本文介紹了(le)一(yi)個單節鋰離子(Li+)電池(chi)的充(chong)電方(fang)案(an),該方(fang)案(an)基于MAX5022芯片,適用于全球的交流電源,而且無需軟件控制或微處理(li)器(qi)干(gan)預就能實現所有的充(chong)電功能。   

    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)和電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)最大(da)值在(zai)規(gui)定的(de)范圍(wei)內,當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)維(wei)持在(zai)最大(da)單節電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya),充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)下降到一個較低(di)值時,充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器終止充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。Li+和鉛酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器的(de)區別在(zai)于(yu)所(suo)(suo)允許的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)、最大(da)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya),另外(wai)鉛酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器一般具有(you)浮(fu)充(chong)(chong)(chong)(chong)能力(浮(fu)充(chong)(chong)(chong)(chong)是為了補充(chong)(chong)(chong)(chong)鉛酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)自(zi)放電(dian)(dian)(dian)(dian)(dian)(dian),而對一個已經完全充(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)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)技術),Li+電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)自(zi)放電(dian)(dian)(dian)(dian)(dian)(dian)非(fei)常低(di),所(suo)(suo)以(yi)不需要(yao)浮(fu)充(chong)(chong)(chong)(chong)。   

    Li+電(dian)池   

    為(wei)(wei)便攜式產品(pin)選(xuan)擇(ze)電(dian)(dian)(dian)池(chi)時(shi),最(zui)重要的(de)是高能(neng)量密(mi)度(du)、尺寸、重量和價格。迄今為(wei)(wei)止(zhi)(zhi),Li+電(dian)(dian)(dian)池(chi)在(zai)最(zui)為(wei)(wei)流行(xing)的(de)電(dian)(dian)(dian)池(chi)中(zhong)能(neng)夠提(ti)供最(zui)高的(de)體積和能(neng)量密(mi)度(du),但其每(mei)瓦(wa)時(shi)的(de)成本也較高。鉛酸電(dian)(dian)(dian)池(chi)的(de)每(mei)瓦(wa)時(shi)成本最(zui)低,但比較笨重。本文(wen)以Li+電(dian)(dian)(dian)池(chi)為(wei)(wei)例討論充(chong)電(dian)(dian)(dian)器的(de)設(she)計,它(ta)在(zai)便攜式產品(pin)中(zhong)已經被普遍使用。我們選(xuan)擇(ze)780mA的(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流和4.2V的(de)終止(zhi)(zhi)電(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(xu)微處理(li)器(qi)干預,輸入電(dian)(dian)(dian)源可以采用全球范圍的(de)任何交流(liu)電(dian)(dian)(dian)源,省去了(le)大體積60Hz變(bian)壓器(qi),而且可提供單節Li+電(dian)(dian)(dian)池所要求的(de)精確(que)的(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓和(he)電(dian)(dian)(dian)流(liu)。充(chong)電(dian)(dian)(dian)器(qi)IC(U4)集成了(le)全面的(de)保護功能(電(dian)(dian)(dian)壓、電(dian)(dian)(dian)流(liu)和(he)自(zi)保護),確(que)保Li+電(dian)(dian)(dian)池的(de)安全充(chong)電(dian)(dian)(dian)。   

    假設Li+電(dian)池帶有(you)(you)過(guo)(guo)(guo)(guo)流、過(guo)(guo)(guo)(guo)壓和(he)過(guo)(guo)(guo)(guo)熱保(bao)護,這些保(bao)護特性(xing)(xing)在(zai)電(dian)池包里是必需(xu)的,因為(wei)充電(dian)期間一(yi)旦電(dian)路出現(xian)故障,Li+電(dian)池將(jiang)存在(zai)很大的危險(xian)性(xing)(xing),過(guo)(guo)(guo)(guo)流、過(guo)(guo)(guo)(guo)壓或溫度過(guo)(guo)(guo)(guo)高都有(you)(you)可能造成Li+電(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(zhi)調整管(guan),結合(he)其熱控制環路提供快(kuai)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)(de)電(dian)源(yuan)端MAX5022評估板不(bu)需要作(zuo)任(ren)何(he)修改,隔離(li)端只需對評估板的(de)(de)電(dian)阻值稍作(zuo)修改。   

    對于(yu)更大功率的(de)(de)(de)(de)應用,只需(xu)選取功率較(jiao)大的(de)(de)(de)(de)開關(guan)管和(he)能夠處理更大功率的(de)(de)(de)(de)變(bian)壓器(qi)即可(ke)。圖1所(suo)示電(dian)(dian)路(lu)要(yao)求(qiu)充電(dian)(dian)電(dian)(dian)流為780mA,最大電(dian)(dian)池電(dian)(dian)壓為4.2V。對充電(dian)(dian)電(dian)(dian)源的(de)(de)(de)(de)要(yao)求(qiu)與MAX5022評(ping)估板所(suo)提(ti)供(gong)的(de)(de)(de)(de)輸出相(xiang)吻合：5V@1A,因此,不需(xu)要(yao)更換(huan)評(ping)估板的(de)(de)(de)(de)晶體管和(he)變(bian)壓器(qi)。U4采(cai)用SOT23封裝,所(suo)以,充電(dian)(dian)器(qi)的(de)(de)(de)(de)尺寸(cun)在很(hen)大程(cheng)度上(shang)取決(jue)于(yu)應用對充電(dian)(dian)電(dian)(dian)源的(de)(de)(de)(de)需(xu)求(qiu)。變(bian)壓器(qi)是(shi)電(dian)(dian)路(lu)中尺寸(cun)最大的(de)(de)(de)(de)元件(jian),由(you)于(yu)開關(guan)控制器(qi)的(de)(de)(de)(de)工作頻率大于(yu)250kHz,允許系統(tong)選用小(xiao)尺寸(cun)的(de)(de)(de)(de)變(bian)壓器(qi)。    

    上電(dian)(dian)(dian)時(shi),在(zai)(zai)(zai)開關控制器工作之前(qian),U1調節器直接通過(guo)泄漏電(dian)(dian)(dian)阻(zu)(zu)R1、R2從整流(liu)通路吸取(qu)少量(liang)的(de)(de)電(dian)(dian)(dian)流(liu),兩個電(dian)(dian)(dian)阻(zu)(zu)阻(zu)(zu)值保(bao)證每個電(dian)(dian)(dian)阻(zu)(zu)上的(de)(de)壓(ya)降不會超(chao)出每個電(dian)(dian)(dian)阻(zu)(zu)的(de)(de)容限,Vin引(yin)腳電(dian)(dian)(dian)壓(ya)不會超(chao)出其28V額定值(30V為(wei)絕對最大值),U1在(zai)(zai)(zai)輸(shu)入電(dian)(dian)(dian)壓(ya)達(da)到(dao)24V時(shi)開始開關操作,并吸取(qu)更大的(de)(de)電(dian)(dian)(dian)流(liu)(高于(yu)R1、R2所能(neng)提(ti)供(gong)(gong)的(de)(de)電(dian)(dian)(dian)流(liu)),在(zai)(zai)(zai)變壓(ya)器副邊線圈能(neng)夠提(ti)供(gong)(gong)足(zu)夠的(de)(de)能(neng)量(liang)之前(qian),額外的(de)(de)電(dian)(dian)(dian)流(liu)由Vin引(yin)腳的(de)(de)旁(pang)路電(dian)(dian)(dian)容供(gong)(gong)給(gei)。這種處理方式能(neng)夠適合較寬的(de)(de)輸(shu)入電(dian)(dian)(dian)壓(ya)范圍,對效率的(de)(de)影響也很小,這是(shi)因為(wei)在(zai)(zai)(zai)啟(qi)動(dong)過(guo)程中只需極小的(de)(de)供(gong)(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(典型值為(wei)50uA)。  

    為了(le)防止(zhi)U1的(de)Vin引腳(jiao)出現(xian)過壓(ya),可以(yi)在Vin與(yu)地之間(jian)接一個26V至30V的(de)齊納管,電壓(ya)值需要高于欠(qian)壓(ya)鎖(suo)存電壓(ya)的(de)最大值,低(di)于該引腳(jiao)所(suo)允許的(de)最大絕(jue)對電壓(ya)。如果器件(jian)沒有(you)啟動正常(chang)的(de)開(kai)關操作(zuo),則可認為電路發生了(le)某些問題,所(suo)以(yi),這(zhe)一保護措(cuo)施(shi)對于U1來說(shuo)并不是(shi)必需的(de)。    

    U1是(shi)一款電(dian)流模式PWM控制(zhi)器(qi),具有逐周(zhou)期限(xian)(xian)流電(dian)路,必要時其占空(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(kai)關電(dian)流檢測采用尺寸為1206的1.78Ω電(dian)阻(R7),該電(dian)阻限(xian)(xian)制(zhi)了(le)變壓器(qi)原邊的最(zui)大電(dian)流。固定開(kai)關頻率和(he)最(zui)大占空(kong)比限(xian)(xian)制(zhi)使得最(zui)大限(xian)(xian)流具有輸出短路保護功(gong)能。  

    一旦短路輸出造成(cheng)電路達到了(le)上(shang)(shang)述(shu)限(xian)制(zhi)條件,第三(san)組線圈將無法(fa)提供(gong)10V以上(shang)(shang)的(de)電壓(ya)(UVLO的(de)低電壓(ya)門限(xian)),U1將再(zai)次進入(ru)啟動狀態,停止開關操作(zuo)。短路故障解除后(hou)系統會自動恢復正常的(de)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低(di)功率損耗。  

    當(dang)調節(jie)點電壓(ya)(ya)高于1.24V時,并聯型穩壓(ya)(ya)器將(jiang)吸入(ru)電流,導通(tong)光(guang)耦(ou)LED,原(yuan)邊的(de)(de)(de)光(guang)敏晶(jing)體管將(jiang)處于發光(guang)狀態(tai)。U1的(de)(de)(de)OPTO輸入(ru)引(yin)(yin)腳(jiao)用(yong)于直接(jie)連(lian)接(jie)光(guang)敏晶(jing)體管,以(yi)極其(qi)簡單(dan)的(de)(de)(de)方式(shi)構成閉(bi)合環路。光(guang)敏晶(jing)體管導通(tong)時,OPTO引(yin)(yin)腳(jiao)被拉(la)低(di),內部比(bi)較器在它的(de)(de)(de)一個輸入(ru)端檢(jian)測(ce)到(dao)較低(di)的(de)(de)(de)電壓(ya)(ya),比(bi)較器的(de)(de)(de)另一輸入(ru)電流檢(jian)測(ce)引(yin)(yin)腳(jiao)(CS)的(de)(de)(de)峰值電壓(ya)(ya),OPTO引(yin)(yin)腳(jiao)的(de)(de)(de)低(di)電壓(ya)(ya)將(jiang)在每(mei)個周期直接(jie)限制功(gong)率MOSFETN1的(de)(de)(de)峰值電流。由于U1是一個PWM控制器,電流限制使(shi)得(de)電壓(ya)(ya)調節(jie)受作用(yong)在N1上(shang)的(de)(de)(de)占空比(bi)(導通(tong)時間(jian)與(yu)斷開(kai)時間(jian)的(de)(de)(de)比(bi)值)的(de)(de)(de)影響,環路穩定性(xing)通(tong)過調節(jie)R11和(he)C12來保證。R10和(he)C5(連(lian)接(jie)在U3的(de)(de)(de)第3和(he)第4引(yin)(yin)腳(jiao))可消除穩定工作情況(kuang)下(xia)的(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、功能(neng)完備(bei)的充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器,采用線性充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)模(mo)式,內置調整管和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)檢(jian)測(ce)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。另外,它還(huan)集成了一個反向抑制(zhi)二極管,在(zai)去掉輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源時(shi)(shi)可防止電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)方向放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。接入(ru)一個深度放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)時(shi)(shi),U4能(neng)夠檢(jian)測(ce)到(dao)(dao)低(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(低(di)(di)于2.5V),這樣(yang),U4將首先啟(qi)動涓流(liu)(liu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程,在(zai)快充(chong)周期的1/10時(shi)(shi)間段對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行(xing)涓流(liu)(liu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian),直到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)上(shang)(shang)(shang)升(sheng)到(dao)(dao)2.5V以上(shang)(shang)(shang)。在(zai)涓流(liu)(liu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)到(dao)(dao)快速充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)轉換(huan)時(shi)(shi),軟(ruan)啟(qi)動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)迫(po)使充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)在(zai)3ms時(shi)(shi)間內緩(huan)慢(man)上(shang)(shang)(shang)升(sheng),避免較(jiao)大的浪涌(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)拉低(di)(di)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源。   

   上述功(gong)能的(de)實施(shi)不需要微控(kong)制(zhi)器的(de)監(jian)管,而(er)且,U4還具有(you)可編程的(de)溫度限制(zhi)功(gong)能,我們會在(zai)下面(mian)就這一點進行詳細討論。用一個電阻(zu)設置(zhi)最大充(chong)電電流(liu),電阻(zu)兩端的(de)電壓與充(chong)電電流(liu)成正比,通過監(jian)視該電壓即可連續跟蹤充(chong)電電流(liu),更為復雜的(de)系統也(ye)可以采用ADC跟蹤監(jian)視充(chong)電電流(liu)。   

    Maxim還(huan)提供有(you)另一款與MAX1507非常相似(si)的充電(dian)器―MAX1555,這款IC能夠在沒(mei)有(you)交(jiao)流電(dian)源(yuan)的情況下從USB主機(ji)獲得充電(dian)電(dian)源(yuan)。  

    電流調節

    如果把Li+電(dian)(dian)(dian)(dian)池直接(jie)與一(yi)個(ge)低阻(zu)電(dian)(dian)(dian)(dian)壓源連接(jie),充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)將不受(shou)任何限制,這種(zhong)狀(zhuang)況會對(dui)電(dian)(dian)(dian)(dian)池及其(qi)周圍環境造成(cheng)災難性(xing)(xing)的損害,從Li+電(dian)(dian)(dian)(dian)池的安全性(xing)(xing)考慮,必須(xu)將其(qi)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)限制在(zai)額定范圍以內。U4根據(ju)連接(jie)在(zai)ISET(第5引腳(jiao))的電(dian)(dian)(dian)(dian)阻(zu)限制充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu),圖1電(dian)(dian)(dian)(dian)路中選用了一(yi)個(ge)1.87kΩ的電(dian)(dian)(dian)(dian)阻(zu),將最大電(dian)(dian)(dian)(dian)流(liu)設置(zhi)在(zai)780mA:

    Ifast=1461V/Rset=1461/1870≈780mA

    電池(chi)電壓(ya)(ya)(ya)最(zui)小時,由于輸入(ru)穩(wen)定(ding)在4.5V,U4輸入(ru)與(yu)輸出的壓(ya)(ya)(ya)差(cha)最(zui)大(da),如果此(ci)時電池(chi)是以(yi)最(zui)大(da)電流充(chong)電,U4功耗將達到最(zui)大(da)值(zhi)。例如,假(jia)設電池(chi)電壓(ya)(ya)(ya)為2.5V,則對(dui)應的功耗為：

    P=IV=(0.78A)×(4.5V-2.5V)=1.56W

    U4封裝(8引腳薄型(xing)DFN-EP,EP表示(shi)裸(luo)露焊(han)盤)在溫(wen)(wen)度高(gao)(gao)達(da)70℃時可(ke)以(yi)耗散(san)的(de)(de)(de)(de)(de)(de)最(zui)大(da)功(gong)率是1.951W,這樣,在整個電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)范圍內以(yi)780mA的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)應該沒(mei)有(you)任何問(wen)題(ti)。但是,如(ru)果IC管芯(xin)由于較高(gao)(gao)的(de)(de)(de)(de)(de)(de)環境溫(wen)(wen)度或不良的(de)(de)(de)(de)(de)(de)散(san)熱條(tiao)件達(da)到(dao)(dao)(dao)(dao)了(le)70℃,U4內部的(de)(de)(de)(de)(de)(de)熱調節環路(lu)將自動降(jiang)(jiang)低充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu),這一過程有(you)別于其(qi)它充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)IC中的(de)(de)(de)(de)(de)(de)“熱關(guan)斷”,“熱關(guan)斷”方(fang)式只是簡單地中止芯(xin)片(pian)中的(de)(de)(de)(de)(de)(de)所(suo)有(you)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)工作,直到(dao)(dao)(dao)(dao)晶(jing)片(pian)溫(wen)(wen)度降(jiang)(jiang)至規定的(de)(de)(de)(de)(de)(de)數值(zhi)。MAX1507所(suo)采用(yong)的(de)(de)(de)(de)(de)(de)方(fang)案(an)能夠(gou)保(bao)證(zheng)在芯(xin)片(pian)溫(wen)(wen)度不超(chao)出最(zui)大(da)限制范圍的(de)(de)(de)(de)(de)(de)條(tiao)件下提供最(zui)快(kuai)的(de)(de)(de)(de)(de)(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)速率,隨(sui)著電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)(de)(de)(de)升高(gao)(gao),充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)在保(bao)持最(zui)高(gao)(gao)溫(wen)(wen)度的(de)(de)(de)(de)(de)(de)前提下逐漸升高(gao)(gao),直到(dao)(dao)(dao)(dao)達(da)到(dao)(dao)(dao)(dao)最(zui)大(da)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。在此之(zhi)后(hou),充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器在滿足芯(xin)片(pian)溫(wen)(wen)度限制的(de)(de)(de)(de)(de)(de)條(tiao)件下將以(yi)最(zui)大(da)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian),直到(dao)(dao)(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)達(da)到(dao)(dao)(dao)(dao)內部設置的(de)(de)(de)(de)(de)(de)4.2V±1%。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)達(da)到(dao)(dao)(dao)(dao)門限值(zhi)后(hou),U4將輸出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)保(bao)持在4.2V,從而使充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)開始下降(jiang)(jiang)。充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)降(jiang)(jiang)低到(dao)(dao)(dao)(dao)快(kuai)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)(de)10%時,充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)指示(shi)燈關(guan)閉,表示(shi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)周期結束(shu)。

    如(ru)果充電(dian)過(guo)程中輸出負載增大(da),例(li)如(ru),用戶在(zai)電(dian)池(chi)充電(dian)時(shi)啟動了其它電(dian)路,U4允許返回(hui)到(dao)限流模式。

    測試結果

    圖1電(dian)(dian)路(lu)(lu)輸(shu)入為110V交(jiao)流(liu)(liu)電(dian)(dian)源(yuan),輸(shu)出(chu)為4.14V、740mA負載,效率可(ke)達到46%。當(dang)負載電(dian)(dian)流(liu)(liu)增大使電(dian)(dian)池(chi)電(dian)(dian)壓降至(zhi)2.7V時,電(dian)(dian)路(lu)(lu)將輸(shu)出(chu)電(dian)(dian)流(liu)(liu)限制在802mA,比設置的(de)(de)(de)780mA限流(liu)(liu)門限提高不到3%,在規(gui)(gui)定(ding)的(de)(de)(de)參數指標以(yi)(yi)內(nei)。MAX1507允許(xu)±8%的(de)(de)(de)變化。當(dang)電(dian)(dian)池(chi)電(dian)(dian)壓拉至(zhi)2.5V時,輸(shu)出(chu)電(dian)(dian)流(liu)(liu)降至(zhi)76.1mA,在78mA(780mA的(de)(de)(de)1/10)的(de)(de)(de)3%以(yi)(yi)內(nei)。U4數據手冊中規(gui)(gui)定(ding)允許(xu)±5%的(de)(de)(de)范圍。輸(shu)出(chu)短(duan)路(lu)(lu)時電(dian)(dian)路(lu)(lu)還允許(xu)返回(hui)到該模式。

    空載時,輸出穩定在4.2V左(zuo)右,形(xing)成一個三角波,在U4輸出接一個負載電阻可以(yi)消除這個偏差,保持其連(lian)續性(xing),但(dan)會(hui)降低系統(tong)效率(lv)(lv),但(dan)對于交(jiao)流電供電系統(tong)來說,效率(lv)(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(gai)方(fang)案不需要任(ren)何額外的控(kong)制電(dian)路(如微控(kong)制器的干(gan)預(yu)),也不需要軟件開發(fa)(fa)。硬件開發(fa)(fa)只需對Maxim提供的標準評估板稍作修改即(ji)可(ke),具有成本(ben)低(di)、開發(fa)(fa)周(zhou)期(qi)短等優勢。

    由于(yu)系(xi)統(tong)沒有(you)60Hz的隔離變壓(ya)器(qi),具有(you)尺寸(cun)小、輕便等特點,可用于(yu)手(shou)機或(huo)其它手(shou)持設備(bei)的充(chong)電。所有(you)熱(re)量均集中在交流適配器(qi)內,與內置(zhi)充(chong)電器(qi)的手(shou)持設備(bei)相比(bi),不需要過多考慮散熱(re)問題(ti)。