鋰電池保護板根據使用電池保護IC，電壓等不同參數有所不同，保護板有兩個核心部件：一塊保護IC，它是由精確的比較高來獲得可靠的保護參數；另外是MOSFET串在主充放電回路中擔當高速開關，執行保護動作。下面以DW01配雙NMOS管8205A進行講解。

鋰電池平衡電路保護裝置的電路原理如上圖所示，總體來講主要是由電池保護控制ICDW01和外接放電開關M1以及充電開關M2來實現。控制IC負責監測電池電壓與回路電流，并控制兩個MOSFET的柵極，MOSFET在電路中起開關作用，當P+/P-端連接充電器，給電池正常充電時，M1，M2均處于導通狀態；當控制IC檢測到充電異常時，將M2關斷終止充電。當P+/P-端連接負載，電池正常放電時，M1，M2均導通；當控制IC檢測到放電異常時，將M1關斷終止放電。

該電路(lu)具有過(guo)充(chong)電保(bao)護、過(guo)放電保(bao)護、過(guo)電流(liu)保(bao)護與短路(lu)保(bao)護功能。

電(dian)池平衡(heng)電(dian)路工作原理分析(xi)如下(xia)：

1）正常(chang)狀(zhuang)態

在正常(chang)狀態下電(dian)(dian)(dian)路中DW01的“CO”與(yu)“DO”腳都輸出高電(dian)(dian)(dian)壓，兩個MOSFET都處于導(dao)(dao)通(tong)狀態，電(dian)(dian)(dian)池可(ke)以自(zi)由(you)地進行充電(dian)(dian)(dian)和放電(dian)(dian)(dian)，由(you)于MOSFET的導(dao)(dao)通(tong)阻(zu)抗很小，通(tong)常(chang)小于30毫歐，因此其導(dao)(dao)通(tong)電(dian)(dian)(dian)阻(zu)對電(dian)(dian)(dian)路的性能影(ying)響(xiang)很小。

此狀態(tai)下保護電路(lu)的消(xiao)耗電流(liu)為uA級。

2）過充電保護

鋰(li)離子電(dian)(dian)(dian)(dian)池(chi)要求的(de)充(chong)電(dian)(dian)(dian)(dian)方式為恒流/恒壓，在(zai)充(chong)電(dian)(dian)(dian)(dian)初期，為恒流充(chong)電(dian)(dian)(dian)(dian)，隨著充(chong)電(dian)(dian)(dian)(dian)過程(cheng)，電(dian)(dian)(dian)(dian)壓會(hui)上升到4.2V（根據正極材料不同，有(you)的(de)電(dian)(dian)(dian)(dian)池(chi)要求恒壓值為4.1V），轉為恒壓充(chong)電(dian)(dian)(dian)(dian)，直至(zhi)電(dian)(dian)(dian)(dian)流越來越小。電(dian)(dian)(dian)(dian)池(chi)在(zai)被(bei)充(chong)電(dian)(dian)(dian)(dian)過程(cheng)中(zhong)，如果充(chong)電(dian)(dian)(dian)(dian)器電(dian)(dian)(dian)(dian)路失去控制(zhi)，會(hui)使電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓超過4.2V后繼續(xu)恒流充(chong)電(dian)(dian)(dian)(dian)，此時電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓仍會(hui)繼續(xu)上升，當電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓被(bei)充(chong)電(dian)(dian)(dian)(dian)至(zhi)超過4.3V時，電(dian)(dian)(dian)(dian)池(chi)的(de)化學副反應將加劇，會(hui)導致電(dian)(dian)(dian)(dian)池(chi)損壞或出現安全問題。

在(zai)帶有(you)保(bao)護電(dian)(dian)(dian)(dian)(dian)路的(de)電(dian)(dian)(dian)(dian)(dian)池(chi)中，當控(kong)制IC（DWO1）檢測到電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓達到4.3V（該值由控(kong)制IC決定，不同的(de)IC有(you)不同的(de)值）時(shi)(shi)，其“CO”腳將(jiang)由高(gao)電(dian)(dian)(dian)(dian)(dian)壓轉(zhuan)變為(wei)零電(dian)(dian)(dian)(dian)(dian)壓，使(shi)(shi)M2由導通(tong)(tong)轉(zhuan)為(wei)關(guan)斷，從而切斷了(le)充(chong)電(dian)(dian)(dian)(dian)(dian)回路，使(shi)(shi)充(chong)電(dian)(dian)(dian)(dian)(dian)器無法再對(dui)電(dian)(dian)(dian)(dian)(dian)池(chi)進(jin)行充(chong)電(dian)(dian)(dian)(dian)(dian)，起到過充(chong)電(dian)(dian)(dian)(dian)(dian)保(bao)護作用。而此時(shi)(shi)由于M2自帶的(de)體(ti)二(er)(er)極管(guan)VD2的(de)存(cun)在(zai)，電(dian)(dian)(dian)(dian)(dian)池(chi)可(ke)以通(tong)(tong)過該二(er)(er)極管(guan)對(dui)外部負載(zai)進(jin)行放電(dian)(dian)(dian)(dian)(dian)。在(zai)控(kong)制IC檢測到電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓超過4.05V至(zhi)發(fa)出關(guan)斷M2信(xin)號之間時(shi)(shi)過充(chong)釋放，M2轉(zhuan)為(wei)打開，開始(shi)充(chong)電(dian)(dian)(dian)(dian)(dian)。

3、過放電(dian)保護

電池(chi)在(zai)對外部負載放電過程(cheng)中，其電壓(ya)會(hui)隨著(zhu)放電過程(cheng)逐漸降(jiang)低，當(dang)電池(chi)電壓(ya)降(jiang)至2.5V時(shi)，其容量已被完全放光(guang)，此(ci)時(shi)如果讓電池(chi)繼續對負載放電，將造成(cheng)電池(chi)的永久性損壞

在電(dian)池(chi)(chi)放(fang)電(dian)過程中，當(dang)控(kong)制IC檢測到電(dian)池(chi)(chi)電(dian)壓低(di)于(yu)2.5V（該值由控(kong)制IC決定，不(bu)同(tong)的(de)(de)IC有不(bu)同(tong)的(de)(de)值）時，其“DO”腳將由高電(dian)壓轉變為(wei)零(ling)電(dian)壓，使(shi)M1由導通轉為(wei)關斷(duan)，從而(er)切斷(duan)了放(fang)電(dian)回路，使(shi)電(dian)池(chi)(chi)無法再對負(fu)載進行放(fang)電(dian)，起(qi)到過放(fang)電(dian)保護作(zuo)用。而(er)此時由于(yu)M1自帶的(de)(de)體二極管VD1的(de)(de)存在，充(chong)電(dian)器可以通過該二極管對電池進行充電。

由(you)于在過放電(dian)(dian)保護(hu)(hu)狀態下電(dian)(dian)池電(dian)(dian)壓不能再降低，因此(ci)要求(qiu)保護(hu)(hu)電(dian)(dian)路的消耗(hao)電(dian)(dian)流(liu)極小(xiao)，此(ci)時控制IC會進入低功耗(hao)狀態，整個保護(hu)(hu)電(dian)(dian)路耗(hao)電(dian)(dian)會小(xiao)于0.1uA。

4、過電流保護

電(dian)池在對(dui)負載(zai)正常放(fang)電(dian)過程中，放(fang)電(dian)電(dian)流(liu)在經(jing)過串(chuan)聯的(de)2個(ge)MOSFET時，由于(yu)MOSFET的(de)導(dao)(dao)通(tong)阻抗，會在其兩端產生一個(ge)電(dian)壓，該電(dian)壓值(zhi)U=I*RDS*2，RDS為(wei)單個(ge)MOSFET導(dao)(dao)通(tong)阻抗，控制IC上的(de)“CS”腳對(dui)該電(dian)壓值(zhi)進(jin)行檢測(ce)，若負載(zai)因(yin)某種原因(yin)導(dao)(dao)致(zhi)異常，使(shi)回(hui)路(lu)電(dian)流(liu)增(zeng)大，當回(hui)路(lu)電(dian)流(liu)大到使(shi)U>0.15V（該值(zhi)由控制IC決定，不同(tong)(tong)的(de)IC有不同(tong)(tong)的(de)值(zhi)）時，其“DO”腳將(jiang)由高(gao)電(dian)壓轉(zhuan)變為(wei)零電(dian)壓，使(shi)M1由導(dao)(dao)通(tong)轉(zhuan)為(wei)關(guan)斷，從而切斷了放(fang)電(dian)回(hui)路(lu)，使(shi)回(hui)路(lu)中電(dian)流(liu)為(wei)零，起到過電(dian)流(liu)保護作用(yong)。

在上述控(kong)制(zhi)過程(cheng)中可知，其過電(dian)流檢測值(zhi)大小(xiao)(xiao)不僅取(qu)決(jue)于控(kong)制(zhi)IC的控(kong)制(zhi)值(zhi)，還取(qu)決(jue)于MOSFET的導(dao)通(tong)阻(zu)抗(kang)，當MOSFET導(dao)通(tong)阻(zu)抗(kang)越大時，對(dui)同(tong)樣的控(kong)制(zhi)IC，其過電(dian)流保護值(zhi)越小(xiao)(xiao)。

5、短路保護(hu)

電(dian)池(chi)在(zai)對(dui)負(fu)載放電(dian)過(guo)程中，若回路(lu)電(dian)流大(da)到使(shi)U>1V（該值由控制IC決(jue)定，不(bu)同的(de)IC有不(bu)同的(de)值）時，控制IC則(ze)判(pan)斷(duan)為(wei)負(fu)載短(duan)路(lu)，其(qi)“DO”腳將(jiang)迅(xun)速由高電(dian)壓(ya)轉變為(wei)零(ling)電(dian)壓(ya)，使(shi)M1由導通轉為(wei)關斷(duan)，從而切斷(duan)放電(dian)回路(lu)，起到短(duan)路(lu)保(bao)護作用。短(duan)路(lu)保(bao)護的(de)延時時間極短(duan)，通常小于7微秒。其(qi)工(gong)作原理(li)與過(guo)電(dian)流保(bao)護類似

DW01的(de)CS腳(jiao)為電(dian)流(liu)(liu)檢(jian)測腳(jiao)，輸(shu)(shu)出(chu)短路時，充放電(dian)控制MOSFET的(de)導通壓降劇增，CS腳(jiao)電(dian)壓迅速升高，DW01輸(shu)(shu)出(chu)信號使充放電(dian)控制MO SFET迅速關斷，從而(er)實現(xian)過電(dian)流(liu)(liu)或(huo)短路保護。