電路具有過(guo)充(chong)電保護、過(guo)放電保護、過(guo)電流保護與短路保護功(gong)能(neng)，其工作原理(li)分(fen)析如下：

1  正常狀態

在(zai)正常(chang)狀(zhuang)態下電(dian)路中(zhong)N1的“CO"與“DO"腳都輸出(chu)高電(dian)壓，兩個MOSFET都處(chu)于導通(tong)狀(zhuang)態，電(dian)池可(ke)以自由地進行(xing)充電(dian)和放電(dian)，由于MOSFET的導通(tong)阻抗很小，通(tong)常(chang)小于30毫(hao)歐(ou)，因此(ci)其導通(tong)電(dian)阻對(dui)電(dian)路的性能(neng)影(ying)響很小。 此(ci)狀(zhuang)態下保護電(dian)路的消耗(hao)電(dian)流為μA級，通(tong)常(chang)小于7μA。

2  過充電保護(hu)

鋰離子電池作為(wei)可充(chong)電(dian)(dian)(dian)池(chi)的一種(zhong)，要求(qiu)的充(chong)電(dian)(dian)(dian)方(fang)式為(wei)恒(heng)(heng)流/恒(heng)(heng)壓(ya)，在(zai)(zai)充(chong)電(dian)(dian)(dian)初期，為(wei)恒(heng)(heng)流充(chong)電(dian)(dian)(dian)，隨著充(chong)電(dian)(dian)(dian)過程，電(dian)(dian)(dian)壓(ya)會(hui)上升到4.2V（根據正極材料不同(tong)，有的電(dian)(dian)(dian)池(chi)要求(qiu)恒(heng)(heng)壓(ya)值為(wei)4.1V），轉為(wei)恒(heng)(heng)壓(ya)充(chong)電(dian)(dian)(dian)，直至電(dian)(dian)(dian)流越來越小。 電(dian)(dian)(dian)池(chi)在(zai)(zai)被(bei)充(chong)電(dian)(dian)(dian)過程中，如果充(chong)電(dian)(dian)(dian)器(qi)電(dian)(dian)(dian)路失去控制(zhi)，會(hui)使電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(ya)超過4.2V后繼(ji)續(xu)恒(heng)(heng)流充(chong)電(dian)(dian)(dian)，此時電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(ya)仍會(hui)繼(ji)續(xu)上升，當電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(ya)被(bei)充(chong)電(dian)(dian)(dian)至超過4.3V時，電(dian)(dian)(dian)池(chi)的化學副反應將加劇，會(hui)導(dao)致電(dian)(dian)(dian)池(chi)損壞或(huo)出現安(an)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，使充電器無法再對電(dian)(dian)池(chi)進(jin)行(xing)充電(dian)(dian)，起到過充電(dian)(dian)保(bao)護作用。而此(ci)時(shi)由于V2自帶的(de)體二極管VD2的(de)存在，電(dian)(dian)池(chi)可以通過該二極管對外部負載進(jin)行(xing)放(fang)電(dian)(dian)。

在控制IC檢測(ce)到電(dian)池電(dian)壓超過(guo)4.28V至發出關斷V2信號(hao)之間，還有(you)一段延時(shi)(shi)時(shi)(shi)間，該(gai)延時(shi)(shi)時(shi)(shi)間的長(chang)短由C3決(jue)定(ding)，通(tong)常設為1秒左(zuo)右，以避免因(yin)干擾(rao)而造成(cheng)誤判斷。

3  過放(fang)電保護

電(dian)(dian)(dian)(dian)(dian)池(chi)在(zai)對外部負載放(fang)電(dian)(dian)(dian)(dian)(dian)過程中(zhong)，其(qi)電(dian)(dian)(dian)(dian)(dian)壓會隨(sui)著放(fang)電(dian)(dian)(dian)(dian)(dian)過程逐漸(jian)降低，當(dang)電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓降至2.5V時，其(qi)容(rong)量(liang)已被(bei)完全放(fang)光，此時如果讓(rang)電(dian)(dian)(dian)(dian)(dian)池(chi)繼續(xu)對負載放(fang)電(dian)(dian)(dian)(dian)(dian)，將造成電(dian)(dian)(dian)(dian)(dian)池(chi)的永(yong)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，充電器可以通(tong)過該二(er)極管(guan)對電(dian)池進行充(chong)電(dian)。

由于(yu)在過放(fang)電(dian)保(bao)護(hu)狀態下電(dian)池電(dian)壓不能再降低，因此(ci)要求保(bao)護(hu)電(dian)路的消耗電(dian)流極小(xiao)，此(ci)時控制(zhi)IC會進入低功耗狀態，整個保(bao)護(hu)電(dian)路耗電(dian)會小(xiao)于(yu)0.1μA。

在(zai)控制IC檢測到電池電壓(ya)低(di)于(yu)2.3V至(zhi)發出關斷V1信號之間(jian)，也(ye)有一段延時時間(jian)，該(gai)延時時間(jian)的長(chang)短(duan)由C3決(jue)定，通(tong)常設(she)為100毫秒左(zuo)右，以避免(mian)因干擾(rao)而造成誤判斷。

4  過(guo)電(dian)流保護

由于鋰(li)電(dian)(dian)池(chi)(chi)的(de)化學特性，電(dian)(dian)池(chi)(chi)生產廠家規定了其(qi)放(fang)電(dian)(dian)電(dian)(dian)流(liu)最大不能超過2C（C=電(dian)(dian)池(chi)(chi)容量/小時），當(dang)電(dian)(dian)池(chi)(chi)超過2C電(dian)(dian)流(liu)放(fang)電(dian)(dian)時，將(jiang)會導致電(dian)(dian)池(chi)(chi)的(de)永久性損壞或出現安(an)全問(wen)題。

電(dian)(dian)池在(zai)對負載正常(chang)(chang)放電(dian)(dian)過(guo)程中(zhong)，放電(dian)(dian)電(dian)(dian)流(liu)在(zai)經過(guo)串聯(lian)的(de)2個(ge)MOSFET時，由于(yu)MOSFET的(de)導通(tong)阻抗，會在(zai)其兩端產(chan)生一個(ge)電(dian)(dian)壓，該電(dian)(dian)壓值(zhi)U=I*RDS*2, RDS為(wei)單個(ge)MOSFET導通(tong)阻抗，控(kong)(kong)制IC上(shang)的(de)“V-"腳(jiao)對該電(dian)(dian)壓值(zhi)進行檢測，若負載因(yin)某種原因(yin)導致異常(chang)(chang)，使回(hui)(hui)路(lu)電(dian)(dian)流(liu)增大(da)，當回(hui)(hui)路(lu)電(dian)(dian)流(liu)大(da)到(dao)使U>0.1V（該值(zhi)由控(kong)(kong)制IC決定(ding)，不(bu)同的(de)IC有不(bu)同的(de)值(zhi)）時，其“DO"腳(jiao)將由高電(dian)(dian)壓轉變(bian)為(wei)零(ling)電(dian)(dian)壓，使V1由導通(tong)轉為(wei)關斷，從而切斷了放電(dian)(dian)回(hui)(hui)路(lu)，使回(hui)(hui)路(lu)中(zhong)電(dian)(dian)流(liu)為(wei)零(ling)，起到(dao)過(guo)電(dian)(dian)流(liu)保(bao)護作(zuo)用。

在控制(zhi)IC檢測到過電流發生至發出關斷V1信(xin)號之間，也有一段延時(shi)時(shi)間，該延時(shi)時(shi)間的(de)長短由(you)C3決(jue)定，通常(chang)為13毫(hao)秒左右，以避(bi)免因干擾而造成誤判(pan)斷。

在上(shang)述控制(zhi)(zhi)過(guo)(guo)程中可知，其過(guo)(guo)電流檢測值(zhi)大小不僅取決于控制(zhi)(zhi)IC的控制(zhi)(zhi)值(zhi)，還取決于MOSFET的導通(tong)阻抗，當MOSFET導通(tong)阻抗越大時，對同樣的控制(zhi)(zhi)IC，其過(guo)(guo)電流保護值(zhi)越小。

5  短路保護

電(dian)(dian)(dian)池(chi)在對負載(zai)放電(dian)(dian)(dian)過程中(zhong)，若(ruo)回路(lu)電(dian)(dian)(dian)流大到使U>0.9V（該值由(you)控制(zhi)IC決定，不(bu)同(tong)的(de)IC有不(bu)同(tong)的(de)值）時(shi)，控制(zhi)IC則(ze)判斷(duan)為負載(zai)短路(lu)，其(qi)“DO"腳將迅速由(you)高(gao)電(dian)(dian)(dian)壓轉(zhuan)(zhuan)變(bian)為零(ling)電(dian)(dian)(dian)壓，使V1由(you)導通(tong)轉(zhuan)(zhuan)為關(guan)斷(duan)，從而切斷(duan)放電(dian)(dian)(dian)回路(lu)，起(qi)到短路(lu)保(bao)(bao)護(hu)(hu)作(zuo)用。短路(lu)保(bao)(bao)護(hu)(hu)的(de)延(yan)時(shi)時(shi)間(jian)極短，通(tong)常小于7微秒。其(qi)工作(zuo)原理(li)與過電(dian)(dian)(dian)流保(bao)(bao)護(hu)(hu)類似，只(zhi)是判斷(duan)方法不(bu)同(tong)，保(bao)(bao)護(hu)(hu)延(yan)時(shi)時(shi)間(jian)也不(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)(de)(de)保護原理與之(zhi)類(lei)似，在此不再贅述(shu)，上(shang)面電(dian)(dian)路(lu)中(zhong)所(suo)用的(de)(de)(de)控(kong)制(zhi)IC為(wei)日本理光公司的(de)(de)(de)R5421系(xi)列(lie)，在實際的(de)(de)(de)電(dian)(dian)池保護電(dian)(dian)路(lu)中(zhong)，還有(you)(you)許(xu)多(duo)其(qi)(qi)(qi)它(ta)(ta)(ta)類(lei)型的(de)(de)(de)控(kong)制(zhi)IC，如(ru)日本精工的(de)(de)(de)S-8241系(xi)列(lie)、日本MITSUMI的(de)(de)(de)MM3061系(xi)列(lie)、臺(tai)(tai)灣富(fu)晶的(de)(de)(de)FS312和FS313系(xi)列(lie)、臺(tai)(tai)灣類(lei)比科技的(de)(de)(de)AAT8632系(xi)列(lie)等(deng)(deng)等(deng)(deng)，其(qi)(qi)(qi)工作(zuo)原理大同小異，只是在具(ju)體參數(shu)上(shang)有(you)(you)所(suo)差別(bie)，有(you)(you)些(xie)控(kong)制(zhi)IC為(wei)了(le)節省(sheng)外(wai)圍(wei)電(dian)(dian)路(lu)，將濾波電(dian)(dian)容(rong)和延時(shi)電(dian)(dian)容(rong)做到了(le)芯片內部，其(qi)(qi)(qi)外(wai)圍(wei)電(dian)(dian)路(lu)可以很(hen)少，如(ru)日本精工的(de)(de)(de)S-8241系(xi)列(lie)。 除了(le)控(kong)制(zhi)IC外(wai)，電(dian)(dian)路(lu)中(zhong)還有(you)(you)一個重要元件，就(jiu)是MOSFET，它(ta)(ta)(ta)在電(dian)(dian)路(lu)中(zhong)起(qi)著(zhu)開關(guan)的(de)(de)(de)作(zuo)用，由于它(ta)(ta)(ta)直接串接在電(dian)(dian)池與外(wai)部負載之(zhi)間(jian)，因(yin)此它(ta)(ta)(ta)的(de)(de)(de)導通阻抗對電(dian)(dian)池的(de)(de)(de)性能有(you)(you)影響(xiang)，當選用的(de)(de)(de)MOSFET較好時(shi)，其(qi)(qi)(qi)導通阻抗很(hen)小，電(dian)(dian)池包的(de)(de)(de)內阻就(jiu)小，帶載能力(li)也(ye)強，在放電(dian)(dian)時(shi)其(qi)(qi)(qi)消耗的(de)(de)(de)電(dian)(dian)能也(ye)少。

隨(sui)(sui)著(zhu)科(ke)技的(de)(de)發展，便(bian)攜(xie)式設備的(de)(de)體積越(yue)(yue)做(zuo)越(yue)(yue)小，而隨(sui)(sui)著(zhu)這種趨(qu)勢，對(dui)鋰離子電(dian)(dian)池(chi)的(de)(de)保護電(dian)(dian)路體積的(de)(de)要求也越(yue)(yue)來越(yue)(yue)小，在這兩(liang)年(nian)已出(chu)現了將控制IC和MOSFET整合成(cheng)一顆保護IC的(de)(de)產品，如(ru)DIALOG公(gong)司的(de)(de)DA7112系列(lie)，有的(de)(de)廠家甚至將整個保護電(dian)(dian)路封裝(zhuang)成(cheng)一顆小尺寸的(de)(de)IC，如(ru)MITSUMI公(gong)司的(de)(de)產品。