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(bu)同(tong)化學類型的電池對(dui)充電器的要求   

    通常快速充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)比涓(juan)流(liu)(liu)(liu)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)更(geng)受歡迎(ying)，但(dan)快速充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路的(de)(de)(de)(de)要求也(ye)(ye)復(fu)雜，鎳氫或鎳鎘電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)(de)(de)快速充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)技術與其(qi)它電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)也(ye)(ye)是(shi)不同的(de)(de)(de)(de)。鎳鎘和(he)鎳氫電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)通常在(zai)恒流(liu)(liu)(liu)狀態下(xia)(xia)快充(chong)(chong)(chong)(chong)(chong)，而不是(shi)恒壓(ya)狀態下(xia)(xia)。快充(chong)(chong)(chong)(chong)(chong)終止(zhi)檢測(ce)基于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)和(he)溫(wen)度的(de)(de)(de)(de)變化率，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)還應具備過壓(ya)保護和(he)過熱保護功能。Li+和(he)鉛(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)必須(xu)保證(zheng)作用(yong)到電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)上的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)和(he)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)最(zui)大(da)值(zhi)在(zai)規(gui)定的(de)(de)(de)(de)范圍內，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)維持在(zai)最(zui)大(da)單(dan)節電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)下(xia)(xia)降到一個(ge)較(jiao)低值(zhi)時，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)終止(zhi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。Li+和(he)鉛(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)的(de)(de)(de)(de)區別在(zai)于(yu)(yu)所允許的(de)(de)(de)(de)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)、最(zui)大(da)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，另外(wai)鉛(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)一般具有(you)浮充(chong)(chong)(chong)(chong)(chong)能力(浮充(chong)(chong)(chong)(chong)(chong)是(shi)為了補充(chong)(chong)(chong)(chong)(chong)鉛(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)(de)(de)自放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，而對(dui)一個(ge)已經完全充(chong)(chong)(chong)(chong)(chong)滿的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)繼續輸(shu)入充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)的(de)(de)(de)(de)技術)，Li+電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)(de)(de)自放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)非(fei)常低，所以不需(xu)要浮充(chong)(chong)(chong)(chong)(chong)。    

    Li+電池    

    為(wei)便(bian)(bian)攜式(shi)產品選擇電(dian)(dian)池(chi)時(shi)，最(zui)重(zhong)要的(de)(de)是高(gao)能(neng)量(liang)密度(du)、尺寸(cun)、重(zhong)量(liang)和價(jia)格。迄(qi)今為(wei)止，Li+電(dian)(dian)池(chi)在(zai)最(zui)為(wei)流行的(de)(de)電(dian)(dian)池(chi)中(zhong)能(neng)夠提供最(zui)高(gao)的(de)(de)體積和能(neng)量(liang)密度(du)，但(dan)其每瓦時(shi)的(de)(de)成(cheng)本也(ye)較高(gao)。鉛酸電(dian)(dian)池(chi)的(de)(de)每瓦時(shi)成(cheng)本最(zui)低，但(dan)比(bi)較笨重(zhong)。本文以Li+電(dian)(dian)池(chi)為(wei)例討論充電(dian)(dian)器的(de)(de)設計(ji)，它(ta)在(zai)便(bian)(bian)攜式(shi)產品中(zhong)已(yi)經被普遍使用。我們選擇780mA的(de)(de)充電(dian)(dian)電(dian)(dian)流和4.2V的(de)(de)終止電(dian)(dian)壓。 

 通用(yong)輸入交流電壓的離線式Li+電池充電器(qi)。    

    所示(shi)充電(dian)(dian)(dian)器無需(xu)微處理(li)器干預，輸(shu)入電(dian)(dian)(dian)源(yuan)可(ke)以采用全球范圍的(de)任何交流電(dian)(dian)(dian)源(yuan)，省去了大體積60Hz變壓(ya)(ya)器，而且可(ke)提(ti)供單(dan)節Li+電(dian)(dian)(dian)池所要求(qiu)的(de)精確的(de)充電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)(ya)和電(dian)(dian)(dian)流。充電(dian)(dian)(dian)器IC(U4)集成了全面(mian)的(de)保(bao)護功能(電(dian)(dian)(dian)壓(ya)(ya)、電(dian)(dian)(dian)流和自保(bao)護)，確保(bao)Li+電(dian)(dian)(dian)池的(de)安全充電(dian)(dian)(dian)。    

    假(jia)設Li+電池帶有過(guo)(guo)流、過(guo)(guo)壓和過(guo)(guo)熱保(bao)(bao)護，這些保(bao)(bao)護特性在(zai)電池包里是必需的，因為充電期(qi)間一(yi)旦(dan)電路(lu)出現故障，Li+電池將存在(zai)很大的危(wei)險性，過(guo)(guo)流、過(guo)(guo)壓或溫度過(guo)(guo)高都有可能造(zao)成(cheng)Li+電池爆(bao)炸。    

    電路描述     

    包括(kuo)兩(liang)顆主器(qi)(qi)件(jian)(U1和U4)、精密基(ji)準(zhun)(U3)和光耦(ou)(U2)。U1是離線(xian)式開(kai)關(guan)控(kong)制器(qi)(qi)，配合(he)隔(ge)離變壓器(qi)(qi)、光耦(ou)和基(ji)準(zhun)產生隔(ge)離的穩壓直流輸出。直流電(dian)(dian)(dian)(dian)(dian)壓供給(gei)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(U4)，U4提(ti)供電(dian)(dian)(dian)(dian)(dian)流限(xian)制、電(dian)(dian)(dian)(dian)(dian)壓調節、電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)和充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)指示(shi)等功(gong)能(neng)。本方案中，U4是一款簡單的線(xian)性充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)，內置調整管，結合(he)其熱控(kong)制環(huan)路提(ti)供快速充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)。    

    MAX5022的(de)特性     

    U1(MAX5022)在寬輸(shu)入(ru)范(fan)圍(wei)的(de)(de)應用中很容易設(she)(she)計，本文所(suo)提供的(de)(de)方案要求能(neng)夠滿(man)足全球各地的(de)(de)交流電(dian)(dian)(dian)源(yuan)(yuan)規格(ge)，這里假設(she)(she)通用的(de)(de)輸(shu)入(ru)電(dian)(dian)(dian)源(yuan)(yuan)電(dian)(dian)(dian)壓范(fan)圍(wei)為85VAC至(zhi)265VAC。MAX5022的(de)(de)輸(shu)入(ru)范(fan)圍(wei)指標以及評(ping)估(gu)(gu)板電(dian)(dian)(dian)路的(de)(de)輸(shu)入(ru)范(fan)圍(wei)恰好滿(man)足這一(yi)需(xu)求。對于所(suo)示充電(dian)(dian)(dian)器的(de)(de)電(dian)(dian)(dian)源(yuan)(yuan)端MAX5022評(ping)估(gu)(gu)板不需(xu)要作(zuo)任(ren)何修(xiu)改，隔離端只(zhi)需(xu)對評(ping)估(gu)(gu)板的(de)(de)電(dian)(dian)(dian)阻值稍(shao)作(zuo)修(xiu)改。    

    對于(yu)更(geng)(geng)大(da)功率的(de)(de)應用，只(zhi)需選取(qu)功率較大(da)的(de)(de)開關管(guan)和(he)能夠處理更(geng)(geng)大(da)功率的(de)(de)變壓(ya)器(qi)(qi)(qi)即可。圖(tu)1所示電(dian)(dian)路要(yao)求充(chong)電(dian)(dian)電(dian)(dian)流為780mA，最(zui)大(da)電(dian)(dian)池電(dian)(dian)壓(ya)為4.2V。對充(chong)電(dian)(dian)電(dian)(dian)源的(de)(de)要(yao)求與(yu)MAX5022評估(gu)板(ban)所提供的(de)(de)輸出相(xiang)吻合：5V@1A，因此，不(bu)需要(yao)更(geng)(geng)換評估(gu)板(ban)的(de)(de)晶體管(guan)和(he)變壓(ya)器(qi)(qi)(qi)。U4采(cai)用SOT23封裝(zhuang)，所以，充(chong)電(dian)(dian)器(qi)(qi)(qi)的(de)(de)尺(chi)寸(cun)在(zai)很大(da)程度(du)上取(qu)決于(yu)應用對充(chong)電(dian)(dian)電(dian)(dian)源的(de)(de)需求。變壓(ya)器(qi)(qi)(qi)是電(dian)(dian)路中尺(chi)寸(cun)最(zui)大(da)的(de)(de)元件，由于(yu)開關控制器(qi)(qi)(qi)的(de)(de)工作頻率大(da)于(yu)250kHz，允許(xu)系統選用小尺(chi)寸(cun)的(de)(de)變壓(ya)器(qi)(qi)(qi)。     

    上電(dian)(dian)(dian)時，在(zai)開關控制(zhi)器(qi)工作之前，U1調節器(qi)直接通(tong)過(guo)泄漏電(dian)(dian)(dian)阻(zu)(zu)R1、R2從整(zheng)流(liu)通(tong)路(lu)吸取(qu)少量的(de)(de)電(dian)(dian)(dian)流(liu)，兩個電(dian)(dian)(dian)阻(zu)(zu)阻(zu)(zu)值保證每(mei)個電(dian)(dian)(dian)阻(zu)(zu)上的(de)(de)壓降不會超出每(mei)個電(dian)(dian)(dian)阻(zu)(zu)的(de)(de)容限，Vin引腳電(dian)(dian)(dian)壓不會超出其(qi)28V額(e)定值(30V為(wei)絕對最大值)，U1在(zai)輸入電(dian)(dian)(dian)壓達到24V時開始開關操作，并吸取(qu)更(geng)大的(de)(de)電(dian)(dian)(dian)流(liu)(高(gao)于R1、R2所能(neng)提供(gong)的(de)(de)電(dian)(dian)(dian)流(liu))，在(zai)變(bian)壓器(qi)副邊(bian)線圈(quan)能(neng)夠(gou)(gou)提供(gong)足夠(gou)(gou)的(de)(de)能(neng)量之前，額(e)外(wai)的(de)(de)電(dian)(dian)(dian)流(liu)由Vin引腳的(de)(de)旁(pang)路(lu)電(dian)(dian)(dian)容供(gong)給。這(zhe)種(zhong)處理方(fang)式能(neng)夠(gou)(gou)適(shi)合較寬(kuan)的(de)(de)輸入電(dian)(dian)(dian)壓范圍，對效率的(de)(de)影響也很小(xiao)，這(zhe)是因為(wei)在(zai)啟動過(guo)程(cheng)中只(zhi)需極小(xiao)的(de)(de)供(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(典型值為(wei)50uA)。   

    為了(le)防(fang)止U1的(de)(de)Vin引腳出現過壓，可(ke)以在Vin與地之間接(jie)一個26V至30V的(de)(de)齊納管，電壓值需要高于欠壓鎖存(cun)電壓的(de)(de)最(zui)大(da)值，低于該(gai)引腳所(suo)允許的(de)(de)最(zui)大(da)絕對(dui)電壓。如(ru)果器件沒有啟(qi)動正常(chang)的(de)(de)開關操(cao)作，則(ze)可(ke)認為電路(lu)發(fa)生了(le)某些問題，所(suo)以，這(zhe)一保護措施(shi)對(dui)于U1來說并不是必需的(de)(de)。     

    U1是一款電(dian)(dian)(dian)(dian)流(liu)(liu)模式PWM控(kong)制器(qi)，具有逐周期限(xian)流(liu)(liu)電(dian)(dian)(dian)(dian)路，必要時其占空比可以提高到75%，非(fei)常適合圖1所示的(de)(de)反激拓(tuo)撲。原邊開(kai)(kai)關電(dian)(dian)(dian)(dian)流(liu)(liu)檢測采用尺(chi)寸為1206的(de)(de)1.78Ω電(dian)(dian)(dian)(dian)阻(R7)，該(gai)電(dian)(dian)(dian)(dian)阻限(xian)制了變壓器(qi)原邊的(de)(de)最(zui)大電(dian)(dian)(dian)(dian)流(liu)(liu)。固定(ding)開(kai)(kai)關頻率(lv)和(he)最(zui)大占空比限(xian)制使得最(zui)大限(xian)流(liu)(liu)具有輸出(chu)短路保護功能。   

    一旦(dan)短路輸(shu)出造(zao)成電(dian)路達到了上(shang)述限(xian)制條件，第三組線(xian)圈將(jiang)無法提供10V以上(shang)的(de)(de)電(dian)壓(ya)(UVLO的(de)(de)低電(dian)壓(ya)門限(xian))，U1將(jiang)再次進入啟動狀(zhuang)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)(de)工作(zuo)狀(zhuang)態。   

    電壓調節   

    變壓器(qi)(qi)副邊(bian)的(de)(de)電(dian)(dian)(dian)壓經過整流(liu)、濾波，然(ran)后(hou)由(you)R4、R5分壓在并(bing)聯型穩(wen)壓器(qi)(qi)U3的(de)(de)調節(jie)點產生1.24V(對(dui)應于4.5V輸(shu)出)的(de)(de)反饋電(dian)(dian)(dian)壓。為(wei)保證電(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)器(qi)(qi)正常工作(zuo)，4.5V是(shi)最低電(dian)(dian)(dian)壓(包括(kuo)容(rong)差(cha))。因為(wei)充(chong)(chong)電(dian)(dian)(dian)器(qi)(qi)采用的(de)(de)是(shi)線(xian)性(xing)結構，充(chong)(chong)電(dian)(dian)(dian)效率與輸(shu)入、輸(shu)出電(dian)(dian)(dian)壓的(de)(de)差(cha)值成反比，用最低電(dian)(dian)(dian)壓為(wei)充(chong)(chong)電(dian)(dian)(dian)器(qi)(qi)供電(dian)(dian)(dian)有助于降低功率損耗。   

    當調(diao)節點電(dian)壓高(gao)于(yu)(yu)(yu)1.24V時(shi)(shi)，并(bing)聯型(xing)穩(wen)(wen)壓器(qi)(qi)將吸入(ru)電(dian)流(liu)，導通光(guang)耦LED，原邊的(de)(de)(de)光(guang)敏晶體管(guan)將處于(yu)(yu)(yu)發光(guang)狀(zhuang)態。U1的(de)(de)(de)OPTO輸入(ru)引(yin)(yin)腳(jiao)用(yong)于(yu)(yu)(yu)直接(jie)連接(jie)光(guang)敏晶體管(guan)，以極(ji)其簡單的(de)(de)(de)方式(shi)構成閉合環(huan)路。光(guang)敏晶體管(guan)導通時(shi)(shi)，OPTO引(yin)(yin)腳(jiao)被拉低，內部比(bi)(bi)較器(qi)(qi)在(zai)它的(de)(de)(de)一(yi)個(ge)(ge)輸入(ru)端檢(jian)測(ce)到較低的(de)(de)(de)電(dian)壓，比(bi)(bi)較器(qi)(qi)的(de)(de)(de)另一(yi)輸入(ru)電(dian)流(liu)檢(jian)測(ce)引(yin)(yin)腳(jiao)(CS)的(de)(de)(de)峰值(zhi)電(dian)壓，OPTO引(yin)(yin)腳(jiao)的(de)(de)(de)低電(dian)壓將在(zai)每個(ge)(ge)周期直接(jie)限制功率MOSFETN1的(de)(de)(de)峰值(zhi)電(dian)流(liu)。由于(yu)(yu)(yu)U1是一(yi)個(ge)(ge)PWM控制器(qi)(qi)，電(dian)流(liu)限制使(shi)得電(dian)壓調(diao)節受作用(yong)在(zai)N1上的(de)(de)(de)占空比(bi)(bi)(導通時(shi)(shi)間與斷開時(shi)(shi)間的(de)(de)(de)比(bi)(bi)值(zhi))的(de)(de)(de)影響，環(huan)路穩(wen)(wen)定性通過調(diao)節R11和(he)(he)C12來保證(zheng)。R10和(he)(he)C5(連接(jie)在(zai)U3的(de)(de)(de)第(di)3和(he)(he)第(di)4引(yin)(yin)腳(jiao))可消除穩(wen)(wen)定工(gong)作情(qing)況下(xia)的(de)(de)(de)噪(zao)聲干擾。    

    U4的工作(zuo)特點    

    U4是一款用于單節Li+電池充電、功能完備的充電器，采用線性充(chong)電(dian)(dian)(dian)(dian)模(mo)式，內(nei)置調(diao)整管(guan)和電(dian)(dian)(dian)(dian)流檢(jian)(jian)測(ce)電(dian)(dian)(dian)(dian)路。另(ling)外(wai)，它(ta)還(huan)集成了一個(ge)反向(xiang)抑制(zhi)二(er)極管(guan)，在(zai)去掉輸(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)源時(shi)可(ke)防止電(dian)(dian)(dian)(dian)池(chi)方(fang)向(xiang)放電(dian)(dian)(dian)(dian)。接(jie)入(ru)一個(ge)深度放電(dian)(dian)(dian)(dian)的(de)(de)電(dian)(dian)(dian)(dian)池(chi)時(shi)，U4能夠檢(jian)(jian)測(ce)到(dao)(dao)低(di)電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(低(di)于(yu)2.5V)，這樣(yang)，U4將首先啟動(dong)涓流充(chong)電(dian)(dian)(dian)(dian)過程，在(zai)快充(chong)周(zhou)期的(de)(de)1/10時(shi)間段對電(dian)(dian)(dian)(dian)池(chi)進行涓流充(chong)電(dian)(dian)(dian)(dian)，直到(dao)(dao)電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓上升(sheng)到(dao)(dao)2.5V以上。在(zai)涓流充(chong)電(dian)(dian)(dian)(dian)到(dao)(dao)快速(su)充(chong)電(dian)(dian)(dian)(dian)轉換時(shi)，軟(ruan)啟動(dong)電(dian)(dian)(dian)(dian)路迫使充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流在(zai)3ms時(shi)間內(nei)緩慢上升(sheng)，避(bi)免較大的(de)(de)浪涌(yong)電(dian)(dian)(dian)(dian)流拉(la)低(di)輸(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)源。    

   上(shang)述(shu)功(gong)能(neng)的(de)實施不需要微控(kong)制器的(de)監(jian)管，而且，U4還具有可編程的(de)溫(wen)度限制功(gong)能(neng)，我們會在下面就(jiu)這一點進行詳細(xi)討論。用(yong)一個(ge)電(dian)阻設置最大充電(dian)電(dian)流，電(dian)阻兩端的(de)電(dian)壓與充電(dian)電(dian)流成(cheng)正比，通(tong)過(guo)監(jian)視該電(dian)壓即可連續跟(gen)蹤(zong)(zong)充電(dian)電(dian)流，更為復雜的(de)系(xi)統(tong)也可以采用(yong)ADC跟(gen)蹤(zong)(zong)監(jian)視充電(dian)電(dian)流。    

    Maxim還提供有另一(yi)款與MAX1507非(fei)常相似(si)的充電器―MAX1555，這(zhe)款IC能夠在(zai)沒有交流(liu)電源(yuan)的情況下從USB主機獲得充電電源(yuan)。   

    電流調節 

    如果把Li+電(dian)(dian)池直接與一個低(di)阻電(dian)(dian)壓源連(lian)接，充電(dian)(dian)電(dian)(dian)流(liu)將不受任何限(xian)制，這種狀況會對電(dian)(dian)池及(ji)其周圍環境(jing)造成災難性的(de)(de)損(sun)害，從Li+電(dian)(dian)池的(de)(de)安全性考慮，必須將其充電(dian)(dian)電(dian)(dian)流(liu)限(xian)制在額, 定(ding)范圍以內。U4根據連(lian)接在ISET(第5引腳)的(de)(de)電(dian)(dian)阻限(xian)制充電(dian)(dian)電(dian)(dian)流(liu)，圖1電(dian)(dian)路中選用了一個1.87kΩ的(de)(de)電(dian)(dian)阻，將最大(da)電(dian)(dian)流(liu)設置(zhi)在780mA: 

    Ifast=1461V/Rset=1461/1870≈780mA 

    電(dian)池(chi)電(dian)壓(ya)最小時(shi)，由(you)于輸入(ru)(ru)穩定在4.5V，U4輸入(ru)(ru)與輸出的(de)(de)壓(ya)差最大，如(ru)果此時(shi)電(dian)池(chi)是以最大電(dian)流充電(dian)，U4功耗將達到最大值。例(li)如(ru)，假設(she)電(dian)池(chi)電(dian)壓(ya)為(wei)2.5V，則對應的(de)(de)功耗為(wei)：  

    P=IV=(0.78A)×(4.5V-2.5V)=1.56W 

    U4封裝(8引腳薄型DFN-EP，EP表示裸露焊盤)在溫度高達70℃時可以耗散的最大功率是1.951W，這樣，在整個電池電壓范圍內以780mA的電流充電應該沒有任何問題。但是，如果IC管芯由于較高的環境溫度或不良的散熱條件達到了70℃，U4內部的熱調節環路將自動降低充電電流，這一過程有別于其它充電IC中的“熱關斷”，“熱關斷”方式只是簡單地中止芯片中的所有電路工作，直到晶片溫度降至規定的數值。MAX1507所采用的方案能夠保證在芯片溫度不超出最大限制范圍的條件下提供最快的充電速率，隨著電池電壓的升高，充電電流在保持最高溫度的前提下逐漸升高，直到達到最大充電電流。在此之后，充電器在滿足(zu)芯片(pian)溫(wen)度(du)限制的(de)條件(jian)下將以最(zui)大充(chong)電(dian)電(dian)流(liu)對電(dian)池充(chong)電(dian)，直到電(dian)池電(dian)壓(ya)達(da)到內部設置的(de)4.2V