锂电池保护板(ban)

一、保护板的构成

锂(li)(li)(li)(li)电(dian)(dian)(dian)池(chi)保(bao)(bao)护(hu)(hu)电(dian)(dian)(dian)路(lu)(lu)，锂(li)(li)(li)(li)电(dian)(dian)(dian)池(chi)锂(li)(li)(li)(li)电(dian)(dian)(dian)池(chi)保(bao)(bao)护(hu)(hu)板(ban)(ban)(ban)（可充(chong)(chong)型）之所以需(xu)要保(bao)(bao)护(hu)(hu)，是由它本身特性决(jue)(jue)定的(de)。由于锂(li)(li)(li)(li)电(dian)(dian)(dian)池(chi)保(bao)(bao)护(hu)(hu)板(ban)(ban)(ban)本身的(de)材料决(jue)(jue)定了它不能被过充(chong)(chong)、过放(fang)、过流(liu)、短路(lu)(lu)及超高(gao)温充(chong)(chong)放(fang)电(dian)(dian)(dian)，因此锂(li)(li)(li)(li)电(dian)(dian)(dian)池(chi)锂(li)(li)(li)(li)电(dian)(dian)(dian)池(chi)保(bao)(bao)护(hu)(hu)板(ban)(ban)(ban)锂(li)(li)(li)(li)电(dian)(dian)(dian)组件总会跟着一(yi)块精致的(de)保(bao)(bao)护(hu)(hu)板(ban)(ban)(ban)和(he)一(yi)片电(dian)(dian)(dian)流(liu)保(bao)(bao)险器出现。锂(li)(li)(li)(li)电(dian)(dian)(dian)池(chi)的(de)保(bao)(bao)护(hu)(hu)功能通常由保(bao)(bao)护(hu)(hu)电(dian)(dian)(dian)路(lu)(lu)板(ban)(ban)(ban)和(he)PTC协同完成，保(bao)(bao)护(hu)(hu)板(ban)(ban)(ban)是由电(dian)(dian)(dian)子电(dian)(dian)(dian)路(lu)(lu)组成，在(zai)-40℃至+85℃的(de)环境下时(shi)刻准确(que)的(de)监视电(dian)(dian)(dian)芯的(de)电(dian)(dian)(dian)压和(he)充(chong)(chong)放(fang)回(hui)路(lu)(lu)的(de)电(dian)(dian)(dian)流(liu)，即(ji)时(shi)控制电(dian)(dian)(dian)流(liu)回(hui)路(lu)(lu)的(de)通断；PTC在(zai)高(gao)温环境下防(fang)止电(dian)(dian)(dian)池(chi)发生恶劣的(de)损坏。

锂电(dian)池保护板通(tong)常包括控(kong)制(zhi)(zhi)IC、MOS开(kai)(kai)关、电(dian)阻、电(dian)容(rong)及辅助器(qi)件NTC、ID存(cun)(cun)储(chu)(chu)器(qi)等。其中(zhong)控(kong)制(zhi)(zhi)IC，在(zai)一切(qie)正常的(de)情况下控(kong)制(zhi)(zhi)MOS开(kai)(kai)关导通(tong)，使电(dian)芯(xin)与(yu)外电(dian)路沟通(tong)，而当电(dian)芯(xin)电(dian)压(ya)或回路电(dian)流(liu)超过规定(ding)值(zhi)时(shi)(shi)，它立(li)刻（数十毫(hao)秒）控(kong)制(zhi)(zhi)MOS开(kai)(kai)关关断，保护电(dian)芯(xin)的(de)安全。NTC是Negative temperaturecoefficient的(de)缩写，意即负温度(du)(du)系数，在(zai)环境温度(du)(du)升高时(shi)(shi)，其阻值(zhi)降低，使用电(dian)设(she)备或充电(dian)设(she)备及时(shi)(shi)反应、控(kong)制(zhi)(zhi)内部中(zhong)断而停(ting)止充放(fang)电(dian)。ID 存(cun)(cun)储(chu)(chu)器(qi)常为单线接口存(cun)(cun)储(chu)(chu)器(qi)，ID是Identification 的(de)缩写即身份(fen)识别的(de)意思，存(cun)(cun)储(chu)(chu)电(dian)池种类、生产日期等信息(xi)。可(ke)起到产品的(de)可(ke)追溯和应用的(de)限制(zhi)(zhi)。

二、锂电池保护板的主要作用

锂(li)电(dian)(dian)(dian)池保护电(dian)(dian)(dian)路(lu)一般要求在(zai)(zai)-25℃～85℃时(shi)Control(IC)检测控制(zhi)电(dian)(dian)(dian)芯(xin)(xin)电(dian)(dian)(dian)压(ya)与充(chong)放电(dian)(dian)(dian)回路(lu)的工(gong)(gong)作电(dian)(dian)(dian)流、电(dian)(dian)(dian)压(ya)，在(zai)(zai)一切正常(chang)情况下(xia)C-MOS开关管(guan)导(dao)通，使(shi)电(dian)(dian)(dian)芯(xin)(xin)与保护电(dian)(dian)(dian)路(lu)板(ban)处于正常(chang)工(gong)(gong)作状态，而(er)当电(dian)(dian)(dian)芯(xin)(xin)电(dian)(dian)(dian)压(ya)或回路(lu)中的工(gong)(gong)作电(dian)(dian)(dian)流超过控制(zhi)IC中比较电(dian)(dian)(dian)路(lu)预设值时(shi)，在(zai)(zai)15～30ms内（不同控制(zhi)IC与C-MOS有不同的响应时(shi)间(jian)），将CMOS关断，即关闭(bi)电(dian)(dian)(dian)芯(xin)(xin)放电(dian)(dian)(dian)或充(chong)电(dian)(dian)(dian)回路(lu)，以保证使(shi)用者与电(dian)(dian)(dian)芯(xin)(xin)的安全(quan)。

1、正常状态

在正常状(zhuang)态(tai)下(xia)电(dian)(dian)(dian)(dian)(dian)路中N1的“CO”与“DO”脚都(dou)输出高电(dian)(dian)(dian)(dian)(dian)压，两个(ge)MOSFET都(dou)处(chu)于导(dao)通(tong)状(zhuang)态(tai)，电(dian)(dian)(dian)(dian)(dian)池可以自(zi)由(you)地进行(xing)充电(dian)(dian)(dian)(dian)(dian)和放电(dian)(dian)(dian)(dian)(dian)，由(you)于MOSFET的导(dao)通(tong)阻抗很(hen)小(xiao)，通(tong)常小(xiao)于30毫欧(ou)，因此其导(dao)通(tong)电(dian)(dian)(dian)(dian)(dian)阻对电(dian)(dian)(dian)(dian)(dian)路的性能(neng)影响(xiang)很(hen)小(xiao)。

此状态下保护(hu)电路的消耗电流(liu)为μA级(ji)，通(tong)常小(xiao)于7μA。

2、过充电保护

锂离(li)子电(dian)(dian)池要求的充电(dian)(dian)方式为恒(heng)流(liu)/恒(heng)压，在充电(dian)(dian)初期，为恒(heng)流(liu)充电(dian)(dian)，随着(zhe)充电(dian)(dian)过程，电(dian)(dian)压会上升到(dao)4.2V(根据正极材料不同，有(you)的电(dian)(dian)池要求恒(heng)压值为4.1V)，转为恒(heng)压充电(dian)(dian)，直至电(dian)(dian)流(liu)越来(lai)越小。

锂电(dian)(dian)(dian)池(chi)(chi)保护板电(dian)(dian)(dian)池(chi)(chi)在被(bei)充电(dian)(dian)(dian)过(guo)程(cheng)中，如(ru)果锂电(dian)(dian)(dian)池(chi)(chi)保护板充电(dian)(dian)(dian)器电(dian)(dian)(dian)路失去(qu)控制，会使电(dian)(dian)(dian)池(chi)(chi)电(dian)(dian)(dian)压(ya)(ya)超过(guo)4.2V后继续恒流充电(dian)(dian)(dian)，此(ci)时(shi)电(dian)(dian)(dian)池(chi)(chi)电(dian)(dian)(dian)压(ya)(ya)仍会继续上(shang)升，当电(dian)(dian)(dian)池(chi)(chi)电(dian)(dian)(dian)压(ya)(ya)被(bei)充电(dian)(dian)(dian)至超过(guo)4.3V时(shi)，电(dian)(dian)(dian)池(chi)(chi)的化学副(fu)反(fan)应(ying)将加剧，会导致电(dian)(dian)(dian)池(chi)(chi)损坏或出现安全问题。

在带(dai)有保护电(dian)(dian)路(lu)的电(dian)(dian)池(chi)中，当控制IC检测到(dao)电(dian)(dian)池(chi)电(dian)(dian)压(ya)达到(dao)4.28V（该值由(you)控制IC决(jue)定，不(bu)(bu)同的IC有不(bu)(bu)同的值）时，其(qi)“CO”脚将(jiang)由(you)高电(dian)(dian)压(ya)转变为 零(ling)电(dian)(dian)压(ya)，使T1由(you)导通转为关断，从而切断了充(chong)(chong)(chong)电(dian)(dian)回路(lu)，使充(chong)(chong)(chong)电(dian)(dian)器(qi)无法再对电(dian)(dian)池(chi)进行充(chong)(chong)(chong)电(dian)(dian)，起到(dao)过(guo)充(chong)(chong)(chong)电(dian)(dian)保护作(zuo)用。而此时由(you)于(yu)T1自带(dai)的体二极(ji)管(guan)VD1的存在，锂(li)电(dian)(dian)池(chi)保护板电(dian)(dian)池(chi)可以通过(guo)该二极(ji)管(guan)对外部负(fu)载进行放电(dian)(dian)。

在控制IC检测到电池电压超过4.28V至发(fa)出(chu)关断(duan)T1信号之间(jian)(jian)，还有一(yi)段延(yan)时(shi)(shi)时(shi)(shi)间(jian)(jian)，该(gai)延(yan)时(shi)(shi)时(shi)(shi)间(jian)(jian)的长短由(you)C2决定，通常设为1秒左右，以避(bi)免因(yin)干(gan)扰(rao)而造成误判断(duan)。

3、过放电保护

电(dian)池在(zai)对外部负载(zai)放(fang)(fang)电(dian)过(guo)(guo)程中，其(qi)电(dian)压会(hui)随着放(fang)(fang)电(dian)过(guo)(guo)程逐渐(jian)降(jiang)低，当锂电(dian)池保护板电(dian)池电(dian)压降(jiang)至2.5V时，其(qi)容(rong)量已被完(wan)全放(fang)(fang)光，此时如(ru)果(guo)让电(dian)池继(ji)续对负载(zai)放(fang)(fang)电(dian)，将造成(cheng)电(dian)池的永久性损坏。

在电(dian)池放电(dian)过(guo)程中(zhong)，当(dang)控制(zhi)(zhi)IC检测到电(dian)池电(dian)压低于2.3V（该值(zhi)由控制(zhi)(zhi)IC决定，不同(tong)(tong)的(de)IC有不同(tong)(tong)的(de)值(zhi)）时，其“DO”脚将由高电(dian)压转变为零电(dian)压， 使(shi)T2由导通转为关(guan)断，从而切(qie)断了放电(dian)回(hui)路，使(shi)锂电(dian)池保(bao)护板电(dian)池无法再(zai)对(dui)负(fu)载进行放电(dian)，起到过(guo)放电(dian)保(bao)护作用(yong)。而此时由于T2自带的(de)体二极(ji)管VD2的(de)存在，充电(dian)器可以通 过(guo)该二极(ji)管对(dui)电(dian)池进行充电(dian)。

由于(yu)在过放电(dian)(dian)保护状态下电(dian)(dian)池电(dian)(dian)压不能(neng)再降低(di)，因此(ci)要求锂电(dian)(dian)池保护板的消耗电(dian)(dian)流极小，此(ci)时(shi)控制IC会进入低(di)功(gong)耗状态，整(zheng)个保护电(dian)(dian)路耗电(dian)(dian)会小于(yu)0.1μA。 在控制IC检测(ce)到(dao)电(dian)(dian)池电(dian)(dian)压低(di)于(yu)2.3V至发出关断T2信号之间(jian)，也有一段延时(shi)时(shi)间(jian)，该延时(shi)时(shi)间(jian)的长短(duan)由C2决定，通常(chang)设为(wei)100毫秒左右，以避免因干扰而(er) 造成误判(pan)断。

4、过电流保护

由于(yu)锂(li)离(li)子电(dian)池的化学特性(xing)，电(dian)池生(sheng)产厂家规定(ding)了其(qi)放电(dian)电(dian)流(liu)最大不(bu)能超过(guo)2C（C=电(dian)池容量/小时(shi)），当(dang)电(dian)池超过(guo)2C电(dian)流(liu)放电(dian)时(shi)，将会导致电(dian)池的永久(jiu)性(xing)损坏或出现安全问题。

锂电(dian)池保护(hu)板在对(dui)负载(zai)正(zheng)常(chang)放(fang)电(dian)过程中(zhong)(zhong)，放(fang)电(dian)电(dian)流(liu)(liu)在经过串联的(de)2个MOSFET时，由于MOSFET的(de)导(dao)通阻抗，会在其两(liang)端产(chan)生一个电(dian)压，该(gai)电(dian)压值(zhi)(zhi) U=I*RDS*2, RDS为(wei)单个MOSFET导(dao)通阻抗，控制IC上的(de)“V-”脚对(dui)该(gai)电(dian)压值(zhi)(zhi)进行(xing)检测，若(ruo)负载(zai)因某种原因导(dao)致异常(chang)，使(shi)(shi)回路(lu)电(dian)流(liu)(liu)增大，当(dang)回路(lu)电(dian)流(liu)(liu)大到使(shi)(shi) U>0.1V（该(gai)值(zhi)(zhi)由控制IC决定，不(bu)同(tong)的(de)IC有(you)不(bu)同(tong)的(de)值(zhi)(zhi)）时，其“DO”脚将(jiang)由高电(dian)压转(zhuan)变为(wei)零(ling)电(dian)压，使(shi)(shi)T2由导(dao)通转(zhuan)为(wei)关断(duan)，从而切(qie)断(duan)了放(fang)电(dian)回路(lu)， 使(shi)(shi)回路(lu)中(zhong)(zhong)电(dian)流(liu)(liu)为(wei)零(ling)，起到过电(dian)流(liu)(liu)保护(hu)作用。

在控制IC检测到过电流发生至发出(chu)关断T2信号之间，也有一段(duan)延(yan)时(shi)时(shi)间，该延(yan)时(shi)时(shi)间的长短由C2决定，通常为13毫秒左(zuo)右，以避免因干扰而造成误(wu)判断。

在上述控制(zhi)过程(cheng)中可(ke)知，其(qi)(qi)过电流检测值大小(xiao)不(bu)仅取(qu)决于控制(zhi)IC的控制(zhi)值，还取(qu)决于MOSFET的导(dao)通阻抗，当(dang)MOSFET导(dao)通阻抗越(yue)大时，对同样的控制(zhi)IC，其(qi)(qi)过电流保护值越(yue)小(xiao)。

5、短路保护

锂电(dian)池保(bao)护(hu)板在对负载放电(dian)过程中(zhong)，若回路(lu)电(dian)流大到使(shi)U>0.9V（该(gai)值(zhi)由(you)控(kong)制(zhi)IC决定，不同的IC有不同的值(zhi)）时(shi)(shi)(shi)，控(kong)制(zhi)IC则判断为负载短(duan)路(lu)，其 “DO”脚将迅速由(you)高电(dian)压(ya)转变为零电(dian)压(ya)，使(shi)T2由(you)导通转为关断，从而切断放电(dian)回路(lu)，起(qi)到短(duan)路(lu)保(bao)护(hu)作用。短(duan)路(lu)保(bao)护(hu)的延(yan)时(shi)(shi)(shi)时(shi)(shi)(shi)间(jian)(jian)极(ji)短(duan)，通常小于7微秒。其工作原 理与过电(dian)流保(bao)护(hu)类似，只(zhi)是判断方法不同，保(bao)护(hu)延(yan)时(shi)(shi)(shi)时(shi)(shi)(shi)间(jian)(jian)也不一样。

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