利盈娱乐(中国)创新平台有限公司

普通状况下普遍用于高端驱动的MOS,导通时需求是栅极电压大于源极电压。而高端驱动的MOS管导通时源极电压与漏极电压（VCC）相同，所以这时栅极电压要比VCC大4V或10V.假如在同一个系统里，要得到比VCC大的电压，就要特地的升压电路了。很多马达驱动器都集成了电荷泵，要留意的是应该选择适宜的外接电容，以得到足够的短路电流去驱动MOS管。

MOS管是(shi)电压驱动，按理说(shuo)只需栅极(ji)(ji)电(dian)(dian)(dian)(dian)压到(dao)(dao)到(dao)(dao)开启电(dian)(dian)(dian)(dian)压就能(neng)导(dao)通(tong)(tong)DS,栅极(ji)(ji)串多大电(dian)(dian)(dian)(dian)阻(zu)均能(neng)导(dao)通(tong)(tong)。但(dan)(dan)假如请(qing)求开关(guan)频率较(jiao)高(gao)时(shi)(shi)，栅对(dui)地或VCC能(neng)够看做是一(yi)(yi)个(ge)电(dian)(dian)(dian)(dian)容(rong)，关(guan)于(yu)一(yi)(yi)个(ge)电(dian)(dian)(dian)(dian)容(rong)来说(shuo)，串的电(dian)(dian)(dian)(dian)阻(zu)越大，栅极(ji)(ji)到(dao)(dao)达导(dao)通(tong)(tong)电(dian)(dian)(dian)(dian)压时(shi)(shi)间(jian)越长(zhang)，MOS处(chu)于(yu)半导(dao)通(tong)(tong)状态时(shi)(shi)间(jian)也越长(zhang)，在半导(dao)通(tong)(tong)状态内(nei)阻(zu)较(jiao)大，发热也会增(zeng)大，极(ji)(ji)易损坏MOS,所以高(gao)频时(shi)(shi)栅极(ji)(ji)栅极(ji)(ji)串的电(dian)(dian)(dian)(dian)阻(zu)不但(dan)(dan)要小，普通(tong)(tong)要加前置驱动电(dian)(dian)(dian)(dian)路的。下面我们先来理解一(yi)(yi)下MOS管(guan)开关(guan)的根(gen)底学问。

MOS管的开关特性

一、静态特性
MOS管作为开关(guan)元件，同(tong)样是工作在截止或导通两种(zhong)状态。由于MOS管是电压(ya)控制元件，所以主(zhu)要(yao)由栅源(yuan)电压(ya)uGS决议其工作状态。　　工作特性(xing)如下：

uGS<开启(qi)电压UT:MOS管(guan)工作在截止(zhi)区，漏源(yuan)电流iDS根本为0,输出电压uDS≈UDD,MOS管(guan)处于(yu)“断开”状态，其(qi)等效电路如下图所示。

uGS>开启电(dian)压UT:MOS管工作在(zai)导通区，漏源电(dian)流iDS=UDD/（RD+rDS）。其中，rDS为MOS管导通时的漏源电(dian)阻。输出电(dian)压UDS=UDD·rDS/（RD+rDS），假如rDS《RD,则uDS≈0V,MOS管处于(yu)“接(jie)通”状态，其等效电(dian)路如上图（c）所示。

二、动态特性
MOS管(guan)在(zai)(zai)导(dao)通(tong)(tong)与(yu)截止两种状态发(fa)作转换时(shi)同(tong)样存在(zai)(zai)过渡(du)过程，但其动态特(te)性主要取决于与(yu)电路有关的(de)杂散电容充、放电所需的(de)时(shi)间(jian)，而管(guan)子自身导(dao)通(tong)(tong)和截止时(shi)电荷(he)积聚和消散的(de)时(shi)间(jian)是很小的(de)。下图 （a）和（b）分别给出(chu)了一个NMOS管(guan)组(zu)成的(de)电路及其动态特(te)性表示图。

NMOS管动态特性表示图

当(dang)输(shu)入电(dian)(dian)压(ya)ui由(you)(you)高(gao)(gao)变(bian)低(di)，MOS管(guan)(guan)由(you)(you)导(dao)(dao)通(tong)状(zhuang)(zhuang)态转(zhuan)换(huan)(huan)为(wei)截(jie)(jie)止(zhi)状(zhuang)(zhuang)态时(shi)(shi)(shi)，电(dian)(dian)源(yuan)UDD经(jing)过(guo)RD向杂散电(dian)(dian)容CL充电(dian)(dian)，充电(dian)(dian)时(shi)(shi)(shi)间常数τ1=RDCL.所以，输(shu)出电(dian)(dian)压(ya)uo要(yao)经(jing)过(guo)一定延时(shi)(shi)(shi)才(cai)由(you)(you)低(di)电(dian)(dian)平变(bian)为(wei)高(gao)(gao)电(dian)(dian)平；当(dang)输(shu)入电(dian)(dian)压(ya)ui由(you)(you)低(di)变(bian)高(gao)(gao)，MOS管(guan)(guan)由(you)(you)截(jie)(jie)止(zhi)状(zhuang)(zhuang)态转(zhuan)换(huan)(huan)为(wei)导(dao)(dao)通(tong)状(zhuang)(zhuang)态时(shi)(shi)(shi)，杂散电(dian)(dian)容CL上的(de)电(dian)(dian)荷经(jing)过(guo)rDS停止(zhi)放电(dian)(dian)，其(qi)放电(dian)(dian)时(shi)(shi)(shi)间常数τ2≈rDSCL.可见，输(shu)出电(dian)(dian)压(ya)Uo也要(yao)经(jing)过(guo)一定延时(shi)(shi)(shi)才(cai)干转(zhuan)变(bian)成低(di)电(dian)(dian)平。但由(you)(you)于rDS比RD小得多，所以，由(you)(you)截(jie)(jie)止(zhi)到导(dao)(dao)通(tong)的(de)转(zhuan)换(huan)(huan)时(shi)(shi)(shi)间比由(you)(you)导(dao)(dao)通(tong)到截(jie)(jie)止(zhi)的(de)转(zhuan)换(huan)(huan)时(shi)(shi)(shi)间要(yao)短。

由于MOS管(guan)(guan)导(dao)通时的(de)(de)漏源电(dian)(dian)(dian)阻rDS比(bi)晶(jing)(jing)体(ti)三极(ji)(ji)管(guan)(guan)的(de)(de)饱和(he)电(dian)(dian)(dian)阻rCES要大(da)得多，漏极(ji)(ji)外接电(dian)(dian)(dian)阻RD也比(bi)晶(jing)(jing)体(ti)管(guan)(guan)集(ji)电(dian)(dian)(dian)极(ji)(ji)电(dian)(dian)(dian)阻RC大(da)，所以，MOS管(guan)(guan)的(de)(de)充(chong)(chong)、放(fang)电(dian)(dian)(dian)时间较(jiao)长(zhang)，使(shi)(shi)MOS管(guan)(guan)的(de)(de)开关速(su)度比(bi)晶(jing)(jing)体(ti)三极(ji)(ji)管(guan)(guan)的(de)(de)开关速(su)度低。不过，在CMOS电(dian)(dian)(dian)路中(zhong)，由于充(chong)(chong)电(dian)(dian)(dian)电(dian)(dian)(dian)路和(he)放(fang)电(dian)(dian)(dian)电(dian)(dian)(dian)路都是低阻电(dian)(dian)(dian)路，因而，其(qi)充(chong)(chong)、放(fang)电(dian)(dian)(dian)过程都比(bi)拟快，从而使(shi)(shi)CMOS电(dian)(dian)(dian)路有较(jiao)高的(de)(de)开关速(su)度。

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