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(de)技術)，Li+電(dian)池的(de)自放電(dian)非常低，所以不需要(yao)浮充。

Li+電池

為便(bian)攜式產(chan)品(pin)(pin)選擇(ze)電(dian)(dian)池(chi)時，最重要的(de)(de)(de)是高(gao)能量密度、尺寸、重量和價格。迄今為止(zhi)(zhi)，Li+電(dian)(dian)池(chi)在(zai)最為流(liu)行的(de)(de)(de)電(dian)(dian)池(chi)中能夠提供最高(gao)的(de)(de)(de)體積(ji)和能量密度，但(dan)其每(mei)瓦(wa)時的(de)(de)(de)成本(ben)也(ye)較高(gao)。鉛酸電(dian)(dian)池(chi)的(de)(de)(de)每(mei)瓦(wa)時成本(ben)最低，但(dan)比較笨重。本(ben)文(wen)以Li+電(dian)(dian)池(chi)為例討論充(chong)電(dian)(dian)器(qi)的(de)(de)(de)設計，它在(zai)便(bian)攜式產(chan)品(pin)(pin)中已經被普(pu)遍使用(yong)。我們(men)選擇(ze)780mA的(de)(de)(de)充(chong)電(dian)(dian)電(dian)(dian)流(liu)和4.2V的(de)(de)(de)終止(zhi)(zhi)電(dian)(dian)壓(ya)。

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)集成了全(quan)面的保護功(gong)能(電壓、電流和自保護)，確保Li+電池的安全(quan)充(chong)電。

假設Li+電池(chi)帶(dai)有過(guo)(guo)(guo)流、過(guo)(guo)(guo)壓(ya)和過(guo)(guo)(guo)熱保(bao)護(hu)，這些保(bao)護(hu)特(te)性(xing)(xing)在電池(chi)包里是必需的，因為充電期(qi)間一旦電路出現故(gu)障，Li+電池(chi)將存在很大的危險(xian)性(xing)(xing)，過(guo)(guo)(guo)流、過(guo)(guo)(guo)壓(ya)或溫度(du)過(guo)(guo)(guo)高都有可(ke)能造成Li+電池(chi)爆炸。

包括兩顆主器(qi)(qi)件(U1和U4)、精密基(ji)準(U3)和光耦(U2)。U1是離(li)線式(shi)開關控制器(qi)(qi)，配合隔離(li)變(bian)壓(ya)器(qi)(qi)、光耦和基(ji)準產生隔離(li)的穩壓(ya)直流輸出。直流電(dian)(dian)壓(ya)供(gong)給電(dian)(dian)池(chi)充電(dian)(dian)器(qi)(qi)(U4)，U4提(ti)(ti)供(gong)電(dian)(dian)流限制、電(dian)(dian)壓(ya)調(diao)節、電(dian)(dian)池(chi)充電(dian)(dian)和充電(dian)(dian)指示等功能。本方案中，U4是一款簡單(dan)的線性(xing)充電(dian)(dian)器(qi)(qi)，內置調(diao)整管，結合其熱控制環路提(ti)(ti)供(gong)快速(su)充電(dian)(dian)。

MAX5022的特性

U1(MAX5022)在寬輸(shu)入(ru)范圍(wei)的(de)應用(yong)中很容易設(she)計，本(ben)文(wen)所(suo)提供(gong)的(de)方案(an)要求能夠滿(man)足全球各地的(de)交流電(dian)(dian)源(yuan)規格，這(zhe)里(li)假設(she)通用(yong)的(de)輸(shu)入(ru)電(dian)(dian)源(yuan)電(dian)(dian)壓范圍(wei)為85VAC至265VAC。MAX5022的(de)輸(shu)入(ru)范圍(wei)指標以(yi)及評(ping)估板(ban)(ban)電(dian)(dian)路的(de)輸(shu)入(ru)范圍(wei)恰好滿(man)足這(zhe)一需求。對于圖(tu)1所(suo)示充(chong)電(dian)(dian)器的(de)電(dian)(dian)源(yuan)端MAX5022評(ping)估板(ban)(ban)不需要作(zuo)任何(he)修改，隔離端只(zhi)需對評(ping)估板(ban)(ban)的(de)電(dian)(dian)阻值(zhi)稍作(zuo)修改。

對于(yu)(yu)(yu)更(geng)大(da)功(gong)(gong)率的(de)應用(yong)，只需(xu)(xu)選取功(gong)(gong)率較(jiao)大(da)的(de)開(kai)關(guan)管(guan)和能夠處(chu)理更(geng)大(da)功(gong)(gong)率的(de)變(bian)壓器即(ji)可。圖1所示(shi)電(dian)(dian)(dian)(dian)路要求(qiu)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流為(wei)780mA，最大(da)電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓為(wei)4.2V。對充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源的(de)要求(qiu)與(yu)MAX5022評(ping)估板所提供的(de)輸出(chu)相吻合：5V@1A，因(yin)此，不(bu)需(xu)(xu)要更(geng)換評(ping)估板的(de)晶體管(guan)和變(bian)壓器。U4采用(yong)SOT23封(feng)裝，所以，充電(dian)(dian)(dian)(dian)器的(de)尺寸在很大(da)程度上取決(jue)于(yu)(yu)(yu)應用(yong)對充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源的(de)需(xu)(xu)求(qiu)。變(bian)壓器是電(dian)(dian)(dian)(dian)路中尺寸最大(da)的(de)元件，由于(yu)(yu)(yu)開(kai)關(guan)控(kong)制器的(de)工(gong)作(zuo)頻(pin)率大(da)于(yu)(yu)(yu)250kHz，允許系統選用(yong)小尺寸的(de)變(bian)壓器。

上電(dian)(dian)(dian)時(shi)，在開關(guan)控制器(qi)工作之前，U1調節(jie)器(qi)直接通過(guo)(guo)泄漏電(dian)(dian)(dian)阻(zu)R1、R2從整流通路(lu)(lu)吸取(qu)(qu)少量的(de)電(dian)(dian)(dian)流，兩個電(dian)(dian)(dian)阻(zu)阻(zu)值保證每個電(dian)(dian)(dian)阻(zu)上的(de)壓降不(bu)會(hui)超(chao)出(chu)(chu)每個電(dian)(dian)(dian)阻(zu)的(de)容(rong)限，Vin引(yin)腳電(dian)(dian)(dian)壓不(bu)會(hui)超(chao)出(chu)(chu)其28V額定值(30V為(wei)絕對最大值)，U1在輸(shu)入(ru)電(dian)(dian)(dian)壓達到24V時(shi)開始(shi)開關(guan)操作，并吸取(qu)(qu)更大的(de)電(dian)(dian)(dian)流(高于(yu)R1、R2所能提(ti)供(gong)(gong)的(de)電(dian)(dian)(dian)流)，在變壓器(qi)副邊線(xian)圈(quan)能夠(gou)提(ti)供(gong)(gong)足(zu)夠(gou)的(de)能量之前，額外的(de)電(dian)(dian)(dian)流由Vin引(yin)腳的(de)旁路(lu)(lu)電(dian)(dian)(dian)容(rong)供(gong)(gong)給。這種處理方式(shi)能夠(gou)適合較寬的(de)輸(shu)入(ru)電(dian)(dian)(dian)壓范圍，對效(xiao)率的(de)影響也很小(xiao)，這是因為(wei)在啟動過(guo)(guo)程中只(zhi)需(xu)極小(xiao)的(de)供(gong)(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(典型值為(wei)50uA)。  

為(wei)了防止U1的Vin引腳(jiao)出現過壓，可以在Vin與地之間接(jie)一(yi)個26V至30V的齊納管，電(dian)(dian)壓值需要高于(yu)(yu)欠壓鎖存電(dian)(dian)壓的最大(da)值，低于(yu)(yu)該引腳(jiao)所允許的最大(da)絕對電(dian)(dian)壓。如果器件(jian)沒(mei)有啟(qi)動正常的開關(guan)操作，則可認為(wei)電(dian)(dian)路(lu)發生了某些問(wen)題，所以，這(zhe)一(yi)保(bao)護措施對于(yu)(yu)U1來說并不是必(bi)需的。

U1是一(yi)款電流(liu)(liu)(liu)模(mo)式PWM控制(zhi)器，具(ju)有(you)逐周(zhou)期限流(liu)(liu)(liu)電路，必要時其占(zhan)空比可以提(ti)高(gao)到75%，非常適合圖1所示的(de)反激拓撲。原邊開關電流(liu)(liu)(liu)檢測(ce)采用尺寸為1206的(de)1.78Ω電阻(R7)，該(gai)電阻限制(zhi)了變(bian)壓器原邊的(de)最(zui)(zui)大電流(liu)(liu)(liu)。固定(ding)開關頻率和最(zui)(zui)大占(zhan)空比限制(zhi)使得最(zui)(zui)大限流(liu)(liu)(liu)具(ju)有(you)輸出短路保護(hu)功能。  

一旦短(duan)路(lu)輸出造成電(dian)路(lu)達到了上(shang)(shang)述限(xian)制條件，第三組線(xian)圈(quan)將無法提供10V以上(shang)(shang)的電(dian)壓(UVLO的低(di)電(dian)壓門(men)限(xian))，U1將再次進入啟動(dong)狀態，停止(zhi)開關(guan)操作。短(duan)路(lu)故障解(jie)除后系統會自(zi)動(dong)恢復正常的工作狀態。  

電壓調節
 
變壓(ya)(ya)器(qi)副邊的(de)電(dian)(dian)壓(ya)(ya)經過整流(liu)、濾波，然后由R4、R5分壓(ya)(ya)在并聯(lian)型穩壓(ya)(ya)器(qi)U3的(de)調節點產生1.24V(對(dui)應于4.5V輸出(chu))的(de)反饋電(dian)(dian)壓(ya)(ya)。為保(bao)證電(dian)(dian)池(chi)充電(dian)(dian)器(qi)正常工作，4.5V是最(zui)低(di)電(dian)(dian)壓(ya)(ya)(包括容差(cha))。因(yin)為充電(dian)(dian)器(qi)采用的(de)是線(xian)性結構，充電(dian)(dian)效率(lv)與輸入、輸出(chu)電(dian)(dian)壓(ya)(ya)的(de)差(cha)值成(cheng)反比，用最(zui)低(di)電(dian)(dian)壓(ya)(ya)為充電(dian)(dian)器(qi)供電(dian)(dian)有助于降低(di)功率(lv)損耗。  

當(dang)調節點電(dian)(dian)壓(ya)高于1.24V時(shi)，并(bing)聯型(xing)穩壓(ya)器(qi)(qi)將吸入電(dian)(dian)流(liu)(liu)(liu)，導(dao)通光(guang)(guang)耦(ou)LED，原邊的(de)(de)(de)光(guang)(guang)敏(min)晶(jing)體(ti)管將處于發(fa)光(guang)(guang)狀態(tai)。U1的(de)(de)(de)OPTO輸入引(yin)(yin)腳用(yong)于直接連接光(guang)(guang)敏(min)晶(jing)體(ti)管，以極(ji)其簡單的(de)(de)(de)方式構成(cheng)閉合環(huan)路(lu)。光(guang)(guang)敏(min)晶(jing)體(ti)管導(dao)通時(shi)，OPTO引(yin)(yin)腳被拉(la)低，內部(bu)比較器(qi)(qi)在(zai)它的(de)(de)(de)一個(ge)輸入端檢測到(dao)較低的(de)(de)(de)電(dian)(dian)壓(ya)，比較器(qi)(qi)的(de)(de)(de)另一輸入電(dian)(dian)流(liu)(liu)(liu)檢測引(yin)(yin)腳(CS)的(de)(de)(de)峰值電(dian)(dian)壓(ya)，OPTO引(yin)(yin)腳的(de)(de)(de)低電(dian)(dian)壓(ya)將在(zai)每個(ge)周期直接限制功(gong)率MOSFETN1的(de)(de)(de)峰值電(dian)(dian)流(liu)(liu)(liu)。由于U1是一個(ge)PWM控(kong)制器(qi)(qi)，電(dian)(dian)流(liu)(liu)(liu)限制使(shi)得電(dian)(dian)壓(ya)調節受作用(yong)在(zai)N1上的(de)(de)(de)占(zhan)空(kong)比(導(dao)通時(shi)間(jian)與斷開時(shi)間(jian)的(de)(de)(de)比值)的(de)(de)(de)影響，環(huan)路(lu)穩定性通過調節R11和(he)C12來保(bao)證。R10和(he)C5(連接在(zai)U3的(de)(de)(de)第(di)3和(he)第(di)4引(yin)(yin)腳)可消除穩定工作情況下(xia)的(de)(de)(de)噪(zao)聲干擾。

U4的工作特點

U4是一(yi)(yi)款用(yong)于單節Li+電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)、功能(neng)(neng)完備的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器，采用(yong)線(xian)性充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)模(mo)式(shi)，內(nei)置調整管和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)檢測(ce)(ce)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。另外，它還集成了一(yi)(yi)個反向(xiang)抑制二極管，在去掉輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源時可防止電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)方向(xiang)放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。接(jie)入一(yi)(yi)個深度放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)時，U4能(neng)(neng)夠檢測(ce)(ce)到(dao)(dao)低電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(低于2.5V)，這樣(yang)，U4將首先啟動(dong)涓流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程，在快充(chong)(chong)周期的(de)1/10時間段對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行涓流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，直(zhi)到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓上升(sheng)到(dao)(dao)2.5V以上。在涓流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)到(dao)(dao)快速充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)轉(zhuan)換時，軟啟動(dong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)迫使充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)在3ms時間內(nei)緩慢上升(sheng)，避免較(jiao)大的(de)浪涌(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)拉低輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源。

   上述功能的(de)(de)實(shi)施不(bu)需要微控(kong)制(zhi)(zhi)器的(de)(de)監管，而且，U4還(huan)具有可(ke)(ke)(ke)編程的(de)(de)溫度限制(zhi)(zhi)功能，我們會在下面就這一點進行詳細討論。用一個電(dian)(dian)(dian)阻設置最(zui)大充電(dian)(dian)(dian)電(dian)(dian)(dian)流，電(dian)(dian)(dian)阻兩端的(de)(de)電(dian)(dian)(dian)壓(ya)與(yu)充電(dian)(dian)(dian)電(dian)(dian)(dian)流成(cheng)正比，通(tong)過監視(shi)該電(dian)(dian)(dian)壓(ya)即可(ke)(ke)(ke)連續跟(gen)蹤充電(dian)(dian)(dian)電(dian)(dian)(dian)流，更為復雜的(de)(de)系(xi)統(tong)也可(ke)(ke)(ke)以采用ADC跟(gen)蹤監視(shi)充電(dian)(dian)(dian)電(dian)(dian)(dian)流。

Maxim還提供有另一款(kuan)與MAX1507非常(chang)相似的充(chong)電器―MAX1555，這款(kuan)IC能夠在沒(mei)有交流電源(yuan)的情(qing)況下(xia)從(cong)USB主機獲得(de)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(tu)1電路中選用了一個1.87kΩ的電阻，將最大電流設置在780mA:

Ifast=1461V/Rset=1461/1870≈780mA

電(dian)(dian)池(chi)電(dian)(dian)壓最小時(shi)，由(you)于(yu)輸入穩定(ding)在4.5V，U4輸入與輸出的壓差(cha)最大(da)(da)，如果此時(shi)電(dian)(dian)池(chi)是以最大(da)(da)電(dian)(dian)流充電(dian)(dian)，U4功(gong)耗將(jiang)達到最大(da)(da)值(zhi)。例如，假設電(dian)(dian)池(chi)電(dian)(dian)壓為2.5V，則對應的功(gong)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(ya)達到(dao)內部設置(zhi)的4.2V±1%。電(dian)(dian)池電(dian)(dian)壓(ya)達到(dao)門(men)限(xian)值后，U4將輸出(chu)電(dian)(dian)壓(ya)保(bao)持在4.2V，從而使充(chong)(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)開始下降。充(chong)(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)降低到(dao)快充(chong)(chong)(chong)(chong)電(dian)(dian)流(liu)的10%時，充(chong)(chong)(chong)(chong)電(dian)(dian)指示(shi)(shi)燈關閉，表示(shi)(shi)充(chong)(chong)(chong)(chong)電(dian)(dian)周期(qi)結束(shu)。

如果(guo)充電過程中(zhong)輸出負載增(zeng)大，例如，用戶在電池(chi)充電時啟(qi)動(dong)了其它(ta)電路，U4允許(xu)返回到限(xian)流模式。

測試結果

圖1電(dian)路輸(shu)(shu)入(ru)為110V交流(liu)(liu)電(dian)源，輸(shu)(shu)出(chu)為4.14V、740mA負載，效率可(ke)達到46%。當負載電(dian)流(liu)(liu)增(zeng)大使(shi)電(dian)池電(dian)壓降至2.7V時，電(dian)路將輸(shu)(shu)出(chu)電(dian)流(liu)(liu)限(xian)(xian)制在802mA，比設置的(de)780mA限(xian)(xian)流(liu)(liu)門限(xian)(xian)提(ti)高(gao)不到3%，在規定的(de)參數指標以內。MAX1507允許±8%的(de)變化。當電(dian)池電(dian)壓拉至2.5V時，輸(shu)(shu)出(chu)電(dian)流(liu)(liu)降至76.1mA，在78mA(780mA的(de)1/10)的(de)3%以內。U4數據手冊(ce)中規定允許±5%的(de)范圍。輸(shu)(shu)出(chu)短路時電(dian)路還允許返回到該模式(shi)。

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，效率并不(bu)重要(yao)。

利用電流模式PWM控制(zhi)器(qi)(qi)(U1)構成(cheng)隔離電源，結合Li+電池(chi)充(chong)電IC(U4)和其它元件(jian)可以構成(cheng)一(yi)個由通用的交(jiao)流電源供(gong)電的Li+電池(chi)充(chong)電器(qi)(qi)。該方案不需(xu)要任(ren)何(he)額外的控制(zhi)電路(如(ru)微控制(zhi)器(qi)(qi)的干預(yu))，也不需(xu)要軟件(jian)開(kai)(kai)發(fa)。硬件(jian)開(kai)(kai)發(fa)只(zhi)需(xu)對Maxim提供(gong)的標準評(ping)估板稍作修改(gai)即可，具有成(cheng)本低、開(kai)(kai)發(fa)周期短等(deng)優(you)勢。

由于(yu)系統沒(mei)有60Hz的(de)隔離變壓器(qi)，具有尺寸小(xiao)、輕便等(deng)特點，可用(yong)于(yu)手機或其它手持設備的(de)充電。所有熱量均(jun)集中(zhong)在交(jiao)流適配器(qi)內，與內置充電器(qi)的(de)手持設備相比(bi)，不需要過(guo)多考慮散熱問(wen)題。