充電(dian)(dian)(dian)電(dian)(dian)(dian)池已經成為當今(jin)電(dian)(dian)(dian)子(zi)產(chan)品的(de)(de)(de)一種標準電(dian)(dian)(dian)源(yuan)，特別是(shi)便(bian)攜(xie)設備(bei)：筆(bi)記本電(dian)(dian)(dian)腦、掌上導航(hang)儀(yi)、手(shou)機(ji)(ji)等(deng)。這些(xie)產(chan)品需要(yao)消耗(hao)的(de)(de)(de)功(gong)率越來越大，而可充電(dian)(dian)(dian)電(dian)(dian)(dian)池容量的(de)(de)(de)增長速(su)度(du)(du)遠遠不能滿足它們(men)的(de)(de)(de)需求。功(gong)耗(hao)增長的(de)(de)(de)主要(yao)原因是(shi)設備(bei)功(gong)能的(de)(de)(de)增強，例如(ru)：數碼相(xiang)機(ji)(ji)與手(shou)機(ji)(ji)的(de)(de)(de)功(gong)能整合(he)，筆(bi)記本電(dian)(dian)(dian)腦更(geng)(geng)(geng)高(gao)的(de)(de)(de)運(yun)算速(su)度(du)(du)以(yi)及大尺(chi)寸屏幕的(de)(de)(de)需求等(deng)等(deng)。便(bian)攜(xie)設備(bei)功(gong)耗(hao)的(de)(de)(de)增大使得(de)用(yong)可充電(dian)(dian)(dian)電(dian)(dian)(dian)池要(yao)比標準電(dian)(dian)(dian)池更(geng)(geng)(geng)便(bian)宜、更(geng)(geng)(geng)環保。

　　本文介紹了可充電(dian)(dian)電(dian)(dian)池(chi)的(de)化學成分；同時說明(ming)了各種充電(dian)(dian)電(dian)(dian)池(chi)的(de)典(dian)型特征和選擇(ze)電(dian)(dian)池(chi)類型時需要重點注意的(de)事(shi)項。另外還討(tao)論了在(zai)不(bu)使用微控制器或使用電(dian)(dian)源浪涌保護的(de)主(zhu)適配(pei)器的(de)情況下如(ru)何構建(jian)單(dan)機結構，安(an)全、快速地(di)對鎳氫和鋰離子充電(dian)(dian)電(dian)(dian)池(chi)進(jin)行充電(dian)(dian)。

　　可充電電池類型

　　20世紀80年代的便攜設備，如數字無繩(sheng)電話(hua)、隨身聽(ting)和電動剃須刀等，主要由(you)鎳(nie)鎘(ge)(NiCd)電池(chi)供(gong)電。到了90年代后期，鎳(nie)氫(NiMH)電池(chi)和鋰(li)離(li)子(zi)(Li-Ion)電池(chi)逐(zhu)漸進(jin)入市場并開(kai)始(shi)流(liu)行(xing) 因為價格比(bi)鎳(nie)氫和鋰(li)離(li)子(zi)電池(chi)便宜(yi)，鎳(nie)鎘(ge)電池(chi)在低端應用中十分普遍。鎳(nie)鎘(ge)電池(chi)可提(ti)供(gong)最高(gao)的放電電流(liu)，適合短時(shi)間內需要大功率輸出的應用。

　　另一(yi)方面，鎳(nie)鎘(ge)電(dian)(dian)池(chi)曾(ceng)經被(bei)所謂的記憶效(xiao)應(ying)困擾(現在(zai)的鎳(nie)鎘(ge)電(dian)(dian)池(chi)很(hen)少考慮這(zhe)個因素)，使電(dian)(dian)池(chi)容量降低。如果(guo)鎳(nie)鎘(ge)電(dian)(dian)池(chi)在(zai)未完(wan)全放電(dian)(dian)的情況下再充電(dian)(dian)，一(yi)些活性物質(zhi)會(hui)累積并且開始結(jie)晶(在(zai)陽極有100微米(mi)的鎘(ge)累積層)，通過化學反(fan)應(ying)這(zhe)層物質(zhi)會(hui)自行消失(shi)(一(yi)塊全新電(dian)(dian)池(chi)的陽極大約有1微米(mi)厚度(du)的鎘(ge)結(jie)晶)。

　　出現(xian)記(ji)憶效應會導致(zhi)電(dian)(dian)(dian)池容量越來(lai)越小，端電(dian)(dian)(dian)壓(ya)越來(lai)越低，使得電(dian)(dian)(dian)池到(dao)達(da)最低可用端電(dian)(dian)(dian)壓(ya)(關斷點)的(de)(de)時間比預期的(de)(de)早許多(duo)，如圖(tu)1所示。鎳(nie)鎘(ge)電(dian)(dian)(dian)池的(de)(de)另一(yi)個(ge)缺點是它的(de)(de)活(huo)性物質中(zhong)含有有毒的(de)(de)鎘(ge)。所以，歐洲法規2000/53/EG在2005年12月31號后禁(jin)止銷售鎳(nie)鎘(ge)充電(dian)(dian)(dian)電(dian)(dian)(dian)池。

　　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(tu)1. 鎳(nie)鎘電(dian)(dian)池的(de)記憶效應與鎳(nie)氫電(dian)(dian)池的(de)惰性(xing)效應之間的(de)比較 鋰電(dian)(dian)子可充電(dian)(dian)電(dian)(dian)池價格最高(gao)，但(dan)具有(you)足(zu)夠高(gao)的(de)能(neng)量密度，因而可以在給(gei)定尺(chi)寸下(xia)提(ti)供更優(you)性(xing)能(neng)，更適合小(xiao)尺(chi)寸、高(gao)集成度的(de)便攜設(she)備。

　　表1給出了各(ge)種(zhong)類型(xing)電池(chi)的主要(yao)特(te)性(xing)。

　　單機(ji)鎳氫電(dian)池快速充電(dian)器

　　雖然(ran)很(hen)多人更偏愛鋰離子電池(chi)(chi)，鎳氫(qing)(qing)(qing)電池(chi)(chi)的使用依然(ran)很(hen)流行(xing)。因(yin)為鎳氫(qing)(qing)(qing)電池(chi)(chi)比鋰離子電池(chi)(chi)便宜很(hen)多，所以(yi)在MP3播放器、閃光燈配件、車燈等設(she)備中經常能看到(dao)標準的AA和AAA鎳氫(qing)(qing)(qing)電池(chi)(chi)。

　　一(yi)塊可充(chong)電(dian)(dian)鎳(nie)氫電(dian)(dian)池(chi)(chi)的(de)溫度和端電(dian)(dian)壓隨著(zhu)電(dian)(dian)池(chi)(chi)的(de)充(chong)電(dian)(dian)逐(zhu)步(bu)上升，在電(dian)(dian)池(chi)(chi)完全充(chong)滿后開(kai)始下(xia)降(圖2)。所以，鎳(nie)氫電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)器的(de)主要任務是檢測(ce)到(dao)這個突(tu)變點并中斷充(chong)電(dian)(dian)，或者從快(kuai)速充(chong)電(dian)(dian)切換(huan)到(dao)涓流充(chong)電(dian)(dian)。另外，在充(chong)電(dian)(dian)過程中對(dui)溫度和電(dian)(dian)壓進行連續監控可以提供系統的(de)安(an)全性。

　　圖2. 這些曲線顯(xian)示了NiMH充(chong)電(dian)電(dian)池充(chong)電(dian)過程中典型的電(dian)壓(頂(ding)部)和溫度(底部)隨(sui)時間的變(bian)化(hua) 

　　DS2711/DS2712充(chong)(chong)電(dian)器(qi)具備上述功能。另外，它們可(ke)以單(dan)(dan)機(ji)工作，不需(xu)要微控(kong)制器(qi)或(huo)微處理器(qi)監(jian)控(kong)。該系(xi)列產品是專門為單(dan)(dan)節(jie)(jie)AA或(huo)AAA可(ke)充(chong)(chong)電(dian)電(dian)池(chi)設計的(de)，同時也適(shi)用于(yu)串(chuan)聯(lian)或(huo)并聯(lian)的(de)兩節(jie)(jie)電(dian)池(chi)。DS2711采用線性控(kong)制結構(gou)，DS2712采用開(kai)關控(kong)制結構(gou)。為了最大限度地延長(chang)工作時間、節(jie)(jie)約電(dian)池(chi)能量，這些充(chong)(chong)電(dian)器(qi)有4種充(chong)(chong)電(dian)模式：預充(chong)(chong)電(dian)、快(kuai)速充(chong)(chong)電(dian)、浮充(chong)(chong)和(he)涓流充(chong)(chong)電(dian)。在浮充(chong)(chong)模式下(xia)，電(dian)池(chi)充(chong)(chong)滿(man)后充(chong)(chong)電(dian)速率(lv)被切換(huan)到(dao)一個比較低的(de)速率(lv)(對于(yu)DS2711而言是25%)。

　　除(chu)監控功能(neng)外，DS2711/DS2712充(chong)(chong)電(dian)(dian)(dian)(dian)器還帶有內部計時(shi)器，通過連接到TMR引腳的外部電(dian)(dian)(dian)(dian)阻設(she)(she)定(ding)最大充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)間，可將快速充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)間設(she)(she)置在0.5到10小時(shi)。浮充(chong)(chong)時(shi)間已經設(she)(she)定(ding)為(wei)最大充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)間的一半(0.25到5小時(shi))。根據所(suo)要求(qiu)的充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)間(TAPPROX)，由下式計算電(dian)(dian)(dian)(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(cong)快速充(chong)(chong)電(dian)模式(shi)切換到浮(fu)(fu)充(chong)(chong)模式(shi)，同時(shi)(shi)(shi)復(fu)位計時(shi)(shi)(shi)器。計時(shi)(shi)(shi)器開始為浮(fu)(fu)充(chong)(chong)過程計時(shi)(shi)(shi)，如果達到預定的(de)浮(fu)(fu)充(chong)(chong)時(shi)(shi)(shi)間，充(chong)(chong)電(dian)器將從(cong)浮(fu)(fu)充(chong)(chong)模式(shi)切換到涓流模式(shi)(圖3)。

　　圖3. 該典型應(ying)用電(dian)路(lu)中，DS2711電(dian)池充電(dian)器(qi)

　　為2個串聯的 鎳(nie)氫(qing)充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian) VP1、VP2用(yong)于監(jian)視(shi)電(dian)(dian)(dian)壓，THM1、THM2配合熱敏電(dian)(dian)(dian)阻用(yong)來(lai)監(jian)測(ce)電(dian)(dian)(dian)池的溫度。TMR (計時(shi)器)和(he)RSNS(檢流電(dian)(dian)(dian)阻)用(yong)于設定充(chong)(chong)(chong)電(dian)(dian)(dian)時(shi)間(jian)和(he)充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流。DS2711/DS2712的另外一個特性是可(ke)以檢測(ce)電(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian)故障和(he)堿性原電(dian)(dian)(dian)池。如(ru)果(guo)發(fa)生這些情況，充(chong)(chong)(chong)電(dian)(dian)(dian)器會自行關機(ji)。

　　如何檢測堿性電池

　　全新的(de)(de)鎳氫AA電(dian)(dian)(dian)池的(de)(de)典型內阻(zu)(zu)在(zai)30mΩ到(dao)(dao)100mΩ，堿性電(dian)(dian)(dian)池的(de)(de)內阻(zu)(zu)一般在(zai)200mΩ到(dao)(dao)300mΩ (根據充(chong)電(dian)(dian)(dian)狀態，最高可到(dao)(dao)700mΩ)，出(chu)現故障的(de)(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)池會(hui)有(you)很(hen)高的(de)(de)內阻(zu)(zu)。DS2711/DS2712通(tong)過檢測到(dao)(dao)的(de)(de)電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)(VP1和(he)(he)VP2)和(he)(he)已設定的(de)(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)可以計算出(chu)待充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)池的(de)(de)內阻(zu)(zu)。

　　CTST引(yin)(yin)腳(用(yong)于電池(chi)(chi)測(ce)試(shi)、設置門限)控制電池(chi)(chi)內阻的測(ce)量(liang)。VCTST是充(chong)電過程中(zhong)的電池(chi)(chi)電壓(ya)減去無(wu)充(chong)電電流(liu)時的開路電池(chi)(chi)電壓(ya)(OCV)后的差值(zhi)。這個(ge)值(zhi)等于充(chong)電電流(liu)乘(cheng)(cheng)以(yi)電池(chi)(chi)內阻的乘(cheng)(cheng)積。如果(guo)檢測(ce)引(yin)(yin)腳(VP1、VP2和(he)VN1)與電池(chi)(chi)沒有采用(yong)Kelvin連接，引(yin)(yin)線電阻也將計入測(ce)量(liang)值(zhi)，影(ying)響(xiang)VCTST。計算外部(bu)電阻RCTST的公式(shi)為：

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

　　例如(ru)，當以C/2速率(lv)(1.1A)為(wei)2200mAh NiMH電池充(chong)電時， 選(xuan)擇RCELL = 150mΩ為(wei)電池內(nei)阻門(men)限(xian)時, VCTST將為(wei): VCTEST = ICHARGE * RCELL = 1.1A * 150mΩ = 0.165V 或(huo): RCTST = 8000 [V2/A] / 0.165V = 48,485Ω

　　(最近的標(biao)準1%阻(zu)值為48.7kΩ) 如果超過VCTST門限(xian)(本(ben)例中> 0.165V)，表明電(dian)池內(nei)阻(zu)高(gao)于150mΩ，芯片(pian)會(hui)提供邏(luo)輯指示(shi)或出錯信(xin)息指示(shi)(LED1、LED2)，同時停止(zhi)充(chong)電(dian)過程(圖4)。

　　圖(tu)(tu)4. 圖(tu)(tu)3中所示充電器的充電流程(cheng)

　　單機鋰離子電池快速充(chong)電器

　　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)(dian)池簡單(dan)。同時(shi)，由于(yu)鋰離子電(dian)(dian)池對過充(chong)非常敏感，充(chong)電(dian)(dian)器需(xu)要(yao)(yao)一個精確的4.2V ± 50mV電(dian)(dian)源保(bao)證恒功率充(chong)電(dian)(dian)。至于(yu)鎳氫(qing)電(dian)(dian)池，充(chong)電(dian)(dian)器不僅(jin)需(xu)要(yao)(yao)電(dian)(dian)壓(ya)監(jian)測，還需(xu)要(yao)(yao)其它監(jian)控(kong)功能(溫度、計時(shi)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(ke)以保(bao)持恒定輸出功率(lv)(圖(tu)5)，外(wai)部電阻(接SETI引(yin)腳(jiao))和外(wai)部電容(接CT引(yin)腳(jiao))可(ke)以設定充(chong)電電流和內部計時。該充(chong)電器(qi)還通過一個(ge)負(fu)溫(wen)(wen)度(du)系數電阻來監控電池的溫(wen)(wen)度(du)。

　　圖5. MAX8601鋰離(li)子電池單機充電器的典型應用電路圖

　　MAX8601充電(dian)(dian)(dian)器(qi)的(de)主(zhu)要優(you)點(dian)是可(ke)以通過(guo)外(wai)部(bu)適(shi)配器(qi)或USB端口給電(dian)(dian)(dian)池充電(dian)(dian)(dian)(圖6)。USB端口根據USEL引腳(jiao)的(de)設置可(ke)以提(ti)供100mA、500mA電(dian)(dian)(dian)流(liu)(典型USB輸出電(dian)(dian)(dian)流(liu))。該芯(xin)片會自動(dong)選擇外(wai)部(bu)電(dian)(dian)(dian)源(yuan)(主(zhu)適(shi)配器(qi)或USB)。如果兩(liang)個電(dian)(dian)(dian)源(yuan)同時(shi)存在，它會選擇主(zhu)適(shi)配器(qi)進行充電(dian)(dian)(dian)。任(ren)何一個電(dian)(dian)(dian)源(yuan)都必須(xu)能夠提(ti)供最(zui)小4.5V的(de)電(dian)(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(ji)電池過壓、高溫/低溫檢測和(he)充電時間的連續監測功能(neng)。

　　圖6. 圖5中充(chong)電器的充(chong)電流程(cheng)圖

　 DS2711/DS2712和MAX8601都是單機充電器，它們(men)具有(you)多種(zhong)監控(kong)功能(電(dian)壓、電(dian)流(liu)、溫(wen)度、計時等)，既不需要微控(kong)制器監控(kong)，也不需要電(dian)源浪涌(yong)保護，而(er)且提(ti)供(gong)清(qing)晰(xi)、簡單(dan)的外部切換。