本文介紹(shao)了(le)一個單節鋰離子(Li+)電(dian)池的(de)充(chong)電(dian)方案(an),該方案(an)基(ji)于MAX5022芯(xin)片(pian),適用于全球(qiu)的(de)交流電(dian)源,而(er)且(qie)無需軟(ruan)件控(kong)制或微(wei)處(chu)理器干(gan)預就(jiu)能實現所有(you)的(de)充(chong)電(dian)功(gong)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(bi)須保證作用到(dao)電(dian)(dian)(dian)(dian)池(chi)上(shang)的(de)電(dian)(dian)(dian)(dian)壓和(he)電(dian)(dian)(dian)(dian)流(liu)(liu)最大值在(zai)規定的(de)范圍內,當電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓維持在(zai)最大單節電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓,充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)下降到(dao)一個較低值時,充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)終止充(chong)(chong)電(dian)(dian)(dian)(dian)。Li+和(he)鉛酸電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)的(de)區別在(zai)于所允許的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)、最大電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓,另(ling)外鉛酸電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)一般具有浮(fu)充(chong)(chong)能力(浮(fu)充(chong)(chong)是(shi)為了(le)補充(chong)(chong)鉛酸電(dian)(dian)(dian)(dian)池(chi)的(de)自(zi)放電(dian)(dian)(dian)(dian),而對(dui)一個已經(jing)完全充(chong)(chong)滿的(de)電(dian)(dian)(dian)(dian)池(chi)繼續(xu)輸入(ru)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)的(de)技術),Li+電(dian)(dian)(dian)(dian)池(chi)的(de)自(zi)放電(dian)(dian)(dian)(dian)非常(chang)低,所以(yi)不需(xu)要浮(fu)充(chong)(chong)。   

    Li+電池   

    為(wei)便(bian)攜(xie)式(shi)產(chan)品選擇電(dian)(dian)池(chi)(chi)時(shi),最(zui)(zui)(zui)重要的(de)(de)(de)是高能量(liang)密(mi)度、尺寸、重量(liang)和價(jia)格。迄今為(wei)止,Li+電(dian)(dian)池(chi)(chi)在(zai)最(zui)(zui)(zui)為(wei)流行的(de)(de)(de)電(dian)(dian)池(chi)(chi)中能夠提供(gong)最(zui)(zui)(zui)高的(de)(de)(de)體積和能量(liang)密(mi)度,但其每瓦時(shi)的(de)(de)(de)成本也較高。鉛酸電(dian)(dian)池(chi)(chi)的(de)(de)(de)每瓦時(shi)成本最(zui)(zui)(zui)低,但比較笨重。本文(wen)以Li+電(dian)(dian)池(chi)(chi)為(wei)例討論充電(dian)(dian)器的(de)(de)(de)設(she)計,它在(zai)便(bian)攜(xie)式(shi)產(chan)品中已經(jing)被普遍使用。我們選擇780mA的(de)(de)(de)充電(dian)(dian)電(dian)(dian)流和4.2V的(de)(de)(de)終止電(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所示充電器無需微處理器干預,輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)源可以采(cai)用(yong)全(quan)(quan)球范圍(wei)的(de)任何交流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)源,省去了大體(ti)積60Hz變壓(ya)器,而且可提供單節Li+電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)所要求的(de)精確(que)(que)的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)和電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)。充電(dian)(dian)(dian)(dian)(dian)(dian)器IC(U4)集成了全(quan)(quan)面的(de)保護功能(電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)、電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)和自保護),確(que)(que)保Li+電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)安全(quan)(quan)充電(dian)(dian)(dian)(dian)(dian)(dian)。   

    假設Li+電池帶有(you)過(guo)(guo)流(liu)(liu)、過(guo)(guo)壓(ya)和(he)過(guo)(guo)熱(re)保(bao)護,這(zhe)些保(bao)護特性(xing)在(zai)電池包里是必需的(de),因為充電期間(jian)一旦(dan)電路出(chu)現(xian)故障,Li+電池將(jiang)存在(zai)很(hen)大(da)的(de)危險性(xing),過(guo)(guo)流(liu)(liu)、過(guo)(guo)壓(ya)或溫度(du)過(guo)(guo)高(gao)都(dou)有(you)可(ke)能(neng)造(zao)成Li+電池爆(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(nei)置調整管,結合其熱控制(zhi)環路提供快速充電(dian)。   

    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(dian)源端MAX5022評估板(ban)不需要作任何修改(gai),隔離端只需對評估板(ban)的電(dian)阻值(zhi)稍作修改(gai)。   

    對(dui)于更大功(gong)(gong)(gong)率的(de)應(ying)(ying)用(yong)(yong),只需選(xuan)取(qu)功(gong)(gong)(gong)率較大的(de)開(kai)關管(guan)和能夠處理更大功(gong)(gong)(gong)率的(de)變壓(ya)器即(ji)可。圖1所示電(dian)路(lu)要求(qiu)(qiu)充電(dian)電(dian)流為780mA,最(zui)大電(dian)池電(dian)壓(ya)為4.2V。對(dui)充電(dian)電(dian)源的(de)要求(qiu)(qiu)與MAX5022評(ping)估(gu)板(ban)(ban)所提供(gong)的(de)輸出相吻合：5V@1A,因此,不(bu)需要更換評(ping)估(gu)板(ban)(ban)的(de)晶體管(guan)和變壓(ya)器。U4采用(yong)(yong)SOT23封(feng)裝,所以,充電(dian)器的(de)尺寸在(zai)很(hen)大程(cheng)度(du)上取(qu)決于應(ying)(ying)用(yong)(yong)對(dui)充電(dian)電(dian)源的(de)需求(qiu)(qiu)。變壓(ya)器是電(dian)路(lu)中尺寸最(zui)大的(de)元件,由于開(kai)關控制器的(de)工作頻率大于250kHz,允許系統選(xuan)用(yong)(yong)小(xiao)尺寸的(de)變壓(ya)器。    

    上電(dian)(dian)(dian)(dian)(dian)時,在開(kai)(kai)關控制器(qi)(qi)工作(zuo)(zuo)之(zhi)前,U1調節器(qi)(qi)直接通過泄漏電(dian)(dian)(dian)(dian)(dian)阻(zu)R1、R2從整(zheng)流(liu)通路(lu)吸(xi)取少量的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu),兩(liang)個電(dian)(dian)(dian)(dian)(dian)阻(zu)阻(zu)值(zhi)保證(zheng)每(mei)個電(dian)(dian)(dian)(dian)(dian)阻(zu)上的(de)(de)(de)(de)壓(ya)(ya)降(jiang)不會(hui)超出(chu)每(mei)個電(dian)(dian)(dian)(dian)(dian)阻(zu)的(de)(de)(de)(de)容限(xian),Vin引(yin)腳電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)不會(hui)超出(chu)其28V額定值(zhi)(30V為絕對(dui)最大(da)值(zhi)),U1在輸(shu)入電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)達到24V時開(kai)(kai)始(shi)開(kai)(kai)關操作(zuo)(zuo),并吸(xi)取更大(da)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(高(gao)于(yu)R1、R2所能提供(gong)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)),在變壓(ya)(ya)器(qi)(qi)副邊線圈(quan)能夠(gou)提供(gong)足夠(gou)的(de)(de)(de)(de)能量之(zhi)前,額外的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)由Vin引(yin)腳的(de)(de)(de)(de)旁路(lu)電(dian)(dian)(dian)(dian)(dian)容供(gong)給。這種處理方式能夠(gou)適合較寬的(de)(de)(de)(de)輸(shu)入電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)范圍(wei),對(dui)效率的(de)(de)(de)(de)影響也很小,這是因為在啟動過程中只需極小的(de)(de)(de)(de)供(gong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(典型值(zhi)為50uA)。  

    為了(le)(le)防(fang)止U1的(de)(de)(de)Vin引腳出現過(guo)壓(ya),可以在(zai)Vin與地之間接一(yi)個26V至30V的(de)(de)(de)齊納(na)管,電(dian)壓(ya)值需(xu)(xu)要高于(yu)欠(qian)壓(ya)鎖(suo)存電(dian)壓(ya)的(de)(de)(de)最大值,低于(yu)該引腳所允許(xu)的(de)(de)(de)最大絕對(dui)電(dian)壓(ya)。如果器(qi)件沒有啟動正(zheng)常的(de)(de)(de)開(kai)關操作,則可認為電(dian)路發生(sheng)了(le)(le)某些問題(ti),所以,這一(yi)保護措施(shi)對(dui)于(yu)U1來說并不是必需(xu)(xu)的(de)(de)(de)。    

    U1是一款電流(liu)(liu)模(mo)式PWM控制器(qi),具有(you)逐周期限(xian)流(liu)(liu)電路,必(bi)要時其占(zhan)(zhan)空比可(ke)以提高到75%,非常適合圖1所示的反激拓(tuo)撲(pu)。原(yuan)邊(bian)開(kai)關(guan)電流(liu)(liu)檢測(ce)采用尺寸為1206的1.78Ω電阻(R7),該電阻限(xian)制了變壓(ya)器(qi)原(yuan)邊(bian)的最大電流(liu)(liu)。固定開(kai)關(guan)頻率和最大占(zhan)(zhan)空比限(xian)制使得(de)最大限(xian)流(liu)(liu)具有(you)輸出短路保護功能(neng)。  

    一旦(dan)短路輸出造(zao)成電(dian)路達(da)到(dao)了上述限制(zhi)條件,第(di)三組線圈(quan)將(jiang)無法提供10V以上的電(dian)壓(ya)(UVLO的低電(dian)壓(ya)門(men)限),U1將(jiang)再次進入啟動(dong)狀態,停止開關操作。短路故障解除后系統會自(zi)動(dong)恢復(fu)正(zheng)常的工作狀態。  

    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(yu)降低功率損耗(hao)。  

    當(dang)調節(jie)點電(dian)(dian)壓(ya)(ya)高于(yu)(yu)1.24V時,并(bing)聯型穩(wen)壓(ya)(ya)器將吸入(ru)(ru)電(dian)(dian)流,導通光(guang)耦(ou)LED,原邊(bian)的(de)(de)光(guang)敏晶體管(guan)將處(chu)于(yu)(yu)發光(guang)狀態。U1的(de)(de)OPTO輸(shu)(shu)入(ru)(ru)引(yin)(yin)腳(jiao)(jiao)用于(yu)(yu)直(zhi)接(jie)連(lian)接(jie)光(guang)敏晶體管(guan),以(yi)極其簡單的(de)(de)方式構成閉合環(huan)(huan)路(lu)。光(guang)敏晶體管(guan)導通時,OPTO引(yin)(yin)腳(jiao)(jiao)被拉低,內(nei)部比(bi)較(jiao)(jiao)器在它的(de)(de)一(yi)個輸(shu)(shu)入(ru)(ru)端檢測(ce)到較(jiao)(jiao)低的(de)(de)電(dian)(dian)壓(ya)(ya),比(bi)較(jiao)(jiao)器的(de)(de)另一(yi)輸(shu)(shu)入(ru)(ru)電(dian)(dian)流檢測(ce)引(yin)(yin)腳(jiao)(jiao)(CS)的(de)(de)峰值(zhi)電(dian)(dian)壓(ya)(ya),OPTO引(yin)(yin)腳(jiao)(jiao)的(de)(de)低電(dian)(dian)壓(ya)(ya)將在每個周期直(zhi)接(jie)限制(zhi)功率MOSFETN1的(de)(de)峰值(zhi)電(dian)(dian)流。由于(yu)(yu)U1是一(yi)個PWM控制(zhi)器,電(dian)(dian)流限制(zhi)使得電(dian)(dian)壓(ya)(ya)調節(jie)受作用在N1上的(de)(de)占(zhan)空比(bi)(導通時間(jian)與斷開(kai)時間(jian)的(de)(de)比(bi)值(zhi))的(de)(de)影響(xiang),環(huan)(huan)路(lu)穩(wen)定(ding)性通過(guo)調節(jie)R11和C12來(lai)保證(zheng)。R10和C5(連(lian)接(jie)在U3的(de)(de)第3和第4引(yin)(yin)腳(jiao)(jiao))可消除穩(wen)定(ding)工(gong)作情(qing)況下的(de)(de)噪聲(sheng)干(gan)擾(rao)。   

    U4的工作特點   

    U4是一款用于單節Li+電池充電、功能完備的充(chong)(chong)(chong)電(dian)(dian)器,采(cai)用線(xian)性充(chong)(chong)(chong)電(dian)(dian)模式,內置調(diao)整(zheng)管和電(dian)(dian)流(liu)(liu)檢(jian)測(ce)電(dian)(dian)路。另外,它還集成了一(yi)個反向(xiang)抑制(zhi)二極管,在去掉輸入電(dian)(dian)源(yuan)時(shi)可(ke)防止電(dian)(dian)池方向(xiang)放(fang)電(dian)(dian)。接入一(yi)個深(shen)度放(fang)電(dian)(dian)的電(dian)(dian)池時(shi),U4能夠檢(jian)測(ce)到(dao)低(di)電(dian)(dian)池電(dian)(dian)壓(低(di)于2.5V),這(zhe)樣,U4將首先啟動涓(juan)流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian)過程(cheng),在快充(chong)(chong)(chong)周期的1/10時(shi)間(jian)段(duan)對電(dian)(dian)池進行涓(juan)流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian),直到(dao)電(dian)(dian)池電(dian)(dian)壓上升(sheng)到(dao)2.5V以(yi)上。在涓(juan)流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian)到(dao)快速充(chong)(chong)(chong)電(dian)(dian)轉(zhuan)換(huan)時(shi),軟啟動電(dian)(dian)路迫(po)使充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)在3ms時(shi)間(jian)內緩(huan)慢(man)上升(sheng),避免較大的浪涌電(dian)(dian)流(liu)(liu)拉低(di)輸入電(dian)(dian)源(yuan)。   

   上述功(gong)能的實施(shi)不需(xu)要(yao)微(wei)控制器的監管,而且(qie),U4還具(ju)有可編(bian)程(cheng)的溫度限(xian)制功(gong)能,我(wo)們會在下(xia)面就這一點進行詳細討論(lun)。用一個(ge)電(dian)(dian)(dian)阻設置最大充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu),電(dian)(dian)(dian)阻兩端的電(dian)(dian)(dian)壓(ya)與充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)成(cheng)正比,通過監視該電(dian)(dian)(dian)壓(ya)即可連(lian)續跟蹤(zong)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu),更為(wei)復雜的系統也可以采用ADC跟蹤(zong)監視充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)。   

    Maxim還提供有(you)另一款與MAX1507非常相似的(de)充電器(qi)―MAX1555,這(zhe)款IC能夠在沒有(you)交流電源的(de)情況(kuang)下從(cong)USB主(zhu)機獲得(de)充電電源。  

    電流調節

    如果把(ba)Li+電(dian)(dian)池(chi)(chi)直接與一個低阻(zu)電(dian)(dian)壓源連(lian)接,充(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)將(jiang)不受任何限(xian)制,這(zhe)種狀況會對電(dian)(dian)池(chi)(chi)及其周圍環(huan)境造成災難性的損害,從(cong)Li+電(dian)(dian)池(chi)(chi)的安全性考慮,必須將(jiang)其充(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)限(xian)制在額定范(fan)圍以內。U4根據連(lian)接在ISET(第5引(yin)腳)的電(dian)(dian)阻(zu)限(xian)制充(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu),圖(tu)1電(dian)(dian)路(lu)中選用(yong)了(le)一個1.87kΩ的電(dian)(dian)阻(zu),將(jiang)最大電(dian)(dian)流(liu)(liu)設(she)置在780mA:

    Ifast=1461V/Rset=1461/1870≈780mA

    電(dian)池電(dian)壓(ya)最(zui)小時,由于(yu)輸(shu)入(ru)(ru)穩定(ding)在(zai)4.5V,U4輸(shu)入(ru)(ru)與輸(shu)出的壓(ya)差最(zui)大,如果此時電(dian)池是以最(zui)大電(dian)流(liu)充電(dian),U4功耗將達到(dao)最(zui)大值。例如,假設電(dian)池電(dian)壓(ya)為2.5V,則對應(ying)的功耗為：

    P=IV=(0.78A)×(4.5V-2.5V)=1.56W

    U4封裝(8引(yin)腳(jiao)薄型DFN-EP,EP表示裸露焊(han)盤)在(zai)(zai)溫度(du)(du)高(gao)(gao)達(da)(da)(da)70℃時可以耗散(san)的(de)(de)(de)(de)(de)最(zui)大功(gong)率是(shi)1.951W,這樣,在(zai)(zai)整(zheng)個(ge)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)范圍(wei)內以780mA的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)應該沒有任何問題。但是(shi),如果IC管芯(xin)由于較(jiao)高(gao)(gao)的(de)(de)(de)(de)(de)環(huan)境溫度(du)(du)或不(bu)良的(de)(de)(de)(de)(de)散(san)熱(re)(re)條(tiao)(tiao)件達(da)(da)(da)到了70℃,U4內部的(de)(de)(de)(de)(de)熱(re)(re)調節(jie)環(huan)路將自動降低(di)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu),這一過程有別于其它充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)IC中的(de)(de)(de)(de)(de)“熱(re)(re)關(guan)斷”,“熱(re)(re)關(guan)斷”方式只是(shi)簡單地(di)中止芯(xin)片中的(de)(de)(de)(de)(de)所(suo)有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路工作,直到晶片溫度(du)(du)降至(zhi)規定的(de)(de)(de)(de)(de)數(shu)值。MAX1507所(suo)采用的(de)(de)(de)(de)(de)方案能夠保證在(zai)(zai)芯(xin)片溫度(du)(du)不(bu)超(chao)出(chu)最(zui)大限(xian)(xian)制范圍(wei)的(de)(de)(de)(de)(de)條(tiao)(tiao)件下提供最(zui)快的(de)(de)(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)速率,隨著電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)(de)(de)升高(gao)(gao),充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)在(zai)(zai)保持(chi)最(zui)高(gao)(gao)溫度(du)(du)的(de)(de)(de)(de)(de)前提下逐漸升高(gao)(gao),直到達(da)(da)(da)到最(zui)大充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。在(zai)(zai)此之后,充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器在(zai)(zai)滿足(zu)芯(xin)片溫度(du)(du)限(xian)(xian)制的(de)(de)(de)(de)(de)條(tiao)(tiao)件下將以最(zui)大充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian),直到電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)達(da)(da)(da)到內部設置的(de)(de)(de)(de)(de)4.2V±1%。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)達(da)(da)(da)到門限(xian)(xian)值后,U4將輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)保持(chi)在(zai)(zai)4.2V,從(cong)而使充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)開始下降。充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)降低(di)到快充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)10%時,充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)指示燈關(guan)閉,表示充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)周期結束。

    如果充電(dian)過程中輸出負載增(zeng)大,例如,用戶在(zai)電(dian)池(chi)充電(dian)時啟動了(le)其它電(dian)路,U4允許返回到(dao)限流(liu)模式。

    測試結果

    圖(tu)1電(dian)路輸(shu)(shu)入(ru)為110V交流(liu)電(dian)源(yuan),輸(shu)(shu)出(chu)為4.14V、740mA負載(zai),效率可達(da)到46%。當負載(zai)電(dian)流(liu)增(zeng)大使電(dian)池(chi)(chi)電(dian)壓降(jiang)至2.7V時,電(dian)路將輸(shu)(shu)出(chu)電(dian)流(liu)限(xian)(xian)制在(zai)802mA,比設置的(de)780mA限(xian)(xian)流(liu)門限(xian)(xian)提高不到3%,在(zai)規定的(de)參數(shu)指標以內(nei)。MAX1507允(yun)許(xu)±8%的(de)變化。當電(dian)池(chi)(chi)電(dian)壓拉至2.5V時,輸(shu)(shu)出(chu)電(dian)流(liu)降(jiang)至76.1mA,在(zai)78mA(780mA的(de)1/10)的(de)3%以內(nei)。U4數(shu)據手冊(ce)中(zhong)規定允(yun)許(xu)±5%的(de)范圍(wei)。輸(shu)(shu)出(chu)短(duan)路時電(dian)路還允(yun)許(xu)返回到該模式(shi)。

    空載(zai)時,輸出(chu)穩定在4.2V左(zuo)右(you),形成一(yi)個三角(jiao)波(bo),在U4輸出(chu)接一(yi)個負載(zai)電(dian)(dian)阻可以消除這個偏差,保(bao)持其連(lian)續性,但會降低系統(tong)效(xiao)率(lv),但對于交流電(dian)(dian)供電(dian)(dian)系統(tong)來說,效(xiao)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(fang)案不需要(yao)任(ren)何(he)額(e)外的控制(zhi)電路(lu)(如微(wei)控制(zhi)器的干預(yu)),也不需要(yao)軟件開(kai)(kai)發。硬件開(kai)(kai)發只(zhi)需對Maxim提(ti)供的標準評估板稍作修改即(ji)可(ke),具有成本低、開(kai)(kai)發周期短(duan)等優(you)勢。

    由于(yu)系統(tong)沒(mei)有60Hz的(de)隔(ge)離變壓器(qi),具有尺寸(cun)小、輕便等特點(dian),可(ke)用于(yu)手機或(huo)其它(ta)手持設備(bei)的(de)充(chong)電。所有熱量均(jun)集中在交流適配器(qi)內,與內置(zhi)充(chong)電器(qi)的(de)手持設備(bei)相比,不需要過多考慮散(san)熱問題。