充電(dian)(dian)電(dian)(dian)池(chi)(chi)已經成(cheng)為當今電(dian)(dian)子產(chan)品(pin)的一種標(biao)準(zhun)電(dian)(dian)源，特別是便(bian)攜設(she)備：筆(bi)記本電(dian)(dian)腦(nao)、掌上導航儀、手機等(deng)。這些(xie)產(chan)品(pin)需(xu)(xu)要(yao)(yao)消耗(hao)的功(gong)(gong)率越來越大，而可充電(dian)(dian)電(dian)(dian)池(chi)(chi)容量的增長速(su)度遠(yuan)遠(yuan)不能滿足(zu)它(ta)們的需(xu)(xu)求。功(gong)(gong)耗(hao)增長的主要(yao)(yao)原因是設(she)備功(gong)(gong)能的增強，例如：數(shu)碼相機與手機的功(gong)(gong)能整合(he)，筆(bi)記本電(dian)(dian)腦(nao)更(geng)高的運算速(su)度以及(ji)大尺寸屏幕的需(xu)(xu)求等(deng)等(deng)。便(bian)攜設(she)備功(gong)(gong)耗(hao)的增大使得用(yong)可充電(dian)(dian)電(dian)(dian)池(chi)(chi)要(yao)(yao)比標(biao)準(zhun)電(dian)(dian)池(chi)(chi)更(geng)便(bian)宜、更(geng)環(huan)保。

　　本文介紹了可充(chong)電(dian)(dian)電(dian)(dian)池的(de)化學(xue)成(cheng)分；同時說明了各(ge)種充(chong)電(dian)(dian)電(dian)(dian)池的(de)典型(xing)特征和(he)選擇(ze)電(dian)(dian)池類型(xing)時需要重點注(zhu)意的(de)事項。另外還討論(lun)了在不使(shi)用(yong)微控制器(qi)或使(shi)用(yong)電(dian)(dian)源(yuan)浪(lang)涌保護的(de)主適(shi)配器(qi)的(de)情(qing)況下如(ru)何(he)構建單(dan)機結構，安全、快速地對鎳(nie)氫和(he)鋰離子(zi)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80年(nian)代的便攜設備，如數(shu)字(zi)無繩電(dian)(dian)話、隨身聽和(he)電(dian)(dian)動剃(ti)須刀等，主要由鎳鎘(NiCd)電(dian)(dian)池(chi)供電(dian)(dian)。到了90年(nian)代后期，鎳氫(NiMH)電(dian)(dian)池(chi)和(he)鋰離子(Li-Ion)電(dian)(dian)池(chi)逐漸進(jin)入(ru)市場(chang)并開始流行 因為價(jia)格比(bi)鎳氫和(he)鋰離子電(dian)(dian)池(chi)便宜，鎳鎘電(dian)(dian)池(chi)在低端應(ying)用中十分普遍。鎳鎘電(dian)(dian)池(chi)可提供最高(gao)的放(fang)電(dian)(dian)電(dian)(dian)流，適合短時間內需要大功率(lv)輸出的應(ying)用。

　　另一方(fang)面，鎳(nie)鎘(ge)電(dian)池曾經被(bei)所(suo)謂的(de)記憶效應困擾(現在的(de)鎳(nie)鎘(ge)電(dian)池很(hen)少考慮(lv)這個因(yin)素)，使(shi)電(dian)池容(rong)量降低(di)。如果鎳(nie)鎘(ge)電(dian)池在未完(wan)全放電(dian)的(de)情況(kuang)下再充電(dian)，一些活性物(wu)質(zhi)(zhi)會(hui)累積并且(qie)開始結(jie)晶(在陽極有(you)(you)100微(wei)米的(de)鎘(ge)累積層)，通過化學(xue)反應這層物(wu)質(zhi)(zhi)會(hui)自行消失(一塊(kuai)全新(xin)電(dian)池的(de)陽極大約(yue)有(you)(you)1微(wei)米厚度的(de)鎘(ge)結(jie)晶)。

　　出(chu)現記憶(yi)效應會(hui)導致電(dian)池(chi)容(rong)量越來(lai)越小，端電(dian)壓越來(lai)越低，使(shi)得(de)電(dian)池(chi)到達最低可用端電(dian)壓(關(guan)斷點(dian)(dian))的(de)時間(jian)比(bi)預期(qi)的(de)早許多，如圖1所示。鎳鎘電(dian)池(chi)的(de)另一個缺點(dian)(dian)是它的(de)活性物質(zhi)中含有有毒的(de)鎘。所以(yi)，歐洲法規2000/53/EG在2005年12月31號后禁止銷售鎳鎘充電(dian)電(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(ge)電(dian)(dian)池的(de)記(ji)憶效應與(yu)鎳氫電(dian)(dian)池的(de)惰性效應之間的(de)比較 鋰電(dian)(dian)子可充(chong)電(dian)(dian)電(dian)(dian)池價格最高(gao)，但具(ju)有(you)足夠高(gao)的(de)能量密度，因而可以在給定尺寸下(xia)提供更優性能，更適合小尺寸、高(gao)集成度的(de)便(bian)攜設備。

　　表1給(gei)出了(le)各種類型電池的(de)主(zhu)要特性。

　　單機鎳氫(qing)電池快速充電器

　　雖然很(hen)多(duo)人更(geng)偏愛鋰(li)(li)離子(zi)電池(chi)，鎳(nie)氫(qing)電池(chi)的使用依然很(hen)流行。因為鎳(nie)氫(qing)電池(chi)比鋰(li)(li)離子(zi)電池(chi)便(bian)宜很(hen)多(duo)，所以在(zai)MP3播放(fang)器、閃(shan)光燈(deng)配(pei)件、車燈(deng)等設備中經(jing)常能看(kan)到標準的AA和AAA鎳(nie)氫(qing)電池(chi)。

　　一塊可(ke)充(chong)(chong)(chong)電(dian)(dian)鎳氫(qing)電(dian)(dian)池的(de)溫度和(he)端(duan)電(dian)(dian)壓(ya)隨著電(dian)(dian)池的(de)充(chong)(chong)(chong)電(dian)(dian)逐步(bu)上升(sheng)，在電(dian)(dian)池完全(quan)充(chong)(chong)(chong)滿后開始下降(圖2)。所(suo)以(yi)，鎳氫(qing)電(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)器的(de)主要任務是檢測到這(zhe)個突變(bian)點并(bing)中(zhong)斷充(chong)(chong)(chong)電(dian)(dian)，或者從快(kuai)速(su)充(chong)(chong)(chong)電(dian)(dian)切換到涓流充(chong)(chong)(chong)電(dian)(dian)。另外，在充(chong)(chong)(chong)電(dian)(dian)過程中(zhong)對溫度和(he)電(dian)(dian)壓(ya)進行連續(xu)監控可(ke)以(yi)提供系統(tong)的(de)安全(quan)性(xing)。

　　圖(tu)2. 這些曲線(xian)顯示了NiMH充電(dian)電(dian)池充電(dian)過程(cheng)中典型的(de)(de)電(dian)壓(頂部(bu))和(he)溫度(底部(bu))隨時間的(de)(de)變化 

　　DS2711/DS2712充(chong)電(dian)(dian)(dian)器(qi)具備上述功(gong)能(neng)。另外，它們(men)可以單機(ji)工(gong)作，不需要微控(kong)制器(qi)或微處理器(qi)監(jian)控(kong)。該系列產品是(shi)專門為(wei)單節(jie)AA或AAA可充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)池設計的(de)，同時也適用(yong)于(yu)串聯(lian)或并聯(lian)的(de)兩節(jie)電(dian)(dian)(dian)池。DS2711采用(yong)線性控(kong)制結構，DS2712采用(yong)開(kai)關(guan)控(kong)制結構。為(wei)了(le)最大限度地延長工(gong)作時間、節(jie)約電(dian)(dian)(dian)池能(neng)量，這些充(chong)電(dian)(dian)(dian)器(qi)有4種充(chong)電(dian)(dian)(dian)模式：預充(chong)電(dian)(dian)(dian)、快速充(chong)電(dian)(dian)(dian)、浮充(chong)和涓流充(chong)電(dian)(dian)(dian)。在浮充(chong)模式下(xia)，電(dian)(dian)(dian)池充(chong)滿(man)后充(chong)電(dian)(dian)(dian)速率(lv)被切換到一個比較低(di)的(de)速率(lv)(對于(yu)DS2711而言是(shi)25%)。

　　除監(jian)控功(gong)能外，DS2711/DS2712充(chong)(chong)(chong)電(dian)(dian)(dian)器還帶有(you)內部(bu)計時(shi)器，通過連(lian)接到TMR引腳的外部(bu)電(dian)(dian)(dian)阻設(she)定(ding)(ding)最大充(chong)(chong)(chong)電(dian)(dian)(dian)時(shi)間(jian)，可(ke)將快速充(chong)(chong)(chong)電(dian)(dian)(dian)時(shi)間(jian)設(she)置(zhi)在0.5到10小(xiao)時(shi)。浮充(chong)(chong)(chong)時(shi)間(jian)已經(jing)設(she)定(ding)(ding)為(wei)最大充(chong)(chong)(chong)電(dian)(dian)(dian)時(shi)間(jian)的一半(0.25到5小(xiao)時(shi))。根據所要(yao)求的充(chong)(chong)(chong)電(dian)(dian)(dian)時(shi)間(jian)(TAPPROX)，由下式計算電(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，充電器會從快速充(chong)電(dian)模(mo)式切換(huan)到浮充(chong)模(mo)式，同時(shi)復位計時(shi)器。計時(shi)器開(kai)始為浮充(chong)過程計時(shi)，如果達到預定的浮充(chong)時(shi)間，充(chong)電(dian)器將從浮充(chong)模(mo)式切換(huan)到涓(juan)流模(mo)式(圖(tu)3)。

　　圖3. 該典(dian)型應用電(dian)路中，DS2711電(dian)池充電(dian)器

　　為2個串聯的(de) 鎳氫充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian) VP1、VP2用于監(jian)視電(dian)(dian)(dian)壓，THM1、THM2配合熱敏電(dian)(dian)(dian)阻(zu)用來監(jian)測(ce)電(dian)(dian)(dian)池(chi)的(de)溫度(du)。TMR (計時器(qi))和(he)(he)RSNS(檢流(liu)電(dian)(dian)(dian)阻(zu))用于設(she)定充(chong)電(dian)(dian)(dian)時間和(he)(he)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)。DS2711/DS2712的(de)另外一個特(te)性是可以檢測(ce)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)故障和(he)(he)堿(jian)性原(yuan)電(dian)(dian)(dian)池(chi)。如果發生這些情(qing)況，充(chong)電(dian)(dian)(dian)器(qi)會自行關機。

　　如何檢測堿性(xing)電(dian)池

　　全(quan)新的(de)(de)鎳氫AA電池(chi)(chi)的(de)(de)典型內(nei)阻(zu)在30mΩ到100mΩ，堿性電池(chi)(chi)的(de)(de)內(nei)阻(zu)一般(ban)在200mΩ到300mΩ (根據充(chong)電狀態，最高可(ke)(ke)到700mΩ)，出現故障的(de)(de)充(chong)電電池(chi)(chi)會有(you)很高的(de)(de)內(nei)阻(zu)。DS2711/DS2712通過檢測到的(de)(de)電池(chi)(chi)電壓(VP1和VP2)和已(yi)設定(ding)的(de)(de)充(chong)電電流可(ke)(ke)以計算出待充(chong)電電池(chi)(chi)的(de)(de)內(nei)阻(zu)。

　　CTST引腳(用于電(dian)(dian)(dian)池(chi)測試、設置(zhi)門限)控制電(dian)(dian)(dian)池(chi)內阻(zu)(zu)的測量。VCTST是充(chong)(chong)電(dian)(dian)(dian)過程(cheng)中的電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓減去無充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流時的開路(lu)電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(OCV)后的差(cha)值(zhi)(zhi)(zhi)。這個值(zhi)(zhi)(zhi)等于充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流乘以電(dian)(dian)(dian)池(chi)內阻(zu)(zu)的乘積(ji)。如果檢測引腳(VP1、VP2和VN1)與電(dian)(dian)(dian)池(chi)沒有采用Kelvin連接，引線電(dian)(dian)(dian)阻(zu)(zu)也將(jiang)計入測量值(zhi)(zhi)(zhi)，影響VCTST。計算外(wai)部電(dian)(dian)(dian)阻(zu)(zu)RCTST的公式為：

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

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

　　(最近的標準1%阻值(zhi)為48.7kΩ) 如(ru)果(guo)超過VCTST門限(本例中> 0.165V)，表明電池內阻高于150mΩ，芯片會(hui)提供邏輯指示或出錯信息指示(LED1、LED2)，同(tong)時(shi)停止(zhi)充電過程(圖4)。

　　圖4. 圖3中所示充(chong)電器的(de)充(chong)電流(liu)程

　　單機鋰離(li)子電池快速充電器(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(nie)氫(qing)電(dian)(dian)(dian)(dian)池簡單。同時，由于鋰離子(zi)電(dian)(dian)(dian)(dian)池對過充非常(chang)敏(min)感，充電(dian)(dian)(dian)(dian)器需(xu)要一個精確(que)的4.2V ± 50mV電(dian)(dian)(dian)(dian)源保證恒(heng)功(gong)率充電(dian)(dian)(dian)(dian)。至于鎳(nie)氫(qing)電(dian)(dian)(dian)(dian)池，充電(dian)(dian)(dian)(dian)器不僅需(xu)要電(dian)(dian)(dian)(dian)壓監測，還需(xu)要其它監控功(gong)能(溫度、計時等(deng))。

　　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(heng)定輸出功率(圖(tu)5)，外部(bu)電(dian)阻(接SETI引腳(jiao))和外部(bu)電(dian)容(接CT引腳(jiao))可以(yi)設定充(chong)電(dian)電(dian)流和內部(bu)計時。該(gai)充(chong)電(dian)器還通過(guo)一個負溫度系數電(dian)阻來監控電(dian)池的溫度。

　　圖5. MAX8601鋰(li)離子(zi)電池單機(ji)充(chong)電器的典型應用電路(lu)圖

　　MAX8601充(chong)電(dian)(dian)(dian)器的主(zhu)要優點(dian)是(shi)可以通過外部(bu)適配(pei)器或USB端口給(gei)電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(圖6)。USB端口根據USEL引(yin)腳的設(she)置可以提供100mA、500mA電(dian)(dian)(dian)流(典型USB輸出(chu)電(dian)(dian)(dian)流)。該芯片會自動選(xuan)(xuan)擇(ze)外部(bu)電(dian)(dian)(dian)源(主(zhu)適配(pei)器或USB)。如果兩個電(dian)(dian)(dian)源同時存在，它會選(xuan)(xuan)擇(ze)主(zhu)適配(pei)器進(jin)行(xing)充(chong)電(dian)(dian)(dian)。任(ren)何一(yi)個電(dian)(dian)(dian)源都(dou)必(bi)須(xu)能夠提供最小4.5V的電(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)有上電復位(wei)以及電池過壓、高溫(wen)/低溫(wen)檢測和(he)充(chong)電時間(jian)的(de)連續監測功能。

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

　 DS2711/DS2712和MAX8601都是單機充電器，它們具有多種監控(kong)(kong)功能(電壓、電流、溫度、計時等)，既(ji)不需要微控(kong)(kong)制器監控(kong)(kong)，也不需要電源浪涌(yong)保護，而且提供清晰、簡單的外部切換(huan)。