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(de)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(shu))，Li+電池的自放電非常低，所以不需要浮充。

Li+電池

為便(bian)攜(xie)(xie)式產品(pin)選擇(ze)電池(chi)時(shi)(shi)，最重(zhong)要的(de)是高(gao)能(neng)量(liang)密(mi)度(du)、尺寸、重(zhong)量(liang)和價(jia)格。迄今為止，Li+電池(chi)在(zai)最為流行(xing)的(de)電池(chi)中能(neng)夠提供最高(gao)的(de)體積和能(neng)量(liang)密(mi)度(du)，但(dan)其每(mei)瓦時(shi)(shi)的(de)成(cheng)本也較高(gao)。鉛(qian)酸電池(chi)的(de)每(mei)瓦時(shi)(shi)成(cheng)本最低，但(dan)比較笨重(zhong)。本文以Li+電池(chi)為例討(tao)論充電器的(de)設計，它(ta)在(zai)便(bian)攜(xie)(xie)式產品(pin)中已經(jing)被(bei)普遍使用。我們選擇(ze)780mA的(de)充電電流和4.2V的(de)終(zhong)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)集成(cheng)了全面的(de)保(bao)護功(gong)能(電壓、電流和自保(bao)護)，確保(bao)Li+電池的(de)安全充(chong)電。

假設Li+電(dian)池帶有過流、過壓和過熱保(bao)護(hu)(hu)，這些保(bao)護(hu)(hu)特(te)性在電(dian)池包里是必需的(de)，因(yin)為充電(dian)期間一旦(dan)電(dian)路出(chu)現故障，Li+電(dian)池將存在很大的(de)危險性，過流、過壓或溫(wen)度過高都有可(ke)能造成(cheng)Li+電(dian)池爆炸。

包(bao)括兩顆主器(qi)件(U1和(he)U4)、精密基準(zhun)(U3)和(he)光耦(U2)。U1是離(li)線式開關控制器(qi)，配合(he)隔(ge)離(li)變壓(ya)(ya)器(qi)、光耦和(he)基準(zhun)產生隔(ge)離(li)的(de)穩(wen)壓(ya)(ya)直流輸(shu)出。直流電(dian)壓(ya)(ya)供(gong)給(gei)電(dian)池充(chong)(chong)電(dian)器(qi)(U4)，U4提供(gong)電(dian)流限制、電(dian)壓(ya)(ya)調節、電(dian)池充(chong)(chong)電(dian)和(he)充(chong)(chong)電(dian)指(zhi)示(shi)等功能。本(ben)方案中，U4是一款簡單的(de)線性充(chong)(chong)電(dian)器(qi)，內置調整管，結合(he)其熱控制環路(lu)提供(gong)快速充(chong)(chong)電(dian)。

MAX5022的特性

U1(MAX5022)在寬輸入范(fan)圍(wei)的(de)應用中很容(rong)易設計，本文所(suo)提(ti)供的(de)方案要(yao)求能夠滿(man)足全球各地的(de)交流(liu)電(dian)(dian)源(yuan)(yuan)規(gui)格，這里假設通用的(de)輸入電(dian)(dian)源(yuan)(yuan)電(dian)(dian)壓(ya)范(fan)圍(wei)為85VAC至265VAC。MAX5022的(de)輸入范(fan)圍(wei)指標以及評(ping)估板電(dian)(dian)路(lu)的(de)輸入范(fan)圍(wei)恰好滿(man)足這一需(xu)求。對(dui)于圖1所(suo)示充電(dian)(dian)器的(de)電(dian)(dian)源(yuan)(yuan)端MAX5022評(ping)估板不需(xu)要(yao)作任(ren)何修改，隔離(li)端只需(xu)對(dui)評(ping)估板的(de)電(dian)(dian)阻值稍作修改。

對于(yu)更(geng)(geng)大(da)功(gong)率(lv)的應用，只需選(xuan)取功(gong)率(lv)較大(da)的開(kai)關管和能夠(gou)處理更(geng)(geng)大(da)功(gong)率(lv)的變(bian)(bian)壓(ya)(ya)器(qi)(qi)(qi)即可(ke)。圖1所(suo)示電(dian)(dian)(dian)(dian)路(lu)要求充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)為780mA，最(zui)大(da)電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(ya)(ya)為4.2V。對充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源(yuan)的要求與MAX5022評估板(ban)所(suo)提供的輸出相吻合：5V@1A，因此，不需要更(geng)(geng)換評估板(ban)的晶體管和變(bian)(bian)壓(ya)(ya)器(qi)(qi)(qi)。U4采用SOT23封裝(zhuang)，所(suo)以，充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)(qi)的尺(chi)寸(cun)(cun)在(zai)很大(da)程度上取決(jue)于(yu)應用對充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源(yuan)的需求。變(bian)(bian)壓(ya)(ya)器(qi)(qi)(qi)是電(dian)(dian)(dian)(dian)路(lu)中尺(chi)寸(cun)(cun)最(zui)大(da)的元件，由于(yu)開(kai)關控制器(qi)(qi)(qi)的工作頻率(lv)大(da)于(yu)250kHz，允(yun)許系統選(xuan)用小尺(chi)寸(cun)(cun)的變(bian)(bian)壓(ya)(ya)器(qi)(qi)(qi)。

上電(dian)(dian)時，在(zai)開關(guan)控制器工(gong)作之前，U1調節(jie)器直接通(tong)過泄漏電(dian)(dian)阻(zu)R1、R2從整(zheng)流(liu)(liu)(liu)通(tong)路(lu)吸(xi)取少量的(de)電(dian)(dian)流(liu)(liu)(liu)，兩個(ge)電(dian)(dian)阻(zu)阻(zu)值保證每個(ge)電(dian)(dian)阻(zu)上的(de)壓(ya)降不會(hui)超出每個(ge)電(dian)(dian)阻(zu)的(de)容(rong)限，Vin引腳電(dian)(dian)壓(ya)不會(hui)超出其(qi)28V額(e)定值(30V為絕對最大(da)值)，U1在(zai)輸(shu)入電(dian)(dian)壓(ya)達到24V時開始開關(guan)操作，并吸(xi)取更大(da)的(de)電(dian)(dian)流(liu)(liu)(liu)(高于R1、R2所能(neng)提供的(de)電(dian)(dian)流(liu)(liu)(liu))，在(zai)變壓(ya)器副邊線圈能(neng)夠(gou)提供足夠(gou)的(de)能(neng)量之前，額(e)外的(de)電(dian)(dian)流(liu)(liu)(liu)由(you)Vin引腳的(de)旁路(lu)電(dian)(dian)容(rong)供給。這(zhe)種(zhong)處(chu)理(li)方式能(neng)夠(gou)適合較寬的(de)輸(shu)入電(dian)(dian)壓(ya)范圍，對效率的(de)影響(xiang)也很小，這(zhe)是(shi)因為在(zai)啟(qi)動過程中只需(xu)極小的(de)供電(dian)(dian)電(dian)(dian)流(liu)(liu)(liu)(典型值為50uA)。  

為了防止U1的(de)Vin引(yin)腳出現(xian)過壓(ya)，可以在Vin與(yu)地之間接(jie)一(yi)個26V至30V的(de)齊納管(guan)，電(dian)壓(ya)值(zhi)需(xu)要高于(yu)欠壓(ya)鎖存(cun)電(dian)壓(ya)的(de)最大值(zhi)，低于(yu)該引(yin)腳所允許的(de)最大絕對電(dian)壓(ya)。如果器件(jian)沒有啟動(dong)正常(chang)的(de)開關(guan)操作(zuo)，則可認為電(dian)路發生(sheng)了某些問題，所以，這一(yi)保護措施對于(yu)U1來(lai)說并不是必(bi)需(xu)的(de)。

U1是一款電(dian)(dian)流(liu)模式PWM控制(zhi)器，具有逐周(zhou)期(qi)限流(liu)電(dian)(dian)路(lu)(lu)，必要時其占(zhan)空比(bi)可以提高到75%，非常適合(he)圖1所示的(de)(de)反(fan)激拓撲。原(yuan)邊開(kai)關電(dian)(dian)流(liu)檢測采用尺寸為1206的(de)(de)1.78Ω電(dian)(dian)阻(zu)(R7)，該電(dian)(dian)阻(zu)限制(zhi)了變壓器原(yuan)邊的(de)(de)最大電(dian)(dian)流(liu)。固定開(kai)關頻率和最大占(zhan)空比(bi)限制(zhi)使(shi)得(de)最大限流(liu)具有輸出(chu)短路(lu)(lu)保護功能。  

一旦短路(lu)輸出(chu)造成電(dian)路(lu)達到了(le)上述限(xian)制條件，第三組線(xian)圈將無法(fa)提供10V以上的電(dian)壓(ya)(UVLO的低(di)電(dian)壓(ya)門限(xian))，U1將再次(ci)進(jin)入(ru)啟動狀態，停(ting)止開關(guan)操作。短路(lu)故障解除后系統會自動恢復正常的工作狀態。  

電壓調節
 
變壓(ya)(ya)(ya)器(qi)副(fu)邊的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)經過整流、濾(lv)波，然后由R4、R5分壓(ya)(ya)(ya)在并聯(lian)型穩壓(ya)(ya)(ya)器(qi)U3的調節點產生1.24V(對應于4.5V輸出)的反饋(kui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)。為保證電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)正常工作，4.5V是最低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(包括容差(cha))。因為充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)采(cai)用的是線(xian)性結構，充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)效率(lv)與輸入、輸出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的差(cha)值成反比，用最低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)為充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)有助于降低(di)功率(lv)損耗。  

當調(diao)(diao)節(jie)(jie)點電(dian)(dian)(dian)壓高于(yu)(yu)1.24V時(shi)，并(bing)聯型(xing)穩(wen)(wen)壓器將(jiang)吸入(ru)電(dian)(dian)(dian)流，導(dao)(dao)通光(guang)耦LED，原邊的(de)(de)(de)光(guang)敏晶(jing)體(ti)管(guan)將(jiang)處于(yu)(yu)發(fa)光(guang)狀態(tai)。U1的(de)(de)(de)OPTO輸(shu)(shu)入(ru)引(yin)(yin)腳(jiao)(jiao)用(yong)于(yu)(yu)直(zhi)接連接光(guang)敏晶(jing)體(ti)管(guan)，以極其簡(jian)單(dan)的(de)(de)(de)方式構(gou)成閉合環路。光(guang)敏晶(jing)體(ti)管(guan)導(dao)(dao)通時(shi)，OPTO引(yin)(yin)腳(jiao)(jiao)被拉低(di)，內部(bu)比(bi)較器在它的(de)(de)(de)一個輸(shu)(shu)入(ru)端檢測到較低(di)的(de)(de)(de)電(dian)(dian)(dian)壓，比(bi)較器的(de)(de)(de)另(ling)一輸(shu)(shu)入(ru)電(dian)(dian)(dian)流檢測引(yin)(yin)腳(jiao)(jiao)(CS)的(de)(de)(de)峰(feng)值電(dian)(dian)(dian)壓，OPTO引(yin)(yin)腳(jiao)(jiao)的(de)(de)(de)低(di)電(dian)(dian)(dian)壓將(jiang)在每(mei)個周(zhou)期(qi)直(zhi)接限制功率(lv)MOSFETN1的(de)(de)(de)峰(feng)值電(dian)(dian)(dian)流。由于(yu)(yu)U1是一個PWM控制器，電(dian)(dian)(dian)流限制使得(de)電(dian)(dian)(dian)壓調(diao)(diao)節(jie)(jie)受作(zuo)(zuo)用(yong)在N1上(shang)的(de)(de)(de)占空比(bi)(導(dao)(dao)通時(shi)間與斷開時(shi)間的(de)(de)(de)比(bi)值)的(de)(de)(de)影響(xiang)，環路穩(wen)(wen)定性通過調(diao)(diao)節(jie)(jie)R11和C12來保(bao)證。R10和C5(連接在U3的(de)(de)(de)第(di)3和第(di)4引(yin)(yin)腳(jiao)(jiao))可消除穩(wen)(wen)定工作(zuo)(zuo)情況下的(de)(de)(de)噪(zao)聲干擾。

U4的工作特點

U4是一(yi)款用于(yu)(yu)單節Li+電(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)、功(gong)能完(wan)備(bei)的充(chong)(chong)電(dian)(dian)(dian)(dian)器，采用線性充(chong)(chong)電(dian)(dian)(dian)(dian)模(mo)式(shi)，內(nei)(nei)置調整管和(he)電(dian)(dian)(dian)(dian)流(liu)檢(jian)測(ce)電(dian)(dian)(dian)(dian)路。另外，它還(huan)集成了一(yi)個反向(xiang)抑制二極管，在(zai)去掉輸(shu)入(ru)電(dian)(dian)(dian)(dian)源時(shi)(shi)可防止電(dian)(dian)(dian)(dian)池方向(xiang)放電(dian)(dian)(dian)(dian)。接入(ru)一(yi)個深度放電(dian)(dian)(dian)(dian)的電(dian)(dian)(dian)(dian)池時(shi)(shi)，U4能夠(gou)檢(jian)測(ce)到低(di)(di)電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(低(di)(di)于(yu)(yu)2.5V)，這樣，U4將首先啟動涓流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)過程，在(zai)快充(chong)(chong)周期的1/10時(shi)(shi)間(jian)段對電(dian)(dian)(dian)(dian)池進行涓流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)，直到電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓上升到2.5V以上。在(zai)涓流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)到快速充(chong)(chong)電(dian)(dian)(dian)(dian)轉換時(shi)(shi)，軟啟動電(dian)(dian)(dian)(dian)路迫使充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)在(zai)3ms時(shi)(shi)間(jian)內(nei)(nei)緩慢上升，避免較(jiao)大的浪涌電(dian)(dian)(dian)(dian)流(liu)拉低(di)(di)輸(shu)入(ru)電(dian)(dian)(dian)(dian)源。

   上述(shu)功(gong)能的(de)實施不需要微控制(zhi)器的(de)監(jian)管，而且，U4還具有可(ke)編程的(de)溫(wen)度限制(zhi)功(gong)能，我們(men)會(hui)在下面就這一(yi)點進行詳(xiang)細討論。用一(yi)個電(dian)阻(zu)設置最大(da)充(chong)電(dian)電(dian)流(liu)(liu)，電(dian)阻(zu)兩端的(de)電(dian)壓(ya)與充(chong)電(dian)電(dian)流(liu)(liu)成正比，通過(guo)監(jian)視該電(dian)壓(ya)即可(ke)連續跟(gen)蹤充(chong)電(dian)電(dian)流(liu)(liu)，更(geng)為復雜的(de)系統(tong)也可(ke)以采用ADC跟(gen)蹤監(jian)視充(chong)電(dian)電(dian)流(liu)(liu)。

Maxim還提供有另一款與MAX1507非(fei)常相似的(de)充(chong)電器(qi)―MAX1555，這款IC能夠在沒有交流電源的(de)情(qing)況下(xia)從(cong)USB主機獲得充(chong)電電源。  

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(dian)路中選(xuan)用了一個1.87kΩ的電(dian)阻，將最大(da)電(dian)流(liu)設置(zhi)在780mA:

Ifast=1461V/Rset=1461/1870≈780mA

電(dian)池(chi)(chi)電(dian)壓(ya)最小時(shi)，由(you)于(yu)輸入(ru)穩定在4.5V，U4輸入(ru)與輸出的壓(ya)差(cha)最大(da)，如果此時(shi)電(dian)池(chi)(chi)是(shi)以最大(da)電(dian)流充(chong)電(dian)，U4功耗將達到最大(da)值。例如，假設(she)電(dian)池(chi)(chi)電(dian)壓(ya)為2.5V，則對應的功耗為：

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，直到(dao)電(dian)(dian)池電(dian)(dian)壓達到(dao)內部設置的(de)(de)4.2V±1%。電(dian)(dian)池電(dian)(dian)壓達到(dao)門限值后，U4將(jiang)輸出電(dian)(dian)壓保持在4.2V，從而使(shi)充(chong)電(dian)(dian)電(dian)(dian)流開(kai)始下降(jiang)。充(chong)電(dian)(dian)電(dian)(dian)流降(jiang)低到(dao)快充(chong)電(dian)(dian)流的(de)(de)10%時，充(chong)電(dian)(dian)指示燈(deng)關閉，表(biao)示充(chong)電(dian)(dian)周期(qi)結束。

如(ru)(ru)果充電(dian)(dian)過程中(zhong)輸(shu)出負載增(zeng)大，例如(ru)(ru)，用(yong)戶在電(dian)(dian)池充電(dian)(dian)時啟(qi)動了其它電(dian)(dian)路(lu)，U4允(yun)許返回到(dao)限流模(mo)式。

測試結果

圖1電(dian)(dian)(dian)(dian)(dian)(dian)路輸(shu)入為110V交(jiao)流電(dian)(dian)(dian)(dian)(dian)(dian)源，輸(shu)出(chu)為4.14V、740mA負載(zai)(zai)，效率可達到(dao)(dao)46%。當負載(zai)(zai)電(dian)(dian)(dian)(dian)(dian)(dian)流增大使電(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)降至(zhi)2.7V時，電(dian)(dian)(dian)(dian)(dian)(dian)路將輸(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)流限制在802mA，比(bi)設(she)置的780mA限流門限提高不到(dao)(dao)3%，在規定的參數(shu)指(zhi)標(biao)以內。MAX1507允許±8%的變化。當電(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)拉至(zhi)2.5V時，輸(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)流降至(zhi)76.1mA，在78mA(780mA的1/10)的3%以內。U4數(shu)據手(shou)冊中規定允許±5%的范圍。輸(shu)出(chu)短路時電(dian)(dian)(dian)(dian)(dian)(dian)路還允許返(fan)回到(dao)(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(tong)來(lai)說，效率并不(bu)重要(yao)。

利用電(dian)(dian)(dian)流模式PWM控(kong)制器(U1)構成(cheng)隔離電(dian)(dian)(dian)源，結合Li+電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)IC(U4)和其它(ta)元件可以(yi)構成(cheng)一個(ge)由(you)通用的交流電(dian)(dian)(dian)源供(gong)電(dian)(dian)(dian)的Li+電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)器。該方(fang)案不需要(yao)任(ren)何額(e)外的控(kong)制電(dian)(dian)(dian)路(如微控(kong)制器的干預)，也不需要(yao)軟件開發(fa)。硬件開發(fa)只需對(dui)Maxim提供(gong)的標準評估板稍作(zuo)修改即可，具有成(cheng)本低、開發(fa)周期短等優勢。

由于(yu)系(xi)統沒有60Hz的隔(ge)離變壓器(qi)，具有尺寸小(xiao)、輕便等特點，可(ke)用于(yu)手機或其它手持(chi)設備的充電(dian)(dian)。所有熱量(liang)均集中在交流適配(pei)器(qi)內，與(yu)內置充電(dian)(dian)器(qi)的手持(chi)設備相比，不需要過(guo)多(duo)考慮(lv)散熱問題(ti)。