電(dian)路具有過充電(dian)保護(hu)、過放電(dian)保護(hu)、過電(dian)流保護(hu)與短路保護(hu)功能，其(qi)工作(zuo)原理分析如下：

1  正常狀態(tai)

在正常(chang)狀(zhuang)態(tai)(tai)下電路(lu)(lu)中N1的(de)“CO"與“DO"腳都輸出高電壓，兩個MOSFET都處于(yu)導(dao)通狀(zhuang)態(tai)(tai)，電池可以自由地進(jin)行充電和(he)放電，由于(yu)MOSFET的(de)導(dao)通阻抗(kang)很小，通常(chang)小于(yu)30毫歐(ou)，因此其(qi)導(dao)通電阻對(dui)電路(lu)(lu)的(de)性能影響很小。 此狀(zhuang)態(tai)(tai)下保(bao)護(hu)電路(lu)(lu)的(de)消耗電流為μA級，通常(chang)小于(yu)7μA。

2  過充電保護

鋰離子電池作(zuo)為(wei)可充(chong)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)一種(zhong)，要求的(de)(de)充(chong)電(dian)(dian)(dian)(dian)方式為(wei)恒(heng)(heng)(heng)流/恒(heng)(heng)(heng)壓(ya)(ya)，在充(chong)電(dian)(dian)(dian)(dian)初期，為(wei)恒(heng)(heng)(heng)流充(chong)電(dian)(dian)(dian)(dian)，隨著充(chong)電(dian)(dian)(dian)(dian)過程，電(dian)(dian)(dian)(dian)壓(ya)(ya)會(hui)上升到4.2V（根據(ju)正極材料(liao)不同(tong)，有的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)要求恒(heng)(heng)(heng)壓(ya)(ya)值為(wei)4.1V），轉(zhuan)為(wei)恒(heng)(heng)(heng)壓(ya)(ya)充(chong)電(dian)(dian)(dian)(dian)，直至(zhi)電(dian)(dian)(dian)(dian)流越(yue)來越(yue)小。 電(dian)(dian)(dian)(dian)池(chi)(chi)在被(bei)充(chong)電(dian)(dian)(dian)(dian)過程中，如果充(chong)電(dian)(dian)(dian)(dian)器電(dian)(dian)(dian)(dian)路(lu)失去控制，會(hui)使電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(ya)超過4.2V后繼續恒(heng)(heng)(heng)流充(chong)電(dian)(dian)(dian)(dian)，此時(shi)電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(ya)仍會(hui)繼續上升，當電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(ya)被(bei)充(chong)電(dian)(dian)(dian)(dian)至(zhi)超過4.3V時(shi)，電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)化學(xue)副反應將加劇，會(hui)導(dao)致(zhi)電(dian)(dian)(dian)(dian)池(chi)(chi)損壞(huai)或出現(xian)安全問題。

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(wu)法(fa)再對(dui)電(dian)(dian)池進行(xing)充電(dian)(dian)，起到過充電(dian)(dian)保護作用(yong)。而此時(shi)由于V2自帶(dai)的(de)體二(er)極管VD2的(de)存在(zai)，電(dian)(dian)池可以通過該二(er)極管對(dui)外(wai)部負載進行(xing)放電(dian)(dian)。

在(zai)控制IC檢測(ce)到(dao)電池電壓(ya)超過4.28V至發出關斷V2信號之間，還有一段延時(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(zuo)右，以避免因干擾而造成誤(wu)判斷。

3  過放電保護

電(dian)(dian)(dian)(dian)池(chi)在對外部負載(zai)放電(dian)(dian)(dian)(dian)過程中，其(qi)電(dian)(dian)(dian)(dian)壓(ya)會隨(sui)著放電(dian)(dian)(dian)(dian)過程逐漸降(jiang)低，當電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(ya)降(jiang)至2.5V時，其(qi)容(rong)量(liang)已被完(wan)全放光，此時如果(guo)讓電(dian)(dian)(dian)(dian)池(chi)繼續對負載(zai)放電(dian)(dian)(dian)(dian)，將造成(cheng)電(dian)(dian)(dian)(dian)池(chi)的永久性(xing)損(sun)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，充電器可以通過(guo)該二極管對電(dian)池進行(xing)充電(dian)。

由(you)于在過放(fang)電(dian)(dian)(dian)保護狀態(tai)下電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓不能再降低(di)，因此(ci)(ci)要求(qiu)保護電(dian)(dian)(dian)路(lu)的消耗(hao)電(dian)(dian)(dian)流極小，此(ci)(ci)時控(kong)制IC會進(jin)入低(di)功耗(hao)狀態(tai)，整個(ge)保護電(dian)(dian)(dian)路(lu)耗(hao)電(dian)(dian)(dian)會小于0.1μA。

在(zai)控制IC檢(jian)測到電池電壓低于(yu)2.3V至發出關斷V1信(xin)號(hao)之間，也有一段延(yan)(yan)時時間，該(gai)延(yan)(yan)時時間的(de)長短(duan)由C3決定，通(tong)常設為100毫秒左右，以避免因干擾而造成誤判(pan)斷。

4  過電流保護

由于鋰電(dian)(dian)池(chi)的化學特性，電(dian)(dian)池(chi)生產廠(chang)家規定了(le)其(qi)放電(dian)(dian)電(dian)(dian)流(liu)最大不能超過2C（C=電(dian)(dian)池(chi)容量/小時），當(dang)電(dian)(dian)池(chi)超過2C電(dian)(dian)流(liu)放電(dian)(dian)時，將會導(dao)致(zhi)電(dian)(dian)池(chi)的永(yong)久性損壞或出現安全問題。

電(dian)(dian)(dian)(dian)池在(zai)對負載(zai)(zai)正常放(fang)(fang)電(dian)(dian)(dian)(dian)過(guo)程中，放(fang)(fang)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)在(zai)經過(guo)串聯的(de)2個(ge)MOSFET時，由(you)(you)于MOSFET的(de)導(dao)(dao)通(tong)阻(zu)抗(kang)，會(hui)在(zai)其兩端產生一個(ge)電(dian)(dian)(dian)(dian)壓(ya)(ya)，該電(dian)(dian)(dian)(dian)壓(ya)(ya)值(zhi)U=I*RDS*2, RDS為(wei)(wei)單個(ge)MOSFET導(dao)(dao)通(tong)阻(zu)抗(kang)，控制(zhi)IC上的(de)“V-"腳(jiao)對該電(dian)(dian)(dian)(dian)壓(ya)(ya)值(zhi)進行(xing)檢測，若負載(zai)(zai)因某種原(yuan)因導(dao)(dao)致異常，使回路(lu)電(dian)(dian)(dian)(dian)流(liu)增(zeng)大(da)，當回路(lu)電(dian)(dian)(dian)(dian)流(liu)大(da)到使U>0.1V（該值(zhi)由(you)(you)控制(zhi)IC決定，不同(tong)的(de)IC有(you)不同(tong)的(de)值(zhi)）時，其“DO"腳(jiao)將由(you)(you)高電(dian)(dian)(dian)(dian)壓(ya)(ya)轉(zhuan)變為(wei)(wei)零電(dian)(dian)(dian)(dian)壓(ya)(ya)，使V1由(you)(you)導(dao)(dao)通(tong)轉(zhuan)為(wei)(wei)關斷，從而切斷了放(fang)(fang)電(dian)(dian)(dian)(dian)回路(lu)，使回路(lu)中電(dian)(dian)(dian)(dian)流(liu)為(wei)(wei)零，起到過(guo)電(dian)(dian)(dian)(dian)流(liu)保(bao)護作用。

在(zai)控制IC檢測到過電(dian)流(liu)發生至發出關(guan)斷(duan)V1信號(hao)之間(jian)，也有一段延時(shi)時(shi)間(jian)，該延時(shi)時(shi)間(jian)的(de)長(chang)短由(you)C3決定，通(tong)常為(wei)13毫秒左右，以避免因干擾(rao)而造成誤(wu)判斷(duan)。

在上述控制(zhi)(zhi)(zhi)過程中可(ke)知，其過電流檢(jian)測值(zhi)大小(xiao)不僅取決于(yu)控制(zhi)(zhi)(zhi)IC的(de)控制(zhi)(zhi)(zhi)值(zhi)，還(huan)取決于(yu)MOSFET的(de)導(dao)通(tong)阻抗，當MOSFET導(dao)通(tong)阻抗越(yue)大時，對同樣的(de)控制(zhi)(zhi)(zhi)IC，其過電流保護值(zhi)越(yue)小(xiao)。

5  短路(lu)保護

電(dian)(dian)池(chi)在對(dui)負載(zai)放電(dian)(dian)過程中，若回(hui)路(lu)(lu)(lu)電(dian)(dian)流大到使U>0.9V（該值由(you)(you)(you)控(kong)制IC決定，不同(tong)的(de)IC有不同(tong)的(de)值）時(shi)(shi)(shi)，控(kong)制IC則判斷為(wei)負載(zai)短路(lu)(lu)(lu)，其“DO"腳將迅速(su)由(you)(you)(you)高電(dian)(dian)壓(ya)轉變為(wei)零電(dian)(dian)壓(ya)，使V1由(you)(you)(you)導(dao)通轉為(wei)關斷，從而切(qie)斷放電(dian)(dian)回(hui)路(lu)(lu)(lu)，起到短路(lu)(lu)(lu)保(bao)(bao)護作用。短路(lu)(lu)(lu)保(bao)(bao)護的(de)延時(shi)(shi)(shi)時(shi)(shi)(shi)間極(ji)短，通常小于7微秒(miao)。其工(gong)作原理與(yu)過電(dian)(dian)流保(bao)(bao)護類似(si)，只是(shi)判斷方法不同(tong)，保(bao)(bao)護延時(shi)(shi)(shi)時(shi)(shi)(shi)間也不一樣。

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)保護(hu)原(yuan)理(li)與之(zhi)類似(si)，在(zai)此不再贅述，上面電(dian)(dian)(dian)路(lu)(lu)中(zhong)所用的(de)(de)控(kong)(kong)制(zhi)IC為(wei)日本(ben)理(li)光公(gong)司(si)的(de)(de)R5421系(xi)列(lie)，在(zai)實(shi)際的(de)(de)電(dian)(dian)(dian)池(chi)保護(hu)電(dian)(dian)(dian)路(lu)(lu)中(zhong)，還有(you)許多其(qi)(qi)它(ta)(ta)類型的(de)(de)控(kong)(kong)制(zhi)IC，如(ru)日本(ben)精工(gong)的(de)(de)S-8241系(xi)列(lie)、日本(ben)MITSUMI的(de)(de)MM3061系(xi)列(lie)、臺灣富晶的(de)(de)FS312和(he)FS313系(xi)列(lie)、臺灣類比科技的(de)(de)AAT8632系(xi)列(lie)等(deng)等(deng)，其(qi)(qi)工(gong)作原(yuan)理(li)大同小異(yi)，只是(shi)在(zai)具體參數上有(you)所差別，有(you)些控(kong)(kong)制(zhi)IC為(wei)了(le)節(jie)省外(wai)(wai)圍(wei)(wei)電(dian)(dian)(dian)路(lu)(lu)，將濾波電(dian)(dian)(dian)容和(he)延時電(dian)(dian)(dian)容做到了(le)芯(xin)片內部，其(qi)(qi)外(wai)(wai)圍(wei)(wei)電(dian)(dian)(dian)路(lu)(lu)可以很(hen)少，如(ru)日本(ben)精工(gong)的(de)(de)S-8241系(xi)列(lie)。 除(chu)了(le)控(kong)(kong)制(zhi)IC外(wai)(wai)，電(dian)(dian)(dian)路(lu)(lu)中(zhong)還有(you)一個重要(yao)元(yuan)件，就是(shi)MOSFET，它(ta)(ta)在(zai)電(dian)(dian)(dian)路(lu)(lu)中(zhong)起著(zhu)開關的(de)(de)作用，由于它(ta)(ta)直接(jie)串接(jie)在(zai)電(dian)(dian)(dian)池(chi)與外(wai)(wai)部負載之(zhi)間，因(yin)此它(ta)(ta)的(de)(de)導通阻抗對(dui)電(dian)(dian)(dian)池(chi)的(de)(de)性(xing)能有(you)影(ying)響，當選用的(de)(de)MOSFET較(jiao)好時，其(qi)(qi)導通阻抗很(hen)小，電(dian)(dian)(dian)池(chi)包的(de)(de)內阻就小，帶(dai)載能力也(ye)(ye)強(qiang)，在(zai)放電(dian)(dian)(dian)時其(qi)(qi)消耗的(de)(de)電(dian)(dian)(dian)能也(ye)(ye)少。

隨著科技(ji)的(de)(de)(de)發展，便攜式(shi)設備的(de)(de)(de)體(ti)積(ji)越(yue)做(zuo)越(yue)小(xiao)，而(er)隨著這種趨(qu)勢(shi)，對鋰離子電池的(de)(de)(de)保護電路(lu)體(ti)積(ji)的(de)(de)(de)要(yao)求也越(yue)來越(yue)小(xiao)，在(zai)這兩年已出(chu)現(xian)了將(jiang)控制IC和(he)MOSFET整(zheng)(zheng)合成一顆保護IC的(de)(de)(de)產(chan)品(pin)，如(ru)(ru)DIALOG公司(si)的(de)(de)(de)DA7112系列(lie)，有的(de)(de)(de)廠家甚至將(jiang)整(zheng)(zheng)個保護電路(lu)封裝成一顆小(xiao)尺寸的(de)(de)(de)IC，如(ru)(ru)MITSUMI公司(si)的(de)(de)(de)產(chan)品(pin)。