電路具有過充電保(bao)護、過放電保(bao)護、過電流保(bao)護與短路保(bao)護功(gong)能，其工作(zuo)原理(li)分析如下：

1  正常狀(zhuang)態

在正常狀態下(xia)電(dian)路(lu)中N1的“CO"與“DO"腳(jiao)都(dou)輸(shu)出高電(dian)壓，兩個MOSFET都(dou)處于(yu)導(dao)(dao)通狀態，電(dian)池(chi)可以自由地進行充電(dian)和放電(dian)，由于(yu)MOSFET的導(dao)(dao)通阻抗很小，通常小于(yu)30毫(hao)歐，因此(ci)其導(dao)(dao)通電(dian)阻對電(dian)路(lu)的性能(neng)影(ying)響(xiang)很小。 此(ci)狀態下(xia)保護(hu)電(dian)路(lu)的消耗電(dian)流為μA級，通常小于(yu)7μA。

2  過充電保護

鋰離子電池作為(wei)(wei)可充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)一種，要求(qiu)的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)方式為(wei)(wei)恒(heng)流/恒(heng)壓(ya)，在(zai)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)初(chu)期，為(wei)(wei)恒(heng)流充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，隨著充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)會(hui)上(shang)升到(dao)4.2V（根據(ju)正極材料不同，有(you)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)要求(qiu)恒(heng)壓(ya)值(zhi)為(wei)(wei)4.1V），轉為(wei)(wei)恒(heng)壓(ya)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，直至電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流越來越小。 電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)在(zai)被(bei)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程中(zhong)，如(ru)果充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路失去控制，會(hui)使電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)超過(guo)4.2V后繼(ji)續恒(heng)流充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，此(ci)時電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)仍會(hui)繼(ji)續上(shang)升，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)被(bei)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)至超過(guo)4.3V時，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)化(hua)學副反應將加劇，會(hui)導致電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)損壞或出現安全問(wen)題(ti)。

在帶有保護電路的電池中，當控制IC檢測到電池電壓達到4.28V（該值由控制IC決定，不同的IC有不同的值）時，其“CO"腳將由高電壓轉變為零電壓，使V2由導通轉為關斷，從而切斷了充電回路，使充電器無法再對電(dian)(dian)池進(jin)行(xing)充電(dian)(dian)，起到過充電(dian)(dian)保護作用。而此時由于(yu)V2自帶的體二(er)極管(guan)VD2的存(cun)在，電(dian)(dian)池可以(yi)通過該二(er)極管(guan)對外部負(fu)載(zai)進(jin)行(xing)放電(dian)(dian)。

在控制(zhi)IC檢測到(dao)電池電壓超過4.28V至(zhi)發出關斷V2信號(hao)之間，還有一(yi)段延時(shi)時(shi)間，該延時(shi)時(shi)間的長短(duan)由C3決定，通常設為1秒左右，以避免因干擾而造成誤判斷。

3  過放電保(bao)護

電(dian)(dian)(dian)(dian)池在對外(wai)部負載放(fang)(fang)電(dian)(dian)(dian)(dian)過程(cheng)中(zhong)，其電(dian)(dian)(dian)(dian)壓會隨(sui)著放(fang)(fang)電(dian)(dian)(dian)(dian)過程(cheng)逐(zhu)漸降低，當(dang)電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓降至2.5V時，其容量已被完全放(fang)(fang)光，此時如果(guo)讓電(dian)(dian)(dian)(dian)池繼續對負載放(fang)(fang)電(dian)(dian)(dian)(dian)，將造成(cheng)電(dian)(dian)(dian)(dian)池的永久性損(sun)壞。

在電池放電過程中，當控制IC檢測到電池電壓低于2.3V（該值由控制IC決定，不同的IC有不同的值）時，其“DO"腳將由高電壓轉變為零電壓，使V1由導通轉為關斷，從而切斷了放電回路，使電池無法再對負載進行放電，起到過放電保護作用。而此時由于V1自帶的體二極管VD1的存在，充電器可以(yi)通過該二極管對(dui)電池進行(xing)充電。

由于在過(guo)放電(dian)(dian)保(bao)(bao)護(hu)狀態(tai)下電(dian)(dian)池(chi)電(dian)(dian)壓(ya)不能再降低，因此要求保(bao)(bao)護(hu)電(dian)(dian)路(lu)的消耗(hao)電(dian)(dian)流極小(xiao)，此時控(kong)制IC會進入低功耗(hao)狀態(tai)，整(zheng)個保(bao)(bao)護(hu)電(dian)(dian)路(lu)耗(hao)電(dian)(dian)會小(xiao)于0.1μA。

在控制IC檢(jian)測到(dao)電池電壓低(di)于2.3V至發出關(guan)斷V1信號之間(jian)，也有一段(duan)延時時間(jian)，該延時時間(jian)的長(chang)短由(you)C3決定(ding)，通常設為100毫秒左右，以(yi)避免因干擾(rao)而造成誤判斷。

4  過電流保護

由于鋰電(dian)池的(de)化學特性，電(dian)池生(sheng)產廠家規定(ding)了其(qi)放電(dian)電(dian)流最大不(bu)能超(chao)過2C（C=電(dian)池容(rong)量/小時），當電(dian)池超(chao)過2C電(dian)流放電(dian)時，將會導(dao)致電(dian)池的(de)永(yong)久性損壞(huai)或出(chu)現(xian)安全問題。

電(dian)(dian)池在(zai)(zai)對負(fu)載正(zheng)常放(fang)電(dian)(dian)過(guo)(guo)程中，放(fang)電(dian)(dian)電(dian)(dian)流(liu)在(zai)(zai)經過(guo)(guo)串聯的2個MOSFET時，由(you)于MOSFET的導(dao)通(tong)阻(zu)抗，會(hui)在(zai)(zai)其(qi)兩(liang)端產生(sheng)一(yi)個電(dian)(dian)壓(ya)，該(gai)(gai)電(dian)(dian)壓(ya)值(zhi)U=I*RDS*2, RDS為(wei)單個MOSFET導(dao)通(tong)阻(zu)抗，控制IC上的“V-"腳對該(gai)(gai)電(dian)(dian)壓(ya)值(zhi)進行(xing)檢測(ce)，若負(fu)載因某種原(yuan)因導(dao)致異常，使(shi)回(hui)路(lu)(lu)電(dian)(dian)流(liu)增大，當回(hui)路(lu)(lu)電(dian)(dian)流(liu)大到使(shi)U>0.1V（該(gai)(gai)值(zhi)由(you)控制IC決(jue)定，不同的IC有(you)不同的值(zhi)）時，其(qi)“DO"腳將由(you)高(gao)電(dian)(dian)壓(ya)轉(zhuan)變(bian)為(wei)零(ling)(ling)電(dian)(dian)壓(ya)，使(shi)V1由(you)導(dao)通(tong)轉(zhuan)為(wei)關(guan)斷(duan)，從而(er)切斷(duan)了放(fang)電(dian)(dian)回(hui)路(lu)(lu)，使(shi)回(hui)路(lu)(lu)中電(dian)(dian)流(liu)為(wei)零(ling)(ling)，起到過(guo)(guo)電(dian)(dian)流(liu)保(bao)護作用。

在控制IC檢測到過電(dian)流發(fa)生至(zhi)發(fa)出關斷(duan)V1信(xin)號之(zhi)間(jian)，也(ye)有(you)一段(duan)延時時間(jian)，該延時時間(jian)的(de)長(chang)短由C3決定(ding)，通常為13毫(hao)秒左右，以避免因(yin)干擾而造成誤(wu)判斷(duan)。

在上述(shu)控制(zhi)(zhi)過程中可知(zhi)，其過電流(liu)檢測值(zhi)大小(xiao)不僅取(qu)決于(yu)控制(zhi)(zhi)IC的(de)控制(zhi)(zhi)值(zhi)，還(huan)取(qu)決于(yu)MOSFET的(de)導通阻(zu)抗(kang)，當MOSFET導通阻(zu)抗(kang)越大時，對同樣的(de)控制(zhi)(zhi)IC，其過電流(liu)保護值(zhi)越小(xiao)。

5  短路保護

電(dian)池(chi)在對負載放(fang)(fang)電(dian)過程(cheng)中，若回路電(dian)流大到使U>0.9V（該值(zhi)由(you)控制IC決定，不同的(de)IC有不同的(de)值(zhi)）時，控制IC則判斷(duan)(duan)為(wei)負載短(duan)(duan)路，其“DO"腳(jiao)將(jiang)迅速(su)由(you)高電(dian)壓(ya)轉變為(wei)零電(dian)壓(ya)，使V1由(you)導通(tong)(tong)轉為(wei)關斷(duan)(duan)，從而切(qie)斷(duan)(duan)放(fang)(fang)電(dian)回路，起到短(duan)(duan)路保(bao)護作用。短(duan)(duan)路保(bao)護的(de)延時時間(jian)極短(duan)(duan)，通(tong)(tong)常(chang)小(xiao)于7微秒。其工作原(yuan)理與(yu)過電(dian)流保(bao)護類似，只(zhi)是判斷(duan)(duan)方(fang)法不同，保(bao)護延時時間(jian)也不一樣。

以上詳細闡述了單節鋰離子電池保護電路的工作原理，多節串聯鋰離子電池的(de)(de)(de)(de)保護(hu)(hu)原理(li)與(yu)之(zhi)類(lei)似(si)，在此不再贅述，上面電(dian)(dian)(dian)路中(zhong)所(suo)用的(de)(de)(de)(de)控制(zhi)IC為日(ri)(ri)(ri)本理(li)光公司的(de)(de)(de)(de)R5421系(xi)列，在實際的(de)(de)(de)(de)電(dian)(dian)(dian)池(chi)(chi)保護(hu)(hu)電(dian)(dian)(dian)路中(zhong)，還(huan)有(you)(you)許多其(qi)(qi)它(ta)類(lei)型的(de)(de)(de)(de)控制(zhi)IC，如日(ri)(ri)(ri)本精工(gong)(gong)的(de)(de)(de)(de)S-8241系(xi)列、日(ri)(ri)(ri)本MITSUMI的(de)(de)(de)(de)MM3061系(xi)列、臺(tai)灣富晶的(de)(de)(de)(de)FS312和FS313系(xi)列、臺(tai)灣類(lei)比(bi)科技的(de)(de)(de)(de)AAT8632系(xi)列等(deng)等(deng)，其(qi)(qi)工(gong)(gong)作原理(li)大同小(xiao)(xiao)異，只是在具體參(can)數上有(you)(you)所(suo)差(cha)別(bie)，有(you)(you)些控制(zhi)IC為了(le)節省外圍電(dian)(dian)(dian)路，將濾波電(dian)(dian)(dian)容和延時電(dian)(dian)(dian)容做到了(le)芯(xin)片內部(bu)，其(qi)(qi)外圍電(dian)(dian)(dian)路可以很(hen)少，如日(ri)(ri)(ri)本精工(gong)(gong)的(de)(de)(de)(de)S-8241系(xi)列。 除了(le)控制(zhi)IC外，電(dian)(dian)(dian)路中(zhong)還(huan)有(you)(you)一個重要元件，就是MOSFET，它(ta)在電(dian)(dian)(dian)路中(zhong)起著開關的(de)(de)(de)(de)作用，由于它(ta)直(zhi)接(jie)串接(jie)在電(dian)(dian)(dian)池(chi)(chi)與(yu)外部(bu)負(fu)載之(zhi)間(jian)，因此它(ta)的(de)(de)(de)(de)導通(tong)阻抗對電(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)性能有(you)(you)影響，當選(xuan)用的(de)(de)(de)(de)MOSFET較好(hao)時，其(qi)(qi)導通(tong)阻抗很(hen)小(xiao)(xiao)，電(dian)(dian)(dian)池(chi)(chi)包的(de)(de)(de)(de)內阻就小(xiao)(xiao)，帶載能力也強，在放電(dian)(dian)(dian)時其(qi)(qi)消耗的(de)(de)(de)(de)電(dian)(dian)(dian)能也少。

隨著科技的(de)(de)(de)發展(zhan)，便攜式設備(bei)的(de)(de)(de)體積越(yue)(yue)(yue)做越(yue)(yue)(yue)小，而隨著這種(zhong)趨(qu)勢，對鋰(li)離子電(dian)池的(de)(de)(de)保(bao)護(hu)電(dian)路體積的(de)(de)(de)要求也越(yue)(yue)(yue)來(lai)越(yue)(yue)(yue)小，在(zai)這兩年(nian)已出現了(le)將控制IC和MOSFET整合成(cheng)一顆(ke)保(bao)護(hu)IC的(de)(de)(de)產品，如(ru)DIALOG公司(si)的(de)(de)(de)DA7112系列，有的(de)(de)(de)廠家甚至將整個保(bao)護(hu)電(dian)路封裝成(cheng)一顆(ke)小尺寸的(de)(de)(de)IC，如(ru)MITSUMI公司(si)的(de)(de)(de)產品。