在有些應用(yong)中，較長的電(dian)(dian)池(chi)(chi)(chi)(chi)壽(shou)命、較多的充(chong)電(dian)(dian)次數(shu)或較安(an)全(quan)的電(dian)(dian)池(chi)(chi)(chi)(chi)比(bi)電(dian)(dian)池(chi)(chi)(chi)(chi)容量(liang)更(geng)重要。本文(wen)介紹幾種可以極大延長電(dian)(dian)池(chi)(chi)(chi)(chi)壽(shou)命的鋰離子電(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)電(dian)(dian)和(he)放電(dian)(dian)方法。

  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(shi)因為與其(qi)他可再充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)池(chi)相比，鋰離子電(dian)(dian)(dian)(dian)(dian)池(chi)有較高(gao)的(de)能(neng)量(liang)密度、較高(gao)的(de)電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓、自放電(dian)(dian)(dian)(dian)(dian)少、周(zhou)期壽命非常長，而且(qie)環保，且(qie)充(chong)電(dian)(dian)(dian)(dian)(dian)和維護(hu)簡單(dan)。另外，由于(yu)其(qi)具有相對高(gao)的(de)電(dian)(dian)(dian)(dian)(dian)壓（2.9V至4.2V），因此很多便攜式產品(pin)都能(neng)用(yong)單(dan)節電(dian)(dian)(dian)(dian)(dian)池(chi)工作，從而簡化了產品(pin)總體設計。C速率等于(yu)特定(ding)條(tiao)件(jian)下(xia)的(de)充(chong)電(dian)(dian)(dian)(dian)(dian)或放電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流，定(ding)義如下(xia)：I=M×Cn

  其(qi)中：I = 充電或放電電流，單位為A；M = C的(de)(de)倍(bei)數或分數；C = 額定(ding)容(rong)量(liang)的(de)(de)數值，單位為Ah；N = 小時(shi)數（對應于(yu)C）。

  以(yi)1倍C速率(lv)(lv)放(fang)(fang)(fang)電(dian)的(de)(de)電(dian)池將在一(yi)個小(xiao)時內釋放(fang)(fang)(fang)標稱(cheng)的(de)(de)額定容量。例如，如果標稱(cheng)容量是1000mAhr,那(nei)么1C的(de)(de)放(fang)(fang)(fang)電(dian)速率(lv)(lv)對(dui)應于1000mA的(de)(de)放(fang)(fang)(fang)電(dian)電(dian)流，C/10的(de)(de)速率(lv)(lv)對(dui)應100mA的(de)(de)放(fang)(fang)(fang)電(dian)電(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)(li)離子(zi)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)推薦(jian)方(fang)法(fa)(fa)(fa)(fa)是(shi)，向電(dian)(dian)(dian)(dian)池(chi)(chi)提(ti)供一(yi)個(ge)±1%限(xian)壓(ya)(ya)(ya)的(de)恒(heng)定電(dian)(dian)(dian)(dian)流(liu)(liu)，直(zhi)(zhi)到(dao)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)滿(man)(man)電(dian)(dian)(dian)(dian)，然后(hou)停止(zhi)充(chong)(chong)電(dian)(dian)(dian)(dian)。用(yong)來(lai)決定電(dian)(dian)(dian)(dian)池(chi)(chi)何(he)時(shi)(shi)充(chong)(chong)滿(man)(man)電(dian)(dian)(dian)(dian)的(de)方(fang)法(fa)(fa)(fa)(fa)包括：給總的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)(shi)間定時(shi)(shi)、監(jian)視(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)或兼用(yong)這兩種(zhong)(zhong)(zhong)方(fang)法(fa)(fa)(fa)(fa)。第一(yi)種(zhong)(zhong)(zhong)方(fang)法(fa)(fa)(fa)(fa)采(cai)用(yong)限(xian)壓(ya)(ya)(ya)恒(heng)定電(dian)(dian)(dian)(dian)流(liu)(liu)，變化(hua)范圍(wei)從C/2到(dao)1C,持續2.5至(zhi)(zhi)3小時(shi)(shi)，使電(dian)(dian)(dian)(dian)池(chi)(chi)達到(dao)100%充(chong)(chong)電(dian)(dian)(dian)(dian)。也可以使用(yong)較低(di)的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)，但(dan)是(shi)將需要(yao)更(geng)長時(shi)(shi)間。第二種(zhong)(zhong)(zhong)方(fang)法(fa)(fa)(fa)(fa)與第一(yi)種(zhong)(zhong)(zhong)方(fang)法(fa)(fa)(fa)(fa)類似(si)，只是(shi)需要(yao)監(jian)視(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)。隨(sui)著(zhu)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)上升，這與采(cai)用(yong)第一(yi)種(zhong)(zhong)(zhong)方(fang)法(fa)(fa)(fa)(fa)時(shi)(shi)完全(quan)相同(tong)。電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)達到(dao)編程限(xian)壓(ya)(ya)(ya)值（也稱(cheng)為(wei)浮動電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)）時(shi)(shi)，充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)開始(shi)下(xia)降(jiang)。電(dian)(dian)(dian)(dian)流(liu)(liu)一(yi)開始(shi)下(xia)降(jiang)時(shi)(shi)，電(dian)(dian)(dian)(dian)池(chi)(chi)約充(chong)(chong)電(dian)(dian)(dian)(dian)至(zhi)(zhi)容量(liang)的(de)50%至(zhi)(zhi)60%.浮動電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)繼(ji)續提(ti)供，直(zhi)(zhi)到(dao)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)降(jiang)至(zhi)(zhi)足(zu)夠低(di)的(de)水(shui)平（C/10至(zhi)(zhi)C/20），這時(shi)(shi)電(dian)(dian)(dian)(dian)池(chi)(chi)約充(chong)(chong)電(dian)(dian)(dian)(dian)至(zhi)(zhi)容量(liang)的(de)92%至(zhi)(zhi)99%,充(chong)(chong)電(dian)(dian)(dian)(dian)周期終止(zhi)。目前，要(yao)為(wei)標準鋰(li)(li)離子(zi)電(dian)(dian)(dian)(dian)池(chi)(chi)快速充(chong)(chong)電(dian)(dian)(dian)(dian)（不(bu)到(dao)1小時(shi)(shi)）至(zhi)(zhi)容量(liang)的(de)100%,還(huan)沒有一(yi)種(zhong)(zhong)(zhong)安全(quan)的(de)方(fang)法(fa)(fa)(fa)(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(dian)曲線(xian)，圖中(zhong)顯示了充(chong)(chong)電(dian)電(dian)流、電(dian)池電(dian)壓和電(dian)池容(rong)量隨(sui)時(shi)間的(de)變化。那么怎樣才能正確地為鋰離子電(dian)池充(chong)(chong)電(dian)呢？鋰離子電(dian)池最適合的(de)充(chong)(chong)電(dian)過程可以分為四個階(jie)段：涓流充(chong)(chong)電(dian)、恒流充(chong)(chong)電(dian)、恒壓充(chong)(chong)電(dian)以及(ji)充(chong)(chong)電(dian)終止。參(can)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)續涓流(liu)充(chong)(chong)電(dian)(dian)。連(lian)續涓流(liu)充(chong)(chong)電(dian)(dian)會導致(zhi)金屬鋰(li)出現極(ji)板電(dian)(dian)鍍(du)效應(ying)。這會使電(dian)(dian)池不穩定，并且有可能導致(zhi)突然的自動快速解體。

  有兩種典型的充(chong)電(dian)(dian)終(zhong)止(zhi)方法(fa)(fa)(fa)：采用最小充(chong)電(dian)(dian)電(dian)(dian)流判斷或(huo)采用定時(shi)器(qi)（或(huo)者(zhe)(zhe)兩者(zhe)(zhe)的結合）。最小電(dian)(dian)流法(fa)(fa)(fa)監視恒壓充(chong)電(dian)(dian)階段(duan)的充(chong)電(dian)(dian)電(dian)(dian)流，并在充(chong)電(dian)(dian)電(dian)(dian)流減小到0.02C至0.07C范(fan)圍時(shi)終(zhong)止(zhi)充(chong)電(dian)(dian)。第(di)二種方法(fa)(fa)(fa)從恒壓充(chong)電(dian)(dian)階段(duan)開始時(shi)計時(shi)，持續充(chong)電(dian)(dian)兩個小時(shi)后終(zhong)止(zhi)充(chong)電(dian)(dian)過程。

  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(an)全措施。例如(ru)(ru)如(ru)(ru)果(guo)電池溫度超出指定窗口(kou)（通常為0℃至45℃），那么充電會(hui)暫停。

  1 決(jue)定鋰離(li)子(zi)電池周期壽(shou)命(ming)或服務(wu)壽(shou)命(ming)的因素

  不存在任何延長(chang)或縮短電池壽(shou)命的單一因素，而常(chang)常(chang)是幾種(zhong)因素合起來發(fa)揮作用。就(jiu)延長(chang)周期壽(shou)命而言有以(yi)下方法可(ke)以(yi)延長(chang)電池壽(shou)命：

1).采用部分(fen)放(fang)(fang)(fang)電(dian)(dian)的(de)做法。在再充(chong)電(dian)(dian)前僅使用20%或(huo)30%的(de)電(dian)(dian)池(chi)容量會極(ji)大延長(chang)周(zhou)期壽(shou)命。作(zuo)為一個(ge)(ge)一般性的(de)規則(ze)，5至10個(ge)(ge)淺放(fang)(fang)(fang)電(dian)(dian)周(zhou)期等于(yu)1個(ge)(ge)滿(man)放(fang)(fang)(fang)電(dian)(dian)周(zhou)期。盡(jin)管(guan)部分(fen)放(fang)(fang)(fang)電(dian)(dian)周(zhou)期可(ke)能達到數千次，但是(shi)保持電(dian)(dian)池(chi)處(chu)于(yu)滿(man)充(chong)電(dian)(dian)狀態(tai)也縮短電(dian)(dian)池(chi)壽(shou)命。如果可(ke)能，應該避免滿(man)放(fang)(fang)(fang)電(dian)(dian)周(zhou)期（降至2.5V或(huo)3V,取決于(yu)化學材料(liao)）。

2).避免充電(dian)至容量(liang)的(de)(de)100%.選擇(ze)一個較低的(de)(de)浮(fu)(fu)動(dong)(dong)電(dian)壓(ya)(ya)可(ke)(ke)以做到這一點(dian)。降(jiang)低浮(fu)(fu)動(dong)(dong)電(dian)壓(ya)(ya)將提高(gao)周期(qi)壽(shou)命和服(fu)務壽(shou)命，代(dai)價(jia)是降(jiang)低電(dian)池容量(liang)。浮(fu)(fu)動(dong)(dong)電(dian)壓(ya)(ya)降(jiang)低100mV至300mV可(ke)(ke)以將周期(qi)壽(shou)命延(yan)長2至5倍或更長。與其他(ta)化學(xue)(xue)材(cai)料相比，鋰(li)離(li)子鈷化學(xue)(xue)材(cai)料對較高(gao)浮(fu)(fu)動(dong)(dong)電(dian)壓(ya)(ya)更敏感。磷酸鋰(li)離(li)子電(dian)池一般比更常見的(de)(de)鋰(li)離(li)子電(dian)池的(de)(de)浮(fu)(fu)動(dong)(dong)電(dian)壓(ya)(ya)低。

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(tong)過(guo)不充電到容量的100%,也可以延長電池(chi)壽(shou)命(ming)(ming)。例如，電流降至(zhi)(zhi)C/5時(shi)結束(shu)充電周期與將浮動電壓(ya)降至(zhi)(zhi)4.1V的效果類似。在這兩(liang)種情況下，電池(chi)都(dou)只充電至(zhi)(zhi)約(yue)為(wei)容量的85%,這是決(jue)定電池(chi)壽(shou)命(ming)(ming)的一(yi)個(ge)重要因素(su)。

4).限制電(dian)(dian)池(chi)(chi)(chi)溫(wen)度(du)(du)。限制電(dian)(dian)池(chi)(chi)(chi)的極(ji)限溫(wen)度(du)(du)可以(yi)(yi)延長電(dian)(dian)池(chi)(chi)(chi)壽命，尤(you)其是禁止在0℃以(yi)(yi)下充電(dian)(dian)。在0℃以(yi)(yi)下充電(dian)(dian)促進金屬在電(dian)(dian)池(chi)(chi)(chi)陽(yang)極(ji)上的鍍敷，這可能(neng)造成(cheng)內部短路，產生熱量(liang)并使(shi)電(dian)(dian)池(chi)(chi)(chi)不穩定和不安全。很多(duo)電(dian)(dian)池(chi)(chi)(chi)充電(dian)(dian)器都有測量(liang)電(dian)(dian)池(chi)(chi)(chi)溫(wen)度(du)(du)的裝置，以(yi)(yi)確保不會在極(ji)限溫(wen)度(du)(du)時充電(dian)(dian)。

5).避(bi)免大的充電(dian)和(he)放電(dian)電(dian)流(liu)，因為這會縮短周期壽命(ming)。有(you)些化學材(cai)料更(geng)適合較大電(dian)流(liu)，如鋰離子錳(meng)和(he)磷(lin)酸(suan)鋰離子電(dian)池(chi)。大電(dian)流(liu)給電(dian)池(chi)施(shi)加了(le)過大的壓力。

6).避免(mian)低于2V或(huo)(huo)2.5V的深度放電(dian)(dian)(dian)(dian)(dian)，因為這(zhe)會(hui)迅(xun)速永久性損(sun)壞鋰離(li)子(zi)(zi)電(dian)(dian)(dian)(dian)(dian)池(chi)。可能發生內部金屬鍍敷，這(zhe)會(hui)引起短路，使電(dian)(dian)(dian)(dian)(dian)池(chi)不(bu)(bu)可用或(huo)(huo)不(bu)(bu)安全(quan)。大多(duo)數鋰離(li)子(zi)(zi)電(dian)(dian)(dian)(dian)(dian)池(chi)在電(dian)(dian)(dian)(dian)(dian)池(chi)組(zu)內部都(dou)有電(dian)(dian)(dian)(dian)(dian)子(zi)(zi)電(dian)(dian)(dian)(dian)(dian)路，如果充電(dian)(dian)(dian)(dian)(dian)或(huo)(huo)放電(dian)(dian)(dian)(dian)(dian)時電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓低于2.5V、超過(guo)4.3V或(huo)(huo)如果電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)流超過(guo)預定(ding)門限值，該電(dian)(dian)(dian)(dian)(dian)子(zi)(zi)電(dian)(dian)(dian)(dian)(dian)路就會(hui)斷開電(dian)(dian)(dian)(dian)(dian)池(chi)連接。

  2 鋰離子充電--系統注(zhu)意事項

  要(yao)快速可靠地完成(cheng)充電過(guo)程需要(yao)一(yi)個(ge)高性能的充電系(xi)統(tong)(tong)。為實現(xian)可靠且經濟高效的解決方案，設計時應(ying)當考慮到(dao)以下系(xi)統(tong)(tong)參數：

2.1 輸入源
   許(xu)多應用(yong)都采用(yong)極廉價的(de)墻(qiang)式適配(pei)器(qi)作為(wei)輸(shu)入(ru)電(dian)源。其輸(shu)出(chu)電(dian)壓(ya)主要依賴于交流(liu)輸(shu)入(ru)電(dian)壓(ya)和從墻(qiang)式適配(pei)器(qi)流(liu)出(chu)的(de)負載電(dian)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)次級繞組的電(dian)(dian)阻(zu)(zu)與初級繞組反(fan)射電(dian)(dian)阻(zu)(zu)的和。RPTC是(shi)PTC的電(dian)(dian)阻(zu)(zu)，VFD是(shi)橋式(shi)整流(liu)器的前向壓降(jiang)。此外變壓器磁芯損失也(ye)會使輸出電(dian)(dian)壓略有(you)降(jiang)低。

  利用(yong)汽(qi)車適(shi)配器充電的應(ying)用(yong)也會遇到類似的問題。汽(qi)車適(shi)配器的輸出電壓(ya)典型(xing)范(fan)圍為9V至(zhi)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(le)盡可(ke)能地充分利用電(dian)(dian)(dian)池容(rong)量(liang)，輸(shu)出(chu)電(dian)(dian)(dian)壓穩(wen)壓精(jing)度非常關(guan)鍵(jian)。輸(shu)出(chu)電(dian)(dian)(dian)壓精(jing)度的小幅(fu)度下降也會導致電(dian)(dian)(dian)池容(rong)量(liang)的大幅(fu)減少。然(ran)而(er)出(chu)于安全和可(ke)靠性方面(mian)的考慮，輸(shu)出(chu)電(dian)(dian)(dian)壓也不能隨意設置得過高。圖(tu)2顯示出(chu)了(le)輸(shu)出(chu)電(dian)(dian)(dian)壓穩(wen)定精(jing)度的重要性。

3 充電終止方法

  毋庸置疑，過充始終(zhong)是鋰離子電(dian)池(chi)充電(dian)的(de)心頭(tou)大患。準確的(de)充電(dian)終(zhong)止(zhi)方法對于安全(quan)可靠的(de)充電(dian)系統來說非(fei)常(chang)關鍵。

3 .1 電池溫度監控
  一般情(qing)況下，鋰(li)離子(zi)電(dian)池(chi)(chi)充(chong)電(dian)時(shi)的溫(wen)度(du)范(fan)(fan)圍應(ying)當在0℃至45℃。在此溫(wen)度(du)范(fan)(fan)圍之外(wai)對(dui)電(dian)池(chi)(chi)充(chong)電(dian)會導(dao)(dao)(dao)致電(dian)池(chi)(chi)過熱。在充(chong)電(dian)周期中，電(dian)池(chi)(chi)內的壓(ya)力上升還(huan)會 導(dao)(dao)(dao)致電(dian)池(chi)(chi)膨脹。隨著溫(wen)度(du)上升，壓(ya)力也(ye)會過大，這可能(neng)(neng)會導(dao)(dao)(dao)致電(dian)池(chi)(chi)內部的機械(xie)破裂(lie)或材料泄漏，嚴(yan)重時(shi)還(huan)有可能(neng)(neng)導(dao)(dao)(dao)致爆炸。在此溫(wen)度(du)范(fan)(fan)圍之外(wai) 對(dui)電(dian)池(chi)(chi)充(chong)電(dian)還(huan)會損害電(dian)池(chi)(chi)的性(xing)能(neng)(neng)，或縮短電(dian)池(chi)(chi)的預期壽命。

  通(tong)常鋰(li)離子電池(chi)包內都采用了熱(re)敏電阻(zu)(zu)來準確(que)測量電池(chi)溫(wen)度。充電器檢測熱(re)敏電阻(zu)(zu)的阻(zu)(zu)值，當阻(zu)(zu)值超(chao)出(chu)規定工(gong)作范圍，即(ji)溫(wen)度超(chao)過規定范圍時，充電被禁止。

3.2 電池放電電流或反向泄漏電流
  在(zai)許多應用(yong)中，即使輸(shu)入電源不(bu)存(cun)在(zai)，充(chong)電系統仍然(ran)與電池(chi)(chi)相連。充(chong)電系統必須保證輸(shu)入電源不(bu)存(cun)在(zai)時，從電池(chi)(chi)汲(ji)取(qu)的電流極(ji)小(xiao)。最大泄漏電流應當小(xiao)于幾個微安，通常應小(xiao)于一個微安。

4 鋰離(li)子充電(dian)--應用實例

  將以上幾(ji)點系(xi)(xi)統(tong)(tong)注意事(shi)項(xiang)事(shi)先充分考慮，就能開發出(chu)適合的充電(dian)管理系(xi)(xi)統(tong)(tong)。

4.1 線性解決方案
  當存在穩壓良(liang)好的輸入電源(yuan)時，通(tong)常采用(yong)線(xian)性充(chong)電解決(jue)方(fang)(fang)案。在此(ci)(ci)類(lei)應用(yong)中，線(xian)性解決(jue)方(fang)(fang)案的優點包括易用(yong)、尺寸小以及成本(ben)低。由(you)于(yu)線(xian)性充(chong)電解決(jue)方(fang)(fang)案 效率低因(yin)此(ci)(ci)影響設計(ji)(ji)的最重要因(yin)素就(jiu)是(shi)(shi)散(san)熱(re)(re)(re)設計(ji)(ji)。最糟的情況是(shi)(shi)器件從(cong)涓流(liu)充(chong)電階(jie)段(duan)向(xiang) 恒(heng)流(liu)充(chong)電階(jie)段(duan)轉換時，在此(ci)(ci)情況下，傳輸晶(jing)體管必(bi)須(xu)散(san)發最大的熱(re)(re)(re)能，必(bi)須(xu)在充(chong)電電流(liu)、系統(tong)尺寸、成本(ben)和散(san)熱(re)(re)(re)要求之(zhi)間進行權衡。

  例如，應用(yong)中(zhong)需要(yao)(yao)利用(yong)一(yi)個5V ±5%的(de)(de)(de)輸入電(dian)源以0.5C或(huo)1C的(de)(de)(de)恒定電(dian)流對(dui)一(yi)個1000mAh的(de)(de)(de)單節鋰離子電(dian)池充(chong)電(dian)。圖3顯示(shi)了如何利用(yong)Microchip的(de)(de)(de) MCP73843構成一(yi)個低成本(ben)的(de)(de)(de)獨立解決(jue)方案，只需要(yao)(yao)極少(shao)量的(de)(de)(de)外部元器件，就可以實現(xian)所需要(yao)(yao)的(de)(de)(de)充(chong)電(dian)算法。MCP73843完美地(di)結合了高精度恒流充(chong)電(dian)、 恒壓穩壓以及(ji)自動(dong)充(chong)電(dian)終止等(deng)功能。

  為(wei)進一(yi)步減小線性(xing)解決方案的(de)(de)尺寸(cun)、降低其成本和(he)復雜性(xing)，許多外部元器件(jian)(jian)都可(ke)以集(ji)成到充電管理(li)控制器中。先進的(de)(de)封裝可(ke)以提供更高的(de)(de)集(ji)成度，當然也(ye)會(hui)犧(xi)牲一(yi)定(ding)的(de)(de)靈活性(xing)。此(ci)外此(ci)類充電管理(li)控制器 還會(hui)實現一(yi)定(ding)的(de)(de)熱調(diao)節(jie)功(gong)(gong)能(neng)。熱調(diao)節(jie)功(gong)(gong)能(neng)可(ke)根據器件(jian)(jian)管芯溫度來限制充電電流，從(cong)而可(ke)在保(bao)證器件(jian)(jian)可(ke)靠性(xing)的(de)(de)情況下優(you)化充電周期時間，熱調(diao)節(jie)功(gong)(gong)能(neng)大大降低了(le)散熱設 計的(de)(de)工作量。

  基于Microchip MCP73861的全集成線性解決方案如(ru)圖4所(suo)示。MCP73861包(bao)(bao)含(han)了MCP73843的所(suo)有(you)功(gong)能(neng)，另外還包(bao)(bao)括電(dian)(dian)流檢測(ce)、傳輸晶體管、反向放(fang)電(dian)(dian)保護(hu)以及(ji)電(dian)(dian)池溫(wen)度監測(ce)。

4.2 充電周期波形
  利用MCP73843在(zai)1C和(he)0.5C恒(heng)流充(chong)(chong)電(dian)(dian)速(su)率(lv)下的整個(ge)充(chong)(chong)電(dian)(dian)周期如圖(tu)5.以(yi)0.5C而不是(shi)1C速(su)率(lv)充(chong)(chong)電(dian)(dian)時(shi)，充(chong)(chong)電(dian)(dian)結束的時(shi)間(jian)大約晚(wan)了一個(ge)小時(shi)。充(chong)(chong)電(dian)(dian)終(zhong)(zhong)止電(dian)(dian)流從0.07C降到0.035C,使得(de)最(zui)終(zhong)(zhong)電(dian)(dian)池容(rong)量從~98%增長到~100%.系統設計師必須在(zai)充(chong)(chong)電(dian)(dian)時(shi)間(jian)、功率(lv)損耗和(he)可用電(dian)(dian)池容(rong)量之間(jian)進行權(quan)衡。

4.3 開關式充電解決方案
  輸(shu)入電(dian)(dian)壓波動(dong)范圍寬或輸(shu)入輸(shu)出(chu)電(dian)(dian)壓差大(da)的應用通常采(cai)用開關式(shi)充(chong)電(dian)(dian)解決方案。例如應用中需要利用汽車適配器以(yi)(yi)0.5C或1C的恒定電(dian)(dian)流對一個2200mAh的單(dan)節鋰離子電(dian)(dian)池充(chong)電(dian)(dian)，由于散熱等問題，利用線性(xing)解決方案實現極(ji)為困難，當(dang)然也(ye)可以(yi)(yi)采(cai)用支持熱調(diao)節的線性(xing)解決方案，但降低充(chong)電(dian)(dian)電(dian)(dian)流造成(cheng)的充(chong)電(dian)(dian)周期延長(chang)是無法(fa)接受的。

  成功設計開關式充電(dian)(dian)解決方(fang)案(an)的(de)第一(yi)步(bu)是選擇設計結構：降(jiang)壓式、升壓式、升/降(jiang)壓式、反激式、單(dan)端初級(ji)電(dian)(dian)感式或者其(qi)他形式。SEPIC拓(tuo)撲結構的(de)優(you)點(dian)是低端柵(zha)極驅動(dong)和(he)電(dian)(dian)流(liu)檢(jian)測、持續(xu)輸(shu) 入電(dian)(dian)流(liu)以及輸(shu)入和(he)輸(shu)出間的(de)直流(liu)隔離，其(qi)主要缺點(dian)是需要兩個電(dian)(dian)感和(he)一(yi)個能量傳(chuan)輸(shu)電(dian)(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。充電器采用的電源結構(gou)是SEPIC.單片機提(ti)供了極大(da)的設計靈活(huo) 性。此外(wai)單片機還可以(yi)與電池包內的電池監控器通(tong)信，從而大(da)大(da)縮短充(chong)電周期時間(jian)。

  利用開關(guan)式充(chong)(chong)電(dian)解決方(fang)案(an)的(de)(de)整個充(chong)(chong)電(dian)周(zhou)期如圖6所(suo)示(shi)。通過在充(chong)(chong)電(dian)系統中采用電(dian)池(chi)監控器，可以大(da)(da)大(da)(da)縮短(duan)充(chong)(chong)電(dian)周(zhou)期，使(shi)用電(dian)池(chi)監控器就不必再(zai)檢測電(dian)池(chi)包保護(hu)電(dian)路兩(liang)端(duan)的(de)(de)電(dian)壓(ya)以及充(chong)(chong)電(dian)電(dian)流的(de)(de)接觸電(dian)阻。

5 結論

  在目前的(de)便攜(xie)式產品中(zhong)，要(yao)正確地實現電(dian)池充(chong)電(dian)需要(yao)仔(zi)細(xi)地設計考慮。本(ben)文討論了鋰(li)離子電(dian)池的(de)線性和開關式充(chong)電(dian)解決方案，本(ben)文所(suo)探討的(de)指導原則和設計考慮要(yao)素(su)，實際上也(ye)是所(suo)有(you)電(dian)池充(chong)電(dian)系統設計都(dou)需要(yao)考慮的(de)。