電路(lu)(lu)具有過(guo)充電保(bao)護、過(guo)放電保(bao)護、過(guo)電流保(bao)護與短路(lu)(lu)保(bao)護功能，其工作原理分析如下：

1  正常狀態

在正常狀態下(xia)電路中N1的(de)(de)“CO"與“DO"腳都輸(shu)出高電壓，兩(liang)個MOSFET都處于(yu)導通(tong)(tong)狀態，電池可(ke)以自由地(di)進行充(chong)電和放(fang)電，由于(yu)MOSFET的(de)(de)導通(tong)(tong)阻抗很小(xiao)(xiao)，通(tong)(tong)常小(xiao)(xiao)于(yu)30毫歐(ou)，因此(ci)其(qi)導通(tong)(tong)電阻對電路的(de)(de)性能影響(xiang)很小(xiao)(xiao)。 此(ci)狀態下(xia)保護電路的(de)(de)消耗電流為μA級，通(tong)(tong)常小(xiao)(xiao)于(yu)7μA。

2  過充電保護

鋰離子電池作(zuo)為(wei)(wei)可充(chong)電(dian)(dian)(dian)(dian)(dian)池(chi)的(de)一種，要(yao)求的(de)充(chong)電(dian)(dian)(dian)(dian)(dian)方式為(wei)(wei)恒流/恒壓(ya)，在充(chong)電(dian)(dian)(dian)(dian)(dian)初期，為(wei)(wei)恒流充(chong)電(dian)(dian)(dian)(dian)(dian)，隨著充(chong)電(dian)(dian)(dian)(dian)(dian)過程，電(dian)(dian)(dian)(dian)(dian)壓(ya)會(hui)上(shang)升到4.2V（根(gen)據正極材料不同，有的(de)電(dian)(dian)(dian)(dian)(dian)池(chi)要(yao)求恒壓(ya)值為(wei)(wei)4.1V），轉為(wei)(wei)恒壓(ya)充(chong)電(dian)(dian)(dian)(dian)(dian)，直(zhi)至電(dian)(dian)(dian)(dian)(dian)流越(yue)(yue)來(lai)越(yue)(yue)小。 電(dian)(dian)(dian)(dian)(dian)池(chi)在被充(chong)電(dian)(dian)(dian)(dian)(dian)過程中，如果(guo)充(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)電(dian)(dian)(dian)(dian)(dian)路失(shi)去控(kong)制，會(hui)使電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)超(chao)過4.2V后繼續恒流充(chong)電(dian)(dian)(dian)(dian)(dian)，此時電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)仍會(hui)繼續上(shang)升，當電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)被充(chong)電(dian)(dian)(dian)(dian)(dian)至超(chao)過4.3V時，電(dian)(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)(dian)池(chi)損壞(huai)或出現安全問題(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(dui)電(dian)(dian)池進行(xing)充電(dian)(dian)，起(qi)到過充電(dian)(dian)保護作用。而此時由(you)于V2自(zi)帶的(de)體二(er)極管(guan)VD2的(de)存(cun)在，電(dian)(dian)池可以通過該二(er)極管(guan)對(dui)外(wai)部負載進行(xing)放(fang)電(dian)(dian)。

在(zai)控制(zhi)IC檢測到電池電壓超(chao)過4.28V至發出關斷V2信號之(zhi)間(jian)(jian)，還有一段延時(shi)時(shi)間(jian)(jian)，該延時(shi)時(shi)間(jian)(jian)的長(chang)短由C3決定(ding)，通常設(she)為1秒左右(you)，以避免(mian)因干擾而(er)造成誤判斷。

3  過放電保護

電(dian)(dian)(dian)池(chi)在對外部負載放(fang)電(dian)(dian)(dian)過(guo)(guo)程中，其電(dian)(dian)(dian)壓(ya)會隨著放(fang)電(dian)(dian)(dian)過(guo)(guo)程逐漸(jian)降低，當電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(ya)降至2.5V時(shi)，其容量已(yi)被完全放(fang)光，此時(shi)如果讓電(dian)(dian)(dian)池(chi)繼續對負載放(fang)電(dian)(dian)(dian)，將造(zao)成電(dian)(dian)(dian)池(chi)的(de)永(yong)久性(xing)損壞。

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，充電器可以通過該(gai)二極管對電(dian)池(chi)進行(xing)充電(dian)。

由于在過放電(dian)(dian)保(bao)護(hu)狀(zhuang)態下電(dian)(dian)池(chi)電(dian)(dian)壓(ya)不能(neng)再降低，因(yin)此要求保(bao)護(hu)電(dian)(dian)路的消耗電(dian)(dian)流極小，此時控(kong)制IC會進入低功耗狀(zhuang)態，整個保(bao)護(hu)電(dian)(dian)路耗電(dian)(dian)會小于0.1μA。

在控制IC檢測(ce)到電池(chi)電壓低于2.3V至發出關(guan)斷V1信號之間(jian)，也有一段延時時間(jian)，該(gai)延時時間(jian)的長(chang)短(duan)由C3決定(ding)，通(tong)常(chang)設為100毫秒左右(you)，以避免因(yin)干擾而造(zao)成誤判斷。

4  過電流(liu)保護

由于鋰(li)電(dian)池(chi)(chi)的(de)(de)化學特性(xing)，電(dian)池(chi)(chi)生產廠家規定了其放(fang)電(dian)電(dian)流最大不能超(chao)過2C（C=電(dian)池(chi)(chi)容(rong)量/小時(shi)），當電(dian)池(chi)(chi)超(chao)過2C電(dian)流放(fang)電(dian)時(shi)，將(jiang)會導致電(dian)池(chi)(chi)的(de)(de)永(yong)久性(xing)損壞或出現安全問題(ti)。

電(dian)(dian)(dian)(dian)池在(zai)對(dui)負(fu)載正常(chang)(chang)放電(dian)(dian)(dian)(dian)過(guo)程中，放電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)在(zai)經過(guo)串(chuan)聯的(de)2個(ge)(ge)MOSFET時，由(you)于(yu)MOSFET的(de)導通阻抗，會在(zai)其兩端產生(sheng)一(yi)個(ge)(ge)電(dian)(dian)(dian)(dian)壓，該(gai)(gai)電(dian)(dian)(dian)(dian)壓值U=I*RDS*2, RDS為單個(ge)(ge)MOSFET導通阻抗，控(kong)制IC上的(de)“V-"腳對(dui)該(gai)(gai)電(dian)(dian)(dian)(dian)壓值進(jin)行檢測，若負(fu)載因(yin)某種原因(yin)導致異常(chang)(chang)，使回(hui)路(lu)電(dian)(dian)(dian)(dian)流(liu)增大(da)，當(dang)回(hui)路(lu)電(dian)(dian)(dian)(dian)流(liu)大(da)到使U>0.1V（該(gai)(gai)值由(you)控(kong)制IC決定(ding)，不(bu)(bu)同(tong)(tong)的(de)IC有不(bu)(bu)同(tong)(tong)的(de)值）時，其“DO"腳將由(you)高電(dian)(dian)(dian)(dian)壓轉變為零電(dian)(dian)(dian)(dian)壓，使V1由(you)導通轉為關斷，從而切斷了(le)放電(dian)(dian)(dian)(dian)回(hui)路(lu)，使回(hui)路(lu)中電(dian)(dian)(dian)(dian)流(liu)為零，起(qi)到過(guo)電(dian)(dian)(dian)(dian)流(liu)保護作用。

在控制IC檢(jian)測到(dao)過電(dian)流發生至發出關斷V1信號(hao)之間，也(ye)有一段(duan)延(yan)時(shi)(shi)時(shi)(shi)間，該延(yan)時(shi)(shi)時(shi)(shi)間的長(chang)短由(you)C3決定，通(tong)常為13毫秒左右，以避免因干擾而造成誤判斷。

在(zai)上述控(kong)(kong)制過程中可知，其過電流(liu)檢(jian)測值(zhi)(zhi)大小不僅(jin)取決(jue)(jue)于控(kong)(kong)制IC的(de)控(kong)(kong)制值(zhi)(zhi)，還取決(jue)(jue)于MOSFET的(de)導通阻抗，當MOSFET導通阻抗越大時，對同樣(yang)的(de)控(kong)(kong)制IC，其過電流(liu)保護值(zhi)(zhi)越小。

5  短(duan)路保護

電(dian)(dian)池在(zai)對負載(zai)放電(dian)(dian)過程中，若回路(lu)電(dian)(dian)流大到使(shi)U>0.9V（該值由(you)控制(zhi)IC決定，不同(tong)(tong)的IC有不同(tong)(tong)的值）時(shi)(shi)，控制(zhi)IC則判斷(duan)為(wei)負載(zai)短(duan)(duan)路(lu)，其(qi)“DO"腳將(jiang)迅速由(you)高電(dian)(dian)壓轉變為(wei)零(ling)電(dian)(dian)壓，使(shi)V1由(you)導通轉為(wei)關斷(duan)，從而切斷(duan)放電(dian)(dian)回路(lu)，起到短(duan)(duan)路(lu)保(bao)護作用。短(duan)(duan)路(lu)保(bao)護的延時(shi)(shi)時(shi)(shi)間(jian)極短(duan)(duan)，通常小于(yu)7微秒。其(qi)工(gong)作原理與過電(dian)(dian)流保(bao)護類似，只是判斷(duan)方法(fa)不同(tong)(tong)，保(bao)護延時(shi)(shi)時(shi)(shi)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)保(bao)(bao)護原理與(yu)之(zhi)(zhi)類(lei)似，在(zai)(zai)(zai)此(ci)不再贅述，上面電(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)所用(yong)(yong)的(de)控制IC為日(ri)(ri)本(ben)(ben)理光(guang)公(gong)司的(de)R5421系(xi)列(lie)(lie)，在(zai)(zai)(zai)實際的(de)電(dian)(dian)(dian)(dian)池保(bao)(bao)護電(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)，還有(you)(you)許(xu)多其(qi)(qi)它(ta)類(lei)型的(de)控制IC，如日(ri)(ri)本(ben)(ben)精工(gong)的(de)S-8241系(xi)列(lie)(lie)、日(ri)(ri)本(ben)(ben)MITSUMI的(de)MM3061系(xi)列(lie)(lie)、臺(tai)灣富晶(jing)的(de)FS312和FS313系(xi)列(lie)(lie)、臺(tai)灣類(lei)比科技的(de)AAT8632系(xi)列(lie)(lie)等等，其(qi)(qi)工(gong)作(zuo)原理大同小異，只(zhi)是在(zai)(zai)(zai)具體參數上有(you)(you)所差(cha)別(bie)，有(you)(you)些控制IC為了(le)節(jie)省外(wai)圍(wei)電(dian)(dian)(dian)(dian)路(lu)(lu)，將濾波電(dian)(dian)(dian)(dian)容和延時電(dian)(dian)(dian)(dian)容做到了(le)芯片內部(bu)，其(qi)(qi)外(wai)圍(wei)電(dian)(dian)(dian)(dian)路(lu)(lu)可以很(hen)少，如日(ri)(ri)本(ben)(ben)精工(gong)的(de)S-8241系(xi)列(lie)(lie)。 除了(le)控制IC外(wai)，電(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)還有(you)(you)一(yi)個(ge)重要元件(jian)，就(jiu)是MOSFET，它(ta)在(zai)(zai)(zai)電(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)起著開關的(de)作(zuo)用(yong)(yong)，由(you)于它(ta)直接串接在(zai)(zai)(zai)電(dian)(dian)(dian)(dian)池與(yu)外(wai)部(bu)負載(zai)之(zhi)(zhi)間，因此(ci)它(ta)的(de)導通阻抗(kang)對電(dian)(dian)(dian)(dian)池的(de)性能有(you)(you)影響，當(dang)選用(yong)(yong)的(de)MOSFET較(jiao)好時，其(qi)(qi)導通阻抗(kang)很(hen)小，電(dian)(dian)(dian)(dian)池包(bao)的(de)內阻就(jiu)小，帶載(zai)能力也強，在(zai)(zai)(zai)放電(dian)(dian)(dian)(dian)時其(qi)(qi)消耗的(de)電(dian)(dian)(dian)(dian)能也少。

隨(sui)著(zhu)科(ke)技(ji)的(de)(de)發展，便攜式設備(bei)的(de)(de)體(ti)積越(yue)做越(yue)小，而隨(sui)著(zhu)這種(zhong)趨(qu)勢，對鋰離子(zi)電池的(de)(de)保(bao)護(hu)(hu)電路(lu)體(ti)積的(de)(de)要求也越(yue)來越(yue)小，在(zai)這兩年已出現了將控制(zhi)IC和(he)MOSFET整合(he)成(cheng)一(yi)顆保(bao)護(hu)(hu)IC的(de)(de)產(chan)品(pin)，如DIALOG公司的(de)(de)DA7112系(xi)列，有的(de)(de)廠家甚至將整個保(bao)護(hu)(hu)電路(lu)封裝成(cheng)一(yi)顆小尺寸的(de)(de)IC，如MITSUMI公司的(de)(de)產(chan)品(pin)。