充(chong)電電池(chi)(chi)已(yi)經成為當今電子產品(pin)的一種(zhong)標準(zhun)電源，特別是便攜設(she)備：筆記本電腦、掌上導(dao)航儀、手(shou)(shou)機(ji)等(deng)。這些產品(pin)需要消耗的功率越來越大，而可充(chong)電電池(chi)(chi)容(rong)量的增(zeng)長(chang)速度遠遠不能滿足(zu)它們的需求(qiu)(qiu)。功耗增(zeng)長(chang)的主(zhu)要原因是設(she)備功能的增(zeng)強，例如(ru)：數碼相機(ji)與手(shou)(shou)機(ji)的功能整(zheng)合，筆記本電腦更(geng)高(gao)的運算速度以及大尺寸屏幕的需求(qiu)(qiu)等(deng)等(deng)。便攜設(she)備功耗的增(zeng)大使得用可充(chong)電電池(chi)(chi)要比標準(zhun)電池(chi)(chi)更(geng)便宜、更(geng)環(huan)保。

　　本文介紹了(le)可(ke)充(chong)電(dian)(dian)電(dian)(dian)池的化學(xue)成(cheng)分；同時(shi)(shi)說(shuo)明了(le)各種充(chong)電(dian)(dian)電(dian)(dian)池的典型特征(zheng)和(he)選擇電(dian)(dian)池類型時(shi)(shi)需(xu)要(yao)重(zhong)點注意(yi)的事項。另外還討論了(le)在不使用(yong)微(wei)控制器或使用(yong)電(dian)(dian)源浪涌保護(hu)的主適配(pei)器的情況下如何構建單機結構，安全(quan)、快速地(di)對鎳氫(qing)和(he)鋰離子充(chong)電(dian)(dian)電(dian)(dian)池進行充(chong)電(dian)(dian)。

　　可充電電池類型

　　20世紀(ji)80年代(dai)的便(bian)攜設備，如數字無繩電(dian)話、隨身聽和電(dian)動剃須刀等，主要由鎳鎘(ge)(NiCd)電(dian)池(chi)(chi)供(gong)電(dian)。到了90年代(dai)后期，鎳氫(NiMH)電(dian)池(chi)(chi)和鋰離(li)子(Li-Ion)電(dian)池(chi)(chi)逐漸(jian)進入(ru)市場并開始(shi)流(liu)行 因(yin)為(wei)價格比鎳氫和鋰離(li)子電(dian)池(chi)(chi)便(bian)宜，鎳鎘(ge)電(dian)池(chi)(chi)在(zai)低端應用中(zhong)十分普遍(bian)。鎳鎘(ge)電(dian)池(chi)(chi)可提供(gong)最(zui)高的放電(dian)電(dian)流(liu)，適(shi)合短時間內(nei)需要大功率(lv)輸出的應用。

　　另(ling)一(yi)方面，鎳鎘(ge)(ge)電(dian)池(chi)曾經被所謂(wei)的(de)(de)記憶效應(ying)困擾(rao)(現(xian)在(zai)的(de)(de)鎳鎘(ge)(ge)電(dian)池(chi)很少(shao)考(kao)慮(lv)這個(ge)因(yin)素)，使電(dian)池(chi)容(rong)量降低。如果鎳鎘(ge)(ge)電(dian)池(chi)在(zai)未完(wan)全(quan)放電(dian)的(de)(de)情況下再充電(dian)，一(yi)些活性物質會(hui)累積(ji)并且開始(shi)結晶(jing)(在(zai)陽極(ji)有(you)100微米的(de)(de)鎘(ge)(ge)累積(ji)層)，通過化學反(fan)應(ying)這層物質會(hui)自(zi)行(xing)消失(一(yi)塊全(quan)新電(dian)池(chi)的(de)(de)陽極(ji)大約有(you)1微米厚度的(de)(de)鎘(ge)(ge)結晶(jing))。

　　出現記(ji)憶(yi)效應會導(dao)致電(dian)(dian)(dian)(dian)(dian)池(chi)容(rong)量越來(lai)越小，端(duan)電(dian)(dian)(dian)(dian)(dian)壓越來(lai)越低(di)，使得電(dian)(dian)(dian)(dian)(dian)池(chi)到達(da)最低(di)可用端(duan)電(dian)(dian)(dian)(dian)(dian)壓(關斷點)的(de)(de)時(shi)間比(bi)預期的(de)(de)早許多(duo)，如圖1所(suo)示。鎳鎘電(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)另一個缺(que)點是它的(de)(de)活性物(wu)質中含有有毒(du)的(de)(de)鎘。所(suo)以，歐洲法(fa)規2000/53/EG在2005年12月31號后禁止銷售鎳鎘充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)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. 鎳鎘電(dian)(dian)(dian)池的記憶效應與鎳氫電(dian)(dian)(dian)池的惰性(xing)效應之間(jian)的比(bi)較 鋰電(dian)(dian)(dian)子可(ke)充電(dian)(dian)(dian)電(dian)(dian)(dian)池價格(ge)最高(gao)(gao)(gao)，但具有足夠高(gao)(gao)(gao)的能量密度(du)，因(yin)而可(ke)以在給定尺寸下(xia)提供(gong)更(geng)優性(xing)能，更(geng)適合小(xiao)尺寸、高(gao)(gao)(gao)集(ji)成度(du)的便攜設備。

　　表1給出了各(ge)種類型電池(chi)的主(zhu)要(yao)特性(xing)。

　　單機鎳氫電(dian)池快速充電(dian)器

　　雖然(ran)很多(duo)(duo)人(ren)更偏愛鋰離子(zi)電(dian)池(chi)(chi)(chi)，鎳(nie)氫電(dian)池(chi)(chi)(chi)的(de)使用依然(ran)很流(liu)行。因(yin)為(wei)鎳(nie)氫電(dian)池(chi)(chi)(chi)比鋰離子(zi)電(dian)池(chi)(chi)(chi)便宜很多(duo)(duo)，所以(yi)在MP3播放器(qi)、閃光燈(deng)配件、車燈(deng)等設備中經常(chang)能看到標準的(de)AA和AAA鎳(nie)氫電(dian)池(chi)(chi)(chi)。

　　一塊(kuai)可充電(dian)(dian)(dian)(dian)鎳(nie)氫(qing)(qing)電(dian)(dian)(dian)(dian)池的(de)溫度和端電(dian)(dian)(dian)(dian)壓隨著電(dian)(dian)(dian)(dian)池的(de)充電(dian)(dian)(dian)(dian)逐(zhu)步上升，在(zai)電(dian)(dian)(dian)(dian)池完全充滿后開始下(xia)降(圖2)。所以，鎳(nie)氫(qing)(qing)電(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)器的(de)主(zhu)要任務是檢測(ce)到這個(ge)突變點并(bing)中斷充電(dian)(dian)(dian)(dian)，或者從快(kuai)速充電(dian)(dian)(dian)(dian)切換到涓(juan)流充電(dian)(dian)(dian)(dian)。另外，在(zai)充電(dian)(dian)(dian)(dian)過(guo)程中對(dui)溫度和電(dian)(dian)(dian)(dian)壓進行連(lian)續監控可以提供(gong)系統(tong)的(de)安全性(xing)。

　　圖2. 這些曲線顯示了NiMH充(chong)電電池(chi)充(chong)電過程中典型的電壓(頂部)和溫度(底部)隨時間(jian)的變(bian)化(hua) 

　　DS2711/DS2712充(chong)(chong)電(dian)器(qi)(qi)具備上述功能(neng)。另外，它們可以(yi)單機工(gong)作(zuo)，不需要微(wei)控制(zhi)器(qi)(qi)或(huo)(huo)微(wei)處理(li)器(qi)(qi)監控。該系列(lie)產品是專門為(wei)單節(jie)AA或(huo)(huo)AAA可充(chong)(chong)電(dian)電(dian)池(chi)設(she)計(ji)的，同時(shi)也(ye)適用于串(chuan)聯(lian)或(huo)(huo)并聯(lian)的兩節(jie)電(dian)池(chi)。DS2711采用線性控制(zhi)結(jie)構(gou)，DS2712采用開關(guan)控制(zhi)結(jie)構(gou)。為(wei)了最大(da)限度地延長工(gong)作(zuo)時(shi)間、節(jie)約電(dian)池(chi)能(neng)量，這些充(chong)(chong)電(dian)器(qi)(qi)有4種(zhong)充(chong)(chong)電(dian)模式(shi)(shi)：預(yu)充(chong)(chong)電(dian)、快速(su)充(chong)(chong)電(dian)、浮(fu)充(chong)(chong)和涓流(liu)充(chong)(chong)電(dian)。在浮(fu)充(chong)(chong)模式(shi)(shi)下，電(dian)池(chi)充(chong)(chong)滿后充(chong)(chong)電(dian)速(su)率被切換到(dao)一(yi)個比較低的速(su)率(對(dui)于DS2711而言是25%)。

　　除(chu)監控功能外(wai)，DS2711/DS2712充(chong)電(dian)器還帶有內部(bu)計時器，通過連接(jie)到TMR引(yin)腳的(de)外(wai)部(bu)電(dian)阻(zu)設定(ding)最大充(chong)電(dian)時間(jian)(jian)，可將快速充(chong)電(dian)時間(jian)(jian)設置在0.5到10小時。浮充(chong)時間(jian)(jian)已經設定(ding)為最大充(chong)電(dian)時間(jian)(jian)的(de)一(yi)半(ban)(0.25到5小時)。根據(ju)所要求的(de)充(chong)電(dian)時間(jian)(jian)(TAPPROX)，由下式(shi)計算電(dian)阻(zu)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)電(dian)模(mo)(mo)式(shi)切換(huan)(huan)到浮充(chong)模(mo)(mo)式(shi)，同時(shi)復(fu)位(wei)計時(shi)器。計時(shi)器開始為浮充(chong)過程計時(shi)，如(ru)果達(da)到預定的浮充(chong)時(shi)間，充(chong)電(dian)器將從(cong)浮充(chong)模(mo)(mo)式(shi)切換(huan)(huan)到涓(juan)流模(mo)(mo)式(shi)(圖3)。

　　圖(tu)3. 該典(dian)型應用電路中，DS2711電池充電器

　　為2個串聯的 鎳氫充(chong)電(dian)(dian)電(dian)(dian)池充(chong)電(dian)(dian) VP1、VP2用(yong)于監視(shi)電(dian)(dian)壓，THM1、THM2配合熱(re)敏電(dian)(dian)阻用(yong)來(lai)監測(ce)(ce)電(dian)(dian)池的溫(wen)度。TMR (計時器)和RSNS(檢流電(dian)(dian)阻)用(yong)于設定充(chong)電(dian)(dian)時間和充(chong)電(dian)(dian)電(dian)(dian)流。DS2711/DS2712的另(ling)外一(yi)個特(te)性(xing)是(shi)可以(yi)檢測(ce)(ce)電(dian)(dian)池充(chong)電(dian)(dian)故障和堿性(xing)原電(dian)(dian)池。如(ru)果發生這些情況，充(chong)電(dian)(dian)器會自行關機。

　　如何檢測堿性電池(chi)

　　全新的(de)(de)鎳氫(qing)AA電池的(de)(de)典型(xing)內阻(zu)在30mΩ到(dao)100mΩ，堿性電池的(de)(de)內阻(zu)一般在200mΩ到(dao)300mΩ (根據充電狀態，最高(gao)可到(dao)700mΩ)，出現故障的(de)(de)充電電池會有很高(gao)的(de)(de)內阻(zu)。DS2711/DS2712通過檢測到(dao)的(de)(de)電池電壓(VP1和VP2)和已設定的(de)(de)充電電流可以計算出待(dai)充電電池的(de)(de)內阻(zu)。

　　CTST引腳(jiao)(用于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池測試、設置門限(xian))控制(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池內阻的測量(liang)。VCTST是(shi)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程(cheng)中的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓減去無充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)時的開(kai)路電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(OCV)后的差值。這個(ge)值等于(yu)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)乘(cheng)(cheng)以電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池內阻的乘(cheng)(cheng)積。如果檢測引腳(jiao)(VP1、VP2和VN1)與電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池沒有(you)采用Kelvin連接，引線電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻也將計入測量(liang)值，影響VCTST。計算(suan)外部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻RCTST的公式為：

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

　　例如(ru)，當以C/2速率(1.1A)為(wei)2200mAh NiMH電池充(chong)電時， 選擇(ze)RCELL = 150mΩ為(wei)電池內阻門限時, VCTST將為(wei): VCTEST = ICHARGE * RCELL = 1.1A * 150mΩ = 0.165V 或: RCTST = 8000 [V2/A] / 0.165V = 48,485Ω

　　(最近(jin)的(de)標準1%阻值為48.7kΩ) 如果超過VCTST門限(本例中> 0.165V)，表(biao)明電池(chi)內(nei)阻高于150mΩ，芯片會提(ti)供邏輯指示(shi)或出錯(cuo)信(xin)息指示(shi)(LED1、LED2)，同時(shi)停止(zhi)充(chong)電過程(圖(tu)4)。

　　圖4. 圖3中(zhong)所示充電(dian)器的充電(dian)流程(cheng)

　　單(dan)機鋰離子電池快速充電器

　　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電(dian)池簡單。同時，由(you)于(yu)鋰(li)離(li)子電(dian)池對過充非常敏感(gan)，充電(dian)器(qi)需(xu)要一個精確的4.2V ± 50mV電(dian)源保證恒(heng)功率充電(dian)。至于(yu)鎳氫電(dian)池，充電(dian)器(qi)不僅需(xu)要電(dian)壓監(jian)測(ce)，還需(xu)要其它監(jian)控功能(neng)(溫度、計(ji)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(ke)以(yi)保持(chi)恒(heng)定輸出功率(圖5)，外(wai)部(bu)電(dian)(dian)(dian)阻(接(jie)SETI引(yin)腳)和外(wai)部(bu)電(dian)(dian)(dian)容(接(jie)CT引(yin)腳)可(ke)以(yi)設(she)定充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流和內部(bu)計時。該充(chong)電(dian)(dian)(dian)器還(huan)通過一個負溫度系數電(dian)(dian)(dian)阻來監(jian)控電(dian)(dian)(dian)池(chi)的溫度。

　　圖(tu)5. MAX8601鋰離(li)子電(dian)池(chi)單機充電(dian)器的典(dian)型應用電(dian)路圖(tu)

　　MAX8601充電器(qi)的主(zhu)要優點是可(ke)以(yi)(yi)通過外部適配(pei)器(qi)或USB端口給電池充電(圖(tu)6)。USB端口根據USEL引腳的設置可(ke)以(yi)(yi)提供100mA、500mA電流(典(dian)型USB輸出電流)。該芯片會自動選擇外部電源(yuan)(主(zhu)適配(pei)器(qi)或USB)。如果兩個電源(yuan)同時存在，它會選擇主(zhu)適配(pei)器(qi)進行充電。任何一個電源(yuan)都必須能夠提供最小4.5V的電壓。

　　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(qi)件還(huan)有上(shang)電(dian)(dian)復位(wei)以及電(dian)(dian)池過壓(ya)、高(gao)溫/低溫檢測和充電(dian)(dian)時(shi)間的連續監測功能。

　　圖6. 圖5中充電器的充電流程圖

　 DS2711/DS2712和MAX8601都是單機充電器，它們具有多種監控功能(電(dian)(dian)壓、電(dian)(dian)流(liu)、溫度、計時等(deng))，既不需(xu)要微控制器監控，也不需(xu)要電(dian)(dian)源浪涌保護，而且提供清晰、簡單的外部(bu)切(qie)換(huan)。