本(ben)文介紹了一個單節鋰離子(zi)(Li+)電(dian)(dian)池的充電(dian)(dian)方(fang)案,該方(fang)案基于MAX5022芯片,適用于全球的交流電(dian)(dian)源(yuan),而且(qie)無(wu)需軟件控制(zhi)或微處理(li)器(qi)干預就能實(shi)現所有的充電(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(zheng)作用到電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)上的(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)和電(dian)(dian)(dian)(dian)(dian)流(liu)最大(da)值在規(gui)定(ding)的(de)范圍內,當電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)維持(chi)在最大(da)單(dan)節(jie)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya),充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)下降到一個較低值時,充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器終止充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)。Li+和鉛酸電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器的(de)區別在于(yu)所允許的(de)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)、最大(da)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya),另外(wai)鉛酸電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器一般具(ju)有浮(fu)充(chong)(chong)(chong)(chong)(chong)能力(浮(fu)充(chong)(chong)(chong)(chong)(chong)是為(wei)了補充(chong)(chong)(chong)(chong)(chong)鉛酸電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)自放電(dian)(dian)(dian)(dian)(dian),而(er)對一個已(yi)經完全充(chong)(chong)(chong)(chong)(chong)滿的(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)繼續(xu)輸(shu)入充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)技術),Li+電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)自放電(dian)(dian)(dian)(dian)(dian)非常低,所以(yi)不需(xu)要浮(fu)充(chong)(chong)(chong)(chong)(chong)。   

    Li+電池   

    為(wei)便(bian)攜式產品(pin)選(xuan)擇電(dian)(dian)池時(shi),最(zui)重要的(de)是高(gao)能量(liang)密(mi)度(du)、尺寸、重量(liang)和(he)(he)價格。迄(qi)今為(wei)止,Li+電(dian)(dian)池在(zai)最(zui)為(wei)流行的(de)電(dian)(dian)池中能夠提供(gong)最(zui)高(gao)的(de)體積和(he)(he)能量(liang)密(mi)度(du),但(dan)(dan)其每瓦時(shi)的(de)成本也(ye)較(jiao)高(gao)。鉛酸電(dian)(dian)池的(de)每瓦時(shi)成本最(zui)低,但(dan)(dan)比較(jiao)笨重。本文以(yi)Li+電(dian)(dian)池為(wei)例討論充電(dian)(dian)器(qi)的(de)設計(ji),它在(zai)便(bian)攜式產品(pin)中已(yi)經被普遍使用。我們選(xuan)擇780mA的(de)充電(dian)(dian)電(dian)(dian)流和(he)(he)4.2V的(de)終(zhong)止電(dian)(dian)壓(ya)。

    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(wu)需(xu)微處理器干預,輸入電(dian)(dian)(dian)(dian)(dian)源可(ke)以采用全球范(fan)圍(wei)的(de)任(ren)何交流(liu)電(dian)(dian)(dian)(dian)(dian)源,省去了大體積60Hz變壓(ya)(ya)器,而且可(ke)提(ti)供單節Li+電(dian)(dian)(dian)(dian)(dian)池(chi)所要求(qiu)的(de)精(jing)確的(de)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)和電(dian)(dian)(dian)(dian)(dian)流(liu)。充電(dian)(dian)(dian)(dian)(dian)器IC(U4)集(ji)成(cheng)了全面的(de)保護(hu)功能(電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)、電(dian)(dian)(dian)(dian)(dian)流(liu)和自保護(hu)),確保Li+電(dian)(dian)(dian)(dian)(dian)池(chi)的(de)安(an)全充電(dian)(dian)(dian)(dian)(dian)。   

    假設Li+電池帶有(you)過(guo)(guo)(guo)流、過(guo)(guo)(guo)壓(ya)和過(guo)(guo)(guo)熱保護(hu),這些保護(hu)特性(xing)(xing)在電池包(bao)里是必需的,因為充電期(qi)間一(yi)旦(dan)電路出現故障,Li+電池將存在很大的危(wei)險性(xing)(xing),過(guo)(guo)(guo)流、過(guo)(guo)(guo)壓(ya)或溫(wen)度過(guo)(guo)(guo)高都(dou)有(you)可能造成Li+電池爆炸。   

    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,內置調整管,結合其熱控(kong)制環路提供快速充電(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)(dian)源(yuan)端MAX5022評估(gu)板(ban)不(bu)需(xu)要作任何修(xiu)改,隔離端只(zhi)需(xu)對評估(gu)板(ban)的電(dian)(dian)阻(zu)值稍作修(xiu)改。   

    對于(yu)(yu)更(geng)(geng)大(da)功(gong)率(lv)的(de)(de)應用(yong),只(zhi)需選(xuan)取功(gong)率(lv)較大(da)的(de)(de)開關管和能(neng)夠處理更(geng)(geng)大(da)功(gong)率(lv)的(de)(de)變壓(ya)(ya)器即可(ke)。圖1所(suo)示電(dian)(dian)(dian)路要求充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)為780mA,最大(da)電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)(ya)為4.2V。對充電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)的(de)(de)要求與(yu)MAX5022評估板(ban)所(suo)提(ti)供的(de)(de)輸出相吻(wen)合(he)：5V@1A,因此,不需要更(geng)(geng)換評估板(ban)的(de)(de)晶體管和變壓(ya)(ya)器。U4采用(yong)SOT23封裝,所(suo)以(yi),充電(dian)(dian)(dian)器的(de)(de)尺寸(cun)在很大(da)程度上(shang)取決于(yu)(yu)應用(yong)對充電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)的(de)(de)需求。變壓(ya)(ya)器是電(dian)(dian)(dian)路中尺寸(cun)最大(da)的(de)(de)元件,由于(yu)(yu)開關控制器的(de)(de)工作頻率(lv)大(da)于(yu)(yu)250kHz,允許系統選(xuan)用(yong)小尺寸(cun)的(de)(de)變壓(ya)(ya)器。    

    上電(dian)(dian)(dian)(dian)(dian)(dian)時,在(zai)(zai)開(kai)關(guan)控制器(qi)(qi)工作(zuo)之(zhi)前(qian),U1調節器(qi)(qi)直接(jie)通(tong)過(guo)泄漏(lou)電(dian)(dian)(dian)(dian)(dian)(dian)阻R1、R2從整流(liu)通(tong)路(lu)吸取少量(liang)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu),兩個電(dian)(dian)(dian)(dian)(dian)(dian)阻阻值(zhi)(zhi)保(bao)證每(mei)(mei)個電(dian)(dian)(dian)(dian)(dian)(dian)阻上的(de)(de)(de)壓(ya)降不會(hui)超出每(mei)(mei)個電(dian)(dian)(dian)(dian)(dian)(dian)阻的(de)(de)(de)容限,Vin引腳電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)不會(hui)超出其28V額定值(zhi)(zhi)(30V為絕對最(zui)大(da)值(zhi)(zhi)),U1在(zai)(zai)輸入電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)達到(dao)24V時開(kai)始開(kai)關(guan)操作(zuo),并吸取更大(da)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(高于R1、R2所能(neng)提供(gong)(gong)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)),在(zai)(zai)變壓(ya)器(qi)(qi)副邊(bian)線圈能(neng)夠提供(gong)(gong)足夠的(de)(de)(de)能(neng)量(liang)之(zhi)前(qian),額外的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)由Vin引腳的(de)(de)(de)旁路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)容供(gong)(gong)給。這種(zhong)處理方式能(neng)夠適合(he)較寬的(de)(de)(de)輸入電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)范圍,對效率的(de)(de)(de)影(ying)響(xiang)也很小,這是因為在(zai)(zai)啟動過(guo)程(cheng)中只需(xu)極小的(de)(de)(de)供(gong)(gong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(典型值(zhi)(zhi)為50uA)。  

    為了防止U1的(de)(de)Vin引腳出(chu)現(xian)過壓,可以(yi)在Vin與(yu)地之間接一個26V至(zhi)30V的(de)(de)齊(qi)納管,電壓值需要(yao)高于(yu)欠壓鎖存電壓的(de)(de)最(zui)大值,低于(yu)該(gai)引腳所允許的(de)(de)最(zui)大絕對電壓。如果器件沒有(you)啟動正常的(de)(de)開關操作,則可認為電路(lu)發生了某些問(wen)題,所以(yi),這一保護措(cuo)施對于(yu)U1來說(shuo)并(bing)不是(shi)必需的(de)(de)。    

    U1是一(yi)款電流(liu)(liu)模式(shi)PWM控制(zhi)(zhi)器,具(ju)有逐周期(qi)限(xian)流(liu)(liu)電路,必要(yao)時其占空比(bi)可以提高到(dao)75%,非(fei)常(chang)適合圖(tu)1所示的反(fan)激拓(tuo)撲。原邊(bian)(bian)開(kai)關電流(liu)(liu)檢測采用尺寸為1206的1.78Ω電阻(R7),該電阻限(xian)制(zhi)(zhi)了變壓器原邊(bian)(bian)的最(zui)大電流(liu)(liu)。固(gu)定開(kai)關頻率和(he)最(zui)大占空比(bi)限(xian)制(zhi)(zhi)使得最(zui)大限(xian)流(liu)(liu)具(ju)有輸出短路保護功(gong)能。  

    一旦短(duan)路輸出造成(cheng)電(dian)路達到了上述(shu)限(xian)制條件,第三組線(xian)圈將無法提供10V以上的電(dian)壓(UVLO的低電(dian)壓門限(xian)),U1將再次進入啟(qi)動狀(zhuang)態,停止開關操作。短(duan)路故障解除(chu)后系統(tong)會(hui)自動恢復正常的工作狀(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(dian)有助(zhu)于降(jiang)低功率損耗(hao)。  

    當調(diao)(diao)節點電(dian)(dian)壓(ya)高(gao)于(yu)1.24V時,并(bing)聯型穩(wen)壓(ya)器(qi)將吸入(ru)電(dian)(dian)流(liu),導通光(guang)耦LED,原邊(bian)的(de)(de)(de)光(guang)敏晶體管將處于(yu)發光(guang)狀態。U1的(de)(de)(de)OPTO輸入(ru)引(yin)腳(jiao)用于(yu)直接連接光(guang)敏晶體管,以(yi)極其簡單的(de)(de)(de)方式(shi)構成閉合環路(lu)。光(guang)敏晶體管導通時,OPTO引(yin)腳(jiao)被拉低,內部比(bi)較(jiao)器(qi)在(zai)它的(de)(de)(de)一個(ge)輸入(ru)端檢測到較(jiao)低的(de)(de)(de)電(dian)(dian)壓(ya),比(bi)較(jiao)器(qi)的(de)(de)(de)另一輸入(ru)電(dian)(dian)流(liu)檢測引(yin)腳(jiao)(CS)的(de)(de)(de)峰值(zhi)電(dian)(dian)壓(ya),OPTO引(yin)腳(jiao)的(de)(de)(de)低電(dian)(dian)壓(ya)將在(zai)每(mei)個(ge)周期直接限(xian)制功(gong)率(lv)MOSFETN1的(de)(de)(de)峰值(zhi)電(dian)(dian)流(liu)。由于(yu)U1是(shi)一個(ge)PWM控制器(qi),電(dian)(dian)流(liu)限(xian)制使(shi)得(de)電(dian)(dian)壓(ya)調(diao)(diao)節受作用在(zai)N1上(shang)的(de)(de)(de)占空比(bi)(導通時間與(yu)斷開時間的(de)(de)(de)比(bi)值(zhi))的(de)(de)(de)影響,環路(lu)穩(wen)定(ding)性(xing)通過(guo)調(diao)(diao)節R11和C12來保(bao)證。R10和C5(連接在(zai)U3的(de)(de)(de)第(di)3和第(di)4引(yin)腳(jiao))可消除穩(wen)定(ding)工作情況下的(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、功能完備的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器,采用(yong)線(xian)性充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)模式,內置調整管(guan)和電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)檢測電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。另外,它還集成了一(yi)個反向(xiang)抑制二極管(guan),在(zai)(zai)去掉輸入電(dian)(dian)(dian)(dian)(dian)源(yuan)時(shi)可防止電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)方向(xiang)放電(dian)(dian)(dian)(dian)(dian)。接入一(yi)個深度(du)放電(dian)(dian)(dian)(dian)(dian)的(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)時(shi),U4能夠檢測到(dao)低(di)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)(低(di)于2.5V),這(zhe)樣,U4將(jiang)首先(xian)啟動涓流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)過程,在(zai)(zai)快(kuai)(kuai)充(chong)(chong)(chong)周期的(de)1/10時(shi)間(jian)段(duan)對電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)進(jin)行涓流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian),直(zhi)到(dao)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)上(shang)升到(dao)2.5V以上(shang)。在(zai)(zai)涓流(liu)(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)到(dao)快(kuai)(kuai)速充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)轉換時(shi),軟(ruan)啟動電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)迫使(shi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)在(zai)(zai)3ms時(shi)間(jian)內緩慢上(shang)升,避免較(jiao)大的(de)浪涌電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)拉低(di)輸入電(dian)(dian)(dian)(dian)(dian)源(yuan)。   

   上述功能的(de)實施不需(xu)要微(wei)控(kong)制(zhi)器的(de)監(jian)管,而且,U4還具有可(ke)編程的(de)溫度限制(zhi)功能,我們會在下面就這一點(dian)進行(xing)詳(xiang)細討(tao)論(lun)。用一個電(dian)(dian)(dian)(dian)阻(zu)設置最大(da)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu),電(dian)(dian)(dian)(dian)阻(zu)兩端(duan)的(de)電(dian)(dian)(dian)(dian)壓(ya)與充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)成正比,通過監(jian)視該電(dian)(dian)(dian)(dian)壓(ya)即可(ke)連(lian)續(xu)跟蹤充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu),更為復雜(za)的(de)系統也可(ke)以采用ADC跟蹤監(jian)視充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)。   

    Maxim還提供(gong)有另一(yi)款與MAX1507非常相(xiang)似的充(chong)電(dian)器(qi)―MAX1555,這款IC能夠在沒有交流電(dian)源的情況下從USB主機(ji)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)直接(jie)與一個低阻(zu)電(dian)(dian)(dian)(dian)壓源(yuan)連(lian)接(jie),充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流將(jiang)不受(shou)任何限(xian)制(zhi),這(zhe)種(zhong)狀況會對(dui)電(dian)(dian)(dian)(dian)池(chi)及其周圍環境造成災難性(xing)的損(sun)害(hai),從Li+電(dian)(dian)(dian)(dian)池(chi)的安全性(xing)考(kao)慮(lv),必須將(jiang)其充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流限(xian)制(zhi)在額(e)定范(fan)圍以內。U4根據連(lian)接(jie)在ISET(第5引腳(jiao))的電(dian)(dian)(dian)(dian)阻(zu)限(xian)制(zhi)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流,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(jiang)最(zui)大電(dian)(dian)(dian)(dian)流設置在780mA:

    Ifast=1461V/Rset=1461/1870≈780mA

    電(dian)(dian)池電(dian)(dian)壓(ya)最(zui)小時,由于輸入(ru)穩定在4.5V,U4輸入(ru)與輸出(chu)的壓(ya)差最(zui)大,如果(guo)此(ci)時電(dian)(dian)池是以最(zui)大電(dian)(dian)流充電(dian)(dian),U4功耗將(jiang)達到最(zui)大值。例如,假設電(dian)(dian)池電(dian)(dian)壓(ya)為(wei)2.5V,則對應(ying)的功耗為(wei)：

    P=IV=(0.78A)×(4.5V-2.5V)=1.56W

    U4封(feng)裝(8引腳(jiao)薄型DFN-EP,EP表示裸露焊盤(pan))在溫(wen)度(du)(du)高(gao)達(da)(da)70℃時可以(yi)耗散的(de)(de)(de)(de)最(zui)(zui)大(da)(da)(da)功率是(shi)(shi)1.951W,這(zhe)樣,在整個(ge)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓范圍內以(yi)780mA的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)應該沒有(you)(you)任何問題。但是(shi)(shi),如果(guo)IC管芯(xin)由于(yu)較高(gao)的(de)(de)(de)(de)環境(jing)溫(wen)度(du)(du)或不良的(de)(de)(de)(de)散熱(re)(re)條(tiao)件達(da)(da)到(dao)(dao)(dao)了70℃,U4內部的(de)(de)(de)(de)熱(re)(re)調節環路(lu)將自動降(jiang)(jiang)低充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu),這(zhe)一過程有(you)(you)別于(yu)其它充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)IC中的(de)(de)(de)(de)“熱(re)(re)關(guan)斷”,“熱(re)(re)關(guan)斷”方式只是(shi)(shi)簡(jian)單地中止芯(xin)片(pian)(pian)(pian)中的(de)(de)(de)(de)所有(you)(you)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)工作(zuo),直(zhi)到(dao)(dao)(dao)晶片(pian)(pian)(pian)溫(wen)度(du)(du)降(jiang)(jiang)至規定的(de)(de)(de)(de)數值。MAX1507所采用的(de)(de)(de)(de)方案能夠(gou)保證在芯(xin)片(pian)(pian)(pian)溫(wen)度(du)(du)不超出最(zui)(zui)大(da)(da)(da)限制(zhi)范圍的(de)(de)(de)(de)條(tiao)件下提(ti)供最(zui)(zui)快的(de)(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)速(su)率,隨著電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓的(de)(de)(de)(de)升(sheng)高(gao),充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)在保持最(zui)(zui)高(gao)溫(wen)度(du)(du)的(de)(de)(de)(de)前提(ti)下逐(zhu)漸(jian)升(sheng)高(gao),直(zhi)到(dao)(dao)(dao)達(da)(da)到(dao)(dao)(dao)最(zui)(zui)大(da)(da)(da)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)。在此之后(hou),充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器在滿足(zu)芯(xin)片(pian)(pian)(pian)溫(wen)度(du)(du)限制(zhi)的(de)(de)(de)(de)條(tiao)件下將以(yi)最(zui)(zui)大(da)(da)(da)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian),直(zhi)到(dao)(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓達(da)(da)到(dao)(dao)(dao)內部設置的(de)(de)(de)(de)4.2V±1%。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓達(da)(da)到(dao)(dao)(dao)門限值后(hou),U4將輸出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓保持在4.2V,從而使(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)開始(shi)下降(jiang)(jiang)。充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)降(jiang)(jiang)低到(dao)(dao)(dao)快充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)10%時,充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)指示燈關(guan)閉,表示充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)周期結(jie)束。

    如果充電(dian)(dian)過(guo)程中輸出負載(zai)增大,例(li)如,用戶在電(dian)(dian)池充電(dian)(dian)時啟動(dong)了其它電(dian)(dian)路,U4允許返回到限流模(mo)式(shi)。

    測試結果

    圖1電(dian)(dian)路輸入(ru)為110V交(jiao)流(liu)(liu)(liu)電(dian)(dian)源,輸出(chu)為4.14V、740mA負(fu)(fu)載(zai),效率可達(da)到(dao)(dao)46%。當負(fu)(fu)載(zai)電(dian)(dian)流(liu)(liu)(liu)增大使電(dian)(dian)池電(dian)(dian)壓降至2.7V時(shi),電(dian)(dian)路將輸出(chu)電(dian)(dian)流(liu)(liu)(liu)限制在802mA,比設(she)置的(de)(de)780mA限流(liu)(liu)(liu)門限提(ti)高不到(dao)(dao)3%,在規定(ding)的(de)(de)參數指標以內。MAX1507允(yun)(yun)許±8%的(de)(de)變化(hua)。當電(dian)(dian)池電(dian)(dian)壓拉(la)至2.5V時(shi),輸出(chu)電(dian)(dian)流(liu)(liu)(liu)降至76.1mA,在78mA(780mA的(de)(de)1/10)的(de)(de)3%以內。U4數據手(shou)冊中(zhong)規定(ding)允(yun)(yun)許±5%的(de)(de)范圍。輸出(chu)短路時(shi)電(dian)(dian)路還允(yun)(yun)許返回(hui)到(dao)(dao)該模(mo)式。

    空載時(shi),輸出穩定(ding)在(zai)4.2V左右,形成一個三角波,在(zai)U4輸出接一個負載電阻可以消除這(zhe)個偏差(cha),保持其連續性,但會(hui)降低系(xi)統(tong)效率,但對于(yu)交流電供電系(xi)統(tong)來說,效率并不重要(yao)。

    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(an)不(bu)(bu)需(xu)要任何(he)額(e)外的(de)控(kong)制電路(lu)(如(ru)微控(kong)制器的(de)干(gan)預),也(ye)不(bu)(bu)需(xu)要軟件(jian)(jian)開(kai)發。硬件(jian)(jian)開(kai)發只需(xu)對Maxim提供的(de)標準評估(gu)板稍(shao)作修改即可,具有成本低、開(kai)發周期短等優(you)勢(shi)。

    由于系統沒有(you)(you)60Hz的隔離變壓器,具有(you)(you)尺寸小、輕便等特(te)點(dian),可用于手(shou)機或其它(ta)手(shou)持設備(bei)的充電。所有(you)(you)熱(re)量均(jun)集中在交流(liu)適(shi)配器內(nei),與內(nei)置充電器的手(shou)持設備(bei)相比,不需要過多考慮散(san)熱(re)問題。