電路(lu)具(ju)有過(guo)充電保護(hu)、過(guo)放電保護(hu)、過(guo)電流保護(hu)與短路(lu)保護(hu)功能，其工(gong)作(zuo)原(yuan)理分析如下：

1  正常狀(zhuang)態

在正(zheng)常狀態(tai)(tai)下電(dian)(dian)路中(zhong)N1的“CO"與“DO"腳都輸出高電(dian)(dian)壓，兩個MOSFET都處于導通(tong)狀態(tai)(tai)，電(dian)(dian)池可以自(zi)由地(di)進行充電(dian)(dian)和放電(dian)(dian)，由于MOSFET的導通(tong)阻(zu)抗很小(xiao)，通(tong)常小(xiao)于30毫(hao)歐，因此其導通(tong)電(dian)(dian)阻(zu)對電(dian)(dian)路的性能(neng)影(ying)響很小(xiao)。 此狀態(tai)(tai)下保護電(dian)(dian)路的消耗電(dian)(dian)流為μA級，通(tong)常小(xiao)于7μA。

2  過充電保護

鋰離子電池作為(wei)可充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)一種，要求(qiu)的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)方(fang)式(shi)為(wei)恒(heng)(heng)(heng)流/恒(heng)(heng)(heng)壓(ya)，在(zai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)初期，為(wei)恒(heng)(heng)(heng)流充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，隨著充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)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(ji)材(cai)料不同(tong)，有的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)要求(qiu)恒(heng)(heng)(heng)壓(ya)值為(wei)4.1V），轉為(wei)恒(heng)(heng)(heng)壓(ya)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，直至電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流越來越小(xiao)。 電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)在(zai)被充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程(cheng)中，如果充(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(kong)制，會(hui)使電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)超過(guo)4.2V后繼續恒(heng)(heng)(heng)流充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，此時電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)仍(reng)會(hui)繼續上升(sheng)，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)被充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)至超過(guo)4.3V時，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)化學副(fu)反(fan)應(ying)將(jiang)加劇(ju)，會(hui)導致電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)損壞或(huo)出現(xian)安全問(wen)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(dui)(dui)電(dian)(dian)池進(jin)(jin)行(xing)充電(dian)(dian)，起到過(guo)充電(dian)(dian)保護作用。而此時由于V2自帶(dai)的體二(er)極管VD2的存在，電(dian)(dian)池可以(yi)通過(guo)該(gai)二(er)極管對(dui)(dui)外部負載進(jin)(jin)行(xing)放電(dian)(dian)。

在(zai)控制IC檢測到電(dian)(dian)池電(dian)(dian)壓超(chao)過(guo)4.28V至發出關斷V2信號(hao)之間(jian)，還有一段延時時間(jian)，該延時時間(jian)的長短由C3決定，通常設為1秒左右(you)，以避(bi)免因干擾而(er)造成誤判斷。

3  過(guo)放(fang)電保護

電(dian)(dian)(dian)池在對(dui)外部負載(zai)放電(dian)(dian)(dian)過程(cheng)中(zhong)，其電(dian)(dian)(dian)壓會隨(sui)著放電(dian)(dian)(dian)過程(cheng)逐漸降低，當電(dian)(dian)(dian)池電(dian)(dian)(dian)壓降至2.5V時，其容量已被完全放光，此時如(ru)果讓電(dian)(dian)(dian)池繼續對(dui)負載(zai)放電(dian)(dian)(dian)，將造成(cheng)電(dian)(dian)(dian)池的永久性損壞。

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(tong)過該二極管對電池進行充(chong)電。

由(you)于在(zai)過放電(dian)保護狀態(tai)下電(dian)池電(dian)壓(ya)不能再降低，因此(ci)要(yao)求保護電(dian)路的消耗(hao)電(dian)流(liu)極小(xiao)，此(ci)時控制(zhi)IC會進入低功耗(hao)狀態(tai)，整個(ge)保護電(dian)路耗(hao)電(dian)會小(xiao)于0.1μA。

在(zai)控制(zhi)IC檢測(ce)到電池電壓低于(yu)2.3V至(zhi)發出關(guan)斷(duan)(duan)V1信號(hao)之間，也有一段延時(shi)時(shi)間，該延時(shi)時(shi)間的(de)長短由C3決定，通常設為(wei)100毫秒(miao)左右，以(yi)避免因干擾而造成(cheng)誤判斷(duan)(duan)。

4  過電流保護

由于鋰電(dian)(dian)池的(de)化學(xue)特性，電(dian)(dian)池生(sheng)產廠家規(gui)定了其放(fang)電(dian)(dian)電(dian)(dian)流(liu)最大不能超(chao)過2C（C=電(dian)(dian)池容量/小(xiao)時），當電(dian)(dian)池超(chao)過2C電(dian)(dian)流(liu)放(fang)電(dian)(dian)時，將會(hui)導致電(dian)(dian)池的(de)永久性損(sun)壞或出(chu)現安全(quan)問題(ti)。

電(dian)(dian)(dian)池在對負(fu)載(zai)正(zheng)常放(fang)電(dian)(dian)(dian)過程(cheng)中(zhong)，放(fang)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)在經過串聯的(de)2個MOSFET時(shi)，由于MOSFET的(de)導(dao)通(tong)阻抗，會在其兩(liang)端產生一個電(dian)(dian)(dian)壓，該電(dian)(dian)(dian)壓值(zhi)U=I*RDS*2, RDS為單個MOSFET導(dao)通(tong)阻抗，控制IC上的(de)“V-"腳(jiao)對該電(dian)(dian)(dian)壓值(zhi)進(jin)行檢測(ce)，若負(fu)載(zai)因(yin)某(mou)種(zhong)原(yuan)因(yin)導(dao)致異常，使回路(lu)電(dian)(dian)(dian)流(liu)增大，當回路(lu)電(dian)(dian)(dian)流(liu)大到使U>0.1V（該值(zhi)由控制IC決定，不同(tong)的(de)IC有不同(tong)的(de)值(zhi)）時(shi)，其“DO"腳(jiao)將由高電(dian)(dian)(dian)壓轉變為零電(dian)(dian)(dian)壓，使V1由導(dao)通(tong)轉為關(guan)斷，從(cong)而切(qie)斷了(le)放(fang)電(dian)(dian)(dian)回路(lu)，使回路(lu)中(zhong)電(dian)(dian)(dian)流(liu)為零，起到過電(dian)(dian)(dian)流(liu)保護作(zuo)用。

在(zai)控制IC檢測到過電流發生至發出關斷(duan)V1信號之間，也有(you)一(yi)段(duan)延(yan)(yan)時(shi)時(shi)間，該延(yan)(yan)時(shi)時(shi)間的長(chang)短(duan)由C3決定(ding)，通常為13毫秒左(zuo)右，以避免(mian)因干擾而(er)造成誤判斷(duan)。

在上述控(kong)(kong)制(zhi)過程中(zhong)可(ke)知，其過電流檢測值(zhi)大(da)小不(bu)僅(jin)取(qu)決于控(kong)(kong)制(zhi)IC的控(kong)(kong)制(zhi)值(zhi)，還(huan)取(qu)決于MOSFET的導通(tong)阻抗(kang)(kang)，當MOSFET導通(tong)阻抗(kang)(kang)越(yue)大(da)時，對同樣(yang)的控(kong)(kong)制(zhi)IC，其過電流保護值(zhi)越(yue)小。

5  短路保護

電(dian)池在對負載放(fang)電(dian)過程(cheng)中，若回路電(dian)流(liu)大到(dao)使(shi)U>0.9V（該值由(you)控制IC決定，不(bu)同(tong)的(de)IC有不(bu)同(tong)的(de)值）時，控制IC則判斷(duan)(duan)為(wei)負載短(duan)(duan)路，其“DO"腳將迅速由(you)高電(dian)壓轉變為(wei)零電(dian)壓，使(shi)V1由(you)導通轉為(wei)關斷(duan)(duan)，從而(er)切(qie)斷(duan)(duan)放(fang)電(dian)回路，起到(dao)短(duan)(duan)路保護作用。短(duan)(duan)路保護的(de)延時時間(jian)極短(duan)(duan)，通常小于7微秒。其工作原理與過電(dian)流(liu)保護類似，只是(shi)判斷(duan)(duan)方(fang)法不(bu)同(tong)，保護延時時間(jian)也不(bu)一(yi)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(yu)之類(lei)似，在(zai)(zai)此不(bu)再贅述，上面電(dian)路(lu)(lu)中(zhong)所用(yong)的(de)(de)(de)控(kong)制(zhi)(zhi)IC為日(ri)本(ben)(ben)(ben)理光公司的(de)(de)(de)R5421系(xi)(xi)列，在(zai)(zai)實(shi)際(ji)的(de)(de)(de)電(dian)池保護電(dian)路(lu)(lu)中(zhong)，還有許多其(qi)(qi)它類(lei)型的(de)(de)(de)控(kong)制(zhi)(zhi)IC，如日(ri)本(ben)(ben)(ben)精工的(de)(de)(de)S-8241系(xi)(xi)列、日(ri)本(ben)(ben)(ben)MITSUMI的(de)(de)(de)MM3061系(xi)(xi)列、臺灣(wan)富(fu)晶的(de)(de)(de)FS312和FS313系(xi)(xi)列、臺灣(wan)類(lei)比(bi)科技的(de)(de)(de)AAT8632系(xi)(xi)列等等，其(qi)(qi)工作原理大同(tong)小異(yi)，只(zhi)是(shi)在(zai)(zai)具(ju)體參數上有所差別，有些(xie)控(kong)制(zhi)(zhi)IC為了節(jie)省外(wai)圍電(dian)路(lu)(lu)，將濾波電(dian)容(rong)和延(yan)時(shi)電(dian)容(rong)做到(dao)了芯(xin)片內部，其(qi)(qi)外(wai)圍電(dian)路(lu)(lu)可以很少，如日(ri)本(ben)(ben)(ben)精工的(de)(de)(de)S-8241系(xi)(xi)列。 除了控(kong)制(zhi)(zhi)IC外(wai)，電(dian)路(lu)(lu)中(zhong)還有一個(ge)重要元(yuan)件，就是(shi)MOSFET，它在(zai)(zai)電(dian)路(lu)(lu)中(zhong)起(qi)著(zhu)開關的(de)(de)(de)作用(yong)，由于它直接串接在(zai)(zai)電(dian)池與(yu)外(wai)部負載(zai)之間，因此它的(de)(de)(de)導通阻抗(kang)對電(dian)池的(de)(de)(de)性能(neng)有影響(xiang)，當選用(yong)的(de)(de)(de)MOSFET較好時(shi)，其(qi)(qi)導通阻抗(kang)很小，電(dian)池包的(de)(de)(de)內阻就小，帶載(zai)能(neng)力也(ye)強(qiang)，在(zai)(zai)放電(dian)時(shi)其(qi)(qi)消耗的(de)(de)(de)電(dian)能(neng)也(ye)少。

隨(sui)著科技的(de)(de)(de)發展，便(bian)攜式設備的(de)(de)(de)體(ti)積越做(zuo)越小，而隨(sui)著這種趨勢(shi)，對鋰離子電池的(de)(de)(de)保護(hu)電路體(ti)積的(de)(de)(de)要求也越來越小，在這兩年(nian)已出現了將(jiang)控制IC和(he)MOSFET整合成一顆保護(hu)IC的(de)(de)(de)產品(pin)，如DIALOG公(gong)司的(de)(de)(de)DA7112系列，有的(de)(de)(de)廠家甚至將(jiang)整個保護(hu)電路封(feng)裝(zhuang)成一顆小尺寸的(de)(de)(de)IC，如MITSUMI公(gong)司的(de)(de)(de)產品(pin)。