5-B所示。
1）．场效应(ying)管(guan)(guan)的(de)(de)源极(ji)(ji)S、栅(zha)极(ji)(ji)G、漏极(ji)(ji)D分(fen)别对应(ying)于三(san)极(ji)(ji)管(guan)(guan)的(de)(de)发(fa)射极(ji)(ji)e、基极(ji)(ji)b、集(ji)电(dian)极(ji)(ji)c，它们的(de)(de)作用(yong)相似，图1-6-A所示是N沟道(dao)(dao)MOS管(guan)(guan)和NPN型(xing)晶体三(san)极(ji)(ji)管(guan)(guan)引脚，图1-6-B所示是P沟道(dao)(dao)MOS管(guan)(guan)和PNP型(xing)晶体三(san)极(ji)(ji)管(guan)(guan)引脚对应(ying)图。
2)．场效应管是电(dian)(dian)(dian)压控(kong)制(zhi)电(dian)(dian)(dian)流(liu)(liu)器件(jian)，由VGS控(kong)制(zhi)ID，普通的晶体三极(ji)管是电(dian)(dian)(dian)流(liu)(liu)控(kong)制(zhi)电(dian)(dian)(dian)流(liu)(liu)器件(jian)，由IB控(kong)制(zhi)IC。MOS管道(dao)放大系(xi)数(shu)是（跨导gm）当栅极(ji)电(dian)(dian)(dian)压改变一伏时(shi)能引起漏极(ji)电(dian)(dian)(dian)流(liu)(liu)变化(hua)多少安培(pei)。晶体三极(ji)管是电(dian)(dian)(dian)流(liu)(liu)放大系(xi)数(shu)（贝(bei)塔β）当基极(ji)电(dian)(dian)(dian)流(liu)(liu)改变一毫安时(shi)能引起集(ji)电(dian)(dian)(dian)极(ji)电(dian)(dian)(dian)流(liu)(liu)变化(hua)多少。
3)．场效应(ying)管(guan)栅(zha)极(ji)和其它电(dian)(dian)极(ji)是(shi)绝缘(yuan)的(de)(de)，不(bu)产生电(dian)(dian)流；而三极(ji)管(guan)工作(zuo)时基极(ji)电(dian)(dian)流IB决定(ding)集电(dian)(dian)极(ji)电(dian)(dian)流IC。因此场效应(ying)管(guan)的(de)(de)输(shu)入电(dian)(dian)阻比三极(ji)管(guan)的(de)(de)输(shu)入电(dian)(dian)阻高(gao)的(de)(de)多。
4)．场效(xiao)应管(guan)只有(you)多(duo)(duo)数载流(liu)(liu)子(zi)参与导(dao)(dao)电；三极管(guan)有(you)多(duo)(duo)数载流(liu)(liu)子(zi)和少(shao)数载流(liu)(liu)子(zi)两(liang)种载流(liu)(liu)子(zi)参与导(dao)(dao)电，因少(shao)数载流(liu)(liu)子(zi)浓度(du)受(shou)温度(du)、辐射等因素影响较大(da)，所以场效(xiao)应管(guan)比三极管(guan)的(de)温度(du)稳定性好(hao)。
5)．场效应管在源极(ji)未与衬(chen)底连在一起(qi)时，源极(ji)和漏极(ji)可(ke)以互换使(shi)(shi)用，且(qie)特性(xing)变(bian)化不(bu)大，而(er)三极(ji)管的集电极(ji)与发射(she)极(ji)互换使(shi)(shi)用时，其特性(xing)差(cha)异(yi)很大，b 值(zhi)将减小很多。
6)．场效(xiao)应管(guan)的噪声系数很小，在(zai)低噪声放大电路(lu)的输入(ru)级及要求信(xin)噪比较(jiao)高的电路(lu)中(zhong)要选(xuan)用(yong)场效(xiao)应管(guan)。
7)．场效应(ying)(ying)管(guan)和(he)普通(tong)晶(jing)(jing)体三极(ji)(ji)管(guan)均可组成各(ge)种(zhong)放(fang)大电(dian)(dian)路(lu)和(he)开关电(dian)(dian)路(lu)，但是(shi)场效应(ying)(ying)管(guan)制造工艺简单，并且又具有普通(tong)晶(jing)(jing)体三极(ji)(ji)管(guan)不能比拟(ni)的优秀(xiu)特(te)性，在各(ge)种(zhong)电(dian)(dian)路(lu)及(ji)应(ying)(ying)用中正(zheng)逐步的取(qu)代普通(tong)晶(jing)(jing)体三极(ji)(ji)管(guan)，目(mu)前的大规(gui)模和(he)超大规(gui)模集成电(dian)(dian)路(lu)中，已经广泛的采用场效应(ying)(ying)管(guan)。
1)、输入(ru)阻(zu)(zu)(zu)(zu)抗(kang)高(gao)，驱(qu)(qu)(qu)动功率小：由于(yu)栅(zha)(zha)源(yuan)之间是(shi)二氧化硅（SiO2）绝缘层，栅(zha)(zha)源(yuan)之间的直流(liu)电(dian)阻(zu)(zu)(zu)(zu)基本上就(jiu)(jiu)是(shi)SiO2绝缘电(dian)阻(zu)(zu)(zu)(zu)，一(yi)般达100MΩ左(zuo)右(you)，交流(liu)输入(ru)阻(zu)(zu)(zu)(zu)抗(kang)基本上就(jiu)(jiu)是(shi)输入(ru)电(dian)容的容抗(kang)。由于(yu)输入(ru)阻(zu)(zu)(zu)(zu)抗(kang)高(gao)，对激励信号不(bu)会产(chan)生压(ya)降，有电(dian)压(ya)就(jiu)(jiu)可以(yi)驱(qu)(qu)(qu)动，所以(yi)驱(qu)(qu)(qu)动功率极(ji)(ji)小（灵(ling)敏度高(gao)）。一(yi)般的晶(jing)体三(san)极(ji)(ji)管必需有基极(ji)(ji)电(dian)压(ya)Vb，再产(chan)生基极(ji)(ji)电(dian)流(liu)Ib，才能驱(qu)(qu)(qu)动集电(dian)极(ji)(ji)电(dian)流(liu)的产(chan)生。晶(jing)体三(san)极(ji)(ji)管的驱(qu)(qu)(qu)动是(shi)需要功率的（Vb×Ib）。
2）、开(kai)关(guan)速(su)度(du)快:MOSFET的(de)(de)(de)开(kai)关(guan)速(su)度(du)和输(shu)入的(de)(de)(de)容性特性的(de)(de)(de)有很(hen)大(da)关(guan)系，由于(yu)输(shu)入容性特性的(de)(de)(de)存在，使开(kai)关(guan)的(de)(de)(de)速(su)度(du)变慢，但是在作(zuo)(zuo)为开(kai)关(guan)运用时，可降低驱(qu)动电路(lu)(lu)内阻(zu)，加快开(kai)关(guan)速(su)度(du)（输(shu)入采用了后述的(de)(de)(de)“灌流电路(lu)(lu)”驱(qu)动，加快了容性的(de)(de)(de)充放(fang)电的(de)(de)(de)时间）。MOSFET只靠多子导(dao)电，不存在少(shao)子储(chu)存效(xiao)应，因而关(guan)断过程(cheng)非常迅(xun)速(su)，开(kai)关(guan)时间在10—100ns之间，工作(zuo)(zuo)频率(lv)可达100kHz以(yi)(yi)上，普(pu)通的(de)(de)(de)晶体(ti)三极(ji)管由于(yu)少(shao)数载流子的(de)(de)(de)存储(chu)效(xiao)应，使开(kai)关(guan)总有滞后现象，影响(xiang)开(kai)关(guan)速(su)度(du)的(de)(de)(de)提(ti)高（目前采用MOS管的(de)(de)(de)开(kai)关(guan)电源其(qi)工作(zuo)(zuo)频率(lv)可以(yi)(yi)轻易的(de)(de)(de)做(zuo)到100K/S～150K/S,这(zhei)对于(yu)普(pu)通的(de)(de)(de)大(da)功率(lv)晶体(ti)三极(ji)管来说是难以(yi)(yi)想象的(de)(de)(de)）。
3）、无二(er)次(ci)击(ji)(ji)(ji)穿(chuan)；由(you)于普通(tong)(tong)的功(gong)率(lv)晶(jing)体(ti)三(san)极(ji)管(guan)(guan)具有当(dang)温(wen)(wen)(wen)(wen)(wen)(wen)度(du)上(shang)升(sheng)就(jiu)(jiu)会导(dao)致(zhi)集电(dian)(dian)(dian)(dian)(dian)(dian)极(ji)电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)上(shang)升(sheng)（正的温(wen)(wen)(wen)(wen)(wen)(wen)度(du)～电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)特(te)性(xing)）的现(xian)(xian)象(xiang)(xiang)，而(er)集电(dian)(dian)(dian)(dian)(dian)(dian)极(ji)电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的上(shang)升(sheng)又会导(dao)致(zhi)温(wen)(wen)(wen)(wen)(wen)(wen)度(du)进一(yi)步的上(shang)升(sheng)，温(wen)(wen)(wen)(wen)(wen)(wen)度(du)进一(yi)步的上(shang)升(sheng)，更(geng)进一(yi)步的导(dao)致(zhi)集电(dian)(dian)(dian)(dian)(dian)(dian)极(ji)电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的上(shang)升(sheng)这一(yi)恶性(xing)循(xun)环。而(er)晶(jing)体(ti)三(san)极(ji)管(guan)(guan)的耐(nai)压VCEO随管(guan)(guan)温(wen)(wen)(wen)(wen)(wen)(wen)度(du)升(sheng)高(gao)是逐步下(xia)(xia)降(jiang)，这就(jiu)(jiu)形(xing)成了管(guan)(guan)温(wen)(wen)(wen)(wen)(wen)(wen)继(ji)续(xu)上(shang)升(sheng)、耐(nai)压继(ji)续(xu)下(xia)(xia)降(jiang)最(zui)终导(dao)致(zhi)晶(jing)体(ti)三(san)极(ji)管(guan)(guan)的击(ji)(ji)(ji)穿(chuan)，这是一(yi)种导(dao)致(zhi)电(dian)(dian)(dian)(dian)(dian)(dian)视(shi)机开关电(dian)(dian)(dian)(dian)(dian)(dian)源管(guan)(guan)和行输出(chu)管(guan)(guan)损坏(huai)率(lv)占(zhan)95%的破环性(xing)的热电(dian)(dian)(dian)(dian)(dian)(dian)击(ji)(ji)(ji)穿(chuan)现(xian)(xian)象(xiang)(xiang)，也称(cheng)为(wei)二(er)次(ci)击(ji)(ji)(ji)穿(chuan)现(xian)(xian)象(xiang)(xiang)。MOS管(guan)(guan)具有和普通(tong)(tong)晶(jing)体(ti)三(san)极(ji)管(guan)(guan)相(xiang)反的温(wen)(wen)(wen)(wen)(wen)(wen)度(du)～电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)特(te)性(xing)，即当(dang)管(guan)(guan)温(wen)(wen)(wen)(wen)(wen)(wen)度(du)（或环境温(wen)(wen)(wen)(wen)(wen)(wen)度(du)）上(shang)升(sheng)时(shi)，沟道(dao)电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)IDS反而(er)下(xia)(xia)降(jiang)。例如；一(yi)只IDS=10A的MOS FET开关管(guan)(guan)，当(dang)VGS控制电(dian)(dian)(dian)(dian)(dian)(dian)压不变时(shi)，在(zai)250C温(wen)(wen)(wen)(wen)(wen)(wen)度(du)下(xia)(xia)IDS=3A，当(dang)芯片温(wen)(wen)(wen)(wen)(wen)(wen)度(du)升(sheng)高(gao)为(wei)1000C时(shi)，IDS降(jiang)低到2A，这种因温(wen)(wen)(wen)(wen)(wen)(wen)度(du)上(shang)升(sheng)而(er)导(dao)致(zhi)沟道(dao)电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)IDS下(xia)(xia)降(jiang)的负(fu)温(wen)(wen)(wen)(wen)(wen)(wen)度(du)电(dian)(dian)(dian)(dian)(dian)(dian)流(liu)特(te)性(xing)，使之不会产生恶性(xing)循(xun)环而(er)热击(ji)(ji)(ji)穿(chuan)。也就(jiu)(jiu)是MOS管(guan)(guan)没有二(er)次(ci)击(ji)(ji)(ji)穿(chuan)现(xian)(xian)象(xiang)(xiang)，可见采(cai)用MOS管(guan)(guan)作为(wei)开关管(guan)(guan)，其开关管(guan)(guan)的损坏(huai)率(lv)大幅度(du)的降(jiang)低，近(jin)两(liang)年电(dian)(dian)(dian)(dian)(dian)(dian)视(shi)机开关电(dian)(dian)(dian)(dian)(dian)(dian)源采(cai)用MOS管(guan)(guan)代替过(guo)去的普通(tong)(tong)晶(jing)体(ti)三(san)极(ji)管(guan)(guan)后，开关管(guan)(guan)损坏(huai)率(lv)大大降(jiang)低也是一(yi)个极(ji)好的证明(ming)。
4）、MOS管(guan)导通后其(qi)导通特(te)性呈(cheng)纯阻性；
普(pu)通(tong)晶(jing)体(ti)三(san)极(ji)(ji)管在(zai)(zai)饱(bao)和(he)导通(tong)是(shi)(shi)，几乎是(shi)(shi)直(zhi)通(tong)，有一(yi)(yi)(yi)(yi)个极(ji)(ji)低的(de)(de)(de)(de)压(ya)(ya)(ya)降(jiang)，称为饱(bao)和(he)压(ya)(ya)(ya)降(jiang)，既(ji)然(ran)有一(yi)(yi)(yi)(yi)个压(ya)(ya)(ya)降(jiang)，那么(me)也就(jiu)(jiu)是(shi)(shi)；普(pu)通(tong)晶(jing)体(ti)三(san)极(ji)(ji)管在(zai)(zai)饱(bao)和(he)导通(tong)后(hou)等效(xiao)是(shi)(shi)一(yi)(yi)(yi)(yi)个阻(zu)(zu)值极(ji)(ji)小(xiao)的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)阻(zu)(zu)，但是(shi)(shi)这个等效(xiao)的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)阻(zu)(zu)是(shi)(shi)一(yi)(yi)(yi)(yi)个非线(xian)性(xing)(xing)的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)阻(zu)(zu)（电(dian)(dian)(dian)(dian)阻(zu)(zu)上的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)压(ya)(ya)(ya)和(he)流(liu)(liu)过的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)流(liu)(liu)不(bu)(bu)能符(fu)合(he)(he)欧姆(mu)定(ding)律），而MOS管作(zuo)为开关(guan)管应(ying)(ying)用，在(zai)(zai)饱(bao)和(he)导通(tong)后(hou)也存在(zai)(zai)一(yi)(yi)(yi)(yi)个阻(zu)(zu)值极(ji)(ji)小(xiao)的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)阻(zu)(zu)，但是(shi)(shi)这个电(dian)(dian)(dian)(dian)阻(zu)(zu)等效(xiao)一(yi)(yi)(yi)(yi)个线(xian)性(xing)(xing)电(dian)(dian)(dian)(dian)阻(zu)(zu)，其电(dian)(dian)(dian)(dian)阻(zu)(zu)的(de)(de)(de)(de)阻(zu)(zu)值和(he)两(liang)端的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)压(ya)(ya)(ya)降(jiang)和(he)流(liu)(liu)过的(de)(de)(de)(de)电(dian)(dian)(dian)(dian)流(liu)(liu)符(fu)合(he)(he)欧姆(mu)定(ding)律的(de)(de)(de)(de)关(guan)系，电(dian)(dian)(dian)(dian)流(liu)(liu)大(da)压(ya)(ya)(ya)降(jiang)就(jiu)(jiu)大(da)，电(dian)(dian)(dian)(dian)流(liu)(liu)小(xiao)压(ya)(ya)(ya)降(jiang)就(jiu)(jiu)小(xiao)，导通(tong)后(hou)既(ji)然(ran)等效(xiao)是(shi)(shi)一(yi)(yi)(yi)(yi)个线(xian)性(xing)(xing)元(yuan)件(jian)，线(xian)性(xing)(xing)元(yuan)件(jian)就(jiu)(jiu)可以(yi)并联(lian)(lian)(lian)应(ying)(ying)用，当(dang)这样两(liang)个电(dian)(dian)(dian)(dian)阻(zu)(zu)并联(lian)(lian)(lian)在(zai)(zai)一(yi)(yi)(yi)(yi)起，就(jiu)(jiu)有一(yi)(yi)(yi)(yi)个自动电(dian)(dian)(dian)(dian)流(liu)(liu)平衡(heng)(heng)的(de)(de)(de)(de)作(zuo)用，所以(yi)MOS管在(zai)(zai)一(yi)(yi)(yi)(yi)个管子功率不(bu)(bu)够的(de)(de)(de)(de)时候，可以(yi)多管并联(lian)(lian)(lian)应(ying)(ying)用，且(qie)不(bu)(bu)必另外增加平衡(heng)(heng)措施（非线(xian)性(xing)(xing)器件(jian)是(shi)(shi)不(bu)(bu)能直(zhi)接并联(lian)(lian)(lian)应(ying)(ying)用的(de)(de)(de)(de)）。
MOS管(guan)和普通(tong)的(de)(de)晶体(ti)(ti)三极管(guan)相比，有以上四项优(you)点，就足以使(shi)MOS管(guan)在开关运用(yong)状态下完全取代普通(tong)的(de)(de)晶体(ti)(ti)三极管(guan)。目前的(de)(de)技(ji)术MOS管(guan)道VDS能做到(dao)1000V，只能作为开关电源的(de)(de)开关管(guan)应用(yong)，随着制造工艺(yi)的(de)(de)不(bu)断(duan)进步，VDS的(de)(de)不(bu)断(duan)提高，取代显(xian)像管(guan)电视(shi)机的(de)(de)行输出管(guan)也是近(jin)期能实现的(de)(de)。
大功(gong)率(lv)MOS管(guan)和普通(tong)晶(jing)体三极管(guan)相(xiang)比，有(you)诸(zhu)多的(de)(de)(de)优点，但是(shi)(shi)在(zai)作(zuo)为(wei)大功(gong)率(lv)开(kai)(kai)关(guan)管(guan)应用(yong)时，由(you)于MOS管(guan)具(ju)有(you)的(de)(de)(de)容(rong)(rong)性输(shu)(shu)入特性，MOS管(guan)的(de)(de)(de)输(shu)(shu)入端(duan)(duan)，等于是(shi)(shi)一个(ge)小电(dian)容(rong)(rong)器，输(shu)(shu)入的(de)(de)(de)开(kai)(kai)关(guan)激(ji)(ji)励(li)信号，实(shi)际上是(shi)(shi)在(zai)对(dui)这(zhei)个(ge)电(dian)容(rong)(rong)进(jin)行反复的(de)(de)(de)充(chong)电(dian)、放(fang)(fang)电(dian)的(de)(de)(de)过程，在(zai)充(chong)放(fang)(fang)电(dian)的(de)(de)(de)过程中，使MOS管(guan)道(dao)导通(tong)和关(guan)闭产生了滞后，使“开(kai)(kai)”与“关(guan)”的(de)(de)(de)过程变慢(man)，这(zhei)是(shi)(shi)开(kai)(kai)关(guan)元件不能允许的(de)(de)(de)（功(gong)耗增(zeng)加(jia)，烧(shao)坏开(kai)(kai)关(guan)管(guan)），如图(tu)所示，在(zai)图(tu)2-1中 A方波(bo)为(wei)输(shu)(shu)入端(duan)(duan)的(de)(de)(de)激(ji)(ji)励(li)波(bo)形(xing)，电(dian)阻R为(wei)激(ji)(ji)励(li)信号内阻，电(dian)容(rong)(rong)C为(wei)MOS管(guan)输(shu)(shu)入端(duan)(duan)等效电(dian)容(rong)(rong)，激(ji)(ji)励(li)波(bo)形(xing)A加(jia)到输(shu)(shu)入端(duan)(duan)是(shi)(shi)对(dui)等效电(dian)容(rong)(rong)C的(de)(de)(de)充(chong)放(fang)(fang)电(dian)作(zuo)用(yong)，使输(shu)(shu)入端(duan)(duan)实(shi)际的(de)(de)(de)电(dian)
压波形变成B的(de)(de)(de)畸变波形，导致(zhi)开关管不(bu)能(neng)正(zheng)常开关工(gong)作(zuo)而损坏，解(jie)决的(de)(de)(de)方法就(jiu)是(shi)，只要R足够的(de)(de)(de)小，甚至没有(you)阻(zu)值，激(ji)励(li)信号(hao)能(neng)提供足够的(de)(de)(de)电(dian)(dian)流(liu)，就(jiu)能(neng)使等效电(dian)(dian)容迅速的(de)(de)(de)充电(dian)(dian)、放电(dian)(dian)，这样MOS开关管就(jiu)能(neng)迅速的(de)(de)(de)“开”、“关”，保证(zheng)了正(zheng)常工(gong)作(zuo)。由于激(ji)励(li)信号(hao)是(shi)有(you)内(nei)阻(zu)的(de)(de)(de)，信号(hao)的(de)(de)(de)激(ji)励(li)电(dian)(dian)流(liu)也是(shi)有(you)限度，我们在作(zuo)为开关管的(de)(de)(de)MOS管的(de)(de)(de)输入(ru)部分，增加(jia)一(yi)个减少内(nei)阻(zu)、增加(jia)激(ji)励(li)电(dian)(dian)流(liu)的(de)(de)(de)“灌流(liu)电(dian)(dian)路(lu)”来解(jie)决此问题(ti)，如(ru)图2-2所示。
在图2-2中；在作为(wei)开(kai)关(guan)应用的(de)大功率MOS管(guan)(guan)Q3的(de)栅极(ji)(ji)(ji)S和(he)激(ji)励信号之间(jian)增加Q1、Q2两(liang)(liang)(liang)只(zhi)开(kai)关(guan)管(guan)(guan)，此(ci)两(liang)(liang)(liang)只(zhi)管(guan)(guan)均为(wei)普通的(de)晶体三(san)极(ji)(ji)(ji)管(guan)(guan)，两(liang)(liang)(liang)只(zhi)管(guan)(guan)接成(cheng)串(chuan)联(lian)连(lian)接，Q1为(wei)NPN型(xing)Q2为(wei)PNP型(xing)，基极(ji)(ji)(ji)连(lian)接在一起（实际上(shang)是一个PNP、NPN互补的(de)射(she)极(ji)(ji)(ji)跟随器），两(liang)(liang)(liang)只(zhi)管(guan)(guan)等(deng)效是两(liang)(liang)(liang)只(zhi)在方波激(ji)励信号控(kong)制下(xia)轮流导(dao)通的(de)开(kai)关(guan)，如图2-2-A、图2-2-B
当激(ji)励方(fang)波信号的正半周来到时(shi)；晶体(ti)三极(ji)管(guan)Q1（NPN）导通(tong)、Q2（PNP）截止(zhi)，VCC经过Q1导通(tong)对MOS开关管(guan)Q3的栅(zha)极(ji)充电(dian)，由(you)于Q1是(shi)饱和导通(tong)，VCC等效是(shi)直接(jie)加到MOS管(guan)Q3的栅(zha)极(ji)，瞬间(jian)充电(dian)电(dian)流极(ji)大，充电(dian)时(shi)间(jian)极(ji)短，保证了MOS开关管(guan)Q3的迅速的“开”，如图2-2-A所示（图2-2-A和图2-2-B中的电(dian)容C为MOS管(guan)栅(zha)极(ji)S的等效电(dian)容）。
当激励方(fang)波信号(hao)的(de)负半(ban)周来到时(shi)；晶体(ti)三极管Q1（NPN）截止、Q2（PNP）导(dao)通，MOS开(kai)关(guan)管Q3的(de)栅极所(suo)(suo)充的(de)电荷，经过(guo)Q2迅(xun)速放电，由于Q2是饱和导(dao)通，放电时(shi)间极短，保(bao)证了MOS开(kai)关(guan)管Q3的(de)迅(xun)速的(de)“关(guan)”，如图2-2-B所(suo)(suo)示。
由(you)于(yu)大(da)功率(lv)(lv)MOS管在制造(zao)工艺上栅(zha)极(ji)S的(de)(de)(de)引线的(de)(de)(de)电(dian)(dian)流(liu)容量有一(yi)定(ding)的(de)(de)(de)限(xian)(xian)(xian)度，所(suo)(suo)以在Q1在饱和导通时(shi)VCC对MOS管栅(zha)极(ji)S的(de)(de)(de)瞬时(shi)充电(dian)(dian)电(dian)(dian)流(liu)巨大(da)，极(ji)易(yi)损(sun)坏MOS管的(de)(de)(de)输(shu)入端，为了保护MOS管的(de)(de)(de)安全，在具体的(de)(de)(de)电(dian)(dian)路中(zhong)必(bi)须采取(qu)措施限(xian)(xian)(xian)制瞬时(shi)充电(dian)(dian)的(de)(de)(de)电(dian)(dian)流(liu)值(zhi)，在栅(zha)极(ji)充电(dian)(dian)的(de)(de)(de)电(dian)(dian)路中(zhong)串接一(yi)个适(shi)当的(de)(de)(de)充电(dian)(dian)限(xian)(xian)(xian)流(liu)电(dian)(dian)阻(zu)R，如(ru)图2-3-A所(suo)(suo)示(shi)。充电(dian)(dian)限(xian)(xian)(xian)流(liu)电(dian)(dian)阻(zu)R的(de)(de)(de)阻(zu)值(zhi)的(de)(de)(de)选取(qu)；要根据(ju)MOS管的(de)(de)(de)输(shu)入电(dian)(dian)容的(de)(de)(de)大(da)小，激励脉(mai)冲的(de)(de)(de)频率(lv)(lv)及灌流(liu)电(dian)(dian)路的(de)(de)(de)VCC（VCC一(yi)般(ban)为12V）的(de)(de)(de)大(da)小决定(ding)一(yi)般(ban)在数十姆欧(ou)到(dao)一(yi)百欧(ou)姆之(zhi)间。
由于(yu)充电(dian)限(xian)流(liu)(liu)(liu)电(dian)阻(zu)的(de)(de)增加(jia)(jia)，使在(zai)(zai)激励方波负(fu)半周时(shi)Q2导通(tong)时(shi)放电(dian)的(de)(de)速(su)度(du)受到限(xian)制(zhi)（充电(dian)时(shi)是VCC产生(sheng)电(dian)流(liu)(liu)(liu)，放电(dian)时(shi)是栅极所(suo)充的(de)(de)电(dian)压VGS产生(sheng)电(dian)流(liu)(liu)(liu)，VGS远(yuan)远(yuan)小于(yu)VCC,R的(de)(de)存在(zai)(zai)大大的(de)(de)降低了(le)(le)放电(dian)的(de)(de)速(su)率(lv)）使MOS管(guan)(guan)的(de)(de)开关特性变坏，为了(le)(le)使R阻(zu)值在(zai)(zai)放电(dian)时(shi)不影响迅(xun)速(su)放电(dian)的(de)(de)速(su)率(lv)，在(zai)(zai)充电(dian)限(xian)流(liu)(liu)(liu)电(dian)阻(zu)R上并联(lian)一个形成放电(dian)通(tong)路的(de)(de)二极管(guan)(guan)D，图(tu)2-3-B所(suo)示。此二极管(guan)(guan)在(zai)(zai)放电(dian)时(shi)导通(tong)，在(zai)(zai)充电(dian)时(shi)反偏截(jie)止。这样增加(jia)(jia)了(le)(le)充电(dian)限(xian)流(liu)(liu)(liu)电(dian)阻(zu)和(he)放电(dian)二极管(guan)(guan)后(hou)，既保证了(le)(le)大功(gong)率(lv)MOS管(guan)(guan)的(de)(de)安全(quan)，又保证了(le)(le)MOS管(guan)(guan)，“开”与“关”的(de)(de)迅(xun)速(su)动(dong)作。
灌流电路(lu)的(de)另外一种形式(shi)，对于某些(xie)功率较小的(de)开关电源上(shang)采用(yong)的(de)MOS管往(wang)(wang)往(wang)(wang)采用(yong)了(le)图2-4-A的(de)电路(lu)方式(shi)。
图中(zhong) D为(wei)充(chong)(chong)电(dian)(dian)二极管(guan)(guan)(guan)，Q为(wei)放(fang)电(dian)(dian)三极管(guan)(guan)(guan)（PNP）。工作(zuo)过程是这(zhei)样，当激(ji)(ji)励(li)方波正半周时，D导通(tong)，对(dui)MOS管(guan)(guan)(guan)输入端(duan)等效电(dian)(dian)容充(chong)(chong)电(dian)(dian)(此(ci)时Q截止(zhi))，在(zai)当激(ji)(ji)励(li)方波负(fu)半周时，D截止(zhi)，Q导通(tong)，MOS管(guan)(guan)(guan)栅极S所充(chong)(chong)电(dian)(dian)荷，通(tong)过Q放(fang)电(dian)(dian)，MOS管(guan)(guan)(guan)完成“开”与“关(guan)”的动(dong)作(zuo)，如图2-4-B所示。此(ci)电(dian)(dian)路(lu)由激(ji)(ji)励(li)信号(hao)直接“灌流”，激(ji)(ji)励(li)信号(hao)源要求(qiu)内阻较低。该电(dian)(dian)路(lu)一般应用(yong)在(zai)功率(lv)较小的开关(guan)电(dian)(dian)源上。
MOS管在(zai)开(kai)关(guan)状(zhuang)(zhuang)态(tai)工作时(shi)(shi)(shi)；Q1、Q2是(shi)轮流导(dao)(dao)通，MOS管栅(zha)(zha)(zha)极(ji)(ji)(ji)是(shi)在(zai)反复充电(dian)(dian)(dian)、放(fang)电(dian)(dian)(dian)的状(zhuang)(zhuang)态(tai)，如果在(zai)此时(shi)(shi)(shi)关(guan)闭电(dian)(dian)(dian)源，MOS管的栅(zha)(zha)(zha)极(ji)(ji)(ji)就(jiu)有(you)两种状(zhuang)(zhuang)态(tai)；一(yi)(yi)个(ge)状(zhuang)(zhuang)态(tai)是(shi)；放(fang)电(dian)(dian)(dian)状(zhuang)(zhuang)态(tai)，栅(zha)(zha)(zha)极(ji)(ji)(ji)等效电(dian)(dian)(dian)容(rong)没(mei)有(you)电(dian)(dian)(dian)荷(he)存储(chu)，一(yi)(yi)个(ge)状(zhuang)(zhuang)态(tai)是(shi)；充电(dian)(dian)(dian)状(zhuang)(zhuang)态(tai)，栅(zha)(zha)(zha)极(ji)(ji)(ji)等效电(dian)(dian)(dian)容(rong)正好处于电(dian)(dian)(dian)荷(he)充满状(zhuang)(zhuang)态(tai)，图2-5-A所(suo)示。虽(sui)然电(dian)(dian)(dian)源切断，此时(shi)(shi)(shi)Q1、Q2也(ye)都(dou)处于断开(kai)状(zhuang)(zhuang)态(tai)，电(dian)(dian)(dian)荷(he)没(mei)有(you)释(shi)放(fang)的回路，MOS管栅(zha)(zha)(zha)极(ji)(ji)(ji)的电(dian)(dian)(dian)场仍然存在(zai)（能保(bao)持很长(zhang)时(shi)(shi)(shi)间(jian)），建立导(dao)(dao)电(dian)(dian)(dian)沟道的条件并没(mei)有(you)消失。这样在(zai)再次开(kai)机瞬(shun)间(jian)，由于激励信号(hao)还没(mei)有(you)建立，而开(kai)机瞬(shun)间(jian)MOS管的漏极(ji)(ji)(ji)电(dian)(dian)(dian)源(VDS)随机提供,在(zai)导(dao)(dao)电(dian)(dian)(dian)沟道的作用下，MOS管即刻产(chan)生(sheng)不受控的巨(ju)大漏极(ji)(ji)(ji)电(dian)(dian)(dian)流ID，引起MOS管烧坏(huai)。为了避免此现(xian)象产(chan)生(sheng)，在(zai)MOS管的栅(zha)(zha)(zha)极(ji)(ji)(ji)对源极(ji)(ji)(ji)并接(jie)一(yi)(yi)只泄放(fang)电(dian)(dian)(dian)阻R1，如图2-5-B所(suo)示，关(guan)机后栅(zha)(zha)(zha)极(ji)(ji)(ji)存储(chu)的电(dian)(dian)(dian)荷(he)通过(guo)R1迅速释(shi)放(fang)，此电(dian)(dian)(dian)阻的阻值不可太大，以(yi)保(bao)证(zheng)电(dian)(dian)(dian)荷(he)的迅速释(shi)放(fang)，一(yi)(yi)般在(zai)5K～数10K左右。
灌流电(dian)路(lu)(lu)主要(yao)是针对MOS管在(zai)作为开(kai)(kai)关管运用(yong)时其容性(xing)的输(shu)入特性(xing)，引起“开(kai)(kai)”、“关”动作滞后而设(she)置的电(dian)路(lu)(lu)，当MOS管作为其他用(yong)途；例(li)如线性(xing)放大等(deng)应用(yong)，就(jiu)没(mei)有必要(yao)设(she)置灌流电(dian)路(lu)(lu)。
实(shi)例应(ying)用电路分(fen)析
初步的(de)了解(jie)了以(yi)上的(de)关于大功率MOS管(guan)的(de)一(yi)(yi)些知识后(hou)，一(yi)(yi)般的(de)就可以(yi)简单的(de)分(fen)析，采用MOS管(guan)开关电源(yuan)的(de)电路(lu)了。
1、 三星等离子V2屏开关(guan)电源PFC部(bu)分激(ji)励(li)电路分析；
图(tu)(tu)3-1所示是三星V2屏开关(guan)电(dian)(dian)源，PFC电(dian)(dian)源部分电(dian)(dian)原理图(tu)(tu)，图(tu)(tu)3-2所示是其等效(xiao)电(dian)(dian)路框(kuang)图(tu)(tu)。
图(tu)3-1所示(shi)；是(shi)(shi)(shi)(shi)三星V2屏等(deng)离子开(kai)(kai)(kai)(kai)(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)PFC激(ji)励部分。从图(tu)中(zhong)可以看出(chu)；这是(shi)(shi)(shi)(shi)一(yi)个(ge)并(bing)联(lian)开(kai)(kai)(kai)(kai)(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)(yuan)L1是(shi)(shi)(shi)(shi)储能(neng)电(dian)(dian)(dian)感，D10是(shi)(shi)(shi)(shi)这个(ge)开(kai)(kai)(kai)(kai)(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)整(zheng)流(liu)(liu)二极(ji)(ji)管(guan)，Q1、Q2是(shi)(shi)(shi)(shi)开(kai)(kai)(kai)(kai)(kai)关(guan)(guan)(guan)管(guan)，为(wei)了保证PFC开(kai)(kai)(kai)(kai)(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)(yuan)有(you)足够的(de)(de)(de)功率输出(chu)，采用了两(liang)只MOS管(guan)Q1、Q2并(bing)联(lian)应用（图(tu)3-2所示(shi)；是(shi)(shi)(shi)(shi)该并(bing)联(lian)开(kai)(kai)(kai)(kai)(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)(yuan)等(deng)效电(dian)(dian)(dian)路图(tu)，图(tu)中(zhong)可以看出(chu)该并(bing)联(lian)开(kai)(kai)(kai)(kai)(kai)关(guan)(guan)(guan)电(dian)(dian)(dian)源(yuan)(yuan)是(shi)(shi)(shi)(shi)加在整(zheng)流(liu)(liu)桥(qiao)堆和(he)滤波电(dian)(dian)(dian)容C5之间(jian)的(de)(de)(de)），图(tu)中(zhong)Q3、Q4是(shi)(shi)(shi)(shi)灌流(liu)(liu)激(ji)励管(guan)，Q3、Q4的(de)(de)(de)基极(ji)(ji)输入开(kai)(kai)(kai)(kai)(kai)关(guan)(guan)(guan)激(ji)励信号(hao)， VCC-S-R是(shi)(shi)(shi)(shi)Q3、Q4的(de)(de)(de)VCC供电(dian)(dian)(dian)(22.5V)。两(liang)只开(kai)(kai)(kai)(kai)(kai)关(guan)(guan)(guan)管(guan)Q1、Q2的(de)(de)(de)栅(zha)极(ji)(ji)分别有(you)各自的(de)(de)(de)充电(dian)(dian)(dian)限流(liu)(liu)电(dian)(dian)(dian)阻和(he)放电(dian)(dian)(dian)二极(ji)(ji)管(guan)，R16是(shi)(shi)(shi)(shi)Q2的(de)(de)(de)在激(ji)烈信号(hao)为(wei)正半周(zhou)时的(de)(de)(de)对Q2栅(zha)极(ji)(ji)等(deng)效电(dian)(dian)(dian)容充电(dian)(dian)(dian)的(de)(de)(de)限流(liu)(liu)电(dian)(dian)(dian)阻，D7是(shi)(shi)(shi)(shi)Q2在激(ji)烈信号(hao)为(wei)负(fu)半周(zhou)时的(de)(de)(de)Q2栅(zha)极(ji)(ji)等(deng)效电(dian)(dian)(dian)容放电(dian)(dian)(dian)的(de)(de)(de)放电(dian)(dian)(dian)二极(ji)(ji)管(guan)，同样R14、D6则是(shi)(shi)(shi)(shi)Q1的(de)(de)(de)充电(dian)(dian)(dian)限流(liu)(liu)电(dian)(dian)(dian)阻和(he)放电(dian)(dian)(dian)的(de)(de)(de)放电(dian)(dian)(dian)二极(ji)(ji)管(guan)。R17和(he)R18是(shi)(shi)(shi)(shi)Q1和(he)Q2的(de)(de)(de)关(guan)(guan)(guan)机栅(zha)极(ji)(ji)电(dian)(dian)(dian)荷(he)泄放电(dian)(dian)(dian)阻。D9是(shi)(shi)(shi)(shi)开(kai)(kai)(kai)(kai)(kai)机瞬(shun)间(jian)浪(lang)涌(yong)电(dian)(dian)(dian)流(liu)(liu)分流(liu)(liu)二极(ji)(ji)管(guan)。
MOS管(guan)(guan)(guan)是(shi)属于绝缘栅(zha)(zha)场效应(ying)管(guan)(guan)(guan)，栅(zha)(zha)极(ji)(ji)(ji)是(shi)无直流通路，输入(ru)阻抗极(ji)(ji)(ji)高，极(ji)(ji)(ji)易(yi)引起(qi)(qi)静(jing)电(dian)荷(he)聚集，产生(sheng)较(jiao)(jiao)(jiao)高的(de)(de)(de)(de)(de)(de)(de)(de)(de)电(dian)压将栅(zha)(zha)极(ji)(ji)(ji)和源(yuan)极(ji)(ji)(ji)之(zhi)间的(de)(de)(de)(de)(de)(de)(de)(de)(de)绝缘层(ceng)击穿。早期生(sheng)产的(de)(de)(de)(de)(de)(de)(de)(de)(de)MOS管(guan)(guan)(guan)大(da)(da)都没有防静(jing)电(dian)的(de)(de)(de)(de)(de)(de)(de)(de)(de)措施，所(suo)(suo)以在(zai)(zai)保(bao)(bao)管(guan)(guan)(guan)及应(ying)用上(shang)要非(fei)常小(xiao)(xiao)(xiao)心，特(te)别是(shi)功率(lv)(lv)较(jiao)(jiao)(jiao)小(xiao)(xiao)(xiao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)MOS管(guan)(guan)(guan)，由于功率(lv)(lv)较(jiao)(jiao)(jiao)小(xiao)(xiao)(xiao)的(de)(de)(de)(de)(de)(de)(de)(de)(de)MOS管(guan)(guan)(guan)输入(ru)电(dian)容(rong)比较(jiao)(jiao)(jiao)小(xiao)(xiao)(xiao)，接(jie)触(chu)到静(jing)电(dian)时产生(sheng)的(de)(de)(de)(de)(de)(de)(de)(de)(de)电(dian)压较(jiao)(jiao)(jiao)高，容(rong)易(yi)引起(qi)(qi)静(jing)电(dian)击穿。而(er)近(jin)期的(de)(de)(de)(de)(de)(de)(de)(de)(de)增强型(xing)大(da)(da)功率(lv)(lv)MOS管(guan)(guan)(guan)则有比较(jiao)(jiao)(jiao)大(da)(da)的(de)(de)(de)(de)(de)(de)(de)(de)(de)区别，首先(xian)由于功能(neng)较(jiao)(jiao)(jiao)大(da)(da)输入(ru)电(dian)容(rong)也比较(jiao)(jiao)(jiao)大(da)(da)，这样接(jie)触(chu)到静(jing)电(dian)就有一(yi)个充(chong)电(dian)的(de)(de)(de)(de)(de)(de)(de)(de)(de)过程，产生(sheng)的(de)(de)(de)(de)(de)(de)(de)(de)(de)电(dian)压较(jiao)(jiao)(jiao)小(xiao)(xiao)(xiao)，引起(qi)(qi)击穿的(de)(de)(de)(de)(de)(de)(de)(de)(de)可能(neng)较(jiao)(jiao)(jiao)小(xiao)(xiao)(xiao)，再(zai)者现(xian)在(zai)(zai)的(de)(de)(de)(de)(de)(de)(de)(de)(de)大(da)(da)功率(lv)(lv)MOS管(guan)(guan)(guan)在(zai)(zai)内部的(de)(de)(de)(de)(de)(de)(de)(de)(de)栅(zha)(zha)极(ji)(ji)(ji)和源(yuan)极(ji)(ji)(ji)有一(yi)个保(bao)(bao)护(hu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)稳压管(guan)(guan)(guan)DZ（图4-1所(suo)(suo)示）,把静(jing)电(dian)嵌位于保(bao)(bao)护(hu)稳压二极(ji)(ji)(ji)管(guan)(guan)(guan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)稳压值(zhi)以下，有效的(de)(de)(de)(de)(de)(de)(de)(de)(de)保(bao)(bao)护(hu)了栅(zha)(zha)极(ji)(ji)(ji)和源(yuan)极(ji)(ji)(ji)的(de)(de)(de)(de)(de)(de)(de)(de)(de)绝缘层(ceng)，不同功率(lv)(lv)、不同型(xing)号的(de)(de)(de)(de)(de)(de)(de)(de)(de)MOS管(guan)(guan)(guan)其保(bao)(bao)护(hu)稳压二极(ji)(ji)(ji)管(guan)(guan)(guan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)稳压值(zhi)是(shi)不同的(de)(de)(de)(de)(de)(de)(de)(de)(de)。虽然MOS管(guan)(guan)(guan)内部有了保(bao)(bao)护(hu)措施，我们(men)操作时也应(ying)按照防静(jing)电(dian)的(de)(de)(de)(de)(de)(de)(de)(de)(de)操作规程进行，这是(shi)一(yi)个合(he)格的(de)(de)(de)(de)(de)(de)(de)(de)(de)维修员应(ying)该具备的(de)(de)(de)(de)(de)(de)(de)(de)(de)。
在修理电视机及电器(qi)设备(bei)时，会遇到各种元器(qi)件的损坏，MOS管(guan)也在其中，这就(jiu)是我们的维修人员如何利用常用的万用表来判(pan)断MOS管(guan)的好坏、优劣。在更换MOS管(guan)是如果没有相同厂家(jia)及相同型号时，如何代换的问题。
作为一(yi)般的(de)电(dian)器电(dian)视机维(wei)(wei)修(xiu)人员在测量晶体(ti)三极(ji)(ji)管(guan)(guan)或二极(ji)(ji)管(guan)(guan)时，一(yi)般是采(cai)用普通(tong)的(de)万(wan)用表(biao)来判断(duan)三极(ji)(ji)管(guan)(guan)或者二极(ji)(ji)管(guan)(guan)的(de)好坏(huai)，虽然对所判断(duan)的(de)三极(ji)(ji)管(guan)(guan)或二极(ji)(ji)管(guan)(guan)的(de)电(dian)气参数没(mei)法确(que)(que)认(ren)，但是只要方法正确(que)(que)对于确(que)(que)认(ren)晶体(ti)三极(ji)(ji)管(guan)(guan)的(de)“好”与“坏(huai)”还是没(mei)有问题(ti)的(de)。同样MOS管(guan)(guan)也可(ke)以应用万(wan)用表(biao)来判断(duan)其“好”与“坏(huai)”,从一(yi)般的(de)维(wei)(wei)修(xiu)来说(shuo)，也可(ke)以满足需求(qiu)了。
检(jian)测(ce)必须采用指针(zhen)式(shi)万(wan)用表（数(shu)字表是不适宜测(ce)量半导体(ti)器件的(de)）。对于大功率MOS管(guan)开关管(guan)都属N沟道增强(qiang)型，各生产(chan)厂的(de)产(chan)品也几乎都采用相(xiang)同的(de)TO-220F封装(zhuang)形式(shi)（指用于开关电源(yuan)(yuan)中功率为50—200W的(de)场效应开关管(guan)），其三个电极(ji)排列也一(yi)致(zhi)，即将(jiang)三只引脚(jiao)(jiao)(jiao)向下，打(da)印型号面向自巳，左侧(ce)引脚(jiao)(jiao)(jiao)为栅极(ji)，右测(ce)引脚(jiao)(jiao)(jiao)为源(yuan)(yuan)极(ji)，中间引脚(jiao)(jiao)(jiao)为漏极(ji)如图5-1所示。
首(shou)先在测(ce)(ce)量(liang)前应该会(hui)(hui)(hui)使用(yong)(yong)(yong)万(wan)(wan)用(yong)(yong)(yong)表(biao)，特(te)别是(shi)(shi)(shi)欧(ou)(ou)姆(mu)(mu)档(dang)的(de)(de)应用(yong)(yong)(yong)，要了(le)解欧(ou)(ou)姆(mu)(mu)挡(dang)才会(hui)(hui)(hui)正(zheng)(zheng)确应用(yong)(yong)(yong)欧(ou)(ou)姆(mu)(mu)挡(dang)来测(ce)(ce)量(liang)晶体三(san)极(ji)(ji)管(guan)(guan)及大功率MOS管(guan)(guan)（现在很多(duo)的(de)(de)从事(shi)修理(li)人员，不会(hui)(hui)(hui)使用(yong)(yong)(yong)万(wan)(wan)用(yong)(yong)(yong)表(biao)，特(te)别是(shi)(shi)(shi)万(wan)(wan)用(yong)(yong)(yong)表(biao)的(de)(de)欧(ou)(ou)姆(mu)(mu)挡(dang)，这(zhei)绝不是(shi)(shi)(shi)危言耸听，问问他？他知道欧(ou)(ou)姆(mu)(mu)挡(dang)的(de)(de)R×1 R×10 R×100 R×1K R×10K，在表(biao)笔(bi)短路(lu)时(shi)(shi)，流过(guo)表(biao)笔(bi)的(de)(de)电(dian)流分别有多(duo)大吗？这(zhei)个电(dian)流就是(shi)(shi)(shi)流过(guo)被(bei)测(ce)(ce)元件的(de)(de)电(dian)流。他知道欧(ou)(ou)姆(mu)(mu)挡(dang)在表(biao)笔(bi)开路(lu)时(shi)(shi)表(biao)笔(bi)两端的(de)(de)电(dian)压有多(duo)大吗？这(zhei)就是(shi)(shi)(shi)在测(ce)(ce)量(liang)时(shi)(shi)被(bei)测(ce)(ce)元件在测(ce)(ce)量(liang)时(shi)(shi)所承受的(de)(de)电(dian)压）关于正(zheng)(zheng)确使用(yong)(yong)(yong)万(wan)(wan)用(yong)(yong)(yong)表(biao)欧(ou)(ou)姆(mu)(mu)挡(dang)的(de)(de)问题(ti)，可(ke)以(yi)参(can)阅可(ke)以(yi)参(can)阅“您会(hui)(hui)(hui)用(yong)(yong)(yong)万(wan)(wan)用(yong)(yong)(yong)表(biao)的(de)(de)欧(ou)(ou)姆(mu)(mu)挡(dang)测(ce)(ce)量(liang)二(er)极(ji)(ji)管(guan)(guan)、三(san)极(ji)(ji)管(guan)(guan)吗？”“可(ke)以(yi)参(can)阅本(ben)博(bo)客“您会(hui)(hui)(hui)用(yong)(yong)(yong)万(wan)(wan)用(yong)(yong)(yong)表(biao)的(de)(de)欧(ou)(ou)姆(mu)(mu)挡(dang)测(ce)(ce)量(liang)二(er)极(ji)(ji)管(guan)(guan)、三(san)极(ji)(ji)管(guan)(guan)吗？”一文，因篇(pian)幅(fu)问题(ti)这(zhei)里(li)不再赘述。
用万用表(biao)的(de)欧(ou)姆挡的(de)欧(ou)姆中心刻度(du)不能太大(da)(da)，最好(hao)小于12Ω（500型表(biao)为12Ω），这样在(zai)R×1挡可以有(you)较(jiao)大(da)(da)的(de)电流，对于PN结的(de)正向特(te)性判断比(bi)较(jiao)准确。万用表(biao)R×10K挡内(nei)部(bu)的(de)电池最好(hao)大(da)(da)于9V，这样在(zai)测量PN结反相漏(lou)电流时(shi)比(bi)较(jiao)准确，否则(ze)漏(lou)电也测不出(chu)来。
现在(zai)由于生产工艺(yi)的进步，出厂的筛(shai)选(xuan)、检测都很严格，我们(men)一般判(pan)断只要判(pan)断MOS管不漏电(dian)、不击穿短路、内部(bu)不断路、能放大就(jiu)可以了，方法极为简单：
采用(yong)万用(yong)表(biao)(biao)(biao)的(de)(de)(de)(de)R×10K挡；R×10K挡内(nei)部(bu)的(de)(de)(de)(de)电(dian)池一(yi)般是(shi)(shi)(shi)9V加1.5V达到(dao)10.5V这(zhei)个电(dian)压一(yi)般判(pan)断PN结点反相漏电(dian)是(shi)(shi)(shi)够了，万用(yong)表(biao)(biao)(biao)的(de)(de)(de)(de)红表(biao)(biao)(biao)笔(bi)是(shi)(shi)(shi)负电(dian)位（接内(nei)部(bu)电(dian)池的(de)(de)(de)(de)负极），万用(yong)表(biao)(biao)(biao)的(de)(de)(de)(de)黑表(biao)(biao)(biao)笔(bi)是(shi)(shi)(shi)正电(dian)位（接内(nei)部(bu)电(dian)池的(de)(de)(de)(de)正极），图5-2所示。
把(ba)红表(biao)笔接到MOS管(guan)的源(yuan)极(ji)S；把(ba)黑(hei)表(biao)笔接到MOS管(guan)的漏(lou)极(ji)D，此(ci)时(shi)表(biao)针指示(shi)应(ying)该为(wei)无穷大，如图5-3所示(shi)。如果有欧姆指数，说明被(bei)测管(guan)有漏(lou)电现象，此(ci)管(guan)不能用。
保持上述(shu)状态；此时用一(yi)只100K～200K电(dian)(dian)(dian)阻连接于栅极(ji)(ji)和(he)(he)漏(lou)极(ji)(ji)，如图5-4所(suo)示(shi)；这时表针指(zhi)示(shi)欧姆数应该(gai)越小(xiao)越好(hao)，一(yi)般能指(zhi)示(shi)到0欧姆，这时是(shi)正电(dian)(dian)(dian)荷通过100K电(dian)(dian)(dian)阻对大功(gong)率MOS管栅极(ji)(ji)充电(dian)(dian)(dian)，产(chan)生栅极(ji)(ji)电(dian)(dian)(dian)场，由于电(dian)(dian)(dian)场产(chan)生导致导电(dian)(dian)(dian)沟道致使漏(lou)极(ji)(ji)和(he)(he)源(yuan)极(ji)(ji)导通，所(suo)以(yi)万用表指(zhi)针偏(pian)转，偏(pian)转的角度(du)大（欧姆指(zhi)数小(xiao)）证明放电(dian)(dian)(dian)性能好(hao)。
此时在图5-4的状(zhuang)态；再(zai)把连接的电阻(zu)移开，这时万用表的指针仍(reng)然(ran)应(ying)该(gai)是MOS管导通的指数(shu)不变(bian)，如(ru)图5-5所示。虽然(ran)电阻(zu)拿(na)开，但是因(yin)为电阻(zu)对(dui)栅极(ji)所充(chong)的电荷并没有消失，栅极(ji)电场继续维持，内(nei)部导电沟道仍(reng)然(ran)保(bao)持，这就(jiu)是绝缘(yuan)栅型MOS管的特点。如(ru)果电阻(zu)拿(na)开表针会慢慢的逐步的退回到高阻(zu)甚至退回到无(wu)穷大，要(yao)考虑该(gai)被测管栅极(ji)漏电。
这时用一根导线，连(lian)接(jie)被测管(guan)的(de)栅极(ji)和源(yuan)极(ji)，万(wan)用表的(de)指(zhi)针立即(ji)返回(hui)到无(wu)(wu)穷大，如图(tu)5-6所示。导线的(de)连(lian)接(jie)使被测MOS管(guan)，栅极(ji)电荷(he)释放，内部电场消失(shi)；导电沟道(dao)也消失(shi)，所以漏极(ji)和源(yuan)极(ji)之(zhi)间电阻又变成无(wu)(wu)穷大。
在修理电(dian)(dian)(dian)视机及各种(zhong)电(dian)(dian)(dian)器设备时(shi)，遇到(dao)元(yuan)器件(jian)损坏应该采(cai)用相同(tong)型(xing)(xing)号的(de)元(yuan)件(jian)进(jin)(jin)行(xing)更换(huan)。但(dan)是(shi)(shi)，有时(shi)相同(tong)的(de)元(yuan)件(jian)手边没(mei)有，就(jiu)要(yao)采(cai)用其(qi)(qi)他型(xing)(xing)号的(de)进(jin)(jin)行(xing)代换(huan)，这样就(jiu)要(yao)考(kao)虑到(dao)各方面的(de)性能(neng)、参(can)数、外形尺寸(cun)等，例如电(dian)(dian)(dian)视的(de)里面的(de)行(xing)输(shu)出管(guan)(guan)(guan)，只要(yao)考(kao)虑耐压(ya)、电(dian)(dian)(dian)流、功(gong)率(lv)一般(ban)是(shi)(shi)可(ke)以进(jin)(jin)行(xing)代换(huan)的(de)（行(xing)输(shu)出管(guan)(guan)(guan)外观尺寸(cun)几乎相同(tong)），而且功(gong)率(lv)往(wang)往(wang)大(da)(da)(da)一些(xie)更好(hao)。对于MOS管(guan)(guan)(guan)代换(huan)虽然也(ye)是(shi)(shi)这一原(yuan)(yuan)则，最(zui)好(hao)是(shi)(shi)原(yuan)(yuan)型(xing)(xing)号的(de)最(zui)好(hao)，特别是(shi)(shi)不要(yao)追求功(gong)率(lv)要(yao)大(da)(da)(da)一些(xie)，因为功(gong)率(lv)大(da)(da)(da)；输(shu)入电(dian)(dian)(dian)容(rong)就(jiu)大(da)(da)(da)，换(huan)了(le)(le)后和(he)激(ji)(ji)励(li)电(dian)(dian)(dian)路就(jiu)不匹配了(le)(le)，激(ji)(ji)励(li)灌流电(dian)(dian)(dian)路的(de)充电(dian)(dian)(dian)限流电(dian)(dian)(dian)阻(zu)的(de)阻(zu)值的(de)大(da)(da)(da)小(xiao)和(he)MOS管(guan)(guan)(guan)的(de)输(shu)入电(dian)(dian)(dian)容(rong)是(shi)(shi)有关系(xi)的(de)，选用功(gong)率(lv)大(da)(da)(da)的(de)尽管(guan)(guan)(guan)容(rong)量大(da)(da)(da)了(le)(le)，但(dan)输(shu)入电(dian)(dian)(dian)容(rong)也(ye)就(jiu)大(da)(da)(da)了(le)(le)，激(ji)(ji)励(li)电(dian)(dian)(dian)路的(de)配合就(jiu)不好(hao)了(le)(le)，这反而会使(shi)MOS管(guan)(guan)(guan)的(de)开、关性能(neng)变(bian)坏。所示代换(huan)不同(tong)型(xing)(xing)号的(de)MOS管(guan)(guan)(guan)，要(yao)考(kao)虑到(dao)其(qi)(qi)输(shu)入电(dian)(dian)(dian)容(rong)这一参(can)数。例如有一款42寸(cun)液晶电(dian)(dian)(dian)视的(de)背光高压(ya)板损坏，经过检查是(shi)(shi)内部的(de)大(da)(da)(da)功(gong)率(lv)MOS管(guan)(guan)(guan)损坏，因为无原(yuan)(yuan)型(xing)(xing)号的(de)代换(huan)，就(jiu)选用了(le)(le)一个，电(dian)(dian)(dian)压(ya)、电(dian)(dian)(dian)流、功(gong)率(lv)均不小(xiao)于原(yuan)(yuan)来(lai)的(de)MOS管(guan)(guan)(guan)替换(huan)，结(jie)果是(shi)(shi)背光管(guan)(guan)(guan)出现连续的(de)闪烁（启动(dong)困难），最(zui)后还是(shi)(shi)换(huan)上原(yuan)(yuan)来(lai)一样型(xing)(xing)号的(de)才解决(jue)问题。
检测到MOS管(guan)损(sun)(sun)坏后，更(geng)换(huan)时(shi)其周边的灌流(liu)电(dian)路的元(yuan)件也(ye)(ye)必须全部更(geng)换(huan)，因为(wei)该(gai)(gai)MOS管(guan)的损(sun)(sun)坏也(ye)(ye)可能是灌流(liu)电(dian)路元(yuan)件的欠(qian)佳引(yin)起(qi)MOS管(guan)损(sun)(sun)坏。即便(bian)是MOS管(guan)本(ben)身原(yuan)因损(sun)(sun)坏，在(zai)MOS管(guan)击穿的瞬间(jian)，灌流(liu)电(dian)路元(yuan)件也(ye)(ye)受到伤害，也(ye)(ye)应该(gai)(gai)更(geng)换(huan)。就像我们有(you)很多高明的维修师(shi)傅(fu)在(zai)修理A3开关(guan)电(dian)源(yuan)时(shi)；只(zhi)要发现开关(guan)管(guan)击穿，就也(ye)(ye)把前面的2SC3807激励管(guan)一起(qi)更(geng)换(huan)一样(yang)道理（尽管(guan)2SC3807管(guan)，用万用表测量是好的）。
mos在控制器电路中的工作状(zhuang)态：开通过程（由截(jie)(jie)止(zhi)到导通的过渡过程）、导通状(zhuang)态、关断过程（由导通到截(jie)(jie)止(zhi)的过渡过程）、截(jie)(jie)止(zhi)状(zhuang)态。
Mos主要(yao)损(sun)耗(hao)(hao)(hao)也对应这(zhei)几个(ge)状(zhuang)态，开(kai)关损(sun)耗(hao)(hao)(hao)（开(kai)通过(guo)程和(he)关断过(guo)程），导通损(sun)耗(hao)(hao)(hao)，截止损(sun)耗(hao)(hao)(hao)（漏(lou)电流(liu)引起的(de)，这(zhei)个(ge)忽略不(bu)计），还(hai)有雪崩能(neng)量损(sun)耗(hao)(hao)(hao)。只要(yao)把这(zhei)些(xie)损(sun)耗(hao)(hao)(hao)控制在mos承受规(gui)格之内，mos即会正常(chang)工作，超出承受范围(wei)，即发生(sheng)损(sun)坏。而开(kai)关损(sun)耗(hao)(hao)(hao)往往大(da)于导通状(zhuang)态损(sun)耗(hao)(hao)(hao)（不(bu)同(tong)mos这(zhei)个(ge)差距可(ke)能(neng)很大(da))。
过流(liu)----------持续大电(dian)流(liu)或瞬间超(chao)大电(dian)流(liu)引起的结温过高而烧毁；
过(guo)压(ya)----------源漏过(guo)压(ya)击穿、源栅(zha)极过(guo)压(ya)击穿；
静(jing)(jing)电(dian)(dian)----------静(jing)(jing)电(dian)(dian)击穿。CMOS电(dian)(dian)路都怕静(jing)(jing)电(dian)(dian)；
Mos开关原理（简要）。Mos是电压驱动型器件，只要栅极和源级间给一个适当电压，源级和漏级间通路就形成。这个电流通路的电阻被成为mos内阻，就是导通电阻
Mos问题远没这么简单，麻(ma)烦在它的(de)(de)栅极(ji)和源(yuan)级(ji)(ji)间(jian)(jian)，源(yuan)级(ji)(ji)和漏(lou)(lou)级(ji)(ji)间(jian)(jian)，栅极(ji)和漏(lou)(lou)级(ji)(ji)间(jian)(jian)内(nei)部(bu)都有等效电(dian)(dian)容(rong)。所以给栅极(ji)电(dian)(dian)压(ya)的(de)(de)过程就(jiu)是给电(dian)(dian)容(rong)充(chong)电(dian)(dian)的(de)(de)过程（电(dian)(dian)容(rong)电(dian)(dian)压(ya)不能突(tu)变），所以mos源(yuan)级(ji)(ji)和漏(lou)(lou)级(ji)(ji)间(jian)(jian)由截止到导通的(de)(de)开通过程受栅极(ji)电(dian)(dian)容(rong)的(de)(de)充(chong)电(dian)(dian)过程制约。
然而(er)，这(zhei)三个(ge)等效(xiao)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)是(shi)构成串并联组合关(guan)系，它们相互(hu)影响(xiang)，并不是(shi)独立的，如果独立的就(jiu)很简单了(le)。其(qi)中一(yi)个(ge)关(guan)键电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)就(jiu)是(shi)栅(zha)极(ji)和(he)漏级间的电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)Cgd，这(zhei)个(ge)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)业界称为米(mi)勒(le)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)。这(zhei)个(ge)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)不是(shi)恒定的，随(sui)栅(zha)极(ji)和(he)漏级间电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)压变化而(er)迅(xun)速变化。这(zhei)个(ge)米(mi)勒(le)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)是(shi)栅(zha)极(ji)和(he)源级电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)充(chong)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的绊脚(jiao)石(shi)，因(yin)为栅(zha)极(ji)给(ji)栅(zha)-源电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)Cgs充(chong)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)达(da)到一(yi)个(ge)平(ping)台后(hou)，栅(zha)极(ji)的充(chong)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流必须给(ji)米(mi)勒(le)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)(rong)Cgd充(chong)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，这(zhei)时(shi)栅(zha)极(ji)和(he)源级间电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)压不再(zai)升高(gao)，达(da)到一(yi)个(ge)平(ping)台，这(zhei)个(ge)是(shi)米(mi)勒(le)平(ping)台（米(mi)勒(le)平(ping)台就(jiu)是(shi)给(ji)Cgd充(chong)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的过程(cheng)），米(mi)勒(le)平(ping)台大家首(shou)先(xian)想(xiang)到的麻烦(fan)就(jiu)是(shi)米(mi)勒(le)振荡。（即(ji)，栅(zha)极(ji)先(xian)给(ji)Cgs充(chong)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，到达(da)一(yi)定平(ping)台后(hou)再(zai)给(ji)Cgd充(chong)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)）
因为(wei)这(zhei)个(ge)时候源级和漏级间电(dian)(dian)压迅速(su)变化，内部电(dian)(dian)容相应迅速(su)充(chong)放(fang)电(dian)(dian)，这(zhei)些电(dian)(dian)流(liu)脉冲会导(dao)致mos寄生(sheng)电(dian)(dian)感产生(sheng)很(hen)大感抗，这(zhei)里面就有电(dian)(dian)容，电(dian)(dian)感，电(dian)(dian)阻(zu)组成震荡(dang)电(dian)(dian)路（能形成2个(ge)回(hui)路），并且电(dian)(dian)流(liu)脉冲越(yue)强频率越(yue)高震荡(dang)幅度越(yue)大。所以(yi)最关键(jian)的(de)问题就是(shi)这(zhei)个(ge)米勒平台如何过(guo)渡。
Gs极加电容，减(jian)慢mos管导通时间，有助于减(jian)小米勒振荡(dang)。防止mos管烧毁。
过(guo)快的(de)(de)充电(dian)会导(dao)致激烈的(de)(de)米(mi)勒(le)震(zhen)荡，但过(guo)慢的(de)(de)充电(dian)虽(sui)减(jian)小了震(zhen)荡，但会延长开关从(cong)(cong)而(er)增(zeng)加开关损耗。Mos开通(tong)(tong)(tong)过(guo)程(cheng)(cheng)源级(ji)和漏级(ji)间等效电(dian)阻(zu)(zu)(zu)相当于从(cong)(cong)无(wu)穷大(da)电(dian)阻(zu)(zu)(zu)到(dao)(dao)阻(zu)(zu)(zu)值很(hen)小的(de)(de)导(dao)通(tong)(tong)(tong)内(nei)(nei)阻(zu)(zu)(zu)（导(dao)通(tong)(tong)(tong)内(nei)(nei)阻(zu)(zu)(zu)一(yi)般(ban)低(di)压mos只(zhi)有(you)几毫欧姆）的(de)(de)一(yi)个转变过(guo)程(cheng)(cheng)。比如一(yi)个mos最大(da)电(dian)流100a，电(dian)池电(dian)压96v，在开通(tong)(tong)(tong)过(guo)程(cheng)(cheng)中，有(you)那么一(yi)瞬间（刚进入(ru)米(mi)勒(le)平台时(shi)(shi)(shi)）mos发热功率(lv)是(shi)P=V*I(此时(shi)(shi)(shi)电(dian)流已(yi)达最大(da)，负载尚未跑(pao)起来(lai)，所有(you)的(de)(de)功率(lv)都降落在MOS管上)，P=96*100=9600w！这时(shi)(shi)(shi)它发热功率(lv)最大(da)，然后发热功率(lv)迅速降低(di)直(zhi)到(dao)(dao)完全(quan)导(dao)通(tong)(tong)(tong)时(shi)(shi)(shi)功率(lv)变成100*100*0.003=30w（这里假设(she)这个mos导(dao)通(tong)(tong)(tong)内(nei)(nei)阻(zu)(zu)(zu)3毫欧姆）。开关过(guo)程(cheng)(cheng)中这个发热功率(lv)变化是(shi)惊(jing)人的(de)(de)。
如(ru)果开(kai)(kai)通时间(jian)慢，意味(wei)着发(fa)热从9600w到(dao)30w过渡的(de)慢，mos结(jie)温会升高的(de)厉害。所以(yi)开(kai)(kai)关(guan)越慢，结(jie)温越高，容(rong)易烧(shao)(shao)mos。为了(le)不烧(shao)(shao)mos，只能降(jiang)低(di)(di)mos限(xian)流或(huo)(huo)者降(jiang)低(di)(di)电(dian)池(chi)(chi)电(dian)压(ya)，比如(ru)给它限(xian)制50a或(huo)(huo)电(dian)压(ya)降(jiang)低(di)(di)一(yi)半(ban)成(cheng)48v，这(zhei)样(yang)开(kai)(kai)关(guan)发(fa)热损(sun)(sun)耗(hao)(hao)(hao)也(ye)降(jiang)低(di)(di)了(le)一(yi)半(ban)。不烧(shao)(shao)管子(zi)了(le)。这(zhei)也(ye)是高压(ya)控(kong)容(rong)易烧(shao)(shao)管子(zi)原因，高压(ya)控(kong)制器和(he)低(di)(di)压(ya)的(de)只有开(kai)(kai)关(guan)损(sun)(sun)耗(hao)(hao)(hao)不一(yi)样(yang)（开(kai)(kai)关(guan)损(sun)(sun)耗(hao)(hao)(hao)和(he)电(dian)池(chi)(chi)端电(dian)压(ya)基本成(cheng)正比，假设限(xian)流一(yi)样(yang)），导通损(sun)(sun)耗(hao)(hao)(hao)完全受mos内阻(zu)决定(ding)，和(he)电(dian)池(chi)(chi)电(dian)压(ya)没任(ren)何关(guan)系。
其(qi)实整(zheng)个(ge)mos开(kai)(kai)通过程(cheng)非常复杂(za)。里面变(bian)量太(tai)多。总之就(jiu)是开(kai)(kai)关(guan)(guan)慢不容(rong)易米(mi)勒震(zhen)荡，但开(kai)(kai)关(guan)(guan)损(sun)(sun)(sun)耗(hao)(hao)大，管(guan)子(zi)发热大，开(kai)(kai)关(guan)(guan)速(su)度快理论(lun)上开(kai)(kai)关(guan)(guan)损(sun)(sun)(sun)耗(hao)(hao)低(di)(di)（只(zhi)要能(neng)有(you)(you)效抑制(zhi)米(mi)勒震(zhen)荡），但是往往米(mi)勒震(zhen)荡很厉害(hai)（如果米(mi)勒震(zhen)荡很严重(zhong)，可能(neng)在米(mi)勒平(ping)台就(jiu)烧管(guan)子(zi)了），反而(er)开(kai)(kai)关(guan)(guan)损(sun)(sun)(sun)耗(hao)(hao)也大，并且上臂(bei)mos震(zhen)荡更有(you)(you)可能(neng)引起下臂(bei)mos误导(dao)(dao)通，形成(cheng)上下臂(bei)短(duan)路。所以这(zhei)个(ge)很考验设计师的驱动电(dian)路布(bu)线和主回路布(bu)线技能(neng)。最终就(jiu)是找个(ge)平(ping)衡点（一般开(kai)(kai)通过程(cheng)不超过1us）。开(kai)(kai)通损(sun)(sun)(sun)耗(hao)(hao)这(zhei)个(ge)最简单，只(zhi)和导(dao)(dao)通电(dian)阻成(cheng)正比，想大电(dian)流(liu)低(di)(di)损(sun)(sun)(sun)耗(hao)(hao)找内阻低(di)(di)的。
下面介绍下对普通用户(hu)实用点的。
Mos挑选的重要(yao)参数简要(yao)说明。以datasheet举例(li)说明。
栅(zha)极(ji)电(dian)(dian)荷(he)。Qgs, Qgd Qgs:指的(de)是栅(zha)极(ji)从0v充电(dian)(dian)到(dao)对应电(dian)(dian)流米(mi)勒平(ping)台(tai)时总充入电(dian)(dian)荷(he)（实际电(dian)(dian)流不(bu)同(tong)，这(zhei)个(ge)(ge)平(ping)台(tai)高度不(bu)同(tong)，电(dian)(dian)流越大，平(ping)台(tai)越高，这(zhei)个(ge)(ge)值越大）。这(zhei)个(ge)(ge)阶(jie)段是给Cgs充电(dian)(dian)（也(ye)相当于Ciss，输入电(dian)(dian)容(rong)）。 Qgd:指的(de)是整个(ge)(ge)米(mi)勒平(ping)台(tai)的(de)总充电(dian)(dian)电(dian)(dian)荷(he)（在这(zhei)称(cheng)为米(mi)勒电(dian)(dian)荷(he)）。这(zhei)个(ge)(ge)过程给Cgd（Crss，这(zhei)个(ge)(ge)电(dian)(dian)容(rong)随着gd电(dian)(dian)压不(bu)同(tong)迅速(su)变化）充电(dian)(dian)。
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