本文(wen)介紹了一個單節(jie)鋰離(li)子(Li+)電(dian)池(chi)的充電(dian)方(fang)案,該方(fang)案基于MAX5022芯片,適(shi)用于全球的交流(liu)電(dian)源,而且無需(xu)軟件(jian)控制或微處理器(qi)干預就能(neng)實現所(suo)有的充電(dian)功能(neng)。   

    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(xu)保證作(zuo)用(yong)到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)上(shang)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)和(he)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)最(zui)大(da)值(zhi)(zhi)在(zai)(zai)規(gui)定的(de)(de)(de)范圍內,當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)維持(chi)在(zai)(zai)最(zui)大(da)單節(jie)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya),充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)下降到(dao)(dao)一個較低值(zhi)(zhi)時(shi),充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)終止充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。Li+和(he)鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)的(de)(de)(de)區別在(zai)(zai)于所(suo)允許(xu)的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)、最(zui)大(da)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya),另(ling)外鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)一般具(ju)有浮充(chong)(chong)(chong)能力(浮充(chong)(chong)(chong)是為(wei)了補充(chong)(chong)(chong)鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)(de)自(zi)放電(dian)(dian)(dian)(dian)(dian)(dian),而(er)對一個已經完全(quan)充(chong)(chong)(chong)滿的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)繼續輸(shu)入充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)技術),Li+電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)(de)自(zi)放電(dian)(dian)(dian)(dian)(dian)(dian)非常低,所(suo)以(yi)不需要浮充(chong)(chong)(chong)。   

    Li+電(dian)池   

    為(wei)便攜(xie)式產品(pin)選擇電池(chi)(chi)時(shi),最(zui)重(zhong)要的(de)(de)是高(gao)能量(liang)密(mi)度、尺寸、重(zhong)量(liang)和價格(ge)。迄今為(wei)止,Li+電池(chi)(chi)在最(zui)為(wei)流行的(de)(de)電池(chi)(chi)中(zhong)能夠提供最(zui)高(gao)的(de)(de)體(ti)積和能量(liang)密(mi)度,但其每(mei)瓦時(shi)的(de)(de)成(cheng)本(ben)(ben)也較高(gao)。鉛(qian)酸電池(chi)(chi)的(de)(de)每(mei)瓦時(shi)成(cheng)本(ben)(ben)最(zui)低,但比(bi)較笨重(zhong)。本(ben)(ben)文以Li+電池(chi)(chi)為(wei)例討(tao)論充電器的(de)(de)設(she)計,它在便攜(xie)式產品(pin)中(zhong)已經被(bei)普遍使(shi)用。我們選擇780mA的(de)(de)充電電流和4.2V的(de)(de)終止電壓。

    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(wei)處理器干(gan)預,輸入電(dian)(dian)(dian)(dian)源可(ke)以采用全球范圍的(de)任何交流(liu)電(dian)(dian)(dian)(dian)源,省去了(le)大體積60Hz變(bian)壓(ya)(ya)(ya)器,而且可(ke)提供單節Li+電(dian)(dian)(dian)(dian)池(chi)所要求的(de)精確(que)的(de)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)和電(dian)(dian)(dian)(dian)流(liu)。充電(dian)(dian)(dian)(dian)器IC(U4)集成了(le)全面(mian)的(de)保(bao)(bao)護(hu)功能(neng)(電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)、電(dian)(dian)(dian)(dian)流(liu)和自保(bao)(bao)護(hu)),確(que)保(bao)(bao)Li+電(dian)(dian)(dian)(dian)池(chi)的(de)安全充電(dian)(dian)(dian)(dian)。   

    假(jia)設Li+電池(chi)(chi)(chi)帶有過流、過壓(ya)和過熱保護(hu),這些保護(hu)特性在(zai)電池(chi)(chi)(chi)包里(li)是必需的(de),因為充電期(qi)間一旦(dan)電路出現(xian)故障,Li+電池(chi)(chi)(chi)將存在(zai)很大的(de)危險性,過流、過壓(ya)或溫度(du)過高都有可能造成Li+電池(chi)(chi)(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,結合其熱控制環路提(ti)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(de)電源端MAX5022評(ping)估板不需要作任(ren)何修(xiu)改,隔離端只需對評(ping)估板的(de)電阻值稍作修(xiu)改。   

    對(dui)于更大功(gong)率(lv)(lv)的(de)(de)(de)(de)(de)應(ying)用(yong),只(zhi)需(xu)(xu)選取功(gong)率(lv)(lv)較大的(de)(de)(de)(de)(de)開關管和(he)能夠處理(li)更大功(gong)率(lv)(lv)的(de)(de)(de)(de)(de)變(bian)壓(ya)器即可。圖1所(suo)示(shi)電(dian)(dian)(dian)路(lu)(lu)要(yao)求(qiu)充電(dian)(dian)(dian)電(dian)(dian)(dian)流為780mA,最大電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)為4.2V。對(dui)充電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)(de)要(yao)求(qiu)與MAX5022評(ping)估板(ban)所(suo)提供(gong)的(de)(de)(de)(de)(de)輸出(chu)相吻合(he)：5V@1A,因此(ci),不需(xu)(xu)要(yao)更換評(ping)估板(ban)的(de)(de)(de)(de)(de)晶(jing)體管和(he)變(bian)壓(ya)器。U4采(cai)用(yong)SOT23封裝,所(suo)以(yi),充電(dian)(dian)(dian)器的(de)(de)(de)(de)(de)尺(chi)寸在(zai)很大程度上取決于應(ying)用(yong)對(dui)充電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)(de)需(xu)(xu)求(qiu)。變(bian)壓(ya)器是電(dian)(dian)(dian)路(lu)(lu)中尺(chi)寸最大的(de)(de)(de)(de)(de)元件,由(you)于開關控(kong)制器的(de)(de)(de)(de)(de)工作頻(pin)率(lv)(lv)大于250kHz,允許系統選用(yong)小尺(chi)寸的(de)(de)(de)(de)(de)變(bian)壓(ya)器。    

    上電(dian)(dian)時(shi),在開(kai)(kai)關控制器工(gong)作之(zhi)前,U1調節器直接通過泄(xie)漏(lou)電(dian)(dian)阻R1、R2從整流通路(lu)吸(xi)取少量的電(dian)(dian)流,兩個電(dian)(dian)阻阻值保證每個電(dian)(dian)阻上的壓(ya)(ya)降不會(hui)超(chao)出每個電(dian)(dian)阻的容限,Vin引腳(jiao)(jiao)電(dian)(dian)壓(ya)(ya)不會(hui)超(chao)出其28V額(e)定值(30V為(wei)絕對最大(da)值),U1在輸入電(dian)(dian)壓(ya)(ya)達(da)到(dao)24V時(shi)開(kai)(kai)始開(kai)(kai)關操(cao)作,并吸(xi)取更(geng)大(da)的電(dian)(dian)流(高于(yu)R1、R2所能(neng)(neng)提供(gong)的電(dian)(dian)流),在變壓(ya)(ya)器副(fu)邊(bian)線圈能(neng)(neng)夠(gou)(gou)提供(gong)足夠(gou)(gou)的能(neng)(neng)量之(zhi)前,額(e)外的電(dian)(dian)流由Vin引腳(jiao)(jiao)的旁(pang)路(lu)電(dian)(dian)容供(gong)給。這種(zhong)處(chu)理方式(shi)能(neng)(neng)夠(gou)(gou)適合較(jiao)寬的輸入電(dian)(dian)壓(ya)(ya)范圍,對效率的影(ying)響也很(hen)小,這是因(yin)為(wei)在啟(qi)動過程中只需極小的供(gong)電(dian)(dian)電(dian)(dian)流(典型值為(wei)50uA)。  

    為了防止U1的Vin引腳(jiao)出現過壓(ya),可以在Vin與(yu)地之間接一(yi)(yi)個26V至30V的齊納管,電(dian)壓(ya)值需要高于欠壓(ya)鎖存電(dian)壓(ya)的最大值,低于該引腳(jiao)所允(yun)許的最大絕對電(dian)壓(ya)。如果器件(jian)沒有啟動正常的開關(guan)操作,則可認為電(dian)路(lu)發生了某些問題,所以,這一(yi)(yi)保護措施對于U1來說并(bing)不是(shi)必需的。    

    U1是(shi)一款電流模式(shi)PWM控(kong)制器(qi),具(ju)有(you)逐周期(qi)限流電路,必要時其占空(kong)比(bi)可以提高到75%,非常(chang)適合圖(tu)1所示(shi)的反激(ji)拓撲。原邊開(kai)(kai)關電流檢測采(cai)用尺寸(cun)為1206的1.78Ω電阻(zu)(R7),該電阻(zu)限制了變壓器(qi)原邊的最大電流。固(gu)定(ding)開(kai)(kai)關頻率和最大占空(kong)比(bi)限制使得最大限流具(ju)有(you)輸出(chu)短路保護功能。  

    一(yi)旦短(duan)路輸(shu)出造成電(dian)路達(da)到了上述限(xian)制條件,第三組線圈將無法提供(gong)10V以上的電(dian)壓(UVLO的低(di)電(dian)壓門限(xian)),U1將再次進入啟(qi)動狀態,停止開關操作。短(duan)路故障解(jie)除后系統會自動恢復正常的工(gong)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(gong)電(dian)有(you)助于降低功率損耗。  

    當調節點電(dian)(dian)(dian)(dian)壓(ya)高于1.24V時,并聯型(xing)穩(wen)壓(ya)器(qi)(qi)將吸入(ru)電(dian)(dian)(dian)(dian)流(liu)(liu),導通(tong)光(guang)耦LED,原邊(bian)的(de)(de)(de)光(guang)敏(min)晶體(ti)(ti)管將處于發光(guang)狀態。U1的(de)(de)(de)OPTO輸(shu)入(ru)引(yin)腳用(yong)于直接(jie)連接(jie)光(guang)敏(min)晶體(ti)(ti)管,以極其簡單的(de)(de)(de)方式構(gou)成閉合環(huan)路。光(guang)敏(min)晶體(ti)(ti)管導通(tong)時,OPTO引(yin)腳被拉低,內部比較(jiao)器(qi)(qi)在它(ta)的(de)(de)(de)一個(ge)(ge)(ge)輸(shu)入(ru)端(duan)檢(jian)測到較(jiao)低的(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya),比較(jiao)器(qi)(qi)的(de)(de)(de)另一輸(shu)入(ru)電(dian)(dian)(dian)(dian)流(liu)(liu)檢(jian)測引(yin)腳(CS)的(de)(de)(de)峰值電(dian)(dian)(dian)(dian)壓(ya),OPTO引(yin)腳的(de)(de)(de)低電(dian)(dian)(dian)(dian)壓(ya)將在每個(ge)(ge)(ge)周期直接(jie)限制(zhi)功率MOSFETN1的(de)(de)(de)峰值電(dian)(dian)(dian)(dian)流(liu)(liu)。由于U1是(shi)一個(ge)(ge)(ge)PWM控(kong)制(zhi)器(qi)(qi),電(dian)(dian)(dian)(dian)流(liu)(liu)限制(zhi)使得電(dian)(dian)(dian)(dian)壓(ya)調節受(shou)作(zuo)用(yong)在N1上的(de)(de)(de)占空比(導通(tong)時間(jian)與(yu)斷開時間(jian)的(de)(de)(de)比值)的(de)(de)(de)影響(xiang),環(huan)路穩(wen)定性通(tong)過調節R11和C12來保證(zheng)。R10和C5(連接(jie)在U3的(de)(de)(de)第3和第4引(yin)腳)可消除(chu)穩(wen)定工作(zuo)情(qing)況下的(de)(de)(de)噪聲(sheng)干擾。   

    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)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器,采用線性充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)模式,內(nei)置調整管(guan)(guan)和電(dian)(dian)(dian)(dian)(dian)(dian)流檢(jian)測電(dian)(dian)(dian)(dian)(dian)(dian)路。另外(wai),它(ta)還集成了一(yi)個(ge)反向(xiang)抑制(zhi)二(er)極管(guan)(guan),在去(qu)掉輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)源時(shi)可防止電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)方向(xiang)放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)。接(jie)入(ru)一(yi)個(ge)深(shen)度放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)時(shi),U4能夠檢(jian)測到(dao)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(低(di)于2.5V),這樣,U4將(jiang)首先(xian)啟動(dong)(dong)涓流充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過程,在快充(chong)(chong)周期的(de)1/10時(shi)間段對電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行涓流充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian),直到(dao)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓上升到(dao)2.5V以上。在涓流充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)到(dao)快速充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)轉換時(shi),軟啟動(dong)(dong)電(dian)(dian)(dian)(dian)(dian)(dian)路迫使充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流在3ms時(shi)間內(nei)緩慢上升,避免較(jiao)大(da)的(de)浪(lang)涌電(dian)(dian)(dian)(dian)(dian)(dian)流拉低(di)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)源。   

   上述功能(neng)(neng)的(de)(de)(de)實施(shi)不需要微控(kong)制器的(de)(de)(de)監(jian)管,而且,U4還具有可編程的(de)(de)(de)溫度限制功能(neng)(neng),我們會在下面就這一點進行詳細(xi)討(tao)論。用一個電(dian)(dian)(dian)阻(zu)設置最大充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流,電(dian)(dian)(dian)阻(zu)兩端的(de)(de)(de)電(dian)(dian)(dian)壓與(yu)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流成正(zheng)比,通過(guo)監(jian)視該電(dian)(dian)(dian)壓即可連續跟(gen)(gen)蹤充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流,更為復雜的(de)(de)(de)系統也可以采用ADC跟(gen)(gen)蹤監(jian)視充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流。   

    Maxim還提(ti)供(gong)有另一款(kuan)(kuan)與MAX1507非常相似的充(chong)電(dian)器―MAX1555,這款(kuan)(kuan)IC能(neng)夠在(zai)沒(mei)有交流電(dian)源的情況下(xia)從USB主(zhu)機獲得充(chong)電(dian)電(dian)源。  

    電流調節

    如果把(ba)Li+電(dian)(dian)(dian)(dian)池(chi)(chi)直接與一個(ge)低阻(zu)(zu)電(dian)(dian)(dian)(dian)壓源連接,充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)將(jiang)不受任何限制(zhi)(zhi),這種狀(zhuang)況會對電(dian)(dian)(dian)(dian)池(chi)(chi)及(ji)其周圍環境(jing)造(zao)成災難性(xing)(xing)的損害,從Li+電(dian)(dian)(dian)(dian)池(chi)(chi)的安全性(xing)(xing)考慮,必(bi)須將(jiang)其充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)限制(zhi)(zhi)在(zai)額定范圍以內。U4根據連接在(zai)ISET(第(di)5引腳(jiao))的電(dian)(dian)(dian)(dian)阻(zu)(zu)限制(zhi)(zhi)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu),圖1電(dian)(dian)(dian)(dian)路(lu)中選用了一個(ge)1.87kΩ的電(dian)(dian)(dian)(dian)阻(zu)(zu),將(jiang)最(zui)大(da)電(dian)(dian)(dian)(dian)流(liu)(liu)設(she)置在(zai)780mA:

    Ifast=1461V/Rset=1461/1870≈780mA

    電(dian)池電(dian)壓(ya)最小時,由(you)于輸入穩定在4.5V,U4輸入與輸出的(de)壓(ya)差(cha)最大(da),如果(guo)此時電(dian)池是以最大(da)電(dian)流充電(dian),U4功耗(hao)將達到最大(da)值(zhi)。例如,假設電(dian)池電(dian)壓(ya)為(wei)2.5V,則(ze)對應(ying)的(de)功耗(hao)為(wei)：

    P=IV=(0.78A)×(4.5V-2.5V)=1.56W

    U4封(feng)裝(8引腳(jiao)薄(bo)型DFN-EP,EP表(biao)示裸露焊盤)在(zai)(zai)溫(wen)(wen)度高達(da)70℃時可以(yi)耗散的(de)(de)(de)最(zui)(zui)大(da)功率是1.951W,這樣,在(zai)(zai)整個電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(ya)范(fan)(fan)圍內以(yi)780mA的(de)(de)(de)電(dian)(dian)(dian)(dian)流充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)應該沒有(you)任何問題(ti)。但是,如(ru)果IC管芯由于較高的(de)(de)(de)環(huan)境溫(wen)(wen)度或不良(liang)的(de)(de)(de)散熱(re)(re)條件達(da)到(dao)(dao)了70℃,U4內部(bu)的(de)(de)(de)熱(re)(re)調節環(huan)路將自動(dong)降(jiang)低充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流,這一(yi)過(guo)程有(you)別于其它充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)IC中(zhong)的(de)(de)(de)“熱(re)(re)關(guan)斷”,“熱(re)(re)關(guan)斷”方式只是簡單(dan)地中(zhong)止芯片(pian)(pian)中(zhong)的(de)(de)(de)所有(you)電(dian)(dian)(dian)(dian)路工作,直(zhi)到(dao)(dao)晶片(pian)(pian)溫(wen)(wen)度降(jiang)至規定(ding)的(de)(de)(de)數值(zhi)。MAX1507所采用(yong)的(de)(de)(de)方案能夠保證(zheng)在(zai)(zai)芯片(pian)(pian)溫(wen)(wen)度不超出最(zui)(zui)大(da)限(xian)制(zhi)范(fan)(fan)圍的(de)(de)(de)條件下提供最(zui)(zui)快的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)速率,隨(sui)著電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)升高,充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流在(zai)(zai)保持最(zui)(zui)高溫(wen)(wen)度的(de)(de)(de)前提下逐漸升高,直(zhi)到(dao)(dao)達(da)到(dao)(dao)最(zui)(zui)大(da)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流。在(zai)(zai)此之(zhi)后,充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)在(zai)(zai)滿足(zu)芯片(pian)(pian)溫(wen)(wen)度限(xian)制(zhi)的(de)(de)(de)條件下將以(yi)最(zui)(zui)大(da)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流對(dui)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian),直(zhi)到(dao)(dao)電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(ya)達(da)到(dao)(dao)內部(bu)設(she)置(zhi)的(de)(de)(de)4.2V±1%。電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(ya)達(da)到(dao)(dao)門限(xian)值(zhi)后,U4將輸出電(dian)(dian)(dian)(dian)壓(ya)(ya)保持在(zai)(zai)4.2V,從而使充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流開始下降(jiang)。充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流降(jiang)低到(dao)(dao)快充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)流的(de)(de)(de)10%時,充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)指示燈關(guan)閉,表(biao)示充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)周期結束。

    如(ru)果充電(dian)(dian)過程中輸出負載增大,例(li)如(ru),用戶在(zai)電(dian)(dian)池(chi)充電(dian)(dian)時啟動了其它(ta)電(dian)(dian)路,U4允許(xu)返回到限流模式。

    測試結果

    圖(tu)1電(dian)(dian)路(lu)輸(shu)入為110V交流(liu)電(dian)(dian)源,輸(shu)出(chu)為4.14V、740mA負載(zai),效率可達到46%。當負載(zai)電(dian)(dian)流(liu)增大使電(dian)(dian)池電(dian)(dian)壓降至(zhi)2.7V時(shi),電(dian)(dian)路(lu)將輸(shu)出(chu)電(dian)(dian)流(liu)限(xian)制在802mA,比設置(zhi)的(de)(de)780mA限(xian)流(liu)門(men)限(xian)提高不到3%,在規定的(de)(de)參數(shu)指標(biao)以(yi)內(nei)。MAX1507允許±8%的(de)(de)變化。當電(dian)(dian)池電(dian)(dian)壓拉至(zhi)2.5V時(shi),輸(shu)出(chu)電(dian)(dian)流(liu)降至(zhi)76.1mA,在78mA(780mA的(de)(de)1/10)的(de)(de)3%以(yi)內(nei)。U4數(shu)據手冊中規定允許±5%的(de)(de)范圍。輸(shu)出(chu)短(duan)路(lu)時(shi)電(dian)(dian)路(lu)還允許返回(hui)到該(gai)模式。

    空載(zai)時,輸出(chu)穩定在(zai)4.2V左(zuo)右,形成(cheng)一個(ge)三角波,在(zai)U4輸出(chu)接(jie)一個(ge)負載(zai)電(dian)阻(zu)可以(yi)消(xiao)除這個(ge)偏差,保持其連續(xu)性(xing),但(dan)(dan)會降(jiang)低系(xi)統效率,但(dan)(dan)對于交流電(dian)供(gong)電(dian)系(xi)統來說,效率并(bing)不(bu)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(bu)需要(yao)任何額(e)外的控制電(dian)路(如微控制器的干預),也不(bu)需要(yao)軟件開(kai)發。硬(ying)件開(kai)發只需對Maxim提(ti)供的標(biao)準(zhun)評(ping)估板稍作修(xiu)改(gai)即可,具有成本低(di)、開(kai)發周期短等(deng)優勢。

    由于系(xi)統沒(mei)有(you)60Hz的隔離變壓器(qi),具有(you)尺寸小、輕便等特(te)點,可(ke)用于手(shou)機或其它手(shou)持設(she)備的充(chong)電。所有(you)熱量均集中在交(jiao)流適配器(qi)內,與內置充(chong)電器(qi)的手(shou)持設(she)備相比,不需要過多考慮散熱問題。