鋰電池的(de)(de)保護(hu)功能通(tong)常由(you)保護(hu)電(dian)路(lu)板(ban)和(he)PTC等電(dian)流(liu)器件協同(tong)完成(cheng)，保護(hu)板(ban)是由(you)電(dian)子電(dian)路(lu)組(zu)成(cheng)，在(zai)-40℃至+85℃的(de)(de)環境下(xia)時(shi)刻準(zhun)確(que)的(de)(de)監(jian)視電(dian)芯的(de)(de)電(dian)壓和(he)充放回路(lu)的(de)(de)電(dian)流(liu)，及時(shi)控制電(dian)流(liu)回路(lu)的(de)(de)通(tong)斷;PTC在(zai)高(gao)溫環境下(xia)防止電(dian)池發生惡劣(lie)的(de)(de)損壞。

普通鋰電池保護板通(tong)常包(bao)括控(kong)制IC、MOS開關、電(dian)阻、電(dian)容(rong)及(ji)輔助器件FUSE、PTC、NTC、ID、存儲(chu)器等。其中控(kong)制IC，在一(yi)切正常的情況下(xia)控(kong)制MOS開關導通(tong)，使(shi)電(dian)芯(xin)與外電(dian)路(lu)導通(tong)，而當電(dian)芯(xin)電(dian)壓(ya)或回路(lu)電(dian)流超過規(gui)定值時，它(ta)立(li)刻控(kong)制MOS開關關斷，保(bao)護電(dian)芯(xin)的安全。

在保護板正(zheng)常(chang)的(de)情(qing)況下，Vdd為高(gao)電平，Vss，VM為低電平，DO、CO為高(gao)電平，當Vdd，Vss，VM任何一項參數變換時(shi)，DO或(huo)CO端(duan)的(de)電平將發(fa)生變化。

1、正常狀態

在正(zheng)常(chang)(chang)狀(zhuang)態(tai)下(xia)電(dian)路(lu)中N1的(de)“CO”與“DO”腳都輸出高電(dian)壓，兩個MOSFET都處于(yu)導通(tong)(tong)狀(zhuang)態(tai)，電(dian)池可以自由(you)地進行充(chong)電(dian)和放電(dian)，由(you)于(yu)MOSFET的(de)導通(tong)(tong)阻抗很小(xiao)，通(tong)(tong)常(chang)(chang)小(xiao)于(yu)30毫歐，因此其導通(tong)(tong)電(dian)阻對電(dian)路(lu)的(de)性(xing)能影響很小(xiao)。此狀(zhuang)態(tai)下(xia)保護電(dian)路(lu)的(de)消(xiao)耗電(dian)流為μA級，通(tong)(tong)常(chang)(chang)小(xiao)于(yu)7μA。

2、過充電保護

鋰離子電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)要求的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)方式為(wei)恒流(liu)/恒壓(ya)(ya)，在(zai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)初(chu)期，為(wei)恒流(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，隨(sui)著(zhu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過程，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)會(hui)上(shang)升到(dao)(dao)4.2V(根(gen)據正極材料不(bu)同，有(you)(you)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)要求恒壓(ya)(ya)值(zhi)為(wei)4.1V)，轉為(wei)恒壓(ya)(ya)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，直至電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)越(yue)來越(yue)小(xiao)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)在(zai)被充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過程中(zhong)，如果充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)失去(qu)控(kong)制，會(hui)使(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)超(chao)過4.2V后繼(ji)續恒流(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，此時(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)仍(reng)會(hui)繼(ji)續上(shang)升，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)被充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)至超(chao)過4.3V時(shi)(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)化學副反應將加劇，會(hui)導(dao)(dao)致電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)損壞或出現安全問題。在(zai)帶(dai)有(you)(you)保護(hu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)中(zhong)，當控(kong)制IC檢(jian)測到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)達(da)到(dao)(dao)4.28V(該值(zhi)由(you)控(kong)制IC決定，不(bu)同的(de)IC有(you)(you)不(bu)同的(de)值(zhi))時(shi)(shi)，其(qi)“CO”腳將由(you)高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)轉變為(wei)零(ling)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，使(shi)(shi)V2由(you)導(dao)(dao)通(tong)轉為(wei)關斷，從而切(qie)斷了充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)回路(lu)(lu)，使(shi)(shi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器無法再(zai)對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)進行(xing)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，起到(dao)(dao)過充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)保護(hu)作用(yong)。而此時(shi)(shi)由(you)于V2自帶(dai)的(de)體二極管VD2的(de)存在(zai)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)可以通(tong)過該二極管對(dui)外部負(fu)載(zai)進行(xing)放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。在(zai)控(kong)制IC檢(jian)測到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)超(chao)過4.28V至發出關斷V2信號之間，還(huan)有(you)(you)一段延(yan)時(shi)(shi)時(shi)(shi)間，該延(yan)時(shi)(shi)時(shi)(shi)間的(de)長短由(you)C3決定，通(tong)常設為(wei)1秒左右，以避免因干(gan)擾而造成誤判斷。

3、過放電保護

電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)在(zai)對(dui)外部(bu)負(fu)載(zai)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程(cheng)中(zhong)，其電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)會(hui)隨(sui)著(zhu)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程(cheng)逐漸(jian)降(jiang)低，當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)降(jiang)至(zhi)2.5V時(shi)，其容量已被完全放(fang)(fang)(fang)光(guang)，此(ci)時(shi)如果讓電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)繼續(xu)對(dui)負(fu)載(zai)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)，將造成(cheng)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的永久(jiu)性(xing)損壞。在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程(cheng)中(zhong)，當控(kong)制(zhi)(zhi)IC檢測(ce)到電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)低于(yu)2.3V(該值由控(kong)制(zhi)(zhi)IC決(jue)定(ding)，不(bu)同的IC有不(bu)同的值)時(shi)，其“DO”腳將由高電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)轉變為(wei)零電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，使(shi)V1由導通轉為(wei)關斷(duan)，從(cong)而(er)(er)切斷(duan)了放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)回(hui)路(lu)，使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)無法再對(dui)負(fu)載(zai)進行放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)，起到過(guo)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)保護作用(yong)。而(er)(er)此(ci)時(shi)由于(yu)V1自帶(dai)的體二極(ji)管(guan)VD1的存(cun)在(zai)，充電(dian)(dian)(dian)(dian)(dian)(dian)器可以通過(guo)該二極(ji)管(guan)對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)進行充電(dian)(dian)(dian)(dian)(dian)(dian)。由于(yu)在(zai)過(guo)放(fang)(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)保護狀(zhuang)態下電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)不(bu)能再降(jiang)低，因此(ci)要求(qiu)保護電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)的消耗(hao)電(dian)(dian)(dian)(dian)(dian)(dian)流極(ji)小，此(ci)時(shi)控(kong)制(zhi)(zhi)IC會(hui)進入(ru)低功耗(hao)狀(zhuang)態，整個保護電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)耗(hao)電(dian)(dian)(dian)(dian)(dian)(dian)會(hui)小于(yu)0.1μA。在(zai)控(kong)制(zhi)(zhi)IC檢測(ce)到電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)低于(yu)2.3V至(zhi)發出關斷(duan)V1信(xin)號之間，也有一段(duan)延(yan)時(shi)時(shi)間，該延(yan)時(shi)時(shi)間的長短由C3決(jue)定(ding)，通常設(she)為(wei)100毫(hao)秒左右，以避免因干(gan)擾而(er)(er)造成(cheng)誤判(pan)斷(duan).

4、短路保護

電(dian)(dian)(dian)池在(zai)對負(fu)載(zai)放電(dian)(dian)(dian)過(guo)程中(zhong)，若(ruo)回路(lu)電(dian)(dian)(dian)流大到使U>0.9V(該值由(you)控制IC決定，不(bu)同的IC有不(bu)同的值)時(shi)，控制IC則判(pan)斷(duan)為(wei)(wei)負(fu)載(zai)短(duan)路(lu)，其(qi)(qi)“DO”腳(jiao)將迅速由(you)高電(dian)(dian)(dian)壓(ya)(ya)轉(zhuan)變為(wei)(wei)零電(dian)(dian)(dian)壓(ya)(ya)，使V1由(you)導通(tong)轉(zhuan)為(wei)(wei)關斷(duan)，從而(er)切斷(duan)放電(dian)(dian)(dian)回路(lu)，起到短(duan)路(lu)保(bao)護作用。短(duan)路(lu)保(bao)護的延時(shi)時(shi)間極短(duan)，通(tong)常小(xiao)于(yu)7微(wei)秒。其(qi)(qi)工作原理與(yu)過(guo)電(dian)(dian)(dian)流保(bao)護類似，只是判(pan)斷(duan)方法不(bu)同，保(bao)護延時(shi)時(shi)間也不(bu)一樣。除了控制IC外(wai)，電(dian)(dian)(dian)路(lu)中(zhong)還有一個重要(yao)元(yuan)件，就是MOSFET，它在(zai)電(dian)(dian)(dian)路(lu)中(zhong)起著(zhu)開關的作用，由(you)于(yu)它直接(jie)串接(jie)在(zai)電(dian)(dian)(dian)池與(yu)外(wai)部負(fu)載(zai)之(zhi)間，因此它的導通(tong)阻抗對電(dian)(dian)(dian)池的性(xing)能(neng)有影響，當選用的MOSFET較好時(shi)，其(qi)(qi)導通(tong)阻抗很小(xiao)，電(dian)(dian)(dian)池包的內阻就小(xiao)，帶載(zai)能(neng)力也強，在(zai)放電(dian)(dian)(dian)時(shi)其(qi)(qi)消耗的電(dian)(dian)(dian)能(neng)也少。

5、過電流保護

由(you)于鋰離子電(dian)(dian)(dian)池(chi)(chi)的(de)(de)化(hua)學(xue)特性，電(dian)(dian)(dian)池(chi)(chi)生(sheng)產廠家(jia)規定(ding)了其(qi)(qi)放(fang)(fang)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)最(zui)大(da)不(bu)能超(chao)過(guo)(guo)2C(C=電(dian)(dian)(dian)池(chi)(chi)容量/小(xiao)時(shi))，當(dang)電(dian)(dian)(dian)池(chi)(chi)超(chao)過(guo)(guo)2C電(dian)(dian)(dian)流(liu)放(fang)(fang)電(dian)(dian)(dian)時(shi)，將會導(dao)(dao)(dao)致(zhi)電(dian)(dian)(dian)池(chi)(chi)的(de)(de)永久性損壞或出(chu)現安全問題。電(dian)(dian)(dian)池(chi)(chi)在(zai)(zai)對負載正(zheng)常放(fang)(fang)電(dian)(dian)(dian)過(guo)(guo)程中，放(fang)(fang)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)在(zai)(zai)經過(guo)(guo)串(chuan)聯的(de)(de)2個MOSFET時(shi)，由(you)于MOSFET的(de)(de)導(dao)(dao)(dao)通(tong)(tong)阻抗，會在(zai)(zai)其(qi)(qi)兩端產生(sheng)一個電(dian)(dian)(dian)壓，該電(dian)(dian)(dian)壓值U=I*RDS*2，RDS為(wei)單個MOSFET導(dao)(dao)(dao)通(tong)(tong)阻抗，控(kong)制(zhi)(zhi)IC上(shang)的(de)(de)“V-”腳(jiao)對該電(dian)(dian)(dian)壓值進(jin)行檢測(ce)，若負載因(yin)某種原因(yin)導(dao)(dao)(dao)致(zhi)異常，使回路(lu)電(dian)(dian)(dian)流(liu)增大(da)，當(dang)回路(lu)電(dian)(dian)(dian)流(liu)大(da)到(dao)使U>0.1V(該值由(you)控(kong)制(zhi)(zhi)IC決定(ding)，不(bu)同的(de)(de)IC有不(bu)同的(de)(de)值)時(shi)，其(qi)(qi)“DO”腳(jiao)將由(you)高電(dian)(dian)(dian)壓轉變為(wei)零電(dian)(dian)(dian)壓，使V1由(you)導(dao)(dao)(dao)通(tong)(tong)轉為(wei)關斷，從而切斷了放(fang)(fang)電(dian)(dian)(dian)回路(lu)，使回路(lu)中電(dian)(dian)(dian)流(liu)為(wei)零，起到(dao)過(guo)(guo)電(dian)(dian)(dian)流(liu)保護作(zuo)用。在(zai)(zai)控(kong)制(zhi)(zhi)IC檢測(ce)到(dao)過(guo)(guo)電(dian)(dian)(dian)流(liu)發生(sheng)至(zhi)發出(chu)關斷V1信號之間，也有一段(duan)延時(shi)時(shi)間，該延時(shi)時(shi)間的(de)(de)長短由(you)C3決定(ding)，通(tong)(tong)常為(wei)13毫(hao)秒(miao)左右，以避免(mian)因(yin)干擾而造成誤判斷。在(zai)(zai)上(shang)述(shu)控(kong)制(zhi)(zhi)過(guo)(guo)程中可知(zhi)，其(qi)(qi)過(guo)(guo)電(dian)(dian)(dian)流(liu)檢測(ce)值大(da)小(xiao)不(bu)僅取決于控(kong)制(zhi)(zhi)IC的(de)(de)控(kong)制(zhi)(zhi)值，還取決于MOSFET的(de)(de)導(dao)(dao)(dao)通(tong)(tong)阻抗，當(dang)MOSFET導(dao)(dao)(dao)通(tong)(tong)阻抗越大(da)時(shi)，對同樣的(de)(de)控(kong)制(zhi)(zhi)IC，其(qi)(qi)過(guo)(guo)電(dian)(dian)(dian)流(liu)保護值越小(xiao)。