充(chong)(chong)電(dian)電(dian)池已經成為(wei)當今電(dian)子產品(pin)的(de)一種(zhong)標準(zhun)電(dian)源，特別(bie)是便攜(xie)(xie)設備：筆記本(ben)電(dian)腦、掌上(shang)導航(hang)儀(yi)、手機等。這些產品(pin)需(xu)要消耗的(de)功率越(yue)來越(yue)大，而(er)可充(chong)(chong)電(dian)電(dian)池容量的(de)增長速(su)度(du)遠遠不能滿足(zu)它們的(de)需(xu)求(qiu)。功耗增長的(de)主(zhu)要原因是設備功能的(de)增強，例如：數碼相(xiang)機與手機的(de)功能整合(he)，筆記本(ben)電(dian)腦更高的(de)運(yun)算(suan)速(su)度(du)以及大尺(chi)寸屏(ping)幕的(de)需(xu)求(qiu)等等。便攜(xie)(xie)設備功耗的(de)增大使得(de)用可充(chong)(chong)電(dian)電(dian)池要比標準(zhun)電(dian)池更便宜、更環保(bao)。

　　本文(wen)介紹了(le)可(ke)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)化學(xue)成分(fen)；同時(shi)說明了(le)各種(zhong)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)典型特征和選擇電(dian)(dian)(dian)(dian)池(chi)(chi)類型時(shi)需要重點注意(yi)的(de)(de)事項。另外(wai)還(huan)討(tao)論了(le)在不使(shi)用微控制器或使(shi)用電(dian)(dian)(dian)(dian)源浪涌(yong)保護(hu)的(de)(de)主適(shi)配(pei)器的(de)(de)情況下如何構建單機(ji)結構，安全、快速(su)地對(dui)鎳(nie)氫和鋰(li)離子充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)(chi)進(jin)行充電(dian)(dian)(dian)(dian)。

　　可充電電池類型

　　20世(shi)紀80年代(dai)的便攜(xie)設備(bei)，如(ru)數字(zi)無繩(sheng)電(dian)話(hua)、隨身(shen)聽和電(dian)動剃須刀等，主要由鎳鎘(NiCd)電(dian)池供(gong)電(dian)。到了(le)90年代(dai)后期，鎳氫(NiMH)電(dian)池和鋰(li)離子(zi)(Li-Ion)電(dian)池逐(zhu)漸進(jin)入(ru)市場并開(kai)始流行 因為價格比鎳氫和鋰(li)離子(zi)電(dian)池便宜，鎳鎘電(dian)池在低端應用中(zhong)十分普(pu)遍。鎳鎘電(dian)池可提供(gong)最高的放電(dian)電(dian)流，適合(he)短時間內需要大功率(lv)輸出的應用。

　　另一(yi)(yi)方面，鎳(nie)鎘(ge)電(dian)池(chi)曾經被所謂(wei)的(de)(de)(de)記憶效應困擾(現(xian)在(zai)的(de)(de)(de)鎳(nie)鎘(ge)電(dian)池(chi)很少考慮這(zhe)個因素(su))，使電(dian)池(chi)容(rong)量降低。如果鎳(nie)鎘(ge)電(dian)池(chi)在(zai)未完(wan)全放電(dian)的(de)(de)(de)情況下再充電(dian)，一(yi)(yi)些活性物質(zhi)會累積(ji)(ji)并(bing)且開始(shi)結晶(在(zai)陽(yang)極有(you)100微米(mi)的(de)(de)(de)鎘(ge)累積(ji)(ji)層)，通過(guo)化學反(fan)應這(zhe)層物質(zhi)會自行消失(一(yi)(yi)塊全新電(dian)池(chi)的(de)(de)(de)陽(yang)極大約有(you)1微米(mi)厚(hou)度的(de)(de)(de)鎘(ge)結晶)。

　　出現記憶(yi)效應會導致電(dian)(dian)池容量越來越小，端(duan)電(dian)(dian)壓(ya)越來越低(di)，使得電(dian)(dian)池到達最(zui)低(di)可用端(duan)電(dian)(dian)壓(ya)(關斷點)的時間(jian)比預期的早許多，如(ru)圖1所示。鎳鎘(ge)電(dian)(dian)池的另(ling)一(yi)個(ge)缺點是它的活性物(wu)質中含有(you)有(you)毒的鎘(ge)。所以，歐洲法規(gui)2000/53/EG在2005年12月31號后禁(jin)止(zhi)銷售鎳鎘(ge)充電(dian)(dian)電(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1. 鎳(nie)鎘電(dian)(dian)(dian)池(chi)的記(ji)憶(yi)效應與(yu)鎳(nie)氫電(dian)(dian)(dian)池(chi)的惰性效應之間的比較 鋰電(dian)(dian)(dian)子(zi)可充電(dian)(dian)(dian)電(dian)(dian)(dian)池(chi)價格最高，但具(ju)有足(zu)夠高的能量密度(du)，因而可以在給定尺(chi)(chi)寸下提供更優(you)性能，更適合小尺(chi)(chi)寸、高集成度(du)的便攜(xie)設備(bei)。

　　表1給出了各種類(lei)型(xing)電池(chi)的主要特(te)性。

　　單機(ji)鎳(nie)氫電池快速(su)充電器

　　雖然很多(duo)人更偏愛鋰(li)(li)離子電(dian)(dian)池(chi)(chi)(chi)，鎳氫電(dian)(dian)池(chi)(chi)(chi)的使用依然很流行。因為鎳氫電(dian)(dian)池(chi)(chi)(chi)比(bi)鋰(li)(li)離子電(dian)(dian)池(chi)(chi)(chi)便宜很多(duo)，所以(yi)在MP3播放器(qi)、閃光(guang)燈配件、車燈等(deng)設(she)備中(zhong)經常(chang)能看到(dao)標準的AA和AAA鎳氫電(dian)(dian)池(chi)(chi)(chi)。

　　一塊可充(chong)(chong)電(dian)(dian)鎳氫電(dian)(dian)池(chi)的溫度和端(duan)電(dian)(dian)壓隨著電(dian)(dian)池(chi)的充(chong)(chong)電(dian)(dian)逐步上升，在電(dian)(dian)池(chi)完全充(chong)(chong)滿后開始(shi)下(xia)降(圖2)。所以，鎳氫電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)器的主要任務是檢測(ce)到(dao)這個突變點并中(zhong)(zhong)斷(duan)充(chong)(chong)電(dian)(dian)，或者(zhe)從快速充(chong)(chong)電(dian)(dian)切換到(dao)涓(juan)流(liu)充(chong)(chong)電(dian)(dian)。另(ling)外，在充(chong)(chong)電(dian)(dian)過程中(zhong)(zhong)對溫度和電(dian)(dian)壓進(jin)行連續監控可以提供系統的安(an)全性(xing)。

　　圖2. 這些曲(qu)線顯示了NiMH充電電池充電過程(cheng)中典型的電壓(頂(ding)部(bu))和(he)溫度(du)(底部(bu))隨(sui)時(shi)間(jian)的變(bian)化(hua) 

　　DS2711/DS2712充(chong)電(dian)(dian)器具備上述功(gong)能(neng)。另(ling)外(wai)，它(ta)們可以單(dan)機工作(zuo)，不需(xu)要微控制器或(huo)微處(chu)理器監(jian)控。該系列產品是專門為單(dan)節AA或(huo)AAA可充(chong)電(dian)(dian)電(dian)(dian)池設(she)計的，同時(shi)也適(shi)用于串聯或(huo)并(bing)聯的兩(liang)節電(dian)(dian)池。DS2711采(cai)用線(xian)性控制結(jie)構，DS2712采(cai)用開(kai)關控制結(jie)構。為了最(zui)大限度(du)地延長工作(zuo)時(shi)間、節約電(dian)(dian)池能(neng)量，這(zhe)些(xie)充(chong)電(dian)(dian)器有4種充(chong)電(dian)(dian)模式：預充(chong)電(dian)(dian)、快速(su)充(chong)電(dian)(dian)、浮(fu)充(chong)和涓(juan)流充(chong)電(dian)(dian)。在浮(fu)充(chong)模式下，電(dian)(dian)池充(chong)滿后充(chong)電(dian)(dian)速(su)率被切換到(dao)一個比較低的速(su)率(對于DS2711而言(yan)是25%)。

　　除監(jian)控功(gong)能外，DS2711/DS2712充(chong)(chong)(chong)電(dian)(dian)器還(huan)帶有內部計時(shi)(shi)器，通過連接到TMR引腳(jiao)的(de)外部電(dian)(dian)阻設定最(zui)大充(chong)(chong)(chong)電(dian)(dian)時(shi)(shi)間(jian)(jian)，可將快速充(chong)(chong)(chong)電(dian)(dian)時(shi)(shi)間(jian)(jian)設置在(zai)0.5到10小(xiao)時(shi)(shi)。浮充(chong)(chong)(chong)時(shi)(shi)間(jian)(jian)已經設定為(wei)最(zui)大充(chong)(chong)(chong)電(dian)(dian)時(shi)(shi)間(jian)(jian)的(de)一半(0.25到5小(xiao)時(shi)(shi))。根據所要求的(de)充(chong)(chong)(chong)電(dian)(dian)時(shi)(shi)間(jian)(jian)(TAPPROX)，由下式計算電(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(hui)從快速充(chong)(chong)電模(mo)式(shi)切換到浮充(chong)(chong)模(mo)式(shi)，同時(shi)(shi)復(fu)位(wei)計(ji)時(shi)(shi)器(qi)。計(ji)時(shi)(shi)器(qi)開始為浮充(chong)(chong)過(guo)程計(ji)時(shi)(shi)，如果達(da)到預定的浮充(chong)(chong)時(shi)(shi)間，充(chong)(chong)電器(qi)將(jiang)從浮充(chong)(chong)模(mo)式(shi)切換到涓流模(mo)式(shi)(圖3)。

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

　　為(wei)2個串聯(lian)的 鎳氫充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian) VP1、VP2用于監視電(dian)(dian)壓(ya)，THM1、THM2配合熱敏電(dian)(dian)阻用來監測電(dian)(dian)池(chi)的溫度。TMR (計時器)和RSNS(檢流(liu)電(dian)(dian)阻)用于設定充(chong)(chong)(chong)電(dian)(dian)時間(jian)和充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)。DS2711/DS2712的另外(wai)一個特性是(shi)可以檢測電(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)故(gu)障(zhang)和堿性原電(dian)(dian)池(chi)。如果發(fa)生這些(xie)情況，充(chong)(chong)(chong)電(dian)(dian)器會自行關(guan)機。

　　如何(he)檢測堿(jian)性電(dian)池

　　全新的(de)鎳(nie)氫(qing)AA電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)典型(xing)內(nei)(nei)阻在(zai)30mΩ到(dao)100mΩ，堿性電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)內(nei)(nei)阻一般在(zai)200mΩ到(dao)300mΩ (根(gen)據充電(dian)(dian)(dian)(dian)狀態，最(zui)高可到(dao)700mΩ)，出現故障的(de)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)(chi)會有很高的(de)內(nei)(nei)阻。DS2711/DS2712通過檢(jian)測到(dao)的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(VP1和VP2)和已設(she)定的(de)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流可以計算出待充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)內(nei)(nei)阻。

　　CTST引腳(用于(yu)電(dian)池(chi)測(ce)試、設置門限)控(kong)制電(dian)池(chi)內阻(zu)的測(ce)量。VCTST是(shi)充電(dian)過程中的電(dian)池(chi)電(dian)壓減去(qu)無充電(dian)電(dian)流時的開路電(dian)池(chi)電(dian)壓(OCV)后的差(cha)值(zhi)。這個值(zhi)等于(yu)充電(dian)電(dian)流乘(cheng)以電(dian)池(chi)內阻(zu)的乘(cheng)積。如果檢測(ce)引腳(VP1、VP2和VN1)與電(dian)池(chi)沒(mei)有采用Kelvin連接，引線電(dian)阻(zu)也將計入測(ce)量值(zhi)，影響VCTST。計算外部電(dian)阻(zu)RCTST的公式(shi)為：

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

　　例如，當以C/2速率(1.1A)為2200mAh NiMH電池(chi)充電時， 選擇RCELL = 150mΩ為電池(chi)內阻門限時, VCTST將(jiang)為: VCTEST = ICHARGE * RCELL = 1.1A * 150mΩ = 0.165V 或: RCTST = 8000 [V2/A] / 0.165V = 48,485Ω

　　(最近的(de)標(biao)準1%阻值為48.7kΩ) 如果超過(guo)VCTST門限(本例中> 0.165V)，表(biao)明電(dian)池(chi)內阻高于150mΩ，芯片會提(ti)供邏輯(ji)指示(shi)或出(chu)錯信息指示(shi)(LED1、LED2)，同時停(ting)止充電(dian)過(guo)程(cheng)(圖4)。

　　圖4. 圖3中所示充(chong)電器的充(chong)電流程

　　單(dan)機鋰離子電池快速充電器(qi)

　　因為不需要檢測電壓變化率(dV/dt)，鋰離子電池充電器比(bi)鎳氫電(dian)(dian)池簡(jian)單。同(tong)時(shi)(shi)，由于(yu)鋰離子電(dian)(dian)池對過充(chong)(chong)非常(chang)敏感，充(chong)(chong)電(dian)(dian)器需(xu)要一個精(jing)確的4.2V ± 50mV電(dian)(dian)源(yuan)保(bao)證恒功率充(chong)(chong)電(dian)(dian)。至于(yu)鎳氫電(dian)(dian)池，充(chong)(chong)電(dian)(dian)器不僅需(xu)要電(dian)(dian)壓監測，還需(xu)要其它監控功能(溫度(du)、計時(shi)(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)(ke)以保持恒定輸出(chu)功率(圖(tu)5)，外部(bu)電阻(接(jie)SETI引腳)和(he)外部(bu)電容(接(jie)CT引腳)可(ke)(ke)以設定充電電流和(he)內部(bu)計時(shi)。該充電器還通過一個負溫(wen)(wen)度系數電阻來監控電池的溫(wen)(wen)度。

　　圖(tu)5. MAX8601鋰離子電(dian)池單(dan)機充(chong)電(dian)器的典型應用電(dian)路圖(tu)

　　MAX8601充(chong)電(dian)(dian)器(qi)的主(zhu)要優點(dian)是(shi)可(ke)以通過外部(bu)適配(pei)器(qi)或(huo)(huo)USB端口(kou)給電(dian)(dian)池(chi)充(chong)電(dian)(dian)(圖6)。USB端口(kou)根據USEL引腳的設置可(ke)以提供100mA、500mA電(dian)(dian)流(liu)(典型USB輸出電(dian)(dian)流(liu))。該芯(xin)片會自動選(xuan)擇(ze)外部(bu)電(dian)(dian)源(yuan)(主(zhu)適配(pei)器(qi)或(huo)(huo)USB)。如果兩(liang)個(ge)電(dian)(dian)源(yuan)同時存在(zai)，它(ta)會選(xuan)擇(ze)主(zhu)適配(pei)器(qi)進行充(chong)電(dian)(dian)。任何(he)一個(ge)電(dian)(dian)源(yuan)都必須能夠提供最小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。器件還有上(shang)電(dian)(dian)復(fu)位以(yi)及電(dian)(dian)池過(guo)壓、高溫(wen)/低溫(wen)檢測和(he)充電(dian)(dian)時間的連(lian)續監測功能。

　　圖6. 圖5中(zhong)充(chong)電器的充(chong)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(電壓(ya)、電流、溫度、計(ji)時(shi)等)，既不需(xu)要(yao)微控制器監控，也不需(xu)要(yao)電源浪涌保護，而且(qie)提(ti)供清晰、簡單的外部(bu)切(qie)換(huan)。