充電電池已經成(cheng)為當今電子產品的(de)(de)一種標(biao)準電源，特別是便攜(xie)設備：筆記本電腦(nao)、掌上導航儀、手(shou)機等。這些產品需要消耗(hao)的(de)(de)功率越來越大，而(er)可充電電池容量的(de)(de)增(zeng)長速度遠(yuan)遠(yuan)不能滿足(zu)它們的(de)(de)需求。功耗(hao)增(zeng)長的(de)(de)主要原因是設備功能的(de)(de)增(zeng)強，例(li)如：數(shu)碼(ma)相(xiang)機與手(shou)機的(de)(de)功能整(zheng)合，筆記本電腦(nao)更(geng)高的(de)(de)運(yun)算速度以及大尺寸屏幕的(de)(de)需求等等。便攜(xie)設備功耗(hao)的(de)(de)增(zeng)大使(shi)得用(yong)可充電電池要比標(biao)準電池更(geng)便宜(yi)、更(geng)環保。

　　本(ben)文介紹了可充電(dian)電(dian)池的化學成分；同(tong)時說明了各種(zhong)充電(dian)電(dian)池的典型特征和選(xuan)擇電(dian)池類(lei)型時需要重點注意的事項。另外還討論(lun)了在不(bu)使用微控制器或(huo)使用電(dian)源浪涌(yong)保護的主(zhu)適配器的情況(kuang)下如何構(gou)建(jian)單機結構(gou)，安全、快速地對鎳氫和鋰離子充電(dian)電(dian)池進行充電(dian)。

　　可充電電池類型

　　20世紀80年代的(de)便(bian)(bian)攜設(she)備，如數(shu)字(zi)無繩(sheng)電(dian)(dian)(dian)(dian)(dian)話、隨(sui)身(shen)聽和(he)(he)電(dian)(dian)(dian)(dian)(dian)動剃須刀等，主要由鎳(nie)鎘(ge)(ge)(NiCd)電(dian)(dian)(dian)(dian)(dian)池(chi)供(gong)電(dian)(dian)(dian)(dian)(dian)。到了(le)90年代后期，鎳(nie)氫(NiMH)電(dian)(dian)(dian)(dian)(dian)池(chi)和(he)(he)鋰(li)離子(zi)(Li-Ion)電(dian)(dian)(dian)(dian)(dian)池(chi)逐漸進入市場并(bing)開始流(liu)行 因(yin)為(wei)價格(ge)比鎳(nie)氫和(he)(he)鋰(li)離子(zi)電(dian)(dian)(dian)(dian)(dian)池(chi)便(bian)(bian)宜，鎳(nie)鎘(ge)(ge)電(dian)(dian)(dian)(dian)(dian)池(chi)在(zai)低端應用中十(shi)分普遍(bian)。鎳(nie)鎘(ge)(ge)電(dian)(dian)(dian)(dian)(dian)池(chi)可提供(gong)最高的(de)放電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)，適(shi)合短時(shi)間內(nei)需(xu)要大功(gong)率輸(shu)出的(de)應用。

　　另(ling)一(yi)方面(mian)，鎳(nie)鎘(ge)電(dian)(dian)池(chi)曾經被所謂的記憶(yi)效應(ying)困擾(rao)(現(xian)在(zai)的鎳(nie)鎘(ge)電(dian)(dian)池(chi)很少考慮這(zhe)個因素)，使(shi)電(dian)(dian)池(chi)容量降低。如果鎳(nie)鎘(ge)電(dian)(dian)池(chi)在(zai)未完(wan)全放電(dian)(dian)的情(qing)況下再(zai)充電(dian)(dian)，一(yi)些活性物質會(hui)累積并且開始結晶(在(zai)陽(yang)極(ji)有100微(wei)米的鎘(ge)累積層)，通過化學反應(ying)這(zhe)層物質會(hui)自行(xing)消失(一(yi)塊全新電(dian)(dian)池(chi)的陽(yang)極(ji)大約有1微(wei)米厚度的鎘(ge)結晶)。

　　出現(xian)記憶效應會導致電池(chi)容量越(yue)來越(yue)小，端電壓越(yue)來越(yue)低，使得(de)電池(chi)到達最低可用(yong)端電壓(關斷點)的時(shi)間比預期的早(zao)許多，如圖1所示。鎳(nie)鎘(ge)(ge)電池(chi)的另一個缺點是它的活性物質中含有(you)有(you)毒的鎘(ge)(ge)。所以，歐洲法規(gui)2000/53/EG在(zai)2005年(nian)12月31號后禁止(zhi)銷售鎳(nie)鎘(ge)(ge)充(chong)電電池(chi)。

　　鎳氫電池比鎳鎘電池更環保，但是價格更貴。鎳氫電池的放電電流略小，但受惰性效應的影響。惰性效應是比鎳鎘電池記憶效應稍輕的一種現象。惰性效應是由于鎳的結晶導致的。惰性效應和記憶效應一樣，導致無法完全使用可充電電池的全部容量，但都可以通過使用帶有放電功能的充電器來避免。

　　圖1. 鎳鎘(ge)電池(chi)的(de)(de)記(ji)憶效應與鎳氫(qing)電池(chi)的(de)(de)惰(duo)性(xing)效應之間的(de)(de)比較 鋰電子可(ke)充電電池(chi)價(jia)格(ge)最(zui)高(gao)，但具有足夠高(gao)的(de)(de)能(neng)(neng)量密度，因而可(ke)以在(zai)給定尺寸(cun)下提供更優性(xing)能(neng)(neng)，更適合小(xiao)尺寸(cun)、高(gao)集成(cheng)度的(de)(de)便攜設備。

　　表1給出了各種類(lei)型電池的主要(yao)特性。

　　單(dan)機鎳氫電池快速充電器

　　雖(sui)然(ran)很多(duo)人更(geng)偏愛鋰離子(zi)電(dian)(dian)池，鎳氫(qing)電(dian)(dian)池的(de)使用依然(ran)很流行。因為鎳氫(qing)電(dian)(dian)池比鋰離子(zi)電(dian)(dian)池便宜很多(duo)，所以(yi)在MP3播(bo)放器、閃(shan)光燈配件、車燈等設(she)備中經常(chang)能看(kan)到標(biao)準的(de)AA和(he)AAA鎳氫(qing)電(dian)(dian)池。

　　一(yi)塊可(ke)充(chong)電(dian)(dian)(dian)鎳(nie)氫電(dian)(dian)(dian)池的(de)溫度和端(duan)電(dian)(dian)(dian)壓(ya)隨(sui)著電(dian)(dian)(dian)池的(de)充(chong)電(dian)(dian)(dian)逐步(bu)上升(sheng)，在電(dian)(dian)(dian)池完(wan)全充(chong)滿后開(kai)始下降(圖2)。所以(yi)，鎳(nie)氫電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)器的(de)主(zhu)要任務是檢測到(dao)這個突變點并中斷充(chong)電(dian)(dian)(dian)，或者(zhe)從快速充(chong)電(dian)(dian)(dian)切換到(dao)涓流充(chong)電(dian)(dian)(dian)。另外，在充(chong)電(dian)(dian)(dian)過(guo)程中對溫度和電(dian)(dian)(dian)壓(ya)進行(xing)連續監控可(ke)以(yi)提供系統(tong)的(de)安全性。

　　圖2. 這些曲線顯示了NiMH充(chong)電(dian)(dian)電(dian)(dian)池充(chong)電(dian)(dian)過(guo)程(cheng)中典型(xing)的電(dian)(dian)壓(ya)(頂部(bu))和溫(wen)度(底部(bu))隨時(shi)間(jian)的變(bian)化 

　　DS2711/DS2712充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)(qi)具備上述功(gong)能。另外，它(ta)們可(ke)以單機工作(zuo)，不需要微控制(zhi)器(qi)(qi)(qi)或(huo)微處(chu)理器(qi)(qi)(qi)監控。該系列產(chan)品(pin)是(shi)專門為(wei)單節(jie)AA或(huo)AAA可(ke)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)(chi)設計的，同時(shi)(shi)也適用于(yu)串(chuan)聯(lian)或(huo)并聯(lian)的兩節(jie)電(dian)(dian)(dian)(dian)池(chi)(chi)。DS2711采用線性(xing)控制(zhi)結(jie)構，DS2712采用開(kai)關(guan)控制(zhi)結(jie)構。為(wei)了最大限度地延長工作(zuo)時(shi)(shi)間、節(jie)約電(dian)(dian)(dian)(dian)池(chi)(chi)能量，這些充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)(qi)有4種(zhong)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)模(mo)式(shi)：預充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)、快速充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)、浮充(chong)(chong)(chong)(chong)和涓流充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)。在(zai)浮充(chong)(chong)(chong)(chong)模(mo)式(shi)下，電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)滿后(hou)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)速率(lv)被切換到一個(ge)比(bi)較(jiao)低的速率(lv)(對于(yu)DS2711而言(yan)是(shi)25%)。

　　除監控(kong)功能外，DS2711/DS2712充(chong)(chong)(chong)(chong)電(dian)器還帶有內部(bu)計(ji)時(shi)(shi)器，通(tong)過連(lian)接到TMR引(yin)腳的外部(bu)電(dian)阻設(she)定最大充(chong)(chong)(chong)(chong)電(dian)時(shi)(shi)間，可將快速充(chong)(chong)(chong)(chong)電(dian)時(shi)(shi)間設(she)置在0.5到10小(xiao)時(shi)(shi)。浮(fu)充(chong)(chong)(chong)(chong)時(shi)(shi)間已經設(she)定為最大充(chong)(chong)(chong)(chong)電(dian)時(shi)(shi)間的一半(0.25到5小(xiao)時(shi)(shi))。根據所要求的充(chong)(chong)(chong)(chong)電(dian)時(shi)(shi)間(TAPPROX)，由下式(shi)計(ji)算電(dian)阻值：

　　R = 1000TAPPROX / 1.5(Eq. 1)

　　快速充電模式下，如果超過最大充電時間，充電器會從快速(su)充(chong)(chong)(chong)電(dian)模(mo)(mo)式(shi)切換到(dao)浮(fu)充(chong)(chong)(chong)模(mo)(mo)式(shi)，同時(shi)(shi)復位計(ji)時(shi)(shi)器(qi)(qi)。計(ji)時(shi)(shi)器(qi)(qi)開始為浮(fu)充(chong)(chong)(chong)過程(cheng)計(ji)時(shi)(shi)，如(ru)果達到(dao)預(yu)定的浮(fu)充(chong)(chong)(chong)時(shi)(shi)間，充(chong)(chong)(chong)電(dian)器(qi)(qi)將從浮(fu)充(chong)(chong)(chong)模(mo)(mo)式(shi)切換到(dao)涓流模(mo)(mo)式(shi)(圖3)。

　　圖3. 該典型應用(yong)電路(lu)中(zhong)，DS2711電池充(chong)電器

　　為2個(ge)串聯的(de) 鎳(nie)氫充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian) VP1、VP2用(yong)(yong)于監視電(dian)(dian)(dian)(dian)壓，THM1、THM2配合熱(re)敏電(dian)(dian)(dian)(dian)阻(zu)用(yong)(yong)來監測電(dian)(dian)(dian)(dian)池的(de)溫度。TMR (計時(shi)器)和(he)(he)RSNS(檢流(liu)電(dian)(dian)(dian)(dian)阻(zu))用(yong)(yong)于設定充(chong)電(dian)(dian)(dian)(dian)時(shi)間(jian)和(he)(he)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)。DS2711/DS2712的(de)另(ling)外一個(ge)特性(xing)是可以檢測電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)故障和(he)(he)堿性(xing)原(yuan)電(dian)(dian)(dian)(dian)池。如果發生(sheng)這些情(qing)況，充(chong)電(dian)(dian)(dian)(dian)器會(hui)自行關機。

　　如何檢測堿(jian)性電(dian)池

　　全新的(de)(de)鎳(nie)氫AA電(dian)(dian)池(chi)的(de)(de)典型內(nei)(nei)阻(zu)(zu)在30mΩ到100mΩ，堿性電(dian)(dian)池(chi)的(de)(de)內(nei)(nei)阻(zu)(zu)一般在200mΩ到300mΩ (根據(ju)充電(dian)(dian)狀態，最高可(ke)到700mΩ)，出(chu)(chu)現(xian)故(gu)障的(de)(de)充電(dian)(dian)電(dian)(dian)池(chi)會有(you)很高的(de)(de)內(nei)(nei)阻(zu)(zu)。DS2711/DS2712通過檢(jian)測到的(de)(de)電(dian)(dian)池(chi)電(dian)(dian)壓(VP1和VP2)和已設定的(de)(de)充電(dian)(dian)電(dian)(dian)流可(ke)以計算(suan)出(chu)(chu)待充電(dian)(dian)電(dian)(dian)池(chi)的(de)(de)內(nei)(nei)阻(zu)(zu)。

　　CTST引腳(用(yong)于電(dian)(dian)池(chi)(chi)測試、設置門限)控制電(dian)(dian)池(chi)(chi)內(nei)阻(zu)的(de)(de)(de)測量。VCTST是充電(dian)(dian)過(guo)程中的(de)(de)(de)電(dian)(dian)池(chi)(chi)電(dian)(dian)壓減去無(wu)充電(dian)(dian)電(dian)(dian)流時的(de)(de)(de)開(kai)路電(dian)(dian)池(chi)(chi)電(dian)(dian)壓(OCV)后的(de)(de)(de)差值(zhi)。這個(ge)值(zhi)等(deng)于充電(dian)(dian)電(dian)(dian)流乘以(yi)電(dian)(dian)池(chi)(chi)內(nei)阻(zu)的(de)(de)(de)乘積(ji)。如果(guo)檢測引腳(VP1、VP2和VN1)與(yu)電(dian)(dian)池(chi)(chi)沒有(you)采用(yong)Kelvin連接，引線電(dian)(dian)阻(zu)也將計入測量值(zhi)，影響VCTST。計算外(wai)部電(dian)(dian)阻(zu)RCTST的(de)(de)(de)公式為：

　　RCTST = 8000 [V2/A] / VCTST, 其中VCTST = ICharge * RCELL(Eq. 2)

　　例如，當以C/2速(su)率(lv)(1.1A)為(wei)(wei)2200mAh NiMH電池充電時， 選擇RCELL = 150mΩ為(wei)(wei)電池內阻門限(xian)時, VCTST將為(wei)(wei): VCTEST = ICHARGE * RCELL = 1.1A * 150mΩ = 0.165V 或: RCTST = 8000 [V2/A] / 0.165V = 48,485Ω

　　(最近的標準(zhun)1%阻值為48.7kΩ) 如果超(chao)過VCTST門限(本例(li)中> 0.165V)，表明電(dian)池內阻高(gao)于150mΩ，芯片會提供邏(luo)輯(ji)指示或出錯信息(xi)指示(LED1、LED2)，同時停(ting)止(zhi)充電(dian)過程(圖(tu)4)。

　　圖(tu)4. 圖(tu)3中所示充電(dian)器的充電(dian)流程

　　單機鋰離子電池快速(su)充電器(qi)

　　因為不需要檢測電壓變化率(dV/dt)，鋰離子電池充電器比鎳氫(qing)電(dian)池簡(jian)單。同(tong)時，由(you)于(yu)鋰離(li)子電(dian)池對過充非常敏感，充電(dian)器需要(yao)一個精(jing)確(que)的4.2V ± 50mV電(dian)源保(bao)證恒功率充電(dian)。至于(yu)鎳氫(qing)電(dian)池，充電(dian)器不僅需要(yao)電(dian)壓(ya)監(jian)測，還需要(yao)其(qi)它監(jian)控功能(溫度(du)、計時等)。

　　單機鋰離子電池充電器MAX8601內置所謂的Vbatt可控電壓源，它可以在+25°C提供4.2V ± 0.021V，或在40°C < T < 85°C提供4.2V ± 0.034V的精度。當通過Vbatt連接給鋰離子電池充電時，充電器可以(yi)保持恒定(ding)輸(shu)出(chu)功(gong)率(lv)(圖5)，外(wai)(wai)部電(dian)阻(接(jie)SETI引腳)和外(wai)(wai)部電(dian)容(rong)(接(jie)CT引腳)可以(yi)設(she)定(ding)充電(dian)電(dian)流和內(nei)部計時。該充電(dian)器還通過一個負溫(wen)度(du)系數電(dian)阻來監(jian)控電(dian)池的溫(wen)度(du)。

　　圖5. MAX8601鋰離(li)子電(dian)池單機(ji)充(chong)電(dian)器的典型應用電(dian)路(lu)圖

　　MAX8601充(chong)電(dian)(dian)器的主(zhu)(zhu)要(yao)優點是可(ke)以(yi)通過外部適配(pei)(pei)器或USB端口給(gei)電(dian)(dian)池充(chong)電(dian)(dian)(圖6)。USB端口根據USEL引(yin)腳的設(she)置(zhi)可(ke)以(yi)提供(gong)100mA、500mA電(dian)(dian)流(典型USB輸出電(dian)(dian)流)。該芯片會(hui)自動選擇(ze)外部電(dian)(dian)源(主(zhu)(zhu)適配(pei)(pei)器或USB)。如果(guo)兩個電(dian)(dian)源同(tong)時存在，它會(hui)選擇(ze)主(zhu)(zhu)適配(pei)(pei)器進行充(chong)電(dian)(dian)。任何一個電(dian)(dian)源都必須能夠(gou)提供(gong)最小4.5V的電(dian)(dian)壓。

　　MAX8601具有低電池電壓預充、限壓/限流快速充電和浮充模式等控制算法，優化了鋰離子電池充電。器件還(huan)有(you)上電復位以及電池過(guo)壓、高(gao)溫/低溫檢測和充電時(shi)間的連續監(jian)測功能。

　　圖(tu)6. 圖(tu)5中(zhong)充電器的(de)充電流程圖(tu)

　 DS2711/DS2712和MAX8601都是單機充電器，它們具有多(duo)種監控功能(電(dian)(dian)壓、電(dian)(dian)流、溫度、計時(shi)等)，既不需(xu)要微控制器監控，也不需(xu)要電(dian)(dian)源浪涌保(bao)護，而且提(ti)供清晰、簡單的外部切換。