本文介紹了一個單(dan)節(jie)鋰離子(Li+)電(dian)(dian)(dian)池的充電(dian)(dian)(dian)方(fang)案(an),該方(fang)案(an)基于MAX5022芯片,適用于全(quan)球的交(jiao)流電(dian)(dian)(dian)源(yuan),而且無需軟件控制(zhi)或微(wei)處理器干預(yu)就能實現所有的充電(dian)(dian)(dian)功能。   

    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(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)上的(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)和電(dian)(dian)(dian)(dian)(dian)(dian)流最大值在(zai)規定的(de)范(fan)圍內(nei),當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)維(wei)持在(zai)最大單節電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya),充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流下降到一(yi)個較低(di)值時,充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器終止充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。Li+和鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器的(de)區別(bie)在(zai)于所(suo)允許的(de)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流、最大電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya),另外(wai)鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器一(yi)般具有浮充(chong)(chong)(chong)(chong)(chong)能力(浮充(chong)(chong)(chong)(chong)(chong)是為了補充(chong)(chong)(chong)(chong)(chong)鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)自放電(dian)(dian)(dian)(dian)(dian)(dian),而對一(yi)個已經完全充(chong)(chong)(chong)(chong)(chong)滿的(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)繼續輸入充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)技術),Li+電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)自放電(dian)(dian)(dian)(dian)(dian)(dian)非常(chang)低(di),所(suo)以不需要浮充(chong)(chong)(chong)(chong)(chong)。   

    Li+電(dian)池   

    為(wei)(wei)便攜(xie)式(shi)產品(pin)選擇(ze)電(dian)(dian)池時,最(zui)重要的是高(gao)能(neng)量密度、尺(chi)寸(cun)、重量和(he)價格。迄今為(wei)(wei)止(zhi)(zhi),Li+電(dian)(dian)池在最(zui)為(wei)(wei)流(liu)行的電(dian)(dian)池中(zhong)能(neng)夠提(ti)供最(zui)高(gao)的體積和(he)能(neng)量密度,但其每(mei)瓦時的成(cheng)本也較高(gao)。鉛酸(suan)電(dian)(dian)池的每(mei)瓦時成(cheng)本最(zui)低,但比較笨重。本文以Li+電(dian)(dian)池為(wei)(wei)例討論(lun)充電(dian)(dian)器的設(she)計(ji),它(ta)在便攜(xie)式(shi)產品(pin)中(zhong)已經被(bei)普遍(bian)使(shi)用(yong)。我們(men)選擇(ze)780mA的充電(dian)(dian)電(dian)(dian)流(liu)和(he)4.2V的終止(zhi)(zhi)電(dian)(dian)壓。

    圖1：通用輸入交流電壓的離線式Li+電池充電器。   

    圖1所示充電器無需(xu)微處理器(qi)(qi)干預,輸(shu)入電(dian)(dian)(dian)(dian)源(yuan)可(ke)以(yi)采(cai)用全球范圍(wei)的任(ren)何交(jiao)流(liu)(liu)電(dian)(dian)(dian)(dian)源(yuan),省去了(le)大(da)體積(ji)60Hz變壓器(qi)(qi),而且(qie)可(ke)提供單節Li+電(dian)(dian)(dian)(dian)池(chi)所要求的精確(que)的充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓和電(dian)(dian)(dian)(dian)流(liu)(liu)。充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)IC(U4)集成了(le)全面的保護功(gong)能(電(dian)(dian)(dian)(dian)壓、電(dian)(dian)(dian)(dian)流(liu)(liu)和自保護),確(que)保Li+電(dian)(dian)(dian)(dian)池(chi)的安全充(chong)電(dian)(dian)(dian)(dian)。   

    假設Li+電(dian)(dian)池(chi)帶有過(guo)流、過(guo)壓和過(guo)熱保(bao)護,這些保(bao)護特(te)性在電(dian)(dian)池(chi)包里是必(bi)需的,因為充(chong)電(dian)(dian)期(qi)間一旦電(dian)(dian)路出現故障,Li+電(dian)(dian)池(chi)將存在很大(da)的危險性,過(guo)流、過(guo)壓或(huo)溫度過(guo)高都有可能造成Li+電(dian)(dian)池(chi)爆(bao)炸。   

    電路描述    

    圖1包括兩顆主器件(U1和U4)、精密基準(U3)和光耦(U2)。U1是離線式開關控制器,配合隔離變壓器、光耦和基準產生隔離的穩壓直流輸出。直流電壓供給電池充電器(U4),U4提供電流限制、電壓調節、電池充電和充電指示等功能。本方案中,U4是一款簡單的線性充電器,內置調整管(guan),結合其熱控制環路提供快速(su)充電。   

    MAX5022的特性    

    U1(MAX5022)在寬輸入范圍的應用中很容易設計,本文所提供的方案要求能夠滿足全球各地的交流電源規格,這里假設通用的輸入電源電壓范圍為85VAC至265VAC。MAX5022的輸入范圍指標以及評估板電路的輸入范圍恰好滿足這一需求。對于圖1所示充電器的電源端MAX5022評估(gu)板不(bu)需要(yao)作(zuo)(zuo)任何修(xiu)改,隔離端只需對評估(gu)板的電阻值稍作(zuo)(zuo)修(xiu)改。   

    對于(yu)更大功(gong)(gong)率的(de)(de)(de)應用(yong),只(zhi)需(xu)選取功(gong)(gong)率較大的(de)(de)(de)開關管和能夠處理更大功(gong)(gong)率的(de)(de)(de)變壓(ya)器(qi)即可。圖1所示電(dian)路要(yao)求充(chong)(chong)電(dian)電(dian)流為780mA,最大電(dian)池(chi)電(dian)壓(ya)為4.2V。對充(chong)(chong)電(dian)電(dian)源(yuan)的(de)(de)(de)要(yao)求與MAX5022評(ping)估板所提(ti)供的(de)(de)(de)輸出(chu)相吻(wen)合：5V@1A,因此,不需(xu)要(yao)更換評(ping)估板的(de)(de)(de)晶體(ti)管和變壓(ya)器(qi)。U4采用(yong)SOT23封(feng)裝,所以,充(chong)(chong)電(dian)器(qi)的(de)(de)(de)尺寸(cun)(cun)在很大程度上取決(jue)于(yu)應用(yong)對充(chong)(chong)電(dian)電(dian)源(yuan)的(de)(de)(de)需(xu)求。變壓(ya)器(qi)是電(dian)路中尺寸(cun)(cun)最大的(de)(de)(de)元件,由于(yu)開關控(kong)制器(qi)的(de)(de)(de)工作(zuo)頻率大于(yu)250kHz,允許系統選用(yong)小尺寸(cun)(cun)的(de)(de)(de)變壓(ya)器(qi)。    

    上電(dian)(dian)(dian)時,在(zai)(zai)開(kai)關控(kong)制器工(gong)作之前,U1調節器直接(jie)通過泄漏電(dian)(dian)(dian)阻(zu)R1、R2從整流(liu)(liu)通路(lu)吸(xi)取(qu)少(shao)量的(de)電(dian)(dian)(dian)流(liu)(liu),兩個電(dian)(dian)(dian)阻(zu)阻(zu)值(zhi)(zhi)保證(zheng)每(mei)個電(dian)(dian)(dian)阻(zu)上的(de)壓降不(bu)會超(chao)出(chu)每(mei)個電(dian)(dian)(dian)阻(zu)的(de)容(rong)(rong)限,Vin引(yin)腳(jiao)電(dian)(dian)(dian)壓不(bu)會超(chao)出(chu)其28V額(e)定值(zhi)(zhi)(30V為(wei)絕對最大值(zhi)(zhi)),U1在(zai)(zai)輸入(ru)(ru)電(dian)(dian)(dian)壓達到24V時開(kai)始(shi)開(kai)關操作,并吸(xi)取(qu)更大的(de)電(dian)(dian)(dian)流(liu)(liu)(高于(yu)R1、R2所能提(ti)供(gong)(gong)的(de)電(dian)(dian)(dian)流(liu)(liu)),在(zai)(zai)變壓器副邊線(xian)圈能夠(gou)提(ti)供(gong)(gong)足夠(gou)的(de)能量之前,額(e)外的(de)電(dian)(dian)(dian)流(liu)(liu)由Vin引(yin)腳(jiao)的(de)旁路(lu)電(dian)(dian)(dian)容(rong)(rong)供(gong)(gong)給(gei)。這種(zhong)處理方式能夠(gou)適合較寬的(de)輸入(ru)(ru)電(dian)(dian)(dian)壓范圍,對效率的(de)影響(xiang)也很小(xiao),這是因為(wei)在(zai)(zai)啟動過程中(zhong)只需極小(xiao)的(de)供(gong)(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)(典型值(zhi)(zhi)為(wei)50uA)。  

    為了防(fang)止U1的Vin引腳(jiao)出(chu)現過壓(ya),可以在Vin與地之間接一(yi)個(ge)26V至30V的齊納(na)管,電(dian)(dian)壓(ya)值需(xu)要高于欠壓(ya)鎖存電(dian)(dian)壓(ya)的最(zui)大(da)值,低于該引腳(jiao)所允許的最(zui)大(da)絕對電(dian)(dian)壓(ya)。如(ru)果(guo)器(qi)件沒有(you)啟動正常(chang)的開關操作(zuo),則可認為電(dian)(dian)路發生了某些問題,所以,這一(yi)保護措施對于U1來(lai)說并不是必需(xu)的。    

    U1是一(yi)款電(dian)(dian)流(liu)模式PWM控制器,具有(you)逐周期限(xian)(xian)(xian)(xian)流(liu)電(dian)(dian)路(lu),必要時其占(zhan)空比可(ke)以提高到75%,非常適合圖1所示的(de)反激拓撲(pu)。原(yuan)邊開(kai)關電(dian)(dian)流(liu)檢測采用(yong)尺寸為1206的(de)1.78Ω電(dian)(dian)阻(zu)(R7),該電(dian)(dian)阻(zu)限(xian)(xian)(xian)(xian)制了變壓器原(yuan)邊的(de)最大(da)電(dian)(dian)流(liu)。固定開(kai)關頻(pin)率和(he)最大(da)占(zhan)空比限(xian)(xian)(xian)(xian)制使得最大(da)限(xian)(xian)(xian)(xian)流(liu)具有(you)輸出短路(lu)保護功能。  

    一旦短路輸出造成(cheng)電路達到了上(shang)述限制條件,第三組(zu)線圈將無(wu)法提供10V以上(shang)的電壓(ya)(UVLO的低電壓(ya)門限),U1將再次進入啟動(dong)狀(zhuang)態,停止(zhi)開關(guan)操(cao)作。短路故障解除后系統(tong)會自動(dong)恢復正常的工作狀(zhuang)態。  

    電壓調節
 
    變壓器副邊的電壓經過整流、濾波,然后由R4、R5分壓在并聯型穩壓器U3的調節點產生1.24V(對應于4.5V輸出)的反饋電壓。為保證電池充電器正常工作,4.5V是最低電壓(包括容差)。因為充電器采用的是線性結構,充電效率與輸入、輸出電壓的差值成反比,用最低電壓為充電器供電有助于降低功(gong)率損耗(hao)。  

    當(dang)調節點電(dian)壓高(gao)于1.24V時,并聯型穩(wen)壓器將吸入(ru)(ru)電(dian)流(liu),導(dao)通(tong)(tong)光(guang)耦LED,原邊的(de)(de)(de)光(guang)敏晶體(ti)(ti)管將處于發光(guang)狀態。U1的(de)(de)(de)OPTO輸入(ru)(ru)引(yin)腳用于直接(jie)連接(jie)光(guang)敏晶體(ti)(ti)管,以極(ji)其簡單的(de)(de)(de)方式(shi)構成(cheng)閉合環(huan)路。光(guang)敏晶體(ti)(ti)管導(dao)通(tong)(tong)時,OPTO引(yin)腳被拉低(di),內部(bu)比(bi)(bi)較器在(zai)它的(de)(de)(de)一(yi)個輸入(ru)(ru)端檢測到較低(di)的(de)(de)(de)電(dian)壓,比(bi)(bi)較器的(de)(de)(de)另一(yi)輸入(ru)(ru)電(dian)流(liu)檢測引(yin)腳(CS)的(de)(de)(de)峰(feng)值(zhi)(zhi)電(dian)壓,OPTO引(yin)腳的(de)(de)(de)低(di)電(dian)壓將在(zai)每個周期直接(jie)限(xian)制功率MOSFETN1的(de)(de)(de)峰(feng)值(zhi)(zhi)電(dian)流(liu)。由于U1是一(yi)個PWM控制器,電(dian)流(liu)限(xian)制使得(de)電(dian)壓調節受作(zuo)用在(zai)N1上(shang)的(de)(de)(de)占空比(bi)(bi)(導(dao)通(tong)(tong)時間(jian)與斷開(kai)時間(jian)的(de)(de)(de)比(bi)(bi)值(zhi)(zhi))的(de)(de)(de)影響,環(huan)路穩(wen)定(ding)性通(tong)(tong)過調節R11和C12來(lai)保(bao)證。R10和C5(連接(jie)在(zai)U3的(de)(de)(de)第3和第4引(yin)腳)可消除穩(wen)定(ding)工(gong)作(zuo)情況下的(de)(de)(de)噪聲干(gan)擾(rao)。   

    U4的工作特點   

    U4是一款用于單節Li+電池充電、功能完備的(de)(de)充(chong)電(dian)(dian)(dian)(dian)器(qi),采用線性充(chong)電(dian)(dian)(dian)(dian)模式(shi),內置調整管和電(dian)(dian)(dian)(dian)流(liu)檢(jian)測電(dian)(dian)(dian)(dian)路。另(ling)外,它還集(ji)成了一(yi)個(ge)反向(xiang)抑制二極(ji)管,在去(qu)掉輸(shu)入(ru)電(dian)(dian)(dian)(dian)源時(shi)可防止電(dian)(dian)(dian)(dian)池(chi)方向(xiang)放(fang)電(dian)(dian)(dian)(dian)。接入(ru)一(yi)個(ge)深度放(fang)電(dian)(dian)(dian)(dian)的(de)(de)電(dian)(dian)(dian)(dian)池(chi)時(shi),U4能夠檢(jian)測到(dao)低電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(低于2.5V),這(zhe)樣,U4將首先啟動涓(juan)流(liu)充(chong)電(dian)(dian)(dian)(dian)過程,在快(kuai)充(chong)周期的(de)(de)1/10時(shi)間段對(dui)電(dian)(dian)(dian)(dian)池(chi)進行涓(juan)流(liu)充(chong)電(dian)(dian)(dian)(dian),直到(dao)電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓上升(sheng)到(dao)2.5V以上。在涓(juan)流(liu)充(chong)電(dian)(dian)(dian)(dian)到(dao)快(kuai)速充(chong)電(dian)(dian)(dian)(dian)轉換時(shi),軟啟動電(dian)(dian)(dian)(dian)路迫使充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)在3ms時(shi)間內緩慢上升(sheng),避免(mian)較大的(de)(de)浪涌電(dian)(dian)(dian)(dian)流(liu)拉(la)低輸(shu)入(ru)電(dian)(dian)(dian)(dian)源。   

   上述功能(neng)的(de)實(shi)施不需要微控(kong)制器(qi)的(de)監(jian)管(guan),而且,U4還(huan)具有可(ke)編程的(de)溫度限制功能(neng),我(wo)們會在下面就(jiu)這一(yi)點進行詳細討(tao)論。用(yong)一(yi)個電(dian)(dian)(dian)阻(zu)設置最大(da)充電(dian)(dian)(dian)電(dian)(dian)(dian)流,電(dian)(dian)(dian)阻(zu)兩端的(de)電(dian)(dian)(dian)壓(ya)與充電(dian)(dian)(dian)電(dian)(dian)(dian)流成正(zheng)比,通(tong)過(guo)監(jian)視該電(dian)(dian)(dian)壓(ya)即可(ke)連續跟蹤充電(dian)(dian)(dian)電(dian)(dian)(dian)流,更為(wei)復(fu)雜的(de)系統(tong)也(ye)可(ke)以采(cai)用(yong)ADC跟蹤監(jian)視充電(dian)(dian)(dian)電(dian)(dian)(dian)流。   

    Maxim還提供有另一款(kuan)與MAX1507非常相(xiang)似的充電(dian)器―MAX1555,這款(kuan)IC能夠在沒有交流電(dian)源的情況下從USB主機獲(huo)得充電(dian)電(dian)源。  

    電流調節

    如果把Li+電(dian)(dian)(dian)(dian)池(chi)直接與一個低阻(zu)電(dian)(dian)(dian)(dian)壓(ya)源連接,充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)將不(bu)受任何限(xian)(xian)制,這種狀況會(hui)對電(dian)(dian)(dian)(dian)池(chi)及其周圍(wei)環(huan)境(jing)造成災難性的損(sun)害,從Li+電(dian)(dian)(dian)(dian)池(chi)的安全(quan)性考慮,必須將其充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)限(xian)(xian)制在額定范圍(wei)以內。U4根據連接在ISET(第5引腳)的電(dian)(dian)(dian)(dian)阻(zu)限(xian)(xian)制充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu),圖(tu)1電(dian)(dian)(dian)(dian)路中選用了一個1.87kΩ的電(dian)(dian)(dian)(dian)阻(zu),將最大電(dian)(dian)(dian)(dian)流(liu)設置在780mA:

  ;  Ifast=1461V/Rset=1461/1870≈780mA

    電(dian)池(chi)電(dian)壓最(zui)小時,由(you)于輸(shu)入穩定(ding)在4.5V,U4輸(shu)入與(yu)輸(shu)出的壓差最(zui)大,如果此(ci)時電(dian)池(chi)是以最(zui)大電(dian)流充電(dian),U4功耗將達到(dao)最(zui)大值。例如,假(jia)設電(dian)池(chi)電(dian)壓為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(shi)裸露焊(han)盤)在(zai)溫(wen)度(du)高(gao)(gao)達(da)70℃時可以(yi)耗散的(de)(de)(de)最(zui)大功率是(shi)1.951W,這(zhe)(zhe)樣,在(zai)整個電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓范(fan)(fan)圍(wei)內(nei)以(yi)780mA的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)應該沒有任何問題(ti)。但是(shi),如果IC管芯由于(yu)較(jiao)高(gao)(gao)的(de)(de)(de)環(huan)境(jing)溫(wen)度(du)或不良(liang)的(de)(de)(de)散熱條件達(da)到(dao)(dao)了70℃,U4內(nei)部(bu)的(de)(de)(de)熱調節環(huan)路將(jiang)自動降低(di)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu),這(zhe)(zhe)一(yi)過程有別于(yu)其它(ta)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)IC中(zhong)的(de)(de)(de)“熱關(guan)斷(duan)”,“熱關(guan)斷(duan)”方(fang)式只(zhi)是(shi)簡(jian)單地中(zhong)止芯片(pian)中(zhong)的(de)(de)(de)所(suo)有電(dian)(dian)(dian)(dian)(dian)(dian)路工作(zuo),直(zhi)到(dao)(dao)晶(jing)片(pian)溫(wen)度(du)降至(zhi)規定的(de)(de)(de)數(shu)值。MAX1507所(suo)采(cai)用的(de)(de)(de)方(fang)案能夠保證(zheng)在(zai)芯片(pian)溫(wen)度(du)不超出(chu)最(zui)大限(xian)制(zhi)范(fan)(fan)圍(wei)的(de)(de)(de)條件下提(ti)(ti)供最(zui)快(kuai)的(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)速(su)率,隨著電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)(de)(de)升高(gao)(gao),充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)在(zai)保持最(zui)高(gao)(gao)溫(wen)度(du)的(de)(de)(de)前提(ti)(ti)下逐漸升高(gao)(gao),直(zhi)到(dao)(dao)達(da)到(dao)(dao)最(zui)大充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)。在(zai)此之(zhi)后,充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器在(zai)滿足芯片(pian)溫(wen)度(du)限(xian)制(zhi)的(de)(de)(de)條件下將(jiang)以(yi)最(zui)大充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)對電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian),直(zhi)到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓達(da)到(dao)(dao)內(nei)部(bu)設置的(de)(de)(de)4.2V±1%。電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓達(da)到(dao)(dao)門限(xian)值后,U4將(jiang)輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓保持在(zai)4.2V,從而使(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)開(kai)始(shi)下降。充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)降低(di)到(dao)(dao)快(kuai)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的(de)(de)(de)10%時,充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)指示(shi)燈關(guan)閉(bi),表示(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)周期結束(shu)。

    如果充電過程中輸(shu)出(chu)負載增大,例(li)如,用戶在(zai)電池充電時啟動了其它電路,U4允許返回到限流(liu)模式。

    測試結果

    圖1電(dian)(dian)(dian)(dian)(dian)路(lu)輸入為110V交流電(dian)(dian)(dian)(dian)(dian)源,輸出(chu)為4.14V、740mA負載,效(xiao)率可達到(dao)46%。當負載電(dian)(dian)(dian)(dian)(dian)流增(zeng)大(da)使電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓降(jiang)至2.7V時(shi),電(dian)(dian)(dian)(dian)(dian)路(lu)將輸出(chu)電(dian)(dian)(dian)(dian)(dian)流限(xian)制在802mA,比設置的(de)780mA限(xian)流門限(xian)提高不到(dao)3%,在規定(ding)的(de)參數指標以內。MAX1507允(yun)許±8%的(de)變化。當電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓拉至2.5V時(shi),輸出(chu)電(dian)(dian)(dian)(dian)(dian)流降(jiang)至76.1mA,在78mA(780mA的(de)1/10)的(de)3%以內。U4數據手冊(ce)中規定(ding)允(yun)許±5%的(de)范圍。輸出(chu)短路(lu)時(shi)電(dian)(dian)(dian)(dian)(dian)路(lu)還允(yun)許返(fan)回到(dao)該模式(shi)。

    空載時,輸出(chu)穩定在4.2V左右(you),形成(cheng)一個三角波,在U4輸出(chu)接一個負載電(dian)阻(zu)可以消除這個偏(pian)差(cha),保持其連續性,但會降低系統效率(lv),但對于交流電(dian)供(gong)電(dian)系統來說,效率(lv)并不重要。

    本文小結

    利用電流模式PWM控制器(U1)構成隔離電源,結合Li+電池充電IC(U4)和其它元件可以構成一個由通用的交流電源供電的Li+電池充電器。該方案不需(xu)要(yao)任何額(e)外的(de)控制(zhi)電(dian)路(lu)(如(ru)微控制(zhi)器的(de)干預),也不需(xu)要(yao)軟件開(kai)(kai)發(fa)。硬件開(kai)(kai)發(fa)只需(xu)對(dui)Maxim提供的(de)標(biao)準評(ping)估板稍作修改即可,具有成本低、開(kai)(kai)發(fa)周期短等優勢。

    由于系統(tong)沒有(you)60Hz的隔離變壓器,具有(you)尺寸小(xiao)、輕便(bian)等特點,可用于手機或其它手持設備(bei)的充電。所有(you)熱量均集中在交流適配(pei)器內,與內置充電器的手持設備(bei)相(xiang)比,不需(xu)要過多(duo)考慮散熱問題。