本文(wen)介(jie)紹了一個單(dan)節鋰離子(Li+)電(dian)池的(de)充(chong)電(dian)方(fang)案(an),該方(fang)案(an)基(ji)于(yu)MAX5022芯片,適(shi)用于(yu)全球的(de)交流電(dian)源,而(er)且無需軟件控制或微處理器干(gan)預就能實現所有的(de)充(chong)電(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(bi)須保證作(zuo)用(yong)到電(dian)(dian)(dian)(dian)池(chi)(chi)上的電(dian)(dian)(dian)(dian)壓(ya)和(he)電(dian)(dian)(dian)(dian)流(liu)最大值(zhi)在規定的范圍內,當電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)維持在最大單節電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya),充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)下降到一(yi)個(ge)較(jiao)低(di)值(zhi)時,充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器終止充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)。Li+和(he)鉛(qian)酸電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器的區別在于(yu)所允(yun)許的充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)、最大電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya),另(ling)外鉛(qian)酸電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器一(yi)般具有浮(fu)充(chong)(chong)(chong)(chong)能力(浮(fu)充(chong)(chong)(chong)(chong)是為了(le)補充(chong)(chong)(chong)(chong)鉛(qian)酸電(dian)(dian)(dian)(dian)池(chi)(chi)的自(zi)放電(dian)(dian)(dian)(dian),而對一(yi)個(ge)已經完(wan)全(quan)充(chong)(chong)(chong)(chong)滿的電(dian)(dian)(dian)(dian)池(chi)(chi)繼續(xu)輸入充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)的技(ji)術(shu)),Li+電(dian)(dian)(dian)(dian)池(chi)(chi)的自(zi)放電(dian)(dian)(dian)(dian)非常低(di),所以不需要浮(fu)充(chong)(chong)(chong)(chong)。   

    Li+電池   

    為便攜式(shi)產品選擇電(dian)(dian)(dian)(dian)池(chi)時,最重(zhong)(zhong)要的(de)是高(gao)能(neng)量密度、尺寸、重(zhong)(zhong)量和價(jia)格。迄今為止,Li+電(dian)(dian)(dian)(dian)池(chi)在最為流(liu)行的(de)電(dian)(dian)(dian)(dian)池(chi)中能(neng)夠提供最高(gao)的(de)體積和能(neng)量密度,但(dan)其每(mei)瓦時的(de)成本也(ye)較高(gao)。鉛酸電(dian)(dian)(dian)(dian)池(chi)的(de)每(mei)瓦時成本最低,但(dan)比較笨重(zhong)(zhong)。本文以Li+電(dian)(dian)(dian)(dian)池(chi)為例討(tao)論充(chong)電(dian)(dian)(dian)(dian)器的(de)設計,它(ta)在便攜式(shi)產品中已(yi)經被(bei)普(pu)遍使用。我們(men)選擇780mA的(de)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)和4.2V的(de)終止電(dian)(dian)(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(chu)理器(qi)干預,輸入電(dian)源可以采(cai)用全球范(fan)圍的(de)(de)(de)(de)任何交(jiao)流電(dian)源,省(sheng)去了大(da)體(ti)積60Hz變壓器(qi),而且可提供單節Li+電(dian)池(chi)(chi)所要求的(de)(de)(de)(de)精確的(de)(de)(de)(de)充電(dian)電(dian)壓和電(dian)流。充電(dian)器(qi)IC(U4)集成了全面的(de)(de)(de)(de)保(bao)護功(gong)能(neng)(電(dian)壓、電(dian)流和自保(bao)護),確保(bao)Li+電(dian)池(chi)(chi)的(de)(de)(de)(de)安全充電(dian)。   

    假(jia)設(she)Li+電(dian)(dian)(dian)池帶有過(guo)流、過(guo)壓和過(guo)熱保護(hu),這些保護(hu)特性(xing)在(zai)電(dian)(dian)(dian)池包里是(shi)必需的,因為(wei)充(chong)電(dian)(dian)(dian)期間一旦電(dian)(dian)(dian)路(lu)出現故障,Li+電(dian)(dian)(dian)池將存在(zai)很大的危(wei)險性(xing),過(guo)流、過(guo)壓或(huo)溫度(du)過(guo)高都(dou)有可能造(zao)成Li+電(dian)(dian)(dian)池爆炸。   

    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(zheng)管(guan),結合其熱(re)控(kong)制環路(lu)提供快速充電。   

    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(dian)源端(duan)MAX5022評估(gu)板不需要作任何修改(gai)(gai),隔離(li)端(duan)只需對評估(gu)板的電(dian)阻值稍(shao)作修改(gai)(gai)。   

    對于(yu)更大(da)(da)功率的(de)(de)(de)應用,只(zhi)需選(xuan)取(qu)功率較大(da)(da)的(de)(de)(de)開關管(guan)和能夠處理(li)更大(da)(da)功率的(de)(de)(de)變(bian)壓(ya)器(qi)(qi)(qi)即可。圖1所(suo)示電(dian)路要求(qiu)充電(dian)電(dian)流為780mA,最大(da)(da)電(dian)池電(dian)壓(ya)為4.2V。對充電(dian)電(dian)源的(de)(de)(de)要求(qiu)與MAX5022評估板(ban)(ban)所(suo)提供的(de)(de)(de)輸出相吻合：5V@1A,因此(ci),不需要更換評估板(ban)(ban)的(de)(de)(de)晶體管(guan)和變(bian)壓(ya)器(qi)(qi)(qi)。U4采用SOT23封裝(zhuang),所(suo)以,充電(dian)器(qi)(qi)(qi)的(de)(de)(de)尺(chi)(chi)(chi)寸(cun)在(zai)很(hen)大(da)(da)程度(du)上取(qu)決于(yu)應用對充電(dian)電(dian)源的(de)(de)(de)需求(qiu)。變(bian)壓(ya)器(qi)(qi)(qi)是電(dian)路中尺(chi)(chi)(chi)寸(cun)最大(da)(da)的(de)(de)(de)元件,由于(yu)開關控制器(qi)(qi)(qi)的(de)(de)(de)工(gong)作頻率大(da)(da)于(yu)250kHz,允許(xu)系(xi)統選(xuan)用小尺(chi)(chi)(chi)寸(cun)的(de)(de)(de)變(bian)壓(ya)器(qi)(qi)(qi)。    

    上電(dian)(dian)(dian)時(shi),在開關控(kong)制(zhi)器工作之前,U1調節器直接通(tong)(tong)過泄漏電(dian)(dian)(dian)阻R1、R2從整流(liu)通(tong)(tong)路吸(xi)取少量(liang)的(de)(de)電(dian)(dian)(dian)流(liu),兩(liang)個電(dian)(dian)(dian)阻阻值保證每個電(dian)(dian)(dian)阻上的(de)(de)壓(ya)(ya)(ya)降不會(hui)超出每個電(dian)(dian)(dian)阻的(de)(de)容限,Vin引腳電(dian)(dian)(dian)壓(ya)(ya)(ya)不會(hui)超出其28V額(e)定值(30V為絕對最(zui)大值),U1在輸(shu)入電(dian)(dian)(dian)壓(ya)(ya)(ya)達(da)到24V時(shi)開始開關操作,并吸(xi)取更大的(de)(de)電(dian)(dian)(dian)流(liu)(高(gao)于(yu)R1、R2所能(neng)(neng)提供(gong)的(de)(de)電(dian)(dian)(dian)流(liu)),在變壓(ya)(ya)(ya)器副(fu)邊線圈能(neng)(neng)夠(gou)提供(gong)足夠(gou)的(de)(de)能(neng)(neng)量(liang)之前,額(e)外的(de)(de)電(dian)(dian)(dian)流(liu)由Vin引腳的(de)(de)旁路電(dian)(dian)(dian)容供(gong)給。這(zhe)種處理方式(shi)能(neng)(neng)夠(gou)適(shi)合較寬的(de)(de)輸(shu)入電(dian)(dian)(dian)壓(ya)(ya)(ya)范(fan)圍,對效(xiao)率的(de)(de)影響(xiang)也很小,這(zhe)是因為在啟(qi)動過程(cheng)中只需極(ji)小的(de)(de)供(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(典型值為50uA)。  

    為了(le)防止U1的(de)Vin引(yin)腳出現過壓(ya),可(ke)(ke)以在Vin與地之間(jian)接一(yi)個(ge)26V至(zhi)30V的(de)齊納管,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(da)值(zhi),低(di)于(yu)該引(yin)腳所(suo)(suo)允許的(de)最大(da)絕對電(dian)壓(ya)。如(ru)果器件沒有啟動正常的(de)開(kai)關操作,則可(ke)(ke)認為電(dian)路發生了(le)某些問題,所(suo)(suo)以,這(zhe)一(yi)保護(hu)措施對于(yu)U1來說并(bing)不是必需(xu)的(de)。    

    U1是一款電(dian)(dian)流模式(shi)PWM控制器,具有(you)逐周期(qi)限流電(dian)(dian)路,必要時其(qi)占(zhan)空(kong)比可以(yi)提高到75%,非常適合圖1所示的反激拓撲。原邊開關(guan)電(dian)(dian)流檢測采用尺寸為1206的1.78Ω電(dian)(dian)阻(zu)(R7),該電(dian)(dian)阻(zu)限制了變(bian)壓器原邊的最大電(dian)(dian)流。固定開關(guan)頻率和最大占(zhan)空(kong)比限制使得最大限流具有(you)輸(shu)出短路保護功能。  

    一旦(dan)短路(lu)輸出(chu)造(zao)成電路(lu)達到(dao)了上(shang)述限制條(tiao)件(jian),第(di)三組(zu)線圈將無法提供10V以上(shang)的電壓(UVLO的低電壓門限),U1將再次進入(ru)啟動狀態,停(ting)止開關(guan)操作(zuo)。短路(lu)故障解除后系統會自動恢復(fu)正常(chang)的工作(zuo)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降(jiang)低(di)功率損耗。  

    當(dang)調節(jie)點電(dian)(dian)(dian)壓(ya)高(gao)于1.24V時,并聯(lian)型(xing)穩(wen)(wen)壓(ya)器將吸入(ru)電(dian)(dian)(dian)流,導通(tong)(tong)光(guang)耦LED,原邊(bian)的(de)(de)(de)(de)光(guang)敏晶體管(guan)將處于發光(guang)狀(zhuang)態。U1的(de)(de)(de)(de)OPTO輸入(ru)引(yin)腳(jiao)(jiao)用(yong)于直接連接光(guang)敏晶體管(guan),以極其簡(jian)單的(de)(de)(de)(de)方(fang)式構成閉合環路。光(guang)敏晶體管(guan)導通(tong)(tong)時,OPTO引(yin)腳(jiao)(jiao)被拉低(di),內部比(bi)較(jiao)器在(zai)它的(de)(de)(de)(de)一個(ge)輸入(ru)端檢測到較(jiao)低(di)的(de)(de)(de)(de)電(dian)(dian)(dian)壓(ya),比(bi)較(jiao)器的(de)(de)(de)(de)另(ling)一輸入(ru)電(dian)(dian)(dian)流檢測引(yin)腳(jiao)(jiao)(CS)的(de)(de)(de)(de)峰值(zhi)電(dian)(dian)(dian)壓(ya),OPTO引(yin)腳(jiao)(jiao)的(de)(de)(de)(de)低(di)電(dian)(dian)(dian)壓(ya)將在(zai)每個(ge)周期直接限(xian)制功率MOSFETN1的(de)(de)(de)(de)峰值(zhi)電(dian)(dian)(dian)流。由于U1是一個(ge)PWM控制器,電(dian)(dian)(dian)流限(xian)制使得電(dian)(dian)(dian)壓(ya)調節(jie)受作(zuo)用(yong)在(zai)N1上的(de)(de)(de)(de)占空比(bi)(導通(tong)(tong)時間(jian)與斷開時間(jian)的(de)(de)(de)(de)比(bi)值(zhi))的(de)(de)(de)(de)影響,環路穩(wen)(wen)定性通(tong)(tong)過調節(jie)R11和C12來保證。R10和C5(連接在(zai)U3的(de)(de)(de)(de)第(di)3和第(di)4引(yin)腳(jiao)(jiao))可消除穩(wen)(wen)定工作(zuo)情況下的(de)(de)(de)(de)噪聲干擾。   

    U4的工作特點   

    U4是一款用于單節Li+電池充電、功(gong)能完備的充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器,采用線(xian)性充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)模式,內置調整管和(he)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流檢測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路。另外,它(ta)還集成了一個反向抑制二極管,在(zai)去掉(diao)輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源時可防止(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池方(fang)向放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。接入一個深度放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池時,U4能夠檢測到(dao)(dao)低電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(低于2.5V),這樣,U4將首先啟(qi)動涓(juan)流充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程,在(zai)快(kuai)充(chong)(chong)(chong)(chong)周(zhou)期的1/10時間段對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池進行涓(juan)流充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian),直到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓上升(sheng)到(dao)(dao)2.5V以上。在(zai)涓(juan)流充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)到(dao)(dao)快(kuai)速充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)轉換時,軟啟(qi)動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路迫使(shi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流在(zai)3ms時間內緩慢上升(sheng),避免較大的浪(lang)涌電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流拉低輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源。   

   上述功能的(de)實施不(bu)需要微控(kong)制器的(de)監(jian)管,而(er)且,U4還具有可(ke)編程的(de)溫度限制功能,我們會(hui)在下面(mian)就這一(yi)點進行詳(xiang)細(xi)討論。用(yong)一(yi)個電(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(liang)端的(de)電(dian)(dian)(dian)壓(ya)與充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)成正(zheng)比,通(tong)過監(jian)視(shi)該(gai)電(dian)(dian)(dian)壓(ya)即可(ke)連續跟蹤充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu),更為復雜(za)的(de)系統(tong)也可(ke)以采用(yong)ADC跟蹤監(jian)視(shi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)。   

    Maxim還提供有(you)另一款(kuan)與MAX1507非常相似的充電器―MAX1555,這款(kuan)IC能夠在沒有(you)交流電源(yuan)的情(qing)況下從USB主機獲得充電電源(yuan)。  

    電流調節

    如果把Li+電(dian)(dian)(dian)池(chi)直接(jie)與(yu)一個低阻(zu)電(dian)(dian)(dian)壓源連(lian)接(jie),充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流將不(bu)受(shou)任何(he)限制(zhi),這種狀況(kuang)會對電(dian)(dian)(dian)池(chi)及其周圍環境造成災難性的(de)損害,從Li+電(dian)(dian)(dian)池(chi)的(de)安全性考慮(lv),必(bi)須將其充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流限制(zhi)在(zai)額定范圍以內。U4根據連(lian)接(jie)在(zai)ISET(第5引(yin)腳)的(de)電(dian)(dian)(dian)阻(zu)限制(zhi)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流,圖1電(dian)(dian)(dian)路(lu)中選用(yong)了一個1.87kΩ的(de)電(dian)(dian)(dian)阻(zu),將最(zui)大電(dian)(dian)(dian)流設置在(zai)780mA:

    Ifast=1461V/Rset=1461/1870≈780mA

    電(dian)(dian)池電(dian)(dian)壓最(zui)(zui)小(xiao)時,由于(yu)輸(shu)入穩定在4.5V,U4輸(shu)入與(yu)輸(shu)出的壓差(cha)最(zui)(zui)大,如果此時電(dian)(dian)池是(shi)以最(zui)(zui)大電(dian)(dian)流(liu)充(chong)電(dian)(dian),U4功耗(hao)將達到最(zui)(zui)大值(zhi)。例如,假設電(dian)(dian)池電(dian)(dian)壓為(wei)2.5V,則對應的功耗(hao)為(wei)：

    P=IV=(0.78A)×(4.5V-2.5V)=1.56W

    U4封裝(8引腳(jiao)薄(bo)型DFN-EP,EP表示裸露焊盤)在(zai)(zai)(zai)溫(wen)度(du)高達(da)70℃時可以耗散(san)的(de)(de)(de)(de)(de)最(zui)(zui)大(da)功率是1.951W,這樣,在(zai)(zai)(zai)整個電(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)范圍內以780mA的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)應該(gai)沒有(you)任何問(wen)題。但是,如果IC管芯由于(yu)較高的(de)(de)(de)(de)(de)環境溫(wen)度(du)或不良(liang)的(de)(de)(de)(de)(de)散(san)熱(re)條件達(da)到(dao)(dao)(dao)了70℃,U4內部的(de)(de)(de)(de)(de)熱(re)調節(jie)環路(lu)將(jiang)自動降低充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu),這一(yi)過程有(you)別于(yu)其它充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)IC中的(de)(de)(de)(de)(de)“熱(re)關(guan)斷(duan)”,“熱(re)關(guan)斷(duan)”方(fang)(fang)式(shi)只是簡單(dan)地中止(zhi)芯片(pian)中的(de)(de)(de)(de)(de)所(suo)有(you)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)工(gong)作,直到(dao)(dao)(dao)晶(jing)片(pian)溫(wen)度(du)降至規定的(de)(de)(de)(de)(de)數值(zhi)。MAX1507所(suo)采用的(de)(de)(de)(de)(de)方(fang)(fang)案能夠保證在(zai)(zai)(zai)芯片(pian)溫(wen)度(du)不超(chao)出最(zui)(zui)大(da)限(xian)制范圍的(de)(de)(de)(de)(de)條件下提(ti)供最(zui)(zui)快(kuai)的(de)(de)(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)速率,隨著電(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)(de)(de)升高,充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)在(zai)(zai)(zai)保持(chi)最(zui)(zui)高溫(wen)度(du)的(de)(de)(de)(de)(de)前提(ti)下逐漸升高,直到(dao)(dao)(dao)達(da)到(dao)(dao)(dao)最(zui)(zui)大(da)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。在(zai)(zai)(zai)此之后(hou),充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器在(zai)(zai)(zai)滿足芯片(pian)溫(wen)度(du)限(xian)制的(de)(de)(de)(de)(de)條件下將(jiang)以最(zui)(zui)大(da)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)(dian),直到(dao)(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)達(da)到(dao)(dao)(dao)內部設(she)置的(de)(de)(de)(de)(de)4.2V±1%。電(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)達(da)到(dao)(dao)(dao)門限(xian)值(zhi)后(hou),U4將(jiang)輸出電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)保持(chi)在(zai)(zai)(zai)4.2V,從(cong)而使充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)開始下降。充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)降低到(dao)(dao)(dao)快(kuai)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)10%時,充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)指示燈關(guan)閉,表示充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)周期結束。

    如果(guo)充電過(guo)程中輸出負載增大(da),例如,用戶在電池充電時(shi)啟(qi)動了其它電路,U4允許返回到(dao)限流模式。

    測試結果

    圖1電(dian)路(lu)(lu)輸(shu)(shu)入為(wei)110V交流(liu)(liu)電(dian)源,輸(shu)(shu)出(chu)為(wei)4.14V、740mA負載(zai),效(xiao)率(lv)可(ke)達到46%。當負載(zai)電(dian)流(liu)(liu)增大使電(dian)池電(dian)壓(ya)降至(zhi)2.7V時,電(dian)路(lu)(lu)將(jiang)輸(shu)(shu)出(chu)電(dian)流(liu)(liu)限制在(zai)802mA,比(bi)設置的780mA限流(liu)(liu)門限提高不到3%,在(zai)規定的參數(shu)指標以(yi)內。MAX1507允(yun)許(xu)±8%的變(bian)化。當電(dian)池電(dian)壓(ya)拉至(zhi)2.5V時,輸(shu)(shu)出(chu)電(dian)流(liu)(liu)降至(zhi)76.1mA,在(zai)78mA(780mA的1/10)的3%以(yi)內。U4數(shu)據手冊中規定允(yun)許(xu)±5%的范圍。輸(shu)(shu)出(chu)短(duan)路(lu)(lu)時電(dian)路(lu)(lu)還允(yun)許(xu)返(fan)回到該模式(shi)。

    空載時,輸出穩(wen)定在4.2V左右,形成一(yi)個三角波,在U4輸出接(jie)一(yi)個負載電阻可以消除這(zhe)個偏差,保持(chi)其(qi)連續(xu)性,但(dan)會降低系(xi)統(tong)(tong)效(xiao)(xiao)率,但(dan)對于交流電供電系(xi)統(tong)(tong)來說,效(xiao)(xiao)率并不重要。

    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(gai)方(fang)案(an)不需(xu)要任(ren)何額外(wai)的控制(zhi)電路(如微控制(zhi)器的干預),也不需(xu)要軟件開(kai)發。硬件開(kai)發只(zhi)需(xu)對Maxim提供的標準評估板稍作修改即可(ke),具(ju)有(you)成本低、開(kai)發周期短等優勢。

    由(you)于系統沒有(you)60Hz的(de)隔離(li)變壓器(qi),具有(you)尺寸小、輕便等特點(dian),可用于手機或其它手持設備(bei)的(de)充電。所(suo)有(you)熱量均(jun)集(ji)中在交流適配器(qi)內,與內置充電器(qi)的(de)手持設備(bei)相比,不需要過多考慮散熱問題。