一次性電池不能夠充電，完全放電后的電池即為報廢電池。二次電池可以多次充電，但不同的化學特性對充電的要求也不同，特別是“快充”控制。目前，最常用的可充電電池是Li+、鎳氫(NiMH)、鎳鎘(Nicd)和鉛酸電池，其它類型的電池還很多，但沒有大規模投入使用。因為本文僅討論利用交流適配器供電的充電器設計，沒有考慮汽車電源供電的SLI鉛酸電池或更大容量電池的充電器。

不同化學類型的電池對充電器的要求  

通常快速充電比涓流充電更受歡迎，但快速充電對電路的要求也復雜，鎳氫或鎳鎘電池的快速充電技術與其它電池也是不同的。鎳鎘和鎳氫電池通常在恒流狀態下快充，而不是恒壓狀態下。快充終止檢測基于電壓和溫度的變化率，充電器還應具備過壓保護和過熱保護功能。Li+和鉛酸電池充電器必須保證作用到電池上的電壓和電流最大值在規定的范圍內，當電池電壓維持在最大單節電池電壓，充電電流下降到一個較低值時，充電器終止充電。Li+和鉛酸電池充電器的區別在于所允許的充電電流、最大電池電壓，另外鉛酸電池充電器一般具有浮充能力(浮充是為了補充鉛酸電池的自放電，而對一個已經完全充滿的電池繼續輸入充電電流的技(ji)術)，Li+電池的自放電非(fei)常低，所以(yi)不(bu)需要(yao)浮充。

Li+電池

為(wei)(wei)便攜式(shi)產品(pin)(pin)選擇(ze)電池時，最(zui)重要的(de)是高能(neng)量(liang)密度、尺寸、重量(liang)和價格。迄今為(wei)(wei)止，Li+電池在最(zui)為(wei)(wei)流行的(de)電池中(zhong)能(neng)夠提供最(zui)高的(de)體積和能(neng)量(liang)密度，但(dan)其每瓦(wa)時的(de)成本(ben)也較高。鉛酸電池的(de)每瓦(wa)時成本(ben)最(zui)低，但(dan)比較笨重。本(ben)文以Li+電池為(wei)(wei)例討論充(chong)電器的(de)設計，它在便攜式(shi)產品(pin)(pin)中(zhong)已經被普(pu)遍使用。我們選擇(ze)780mA的(de)充(chong)電電流和4.2V的(de)終止電壓。

充電器無需微處理器干預，輸入電源可以采用全球范圍的任何交流電源，省去了大體積60Hz變壓器，而且可提供單節Li+電池所要求的精確的充電電壓和電流。充電器IC(U4)集(ji)成(cheng)了全面的保(bao)護功能(電(dian)壓、電(dian)流和自保(bao)護)，確保(bao)Li+電(dian)池(chi)的安全充電(dian)。

假設Li+電池(chi)(chi)帶有(you)過(guo)(guo)流(liu)、過(guo)(guo)壓和過(guo)(guo)熱(re)保(bao)護，這些保(bao)護特性在電池(chi)(chi)包(bao)里是必(bi)需(xu)的，因為充電期間一旦電路出現故障，Li+電池(chi)(chi)將存(cun)在很大的危險性，過(guo)(guo)流(liu)、過(guo)(guo)壓或溫度過(guo)(guo)高都有(you)可能造(zao)成(cheng)Li+電池(chi)(chi)爆炸。

包(bao)括(kuo)兩顆主器(qi)件(U1和U4)、精密基(ji)準(U3)和光(guang)耦(ou)(U2)。U1是離(li)(li)線式(shi)開關控(kong)制器(qi)，配(pei)合(he)隔(ge)離(li)(li)變壓(ya)器(qi)、光(guang)耦(ou)和基(ji)準產生(sheng)隔(ge)離(li)(li)的穩壓(ya)直流(liu)輸出。直流(liu)電壓(ya)供(gong)給電池充(chong)電器(qi)(U4)，U4提供(gong)電流(liu)限制、電壓(ya)調(diao)節、電池充(chong)電和充(chong)電指示等功能。本(ben)方案(an)中，U4是一款簡(jian)單的線性充(chong)電器(qi)，內置調(diao)整(zheng)管，結合(he)其熱控(kong)制環路提供(gong)快(kuai)速(su)充(chong)電。

MAX5022的特性

U1(MAX5022)在(zai)寬輸(shu)入(ru)范(fan)圍的(de)應用中很容(rong)易設計，本文所提供的(de)方案要求(qiu)能夠滿足(zu)全球(qiu)各地的(de)交(jiao)流電源(yuan)(yuan)規格，這里假設通用的(de)輸(shu)入(ru)電源(yuan)(yuan)電壓范(fan)圍為85VAC至265VAC。MAX5022的(de)輸(shu)入(ru)范(fan)圍指標以及評(ping)(ping)估(gu)板(ban)電路的(de)輸(shu)入(ru)范(fan)圍恰好滿足(zu)這一(yi)需求(qiu)。對于圖1所示充電器的(de)電源(yuan)(yuan)端(duan)MAX5022評(ping)(ping)估(gu)板(ban)不需要作任(ren)何修改，隔離端(duan)只(zhi)需對評(ping)(ping)估(gu)板(ban)的(de)電阻值稍作修改。

對于更(geng)大(da)(da)(da)功(gong)(gong)率(lv)的(de)應用，只需選(xuan)取(qu)(qu)功(gong)(gong)率(lv)較大(da)(da)(da)的(de)開關管(guan)(guan)和能(neng)夠處理更(geng)大(da)(da)(da)功(gong)(gong)率(lv)的(de)變壓(ya)器(qi)(qi)即可。圖(tu)1所示(shi)電路要求(qiu)充電電流為780mA，最大(da)(da)(da)電池電壓(ya)為4.2V。對充電電源的(de)要求(qiu)與MAX5022評估(gu)板(ban)所提供的(de)輸出相吻合：5V@1A，因此(ci)，不需要更(geng)換評估(gu)板(ban)的(de)晶(jing)體管(guan)(guan)和變壓(ya)器(qi)(qi)。U4采用SOT23封裝，所以(yi)，充電器(qi)(qi)的(de)尺寸(cun)在很大(da)(da)(da)程度(du)上(shang)取(qu)(qu)決(jue)于應用對充電電源的(de)需求(qiu)。變壓(ya)器(qi)(qi)是電路中尺寸(cun)最大(da)(da)(da)的(de)元件，由于開關控制(zhi)器(qi)(qi)的(de)工作頻(pin)率(lv)大(da)(da)(da)于250kHz，允許系統選(xuan)用小尺寸(cun)的(de)變壓(ya)器(qi)(qi)。

上電(dian)(dian)時，在開關(guan)控制器(qi)工作(zuo)(zuo)之(zhi)前，U1調節器(qi)直接通過泄漏電(dian)(dian)阻R1、R2從整流(liu)通路吸取(qu)少(shao)量的(de)電(dian)(dian)流(liu)，兩個電(dian)(dian)阻阻值(zhi)(zhi)保(bao)證每個電(dian)(dian)阻上的(de)壓(ya)降不會超(chao)出(chu)每個電(dian)(dian)阻的(de)容(rong)限(xian)，Vin引(yin)(yin)腳(jiao)電(dian)(dian)壓(ya)不會超(chao)出(chu)其28V額定值(zhi)(zhi)(30V為(wei)(wei)絕對最大值(zhi)(zhi))，U1在輸入電(dian)(dian)壓(ya)達到24V時開始(shi)開關(guan)操作(zuo)(zuo)，并吸取(qu)更大的(de)電(dian)(dian)流(liu)(高(gao)于R1、R2所(suo)能提(ti)供的(de)電(dian)(dian)流(liu))，在變(bian)壓(ya)器(qi)副邊線圈(quan)能夠提(ti)供足夠的(de)能量之(zhi)前，額外的(de)電(dian)(dian)流(liu)由Vin引(yin)(yin)腳(jiao)的(de)旁路電(dian)(dian)容(rong)供給。這(zhe)種處理方(fang)式能夠適合較寬的(de)輸入電(dian)(dian)壓(ya)范圍，對效(xiao)率的(de)影(ying)響也很小，這(zhe)是因為(wei)(wei)在啟動過程中只需極小的(de)供電(dian)(dian)電(dian)(dian)流(liu)(典型值(zhi)(zhi)為(wei)(wei)50uA)。  

為了防止U1的(de)Vin引腳出現過壓(ya)，可(ke)以在(zai)Vin與地(di)之間接一個(ge)26V至30V的(de)齊(qi)納管，電(dian)(dian)壓(ya)值(zhi)需要高于欠壓(ya)鎖存電(dian)(dian)壓(ya)的(de)最(zui)大(da)值(zhi)，低于該引腳所(suo)允(yun)許的(de)最(zui)大(da)絕(jue)對(dui)電(dian)(dian)壓(ya)。如果器件沒有啟動(dong)正常的(de)開關操作(zuo)，則可(ke)認(ren)為電(dian)(dian)路發生了某些問題，所(suo)以，這一保護(hu)措施(shi)對(dui)于U1來說(shuo)并不是(shi)必需的(de)。

U1是一款電(dian)流(liu)模式PWM控制器(qi)，具有(you)逐周期限(xian)流(liu)電(dian)路，必要時(shi)其占(zhan)空比可以提(ti)高到75%，非常適合圖1所示(shi)的反激拓(tuo)撲。原邊開關電(dian)流(liu)檢測采用尺寸為1206的1.78Ω電(dian)阻(zu)(R7)，該電(dian)阻(zu)限(xian)制了變(bian)壓器(qi)原邊的最大電(dian)流(liu)。固定開關頻率(lv)和最大占(zhan)空比限(xian)制使得最大限(xian)流(liu)具有(you)輸出(chu)短路保護功(gong)能。  

一旦短(duan)路(lu)輸出(chu)造成(cheng)電路(lu)達到了(le)上述(shu)限制條件，第(di)三組線(xian)圈將(jiang)無法提(ti)供10V以上的(de)電壓(ya)(ya)(UVLO的(de)低電壓(ya)(ya)門限)，U1將(jiang)再(zai)次進(jin)入啟動(dong)狀(zhuang)態，停止開關操(cao)作(zuo)。短(duan)路(lu)故障解除后系統會自(zi)動(dong)恢復正常的(de)工作(zuo)狀(zhuang)態。  

電壓調節
 
變壓(ya)器(qi)(qi)副邊(bian)的電(dian)(dian)壓(ya)經過整流、濾波，然后由(you)R4、R5分壓(ya)在并聯型穩(wen)壓(ya)器(qi)(qi)U3的調節點產生1.24V(對應于4.5V輸出(chu))的反饋電(dian)(dian)壓(ya)。為保證電(dian)(dian)池充(chong)電(dian)(dian)器(qi)(qi)正常工作，4.5V是最(zui)低(di)電(dian)(dian)壓(ya)(包括容差)。因為充(chong)電(dian)(dian)器(qi)(qi)采用(yong)的是線性結構，充(chong)電(dian)(dian)效(xiao)率(lv)與(yu)輸入、輸出(chu)電(dian)(dian)壓(ya)的差值成反比(bi)，用(yong)最(zui)低(di)電(dian)(dian)壓(ya)為充(chong)電(dian)(dian)器(qi)(qi)供(gong)電(dian)(dian)有助于降低(di)功率(lv)損耗。  

當調節點電(dian)(dian)壓(ya)高于(yu)1.24V時(shi)，并聯型穩(wen)壓(ya)器將吸入電(dian)(dian)流，導(dao)通(tong)光(guang)耦LED，原邊的(de)(de)光(guang)敏(min)晶(jing)體(ti)(ti)管將處于(yu)發光(guang)狀態(tai)。U1的(de)(de)OPTO輸(shu)(shu)入引(yin)腳(jiao)用于(yu)直(zhi)接(jie)連接(jie)光(guang)敏(min)晶(jing)體(ti)(ti)管，以(yi)極其(qi)簡單(dan)的(de)(de)方(fang)式(shi)構(gou)成閉合環路。光(guang)敏(min)晶(jing)體(ti)(ti)管導(dao)通(tong)時(shi)，OPTO引(yin)腳(jiao)被拉低(di)，內部(bu)比(bi)較(jiao)器在它的(de)(de)一(yi)個(ge)輸(shu)(shu)入端檢(jian)測到較(jiao)低(di)的(de)(de)電(dian)(dian)壓(ya)，比(bi)較(jiao)器的(de)(de)另(ling)一(yi)輸(shu)(shu)入電(dian)(dian)流檢(jian)測引(yin)腳(jiao)(CS)的(de)(de)峰值電(dian)(dian)壓(ya)，OPTO引(yin)腳(jiao)的(de)(de)低(di)電(dian)(dian)壓(ya)將在每(mei)個(ge)周期(qi)直(zhi)接(jie)限(xian)制(zhi)功率MOSFETN1的(de)(de)峰值電(dian)(dian)流。由(you)于(yu)U1是一(yi)個(ge)PWM控制(zhi)器，電(dian)(dian)流限(xian)制(zhi)使得電(dian)(dian)壓(ya)調節受作用在N1上的(de)(de)占空比(bi)(導(dao)通(tong)時(shi)間與斷(duan)開時(shi)間的(de)(de)比(bi)值)的(de)(de)影響，環路穩(wen)定性(xing)通(tong)過調節R11和(he)(he)C12來(lai)保證(zheng)。R10和(he)(he)C5(連接(jie)在U3的(de)(de)第(di)3和(he)(he)第(di)4引(yin)腳(jiao))可(ke)消(xiao)除(chu)穩(wen)定工作情況下(xia)的(de)(de)噪聲干擾。

U4的工作特點

U4是一(yi)款用(yong)(yong)于(yu)單節Li+電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)、功能完備的充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器，采用(yong)(yong)線性(xing)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)模(mo)式，內置(zhi)調整管(guan)和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)檢測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。另外，它還集成了一(yi)個反向(xiang)抑制二(er)極(ji)管(guan)，在去(qu)掉輸入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)時(shi)可防止電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)方向(xiang)放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。接入(ru)(ru)一(yi)個深度放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)時(shi)，U4能夠檢測到(dao)低電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(低于(yu)2.5V)，這樣，U4將首(shou)先啟動涓流(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程，在快充(chong)(chong)(chong)周(zhou)期(qi)的1/10時(shi)間(jian)段(duan)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)進行涓流(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，直到(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)上(shang)升到(dao)2.5V以上(shang)。在涓流(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)到(dao)快速充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)轉換時(shi)，軟啟動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)迫使充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)在3ms時(shi)間(jian)內緩慢上(shang)升，避(bi)免較(jiao)大的浪涌電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)拉低輸入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)。

   上述(shu)功(gong)能的(de)(de)實施不需要(yao)微控制器(qi)的(de)(de)監(jian)管(guan)，而且，U4還具有可(ke)(ke)編程的(de)(de)溫度限制功(gong)能，我(wo)們會(hui)在(zai)下(xia)面(mian)就這一(yi)點進行詳細討(tao)論。用一(yi)個(ge)電(dian)(dian)(dian)(dian)阻設置最大(da)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流，電(dian)(dian)(dian)(dian)阻兩端的(de)(de)電(dian)(dian)(dian)(dian)壓與(yu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流成正比，通過監(jian)視該(gai)電(dian)(dian)(dian)(dian)壓即可(ke)(ke)連續跟蹤(zong)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流，更為(wei)復雜的(de)(de)系統也可(ke)(ke)以采用ADC跟蹤(zong)監(jian)視充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流。

Maxim還提供有另一款與MAX1507非(fei)常相(xiang)似(si)的充(chong)電器―MAX1555，這款IC能夠在沒有交流電源(yuan)的情況(kuang)下從USB主(zhu)機獲得充(chong)電電源(yuan)。  

電流調節

如果把Li+電池直接與一個低阻電壓源連接，充電電流將不受任何限制，這種狀況會對電池及其周圍環境造成災難性的損害，從Li+電池的安全性考慮，必須將其充電電流限制在額定范圍以內。U4根據連接在ISET(第5引腳)的電阻限制充電電流，圖1電路中選用(yong)了一個1.87kΩ的電阻，將最大電流設(she)置(zhi)在780mA:

Ifast=1461V/Rset=1461/1870≈780mA

電(dian)池(chi)電(dian)壓(ya)最(zui)小(xiao)時，由于輸入穩定在4.5V，U4輸入與(yu)輸出的壓(ya)差最(zui)大，如(ru)果此時電(dian)池(chi)是以(yi)最(zui)大電(dian)流充電(dian)，U4功耗將達(da)到(dao)最(zui)大值。例如(ru)，假設電(dian)池(chi)電(dian)壓(ya)為(wei)2.5V，則(ze)對應(ying)的功耗為(wei)：

P=IV=(0.78A)×(4.5V-2.5V)=1.56W

U4封裝(8引腳薄型DFN-EP，EP表示裸露焊盤)在溫度高達70℃時可以耗散的最大功率是1.951W，這樣，在整個電池電壓范圍內以780mA的電流充電應該沒有任何問題。但是，如果IC管芯由于較高的環境溫度或不良的散熱條件達到了70℃，U4內部的熱調節環路將自動降低充電電流，這一過程有別于其它充電IC中的“熱關斷”，“熱關斷”方式只是簡單地中止芯片中的所有電路工作，直到晶片溫度降至規定的數值。MAX1507所采用的方案能夠保證在芯片溫度不超出最大限制范圍的條件下提供最快的充電速率，隨著電池電壓的升高，充電電流在保持最高溫度的前提下逐漸升高，直到達到最大充電電流。在此之后，充電器在滿足芯片溫度限制的條件下將以最大充電電流對電池充電，直(zhi)到(dao)電池(chi)電壓達到(dao)內部設置的(de)4.2V±1%。電池(chi)電壓達到(dao)門限(xian)值后，U4將輸出電壓保持在4.2V，從(cong)而(er)使充電電流開始下降(jiang)(jiang)。充電電流降(jiang)(jiang)低到(dao)快充電流的(de)10%時，充電指示燈關閉，表示充電周期結束。

如果充(chong)電(dian)過程中輸出負載增大，例如，用戶在電(dian)池充(chong)電(dian)時啟(qi)動了其它(ta)電(dian)路，U4允許返(fan)回到限流模式(shi)。

測試結果

圖1電(dian)(dian)(dian)路輸入為110V交流(liu)電(dian)(dian)(dian)源，輸出(chu)為4.14V、740mA負載(zai)，效率可達到(dao)46%。當負載(zai)電(dian)(dian)(dian)流(liu)增(zeng)大使電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓降至2.7V時(shi)，電(dian)(dian)(dian)路將輸出(chu)電(dian)(dian)(dian)流(liu)限制在(zai)802mA，比(bi)設置的(de)(de)780mA限流(liu)門(men)限提(ti)高不到(dao)3%，在(zai)規定的(de)(de)參數(shu)指標以內(nei)。MAX1507允許(xu)±8%的(de)(de)變化。當電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓拉至2.5V時(shi)，輸出(chu)電(dian)(dian)(dian)流(liu)降至76.1mA，在(zai)78mA(780mA的(de)(de)1/10)的(de)(de)3%以內(nei)。U4數(shu)據手(shou)冊中規定允許(xu)±5%的(de)(de)范圍。輸出(chu)短路時(shi)電(dian)(dian)(dian)路還允許(xu)返回到(dao)該模式。

空載時，輸出穩定在4.2V左右，形成一個三角波，在U4輸出接一個負載電阻可以消除這個偏差，保持其連續性，但會降低系統效率，但對于交流電供電系統來說，效率并(bing)不(bu)重要。

利(li)用電流模(mo)式PWM控(kong)制(zhi)器(U1)構成(cheng)(cheng)隔離電源(yuan)，結合Li+電池充電IC(U4)和其(qi)它元件(jian)可以構成(cheng)(cheng)一個由通用的(de)交流電源(yuan)供(gong)電的(de)Li+電池充電器。該方(fang)案不需要任(ren)何額(e)外的(de)控(kong)制(zhi)電路(如微控(kong)制(zhi)器的(de)干預)，也不需要軟件(jian)開發(fa)。硬件(jian)開發(fa)只需對Maxim提(ti)供(gong)的(de)標準(zhun)評(ping)估(gu)板稍作修改(gai)即(ji)可，具有成(cheng)(cheng)本低(di)、開發(fa)周期短等優勢。

由于(yu)(yu)系統沒有(you)60Hz的(de)隔離變壓器(qi)，具(ju)有(you)尺寸小、輕便等特點，可(ke)用(yong)于(yu)(yu)手(shou)機或其它手(shou)持(chi)設備的(de)充電。所(suo)有(you)熱量均(jun)集中在交流(liu)適配(pei)器(qi)內，與內置充電器(qi)的(de)手(shou)持(chi)設備相(xiang)比(bi)，不需要過多考慮(lv)散熱問題。