在有些應用中，較長的(de)電(dian)池壽(shou)命(ming)、較多的(de)充電(dian)次數或(huo)較安全的(de)電(dian)池比電(dian)池容(rong)量更(geng)重要。本文介紹幾(ji)種可以極(ji)大延長電(dian)池壽(shou)命(ming)的(de)鋰(li)離子電(dian)池充電(dian)和放電(dian)方(fang)法(fa)。

  幾乎所有高性能便攜式產品都會使用包括鋰離子聚合物電池在內的可再充電鋰離子電池，這是因(yin)為與其他可再充電(dian)(dian)(dian)電(dian)(dian)(dian)池(chi)(chi)相比，鋰(li)離(li)子電(dian)(dian)(dian)池(chi)(chi)有較高的能(neng)量密(mi)度、較高的電(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)壓(ya)(ya)、自(zi)放電(dian)(dian)(dian)少、周期壽命非常長(chang)，而且環保，且充電(dian)(dian)(dian)和維(wei)護簡(jian)(jian)單(dan)。另外(wai)，由于其具(ju)有相對高的電(dian)(dian)(dian)壓(ya)(ya)（2.9V至4.2V），因(yin)此(ci)很多(duo)便攜(xie)式產(chan)品都(dou)能(neng)用單(dan)節電(dian)(dian)(dian)池(chi)(chi)工(gong)作，從(cong)而簡(jian)(jian)化了(le)產(chan)品總體設(she)計。C速率等于特(te)定條件下(xia)的充電(dian)(dian)(dian)或放電(dian)(dian)(dian)電(dian)(dian)(dian)流，定義如下(xia)：I=M×Cn

  其中：I = 充電(dian)或放電(dian)電(dian)流(liu)，單位為A；M = C的倍數(shu)或分數(shu)；C = 額定容量(liang)的數(shu)值，單位為Ah；N = 小時數(shu)（對應于C）。

  以(yi)1倍C速率放(fang)電(dian)(dian)(dian)(dian)的(de)(de)電(dian)(dian)(dian)(dian)池將在一個小時內釋放(fang)標稱的(de)(de)額定容量(liang)。例如(ru)，如(ru)果(guo)標稱容量(liang)是1000mAhr,那么(me)1C的(de)(de)放(fang)電(dian)(dian)(dian)(dian)速率對應于(yu)1000mA的(de)(de)放(fang)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流，C/10的(de)(de)速率對應100mA的(de)(de)放(fang)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流。

  通常生產商標定的電池容量都是指n=5時，即5小時放電的容量。例如，上述電池在200mA恒流放電時能夠提供5小時的工作時間。理論上該電池在1000mA恒流放電時能夠提供1小時的工作時間。然而實際上由于大電池放電時效能降低，此時的工作時間將小于1小時。
 

  給鋰(li)離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)(de)推薦方(fang)法(fa)是，向電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)提供一(yi)(yi)(yi)個±1%限(xian)壓(ya)的(de)(de)(de)(de)(de)恒(heng)定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，直到(dao)(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)(chong)(chong)滿電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，然后停止(zhi)(zhi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。用(yong)來決定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)何(he)時(shi)(shi)充(chong)(chong)(chong)(chong)(chong)滿電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)(de)方(fang)法(fa)包括：給總(zong)的(de)(de)(de)(de)(de)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)間定(ding)時(shi)(shi)、監視充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)或兼(jian)用(yong)這兩種(zhong)(zhong)(zhong)方(fang)法(fa)。第(di)一(yi)(yi)(yi)種(zhong)(zhong)(zhong)方(fang)法(fa)采用(yong)限(xian)壓(ya)恒(heng)定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，變化范圍從C/2到(dao)(dao)(dao)1C,持續2.5至3小時(shi)(shi)，使電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)達到(dao)(dao)(dao)100%充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。也可以使用(yong)較低的(de)(de)(de)(de)(de)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，但是將需(xu)要(yao)更長時(shi)(shi)間。第(di)二種(zhong)(zhong)(zhong)方(fang)法(fa)與(yu)第(di)一(yi)(yi)(yi)種(zhong)(zhong)(zhong)方(fang)法(fa)類(lei)似，只是需(xu)要(yao)監視充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)。隨著電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)(de)(de)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)上升，這與(yu)采用(yong)第(di)一(yi)(yi)(yi)種(zhong)(zhong)(zhong)方(fang)法(fa)時(shi)(shi)完全(quan)相同。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)達到(dao)(dao)(dao)編程限(xian)壓(ya)值（也稱為浮(fu)動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)）時(shi)(shi)，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)開始(shi)下(xia)降。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)一(yi)(yi)(yi)開始(shi)下(xia)降時(shi)(shi)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)約充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)至容(rong)量(liang)的(de)(de)(de)(de)(de)50%至60%.浮(fu)動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)繼續提供，直到(dao)(dao)(dao)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)降至足夠低的(de)(de)(de)(de)(de)水平（C/10至C/20），這時(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)約充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)至容(rong)量(liang)的(de)(de)(de)(de)(de)92%至99%,充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)周期終止(zhi)(zhi)。目前，要(yao)為標準鋰(li)離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)快速充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)（不到(dao)(dao)(dao)1小時(shi)(shi)）至容(rong)量(liang)的(de)(de)(de)(de)(de)100%,還沒(mei)有一(yi)(yi)(yi)種(zhong)(zhong)(zhong)安全(quan)的(de)(de)(de)(de)(de)方(fang)法(fa)。

  有些鋰離子電池充電器允許使用熱敏電阻監視電池溫度。這么做的主要目的是，如果電池溫度超出推薦的0℃至40℃窗口范圍，就禁止充電。與鎳鎘或鎳氫金屬電池不同，鋰離子電池在充電時溫度上升非常少。圖1是一個典型的鋰離子電池充(chong)(chong)電曲線，圖中顯示了(le)充(chong)(chong)電電流、電池電壓(ya)和電池容量隨時間(jian)的變化。那么(me)怎樣才能(neng)正確地為(wei)鋰離子電池充(chong)(chong)電呢(ni)？鋰離子電池最適合(he)的充(chong)(chong)電過程可以(yi)分為(wei)四個階段：涓流充(chong)(chong)電、恒(heng)流充(chong)(chong)電、恒(heng)壓(ya)充(chong)(chong)電以(yi)及充(chong)(chong)電終止。參考圖1.

  階段1:涓流充電--涓流充電用來先對完全放電的電池單元進行預充（恢復性充電）。在電池電壓低于3V左右時，先采用最大0.1C的恒定電流對電池進行充電。
  階段2:恒流充電--當電池電壓上升到涓流充電閾值以上時，提高充電電流進行恒流充電。恒流充電的電流在0.2C至 1.0C之間。恒流充電時的電流并不要求十分精確，準恒定電流也可以。在線性充電器設計中，電流經常隨著電池電壓的上升而上升，以盡量減輕傳輸晶體管上的 散熱問題。大于1C的恒流充電并不會縮短整個充電周期時間，因此這種做法不可取。當以更高電流充電時，由于電極反應的過壓以及電池內部阻抗上的電壓上升，電池電壓會更快速地上升。恒流充電階段會變短，但由于下面恒壓充電階段的時間會相應增加，因此總的充電周期時間并不會縮短。
  階段3:恒壓充電-- 當電池電壓上升到4.2V時，恒流充電結束，開始恒壓充電階段。為使性能達到最佳，穩壓容差應當優于+1%.
階段4:充電終止--與鎳電池不同，并不建議對鋰離子電池連(lian)(lian)續(xu)涓(juan)流充(chong)電(dian)。連(lian)(lian)續(xu)涓(juan)流充(chong)電(dian)會導致金屬鋰出現極(ji)板電(dian)鍍(du)效應。這會使電(dian)池不穩(wen)定，并且(qie)有可能(neng)導致突(tu)然的自動快速解體。

  有兩(liang)種典型的(de)充(chong)電(dian)(dian)(dian)(dian)終止方法(fa)：采(cai)用(yong)最(zui)小(xiao)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)判斷(duan)或采(cai)用(yong)定(ding)時(shi)器（或者兩(liang)者的(de)結合(he)）。最(zui)小(xiao)電(dian)(dian)(dian)(dian)流(liu)法(fa)監視恒壓充(chong)電(dian)(dian)(dian)(dian)階段的(de)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)，并在(zai)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)減小(xiao)到0.02C至0.07C范圍(wei)時(shi)終止充(chong)電(dian)(dian)(dian)(dian)。第二種方法(fa)從恒壓充(chong)電(dian)(dian)(dian)(dian)階段開始(shi)時(shi)計時(shi)，持續充(chong)電(dian)(dian)(dian)(dian)兩(liang)個小(xiao)時(shi)后終止充(chong)電(dian)(dian)(dian)(dian)過程(cheng)。

  上述四階段的充電法完成對完全放電電池的充電約需要2.5至3小時。高級充電器還采用了更多安全(quan)措(cuo)施。例(li)如如果電(dian)池溫度超出指定窗(chuang)口（通常為0℃至45℃），那么充電(dian)會暫(zan)停。

  1 決定鋰離(li)子電池周期(qi)壽(shou)命(ming)或服務(wu)壽(shou)命(ming)的因素

  不存在任(ren)何延長或縮短電(dian)池壽(shou)命的單(dan)一(yi)因素(su)，而(er)常(chang)常(chang)是幾(ji)種(zhong)因素(su)合起來發揮作用(yong)。就延長周期壽(shou)命而(er)言有以(yi)下(xia)方(fang)法可以(yi)延長電(dian)池壽(shou)命：

1).采用(yong)部(bu)分(fen)放電(dian)的(de)(de)做法(fa)。在再充電(dian)前僅(jin)使用(yong)20%或(huo)(huo)30%的(de)(de)電(dian)池(chi)容量會極大延長周(zhou)(zhou)期壽(shou)命(ming)。作為(wei)一個一般性的(de)(de)規則，5至(zhi)10個淺放電(dian)周(zhou)(zhou)期等(deng)于1個滿放電(dian)周(zhou)(zhou)期。盡(jin)管部(bu)分(fen)放電(dian)周(zhou)(zhou)期可(ke)能達到數千次，但是保持電(dian)池(chi)處于滿充電(dian)狀態也縮短電(dian)池(chi)壽(shou)命(ming)。如果(guo)可(ke)能，應該避免(mian)滿放電(dian)周(zhou)(zhou)期（降至(zhi)2.5V或(huo)(huo)3V,取(qu)決(jue)于化學材料）。

2).避免充(chong)電至(zhi)容(rong)量的(de)100%.選(xuan)擇(ze)一(yi)(yi)個較低(di)(di)的(de)浮(fu)動電壓可以(yi)做到這一(yi)(yi)點。降(jiang)低(di)(di)浮(fu)動電壓將提(ti)高周期壽(shou)(shou)命和服務壽(shou)(shou)命，代價(jia)是降(jiang)低(di)(di)電池容(rong)量。浮(fu)動電壓降(jiang)低(di)(di)100mV至(zhi)300mV可以(yi)將周期壽(shou)(shou)命延長2至(zhi)5倍或更(geng)長。與(yu)其(qi)他化學材料相比，鋰離(li)子鈷化學材料對(dui)較高浮(fu)動電壓更(geng)敏(min)感。磷酸(suan)鋰離(li)子電池一(yi)(yi)般比更(geng)常見的(de)鋰離(li)子電池的(de)浮(fu)動電壓低(di)(di)。

3). 選擇合適的充電終止方法。選擇一個采用最小充電電流終止（C/10或C/x）的充電器，通過不充電到容量(liang)(liang)的100%,也可以(yi)延長(chang)電池壽命。例(li)如，電流(liu)降至(zhi)(zhi)C/5時結束(shu)充電周期與將(jiang)浮(fu)動電壓降至(zhi)(zhi)4.1V的效(xiao)果類(lei)似。在這兩種(zhong)情況下，電池都(dou)只充電至(zhi)(zhi)約(yue)為容量(liang)(liang)的85%,這是決(jue)定電池壽命的一個(ge)重(zhong)要因素。

4).限(xian)制電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)溫度(du)。限(xian)制電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)極限(xian)溫度(du)可以延(yan)長電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)壽命(ming)，尤其是禁(jin)止在(zai)(zai)0℃以下(xia)充(chong)電(dian)(dian)(dian)。在(zai)(zai)0℃以下(xia)充(chong)電(dian)(dian)(dian)促進金屬在(zai)(zai)電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)陽極上的(de)(de)(de)鍍(du)敷，這(zhe)可能造成內部(bu)短路，產(chan)生熱量并(bing)使電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)不穩(wen)定(ding)和不安全。很多電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)器(qi)都有測量電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)溫度(du)的(de)(de)(de)裝(zhuang)置，以確保不會(hui)在(zai)(zai)極限(xian)溫度(du)時充(chong)電(dian)(dian)(dian)。

5).避免大的充電(dian)(dian)和(he)放電(dian)(dian)電(dian)(dian)流，因為(wei)這(zhe)會(hui)縮短(duan)周期(qi)壽(shou)命。有些化學材料更適合較大電(dian)(dian)流，如鋰(li)(li)離子錳和(he)磷(lin)酸鋰(li)(li)離子電(dian)(dian)池。大電(dian)(dian)流給(gei)電(dian)(dian)池施(shi)加了過大的壓力。

6).避免低于(yu)2V或2.5V的深度放電(dian)(dian)(dian)(dian)(dian)，因為這會迅速永久性損壞鋰離子(zi)(zi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)。可能發生內部金屬鍍敷，這會引起短路(lu)(lu)，使電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)不可用(yong)或不安(an)全。大多數鋰離子(zi)(zi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)在電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)組內部都有電(dian)(dian)(dian)(dian)(dian)子(zi)(zi)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，如果充電(dian)(dian)(dian)(dian)(dian)或放電(dian)(dian)(dian)(dian)(dian)時電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓低于(yu)2.5V、超(chao)過(guo)4.3V或如果電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)流超(chao)過(guo)預(yu)定門限值，該(gai)電(dian)(dian)(dian)(dian)(dian)子(zi)(zi)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)就會斷(duan)開電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)連接。

  2 鋰(li)離子(zi)充(chong)電(dian)--系統(tong)注意(yi)事項

  要快(kuai)速可(ke)靠地完成充(chong)電過程需要一個高(gao)性能(neng)的充(chong)電系統(tong)。為實(shi)現可(ke)靠且經濟高(gao)效的解(jie)決方案，設(she)計時應當考慮到(dao)以下系統(tong)參數(shu)：

2.1 輸入源
  許多(duo)應(ying)用(yong)都采用(yong)極廉(lian)價的墻式(shi)適配器(qi)作為輸入電源。其輸出電壓主要依賴(lai)于(yu)交流(liu)輸入電壓和從墻式(shi)適配器(qi)流(liu)出的負載電流(liu)。

  在美國標準的墻面插座上交流母線輸入電壓的變化范圍一般為90VRMS至132VRMS.假設額定輸入電壓為120VRMS,容差為+10%, ?25%.充電器必須為電池提供適當的穩壓措施，從而不受輸入電壓的影響。充電器的輸入電壓與交流母線電壓和充電電流成比例：
 
VO=2VIN×a-1O（REQ+RPTC）-2×VFD
  REQ是(shi)次級(ji)(ji)繞(rao)組(zu)的(de)電(dian)阻與初級(ji)(ji)繞(rao)組(zu)反射電(dian)阻的(de)和。RPTC是(shi)PTC的(de)電(dian)阻，VFD是(shi)橋式(shi)整流器的(de)前向壓(ya)降(jiang)(jiang)。此外變壓(ya)器磁芯損失也會使輸出電(dian)壓(ya)略有降(jiang)(jiang)低(di)。

  利(li)用汽車適配器充電的應用也會遇到類(lei)似的問題。汽車適配器的輸出電壓典型范圍為9V至18V.

2.2 恒流充電的速率和精度
   特定應用的拓撲結構選擇可能要由充電電流來決定。出于尺寸和成本方面的考慮，低檔和中檔的快速充電應用則傾向于采用線性解決方案，然 而線性解決方案會以熱的形式損失更多能耗。對于線性充電系統來說，恒流充電的容差變得極為重要。如果穩壓容差太大，傳輸晶體管和其他元器件都需要更大體 積，從而增加尺寸和成本。此外，如果恒流充電電流過小，整個充電周期將會延長。
2.3 輸出電壓的穩定精度
   為了盡可能(neng)地充分利用(yong)電(dian)(dian)池(chi)容量，輸出(chu)電(dian)(dian)壓穩壓精度非常關(guan)鍵。輸出(chu)電(dian)(dian)壓精度的小幅(fu)度下降(jiang)也會導致電(dian)(dian)池(chi)容量的大幅(fu)減少(shao)。然而出(chu)于(yu)安(an)全和可靠性方面的考慮，輸出(chu)電(dian)(dian)壓也不(bu)能(neng)隨意(yi)設置得過(guo)高。圖2顯(xian)示出(chu)了輸出(chu)電(dian)(dian)壓穩定精度的重要(yao)性。

3 充電終止方法

  毋庸(yong)置疑(yi)，過充(chong)始終是(shi)鋰離子電(dian)池充(chong)電(dian)的心(xin)頭大患(huan)。準確(que)的充(chong)電(dian)終止方法對(dui)于安(an)全可靠的充(chong)電(dian)系統來說非常關鍵。

3 .1 電池溫度監控
  一般情況下(xia)，鋰離子電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)時的(de)溫(wen)(wen)度范圍應當在(zai)0℃至45℃。在(zai)此溫(wen)(wen)度范圍之(zhi)外對電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)會(hui)導(dao)致(zhi)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)過熱(re)。在(zai)充(chong)電(dian)(dian)(dian)(dian)周期(qi)中，電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)內的(de)壓(ya)(ya)力(li)上升(sheng)還(huan)會(hui) 導(dao)致(zhi)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)膨脹。隨著溫(wen)(wen)度上升(sheng)，壓(ya)(ya)力(li)也會(hui)過大(da)，這可能(neng)會(hui)導(dao)致(zhi)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)內部的(de)機械破裂或(huo)材料泄漏，嚴重時還(huan)有可能(neng)導(dao)致(zhi)爆炸。在(zai)此溫(wen)(wen)度范圍之(zhi)外 對電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)還(huan)會(hui)損害電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)性能(neng)，或(huo)縮短(duan)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)預(yu)期(qi)壽(shou)命。

  通常鋰離子電池包內都采用了熱(re)敏電阻來(lai)準(zhun)確測量電池溫(wen)度。充電器(qi)檢測熱(re)敏電阻的阻值，當阻值超出規(gui)定工作范(fan)圍，即溫(wen)度超過規(gui)定范(fan)圍時，充電被禁止。

3.2 電池放電電流或反向泄漏電流
  在許(xu)多應(ying)用中，即使(shi)輸入電(dian)(dian)(dian)源(yuan)不存在，充電(dian)(dian)(dian)系(xi)統(tong)仍(reng)然與電(dian)(dian)(dian)池相連。充電(dian)(dian)(dian)系(xi)統(tong)必須保證輸入電(dian)(dian)(dian)源(yuan)不存在時，從(cong)電(dian)(dian)(dian)池汲取的電(dian)(dian)(dian)流(liu)極小。最大(da)泄漏電(dian)(dian)(dian)流(liu)應(ying)當小于幾個(ge)(ge)微安，通常應(ying)小于一個(ge)(ge)微安。

4 鋰離子(zi)充電--應用實例(li)

  將以上幾(ji)點系統注意(yi)事(shi)項事(shi)先充(chong)分考(kao)慮，就能開發出適合的充(chong)電管理系統。

4.1 線性解決方案
  當存在穩壓(ya)良好的(de)輸入(ru)電(dian)(dian)源時(shi)，通常采用線性(xing)充(chong)電(dian)(dian)解(jie)決(jue)方案(an)。在此(ci)類應用中，線性(xing)解(jie)決(jue)方案(an)的(de)優點包括易用、尺寸小以(yi)及成本低。由于(yu)線性(xing)充(chong)電(dian)(dian)解(jie)決(jue)方案(an) 效率低因此(ci)影響設(she)計的(de)最重要因素就(jiu)是散熱(re)(re)(re)設(she)計。最糟的(de)情(qing)況是器件從涓流(liu)(liu)充(chong)電(dian)(dian)階(jie)段(duan)向 恒流(liu)(liu)充(chong)電(dian)(dian)階(jie)段(duan)轉(zhuan)換時(shi)，在此(ci)情(qing)況下，傳輸晶體(ti)管必須(xu)散發最大的(de)熱(re)(re)(re)能，必須(xu)在充(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)、系統尺寸、成本和散熱(re)(re)(re)要求之(zhi)間進行權衡(heng)。

  例如，應用(yong)中需(xu)(xu)要(yao)利用(yong)一(yi)(yi)個5V ±5%的(de)(de)輸入電(dian)(dian)源以(yi)0.5C或1C的(de)(de)恒定電(dian)(dian)流對一(yi)(yi)個1000mAh的(de)(de)單節鋰離(li)子(zi)電(dian)(dian)池(chi)充(chong)電(dian)(dian)。圖3顯(xian)示了(le)(le)如何利用(yong)Microchip的(de)(de) MCP73843構成(cheng)一(yi)(yi)個低成(cheng)本(ben)的(de)(de)獨立解決(jue)方案(an)，只需(xu)(xu)要(yao)極少量的(de)(de)外(wai)部元器件，就可以(yi)實現所需(xu)(xu)要(yao)的(de)(de)充(chong)電(dian)(dian)算法。MCP73843完美地結合了(le)(le)高精度恒流充(chong)電(dian)(dian)、 恒壓(ya)穩(wen)壓(ya)以(yi)及自(zi)動充(chong)電(dian)(dian)終止(zhi)等功(gong)能(neng)。

  為(wei)進一步減小線(xian)性(xing)(xing)解決方案的(de)尺寸、降(jiang)低其成(cheng)本和復雜性(xing)(xing)，許多外部元器(qi)(qi)件(jian)都可(ke)(ke)以集成(cheng)到充(chong)(chong)電管(guan)理控制器(qi)(qi)中。先進的(de)封裝可(ke)(ke)以提供更(geng)高的(de)集成(cheng)度，當然(ran)也會(hui)犧牲一定(ding)(ding)的(de)靈活性(xing)(xing)。此(ci)外此(ci)類充(chong)(chong)電管(guan)理控制器(qi)(qi) 還會(hui)實現一定(ding)(ding)的(de)熱(re)(re)調(diao)(diao)節(jie)(jie)功能(neng)。熱(re)(re)調(diao)(diao)節(jie)(jie)功能(neng)可(ke)(ke)根據器(qi)(qi)件(jian)管(guan)芯溫度來限制充(chong)(chong)電電流，從而(er)可(ke)(ke)在(zai)保證(zheng)器(qi)(qi)件(jian)可(ke)(ke)靠性(xing)(xing)的(de)情況(kuang)下(xia)優(you)化(hua)充(chong)(chong)電周期時間，熱(re)(re)調(diao)(diao)節(jie)(jie)功能(neng)大大降(jiang)低了(le)散熱(re)(re)設 計的(de)工作(zuo)量。

  基于Microchip MCP73861的(de)全(quan)集成(cheng)線性解決方案如(ru)圖4所示。MCP73861包(bao)含了(le)MCP73843的(de)所有功能，另(ling)外還包(bao)括(kuo)電流檢測(ce)、傳輸晶體管、反向(xiang)放電保護以(yi)及電池溫度監測(ce)。

4.2 充電周期波形
  利用MCP73843在1C和0.5C恒流(liu)充(chong)(chong)(chong)電(dian)速(su)(su)率下的(de)整(zheng)個充(chong)(chong)(chong)電(dian)周期如(ru)圖5.以0.5C而(er)不是1C速(su)(su)率充(chong)(chong)(chong)電(dian)時，充(chong)(chong)(chong)電(dian)結束的(de)時間(jian)(jian)大約晚了一個小時。充(chong)(chong)(chong)電(dian)終(zhong)止電(dian)流(liu)從0.07C降到0.035C,使得最(zui)終(zhong)電(dian)池容(rong)量從~98%增長(chang)到~100%.系(xi)統設(she)計師(shi)必須在充(chong)(chong)(chong)電(dian)時間(jian)(jian)、功(gong)率損耗和可用電(dian)池容(rong)量之間(jian)(jian)進(jin)行權(quan)衡(heng)。

4.3 開關式充電解決方案
  輸入電(dian)壓波(bo)動范圍寬或輸入輸出電(dian)壓差(cha)大(da)的應用(yong)通常(chang)采(cai)用(yong)開(kai)關式(shi)充(chong)(chong)(chong)電(dian)解決方(fang)案。例如(ru)應用(yong)中需要利(li)用(yong)汽(qi)車適配器以(yi)0.5C或1C的恒(heng)定電(dian)流對一個2200mAh的單節鋰離子電(dian)池(chi)充(chong)(chong)(chong)電(dian)，由于散熱等(deng)問(wen)題，利(li)用(yong)線(xian)(xian)性解決方(fang)案實現極為(wei)困難(nan)，當(dang)然也可以(yi)采(cai)用(yong)支持熱調(diao)節的線(xian)(xian)性解決方(fang)案，但(dan)降低充(chong)(chong)(chong)電(dian)電(dian)流造成(cheng)的充(chong)(chong)(chong)電(dian)周期延長是無(wu)法接(jie)受的。

  成(cheng)功設(she)計開關式(shi)充電(dian)解決方案的(de)第一步是(shi)選擇設(she)計結構(gou)：降壓式(shi)、升壓式(shi)、升/降壓式(shi)、反激式(shi)、單端(duan)初級電(dian)感式(shi)或者(zhe)其他形式(shi)。SEPIC拓撲結構(gou)的(de)優(you)點(dian)是(shi)低端(duan)柵極驅動和(he)電(dian)流檢測、持續輸 入電(dian)流以及(ji)輸入和(he)輸出間的(de)直流隔離，其主(zhu)要缺點(dian)是(shi)需要兩個電(dian)感和(he)一個能量(liang)傳(chuan)輸電(dian)容。

  MCP1630是一款可配合單片機使用的高速脈寬調制器，配合單片機，MCP1630可控制電源系統占空比，提供輸出電壓或電流穩定 功能。PIC16F684單片機可用于輸出穩壓或穩流，以及開關頻率和最大占空比的調整。MCP1630產生占空比，并可根據不同外部輸入提供快速過流保 護。充電器采用(yong)的(de)電源結構是SEPIC.單(dan)(dan)片機(ji)提供了極大的(de)設計靈活 性。此外單(dan)(dan)片機(ji)還可以與電池包內的(de)電池監控器通信，從而(er)大大縮短充電周期時間。

  利用(yong)開關式充(chong)電(dian)解(jie)決方案(an)的整個(ge)充(chong)電(dian)周(zhou)期如圖(tu)6所示。通過在充(chong)電(dian)系統中(zhong)采用(yong)電(dian)池(chi)監控器(qi)，可(ke)以大(da)大(da)縮短充(chong)電(dian)周(zhou)期，使用(yong)電(dian)池(chi)監控器(qi)就不(bu)必再(zai)檢測電(dian)池(chi)包保護電(dian)路兩(liang)端的電(dian)壓以及充(chong)電(dian)電(dian)流(liu)的接觸(chu)電(dian)阻。

5 結論

  在(zai)目(mu)前的便攜式(shi)產品中，要正確地(di)實現電(dian)池(chi)充電(dian)需要仔細(xi)地(di)設計考慮(lv)。本(ben)文討論(lun)了鋰離子電(dian)池(chi)的線性(xing)和(he)開關式(shi)充電(dian)解決方案，本(ben)文所(suo)探討的指導原則和(he)設計考慮(lv)要素，實際(ji)上也是所(suo)有電(dian)池(chi)充電(dian)系統設計都需要考慮(lv)的。