電(dian)(dian)路具有過(guo)充電(dian)(dian)保護、過(guo)放電(dian)(dian)保護、過(guo)電(dian)(dian)流保護與短路保護功能，其工作原理分(fen)析如(ru)下(xia)：

1  正常狀(zhuang)態

在正常(chang)狀態下電(dian)(dian)路(lu)中N1的(de)“CO"與“DO"腳(jiao)都輸出高電(dian)(dian)壓，兩個MOSFET都處于(yu)導通(tong)狀態，電(dian)(dian)池可(ke)以自由地進行充電(dian)(dian)和放(fang)電(dian)(dian)，由于(yu)MOSFET的(de)導通(tong)阻(zu)抗很小，通(tong)常(chang)小于(yu)30毫歐，因此(ci)其導通(tong)電(dian)(dian)阻(zu)對電(dian)(dian)路(lu)的(de)性(xing)能影響(xiang)很小。 此(ci)狀態下保護電(dian)(dian)路(lu)的(de)消耗電(dian)(dian)流為μA級，通(tong)常(chang)小于(yu)7μA。

2  過充電保護

鋰離子電池作為(wei)(wei)可充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)一種，要求(qiu)的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)方式為(wei)(wei)恒(heng)流(liu)(liu)/恒(heng)壓(ya)，在充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)初期，為(wei)(wei)恒(heng)流(liu)(liu)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，隨著充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過程(cheng)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)會(hui)上升(sheng)到4.2V（根(gen)據正極材料不同(tong)，有的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)要求(qiu)恒(heng)壓(ya)值為(wei)(wei)4.1V），轉為(wei)(wei)恒(heng)壓(ya)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，直(zhi)至(zhi)(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)越(yue)(yue)來越(yue)(yue)小。 電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)在被充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過程(cheng)中，如(ru)果充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路失去控制，會(hui)使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)超過4.2V后繼續恒(heng)流(liu)(liu)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，此時電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)仍會(hui)繼續上升(sheng)，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)被充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)至(zhi)(zhi)超過4.3V時，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)化(hua)學副反應(ying)將加劇，會(hui)導(dao)致(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)損壞或出現安(an)全(quan)問題。

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(fa)再對電(dian)池進行充(chong)電(dian)，起(qi)到過充(chong)電(dian)保護作用。而此時由于V2自(zi)帶的(de)體二(er)極管VD2的(de)存在(zai)，電(dian)池可以通(tong)過該(gai)二(er)極管對外部(bu)負載進行放電(dian)。

在(zai)控(kong)制IC檢測(ce)到電(dian)池電(dian)壓超過4.28V至發出(chu)關(guan)斷V2信(xin)號之間，還有一段延(yan)時(shi)時(shi)間，該延(yan)時(shi)時(shi)間的長短由C3決定，通(tong)常設為1秒(miao)左右，以避(bi)免因干擾而造成誤判斷。

3  過放電(dian)保護

電(dian)(dian)池在對(dui)外部負載(zai)放(fang)電(dian)(dian)過(guo)程(cheng)中，其(qi)電(dian)(dian)壓(ya)(ya)會隨著放(fang)電(dian)(dian)過(guo)程(cheng)逐(zhu)漸降低，當電(dian)(dian)池電(dian)(dian)壓(ya)(ya)降至2.5V時，其(qi)容量已(yi)被(bei)完全放(fang)光，此時如果讓電(dian)(dian)池繼續(xu)對(dui)負載(zai)放(fang)電(dian)(dian)，將造成電(dian)(dian)池的永(yong)久性損壞(huai)。

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(guan)對電池進行充電。

由于在過(guo)放電(dian)(dian)保護狀態下電(dian)(dian)池電(dian)(dian)壓不能再降低(di)，因此要求保護電(dian)(dian)路的消耗(hao)電(dian)(dian)流極小，此時(shi)控制IC會進入低(di)功耗(hao)狀態，整個(ge)保護電(dian)(dian)路耗(hao)電(dian)(dian)會小于0.1μA。

在控制IC檢測到電(dian)池(chi)電(dian)壓低于2.3V至發(fa)出關斷V1信號之(zhi)間，也有(you)一(yi)段延時(shi)時(shi)間，該延時(shi)時(shi)間的長短由C3決定，通(tong)常設為(wei)100毫秒左右，以避免因干(gan)擾而造成誤判斷。

4  過電流(liu)保護

由于鋰電(dian)池(chi)的(de)化學特(te)性，電(dian)池(chi)生產廠(chang)家(jia)規定了其放電(dian)電(dian)流最大(da)不(bu)能超(chao)過2C（C=電(dian)池(chi)容量(liang)/小(xiao)時），當電(dian)池(chi)超(chao)過2C電(dian)流放電(dian)時，將會(hui)導致電(dian)池(chi)的(de)永久性損壞或(huo)出現安全問(wen)題。

電(dian)(dian)池(chi)在對負(fu)載(zai)正常(chang)放(fang)(fang)電(dian)(dian)過程(cheng)中(zhong)，放(fang)(fang)電(dian)(dian)電(dian)(dian)流(liu)(liu)(liu)在經過串聯的(de)2個(ge)(ge)MOSFET時，由于(yu)MOSFET的(de)導(dao)通(tong)阻抗，會在其(qi)兩(liang)端產生一個(ge)(ge)電(dian)(dian)壓，該(gai)電(dian)(dian)壓值(zhi)U=I*RDS*2, RDS為單個(ge)(ge)MOSFET導(dao)通(tong)阻抗，控(kong)制IC上(shang)的(de)“V-"腳(jiao)對該(gai)電(dian)(dian)壓值(zhi)進行檢測(ce)，若負(fu)載(zai)因(yin)某種(zhong)原因(yin)導(dao)致(zhi)異常(chang)，使(shi)回路(lu)(lu)(lu)電(dian)(dian)流(liu)(liu)(liu)增大，當回路(lu)(lu)(lu)電(dian)(dian)流(liu)(liu)(liu)大到使(shi)U>0.1V（該(gai)值(zhi)由控(kong)制IC決定，不同(tong)(tong)的(de)IC有不同(tong)(tong)的(de)值(zhi)）時，其(qi)“DO"腳(jiao)將由高電(dian)(dian)壓轉變為零(ling)電(dian)(dian)壓，使(shi)V1由導(dao)通(tong)轉為關斷，從而(er)切斷了放(fang)(fang)電(dian)(dian)回路(lu)(lu)(lu)，使(shi)回路(lu)(lu)(lu)中(zhong)電(dian)(dian)流(liu)(liu)(liu)為零(ling)，起到過電(dian)(dian)流(liu)(liu)(liu)保(bao)護作(zuo)用(yong)。

在控制IC檢測(ce)到(dao)過電(dian)流發生至發出關(guan)斷V1信號(hao)之間(jian)，也有一段延時(shi)(shi)時(shi)(shi)間(jian)，該(gai)延時(shi)(shi)時(shi)(shi)間(jian)的長短(duan)由(you)C3決定，通常為13毫秒左右，以避免(mian)因干擾(rao)而造成誤判(pan)斷。

在(zai)上述(shu)控(kong)制(zhi)過(guo)(guo)程中可知，其過(guo)(guo)電流檢(jian)測(ce)值大小不僅取決(jue)于(yu)控(kong)制(zhi)IC的控(kong)制(zhi)值，還取決(jue)于(yu)MOSFET的導通阻抗(kang)，當MOSFET導通阻抗(kang)越大時，對同樣的控(kong)制(zhi)IC，其過(guo)(guo)電流保護值越小。

5  短路保護

電池在對負(fu)載放電過(guo)(guo)程中，若回路(lu)(lu)(lu)電流大到(dao)使U>0.9V（該(gai)值由控制(zhi)IC決定(ding)，不(bu)(bu)同的IC有不(bu)(bu)同的值）時(shi)，控制(zhi)IC則判(pan)斷(duan)為負(fu)載短(duan)(duan)路(lu)(lu)(lu)，其(qi)“DO"腳將(jiang)迅速由高電壓轉變為零電壓，使V1由導通(tong)轉為關斷(duan)，從而(er)切斷(duan)放電回路(lu)(lu)(lu)，起到(dao)短(duan)(duan)路(lu)(lu)(lu)保護(hu)作用。短(duan)(duan)路(lu)(lu)(lu)保護(hu)的延時(shi)時(shi)間極短(duan)(duan)，通(tong)常小于(yu)7微秒。其(qi)工(gong)作原(yuan)理與過(guo)(guo)電流保護(hu)類似(si)，只是(shi)判(pan)斷(duan)方法(fa)不(bu)(bu)同，保護(hu)延時(shi)時(shi)間也不(bu)(bu)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)保護(hu)(hu)原理與之(zhi)類似，在(zai)(zai)此不再贅述(shu)，上(shang)面電(dian)路(lu)(lu)中(zhong)所用的(de)控(kong)制(zhi)(zhi)IC為(wei)日(ri)(ri)本(ben)(ben)理光公(gong)司的(de)R5421系(xi)列(lie)，在(zai)(zai)實際的(de)電(dian)池(chi)保護(hu)(hu)電(dian)路(lu)(lu)中(zhong)，還(huan)有(you)(you)許多其(qi)它(ta)類型的(de)控(kong)制(zhi)(zhi)IC，如(ru)日(ri)(ri)本(ben)(ben)精工的(de)S-8241系(xi)列(lie)、日(ri)(ri)本(ben)(ben)MITSUMI的(de)MM3061系(xi)列(lie)、臺(tai)灣富晶的(de)FS312和FS313系(xi)列(lie)、臺(tai)灣類比(bi)科技的(de)AAT8632系(xi)列(lie)等(deng)等(deng)，其(qi)工作原理大同小(xiao)(xiao)(xiao)異(yi)，只是(shi)在(zai)(zai)具體參數上(shang)有(you)(you)所差別，有(you)(you)些控(kong)制(zhi)(zhi)IC為(wei)了(le)節省外圍(wei)電(dian)路(lu)(lu)，將濾波電(dian)容和延時電(dian)容做(zuo)到了(le)芯片內部，其(qi)外圍(wei)電(dian)路(lu)(lu)可以很(hen)少，如(ru)日(ri)(ri)本(ben)(ben)精工的(de)S-8241系(xi)列(lie)。 除了(le)控(kong)制(zhi)(zhi)IC外，電(dian)路(lu)(lu)中(zhong)還(huan)有(you)(you)一個重要元(yuan)件，就是(shi)MOSFET，它(ta)在(zai)(zai)電(dian)路(lu)(lu)中(zhong)起著開(kai)關的(de)作用，由于它(ta)直接串接在(zai)(zai)電(dian)池(chi)與外部負載之(zhi)間，因此它(ta)的(de)導通(tong)阻抗對電(dian)池(chi)的(de)性(xing)能有(you)(you)影(ying)響，當選(xuan)用的(de)MOSFET較好時，其(qi)導通(tong)阻抗很(hen)小(xiao)(xiao)(xiao)，電(dian)池(chi)包(bao)的(de)內阻就小(xiao)(xiao)(xiao)，帶(dai)載能力也(ye)強，在(zai)(zai)放(fang)電(dian)時其(qi)消(xiao)耗的(de)電(dian)能也(ye)少。

隨著(zhu)科技的(de)(de)(de)發展，便攜式設備的(de)(de)(de)體積(ji)越(yue)做越(yue)小(xiao)，而隨著(zhu)這種趨勢，對鋰離子電池的(de)(de)(de)保護(hu)(hu)電路體積(ji)的(de)(de)(de)要求也越(yue)來越(yue)小(xiao)，在這兩(liang)年已出現了將控(kong)制IC和MOSFET整合成一顆保護(hu)(hu)IC的(de)(de)(de)產品，如DIALOG公(gong)司的(de)(de)(de)DA7112系列，有(you)的(de)(de)(de)廠(chang)家甚至將整個保護(hu)(hu)電路封(feng)裝成一顆小(xiao)尺(chi)寸的(de)(de)(de)IC，如MITSUMI公(gong)司的(de)(de)(de)產品。