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(lei)型的電池對充電器的要求   

    通常快(kuai)速(su)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)比涓流(liu)(liu)(liu)(liu)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)更受歡迎，但快(kuai)速(su)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)對(dui)電(dian)(dian)(dian)(dian)(dian)(dian)路的(de)(de)(de)要(yao)求也復雜，鎳(nie)(nie)氫或鎳(nie)(nie)鎘電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)(de)快(kuai)速(su)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)技術與其它(ta)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)也是(shi)不(bu)同的(de)(de)(de)。鎳(nie)(nie)鎘和(he)(he)(he)鎳(nie)(nie)氫電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)通常在恒流(liu)(liu)(liu)(liu)狀態下快(kuai)充(chong)(chong)(chong)(chong)(chong)，而不(bu)是(shi)恒壓(ya)狀態下。快(kuai)充(chong)(chong)(chong)(chong)(chong)終(zhong)止(zhi)檢測基于電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)和(he)(he)(he)溫度的(de)(de)(de)變化(hua)率(lv)，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器還應具(ju)備(bei)過壓(ya)保護和(he)(he)(he)過熱保護功能。Li+和(he)(he)(he)鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器必須保證作用(yong)到電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)上的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)和(he)(he)(he)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)最大值在規定的(de)(de)(de)范圍內，當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)維持在最大單節電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)下降到一個較低(di)值時，充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器終(zhong)止(zhi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。Li+和(he)(he)(he)鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器的(de)(de)(de)區別在于所允許的(de)(de)(de)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)、最大電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，另外鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器一般(ban)具(ju)有浮充(chong)(chong)(chong)(chong)(chong)能力(li)(浮充(chong)(chong)(chong)(chong)(chong)是(shi)為(wei)了補充(chong)(chong)(chong)(chong)(chong)鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)(de)自放電(dian)(dian)(dian)(dian)(dian)(dian)，而對(dui)一個已經完全充(chong)(chong)(chong)(chong)(chong)滿的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)繼續輸入充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的(de)(de)(de)技術)，Li+電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)(de)自放電(dian)(dian)(dian)(dian)(dian)(dian)非常低(di)，所以(yi)不(bu)需(xu)要(yao)浮充(chong)(chong)(chong)(chong)(chong)。    

    Li+電(dian)池    

    為便攜(xie)式產品(pin)選(xuan)擇電(dian)(dian)池(chi)時，最(zui)(zui)(zui)重(zhong)要(yao)的(de)(de)是(shi)高能量密度(du)、尺寸、重(zhong)量和價格。迄今(jin)為止，Li+電(dian)(dian)池(chi)在最(zui)(zui)(zui)為流(liu)行的(de)(de)電(dian)(dian)池(chi)中能夠提供最(zui)(zui)(zui)高的(de)(de)體積和能量密度(du)，但其每瓦時的(de)(de)成本也較(jiao)(jiao)高。鉛酸電(dian)(dian)池(chi)的(de)(de)每瓦時成本最(zui)(zui)(zui)低，但比較(jiao)(jiao)笨重(zhong)。本文以Li+電(dian)(dian)池(chi)為例討論充電(dian)(dian)器的(de)(de)設計，它在便攜(xie)式產品(pin)中已經被普遍使用。我(wo)們(men)選(xuan)擇780mA的(de)(de)充電(dian)(dian)電(dian)(dian)流(liu)和4.2V的(de)(de)終止電(dian)(dian)壓。 

 通用輸(shu)入交(jiao)流(liu)電(dian)壓的離線式Li+電(dian)池(chi)充電(dian)器。    

    所(suo)示充電(dian)器無需微處理器干預，輸入電(dian)源可(ke)(ke)以采用全(quan)球范圍的任何交流電(dian)源，省去(qu)了(le)(le)大體積60Hz變壓(ya)器，而且可(ke)(ke)提(ti)供(gong)單(dan)節Li+電(dian)池(chi)所(suo)要求(qiu)的精(jing)確(que)的充電(dian)電(dian)壓(ya)和電(dian)流。充電(dian)器IC(U4)集(ji)成了(le)(le)全(quan)面(mian)的保(bao)(bao)護(hu)功能(電(dian)壓(ya)、電(dian)流和自保(bao)(bao)護(hu))，確(que)保(bao)(bao)Li+電(dian)池(chi)的安全(quan)充電(dian)。    

    假設Li+電池帶有過(guo)流、過(guo)壓(ya)和(he)過(guo)熱保(bao)護，這些保(bao)護特性在(zai)電池包(bao)里是(shi)必(bi)需的，因為充電期間一旦電路出現故(gu)障，Li+電池將存(cun)在(zai)很大的危險性，過(guo)流、過(guo)壓(ya)或溫度(du)過(guo)高都有可能造成(cheng)Li+電池爆炸。    

    電路(lu)描述     

    包(bao)括兩顆(ke)主(zhu)器(qi)件(U1和U4)、精(jing)密基準(zhun)(U3)和光耦(U2)。U1是離線式開關(guan)控制(zhi)器(qi)，配合隔(ge)離變壓(ya)器(qi)、光耦和基準(zhun)產(chan)生隔(ge)離的穩(wen)壓(ya)直流(liu)輸出。直流(liu)電(dian)(dian)壓(ya)供(gong)給(gei)電(dian)(dian)池充(chong)(chong)電(dian)(dian)器(qi)(U4)，U4提(ti)供(gong)電(dian)(dian)流(liu)限制(zhi)、電(dian)(dian)壓(ya)調節、電(dian)(dian)池充(chong)(chong)電(dian)(dian)和充(chong)(chong)電(dian)(dian)指示等功(gong)能。本方案中(zhong)，U4是一(yi)款簡單的線性充(chong)(chong)電(dian)(dian)器(qi)，內置(zhi)調整管，結合其熱(re)控制(zhi)環路提(ti)供(gong)快(kuai)速充(chong)(chong)電(dian)(dian)。    

    MAX5022的特性     

    U1(MAX5022)在寬輸入(ru)范圍的(de)(de)應用(yong)中(zhong)很容易設計(ji)，本(ben)文(wen)所(suo)提(ti)供的(de)(de)方案要求能夠滿(man)足(zu)全球各地的(de)(de)交流電(dian)(dian)源(yuan)規格(ge)，這(zhe)里假設通用(yong)的(de)(de)輸入(ru)電(dian)(dian)源(yuan)電(dian)(dian)壓范圍為(wei)85VAC至(zhi)265VAC。MAX5022的(de)(de)輸入(ru)范圍指標以及評(ping)估板電(dian)(dian)路(lu)的(de)(de)輸入(ru)范圍恰好(hao)滿(man)足(zu)這(zhe)一(yi)需求。對(dui)于所(suo)示充電(dian)(dian)器的(de)(de)電(dian)(dian)源(yuan)端(duan)MAX5022評(ping)估板不需要作任何修(xiu)改，隔離端(duan)只需對(dui)評(ping)估板的(de)(de)電(dian)(dian)阻值(zhi)稍作修(xiu)改。    

    對(dui)(dui)于更(geng)大(da)功(gong)率(lv)的(de)(de)(de)應用，只(zhi)需(xu)選(xuan)取功(gong)率(lv)較大(da)的(de)(de)(de)開關(guan)管(guan)和能夠處理更(geng)大(da)功(gong)率(lv)的(de)(de)(de)變壓(ya)(ya)器(qi)(qi)(qi)即可。圖1所示電(dian)路要(yao)求充電(dian)電(dian)流為(wei)780mA，最大(da)電(dian)池電(dian)壓(ya)(ya)為(wei)4.2V。對(dui)(dui)充電(dian)電(dian)源的(de)(de)(de)要(yao)求與MAX5022評(ping)估板(ban)所提供的(de)(de)(de)輸(shu)出相吻合(he)：5V@1A，因此，不需(xu)要(yao)更(geng)換評(ping)估板(ban)的(de)(de)(de)晶體管(guan)和變壓(ya)(ya)器(qi)(qi)(qi)。U4采(cai)用SOT23封裝，所以，充電(dian)器(qi)(qi)(qi)的(de)(de)(de)尺寸(cun)(cun)在(zai)很大(da)程度(du)上取決于應用對(dui)(dui)充電(dian)電(dian)源的(de)(de)(de)需(xu)求。變壓(ya)(ya)器(qi)(qi)(qi)是電(dian)路中尺寸(cun)(cun)最大(da)的(de)(de)(de)元件(jian)，由于開關(guan)控制器(qi)(qi)(qi)的(de)(de)(de)工作頻(pin)率(lv)大(da)于250kHz，允許系(xi)統選(xuan)用小尺寸(cun)(cun)的(de)(de)(de)變壓(ya)(ya)器(qi)(qi)(qi)。     

    上電(dian)(dian)(dian)時，在開(kai)(kai)關控制器工作(zuo)之前，U1調(diao)節器直接通過(guo)泄(xie)漏電(dian)(dian)(dian)阻R1、R2從整流通路吸取少(shao)量的(de)電(dian)(dian)(dian)流，兩(liang)個電(dian)(dian)(dian)阻阻值(zhi)保證每個電(dian)(dian)(dian)阻上的(de)壓(ya)降不會(hui)超(chao)(chao)出(chu)每個電(dian)(dian)(dian)阻的(de)容(rong)限，Vin引腳電(dian)(dian)(dian)壓(ya)不會(hui)超(chao)(chao)出(chu)其(qi)28V額定值(zhi)(30V為(wei)絕(jue)對最大值(zhi))，U1在輸(shu)(shu)入(ru)電(dian)(dian)(dian)壓(ya)達到24V時開(kai)(kai)始開(kai)(kai)關操作(zuo)，并吸取更大的(de)電(dian)(dian)(dian)流(高于R1、R2所能(neng)提(ti)供(gong)(gong)的(de)電(dian)(dian)(dian)流)，在變壓(ya)器副邊(bian)線圈能(neng)夠提(ti)供(gong)(gong)足(zu)夠的(de)能(neng)量之前，額外的(de)電(dian)(dian)(dian)流由Vin引腳的(de)旁(pang)路電(dian)(dian)(dian)容(rong)供(gong)(gong)給。這(zhe)種處理方式能(neng)夠適合較寬的(de)輸(shu)(shu)入(ru)電(dian)(dian)(dian)壓(ya)范圍，對效率的(de)影(ying)響也很小(xiao)，這(zhe)是因為(wei)在啟動過(guo)程(cheng)中只(zhi)需極小(xiao)的(de)供(gong)(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(典型值(zhi)為(wei)50uA)。   

    為了防止(zhi)U1的(de)(de)Vin引(yin)腳(jiao)出(chu)現過(guo)壓(ya)(ya)，可以在Vin與地之(zhi)間接(jie)一個26V至30V的(de)(de)齊(qi)納管，電壓(ya)(ya)值(zhi)需要高于欠壓(ya)(ya)鎖(suo)存電壓(ya)(ya)的(de)(de)最大值(zhi)，低于該引(yin)腳(jiao)所允許的(de)(de)最大絕(jue)對電壓(ya)(ya)。如果器(qi)件沒(mei)有啟動正常的(de)(de)開(kai)關(guan)操作，則可認為電路發生了某些問題，所以，這一保護(hu)措施(shi)對于U1來說并不是必需的(de)(de)。     

    U1是一款電流模式PWM控制器，具有逐周期限(xian)流電路，必要時其占(zhan)空(kong)比(bi)可以提高到(dao)75%，非常(chang)適(shi)合圖1所示的(de)反激拓撲。原邊(bian)開關(guan)電流檢(jian)測采用尺(chi)寸為1206的(de)1.78Ω電阻(R7)，該(gai)電阻限(xian)制了變壓器原邊(bian)的(de)最大電流。固定開關(guan)頻率(lv)和最大占(zhan)空(kong)比(bi)限(xian)制使(shi)得(de)最大限(xian)流具有輸出短路保護(hu)功(gong)能。   

    一旦短(duan)(duan)路(lu)輸出造成電(dian)路(lu)達到了上述限(xian)制條件，第(di)三組線圈(quan)將無法(fa)提(ti)供(gong)10V以上的電(dian)壓(UVLO的低電(dian)壓門限(xian))，U1將再次(ci)進(jin)入啟動狀態，停止(zhi)開關(guan)操(cao)作。短(duan)(duan)路(lu)故(gu)障解(jie)除后系統會自動恢復正常的工作狀態。   

    電壓調節   

    變壓(ya)(ya)器副邊的(de)電(dian)(dian)壓(ya)(ya)經過整(zheng)流、濾波，然后(hou)由R4、R5分壓(ya)(ya)在并聯(lian)型(xing)穩壓(ya)(ya)器U3的(de)調節點產生1.24V(對應于4.5V輸(shu)出(chu))的(de)反饋電(dian)(dian)壓(ya)(ya)。為(wei)保證電(dian)(dian)池充(chong)電(dian)(dian)器正常工作，4.5V是最低(di)電(dian)(dian)壓(ya)(ya)(包括容差)。因為(wei)充(chong)電(dian)(dian)器采用(yong)的(de)是線性結構，充(chong)電(dian)(dian)效(xiao)率與輸(shu)入(ru)、輸(shu)出(chu)電(dian)(dian)壓(ya)(ya)的(de)差值成反比(bi)，用(yong)最低(di)電(dian)(dian)壓(ya)(ya)為(wei)充(chong)電(dian)(dian)器供電(dian)(dian)有助于降低(di)功(gong)率損耗。   

    當調(diao)節(jie)點電(dian)(dian)(dian)(dian)壓(ya)高(gao)于1.24V時(shi)(shi)，并聯型穩壓(ya)器將(jiang)吸入(ru)電(dian)(dian)(dian)(dian)流(liu)，導(dao)(dao)通(tong)光(guang)耦LED，原邊的(de)光(guang)敏(min)晶體(ti)管將(jiang)處于發光(guang)狀態(tai)。U1的(de)OPTO輸(shu)(shu)入(ru)引腳用于直(zhi)接(jie)(jie)連接(jie)(jie)光(guang)敏(min)晶體(ti)管，以極其簡單的(de)方式(shi)構成閉(bi)合(he)環(huan)路。光(guang)敏(min)晶體(ti)管導(dao)(dao)通(tong)時(shi)(shi)，OPTO引腳被(bei)拉低，內部(bu)比(bi)(bi)較器在它的(de)一(yi)個(ge)輸(shu)(shu)入(ru)端檢測到較低的(de)電(dian)(dian)(dian)(dian)壓(ya)，比(bi)(bi)較器的(de)另一(yi)輸(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)流(liu)檢測引腳(CS)的(de)峰值(zhi)電(dian)(dian)(dian)(dian)壓(ya)，OPTO引腳的(de)低電(dian)(dian)(dian)(dian)壓(ya)將(jiang)在每個(ge)周期(qi)直(zhi)接(jie)(jie)限(xian)制功(gong)率MOSFETN1的(de)峰值(zhi)電(dian)(dian)(dian)(dian)流(liu)。由于U1是一(yi)個(ge)PWM控制器，電(dian)(dian)(dian)(dian)流(liu)限(xian)制使(shi)得電(dian)(dian)(dian)(dian)壓(ya)調(diao)節(jie)受作用在N1上的(de)占空比(bi)(bi)(導(dao)(dao)通(tong)時(shi)(shi)間與斷開(kai)時(shi)(shi)間的(de)比(bi)(bi)值(zhi))的(de)影響(xiang)，環(huan)路穩定性通(tong)過調(diao)節(jie)R11和(he)C12來保證(zheng)。R10和(he)C5(連接(jie)(jie)在U3的(de)第(di)3和(he)第(di)4引腳)可(ke)消除穩定工作情況下的(de)噪聲干擾。    

    U4的(de)工作特(te)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(xian)性充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)模式，內置調(diao)整管和電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)檢測電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。另外，它還集成了一個反向(xiang)抑制(zhi)二(er)極管，在去(qu)掉(diao)輸入電(dian)(dian)(dian)(dian)(dian)(dian)源時(shi)可防止電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)方向(xiang)放電(dian)(dian)(dian)(dian)(dian)(dian)。接入一個深度(du)放電(dian)(dian)(dian)(dian)(dian)(dian)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)時(shi)，U4能夠檢測到低(di)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(低(di)于2.5V)，這(zhe)樣，U4將首(shou)先啟動(dong)涓(juan)流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程，在快(kuai)(kuai)充(chong)(chong)周(zhou)期(qi)的(de)1/10時(shi)間段對電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進(jin)行涓(juan)流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，直到電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓上升到2.5V以上。在涓(juan)流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)到快(kuai)(kuai)速充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)轉換時(shi)，軟啟動(dong)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)迫使充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)在3ms時(shi)間內緩慢上升，避免(mian)較(jiao)大的(de)浪涌電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)拉低(di)輸入電(dian)(dian)(dian)(dian)(dian)(dian)源。    

   上述功能的(de)(de)實施不需要微控制(zhi)器的(de)(de)監(jian)管，而且，U4還具(ju)有可(ke)編程的(de)(de)溫度(du)限制(zhi)功能，我們會在下(xia)面就(jiu)這一點進行詳(xiang)細討論。用一個電(dian)(dian)阻設置最大(da)充電(dian)(dian)電(dian)(dian)流(liu)，電(dian)(dian)阻兩端(duan)的(de)(de)電(dian)(dian)壓與充電(dian)(dian)電(dian)(dian)流(liu)成正比，通過監(jian)視該電(dian)(dian)壓即可(ke)連(lian)續跟(gen)蹤(zong)充電(dian)(dian)電(dian)(dian)流(liu)，更為(wei)復雜(za)的(de)(de)系統也可(ke)以采(cai)用ADC跟(gen)蹤(zong)監(jian)視充電(dian)(dian)電(dian)(dian)流(liu)。    

    Maxim還提供有另(ling)一款(kuan)與MAX1507非常(chang)相(xiang)似的充電(dian)(dian)(dian)器―MAX1555，這款(kuan)IC能(neng)夠在沒(mei)有交流電(dian)(dian)(dian)源的情況下(xia)從USB主(zhu)機獲得(de)充電(dian)(dian)(dian)電(dian)(dian)(dian)源。   

    電流調節 

    如果(guo)把Li+電(dian)(dian)池直接(jie)(jie)與(yu)一個低阻電(dian)(dian)壓源(yuan)連接(jie)(jie)，充(chong)電(dian)(dian)電(dian)(dian)流將(jiang)不受任何限制，這(zhe)種狀況(kuang)會對電(dian)(dian)池及(ji)其周圍(wei)環境造成災(zai)難性的(de)損害(hai)，從Li+電(dian)(dian)池的(de)安全性考慮，必(bi)須將(jiang)其充(chong)電(dian)(dian)電(dian)(dian)流限制在額, 定范圍(wei)以內。U4根據連接(jie)(jie)在ISET(第5引腳(jiao))的(de)電(dian)(dian)阻限制充(chong)電(dian)(dian)電(dian)(dian)流，圖1電(dian)(dian)路中(zhong)選用了一個1.87kΩ的(de)電(dian)(dian)阻，將(jiang)最大電(dian)(dian)流設置(zhi)在780mA: 

    Ifast=1461V/Rset=1461/1870≈780mA 

    電(dian)(dian)池電(dian)(dian)壓(ya)最(zui)小時，由于輸(shu)入穩定在4.5V，U4輸(shu)入與輸(shu)出的壓(ya)差最(zui)大(da)，如果此時電(dian)(dian)池是以(yi)最(zui)大(da)電(dian)(dian)流充電(dian)(dian)，U4功(gong)(gong)耗將達到最(zui)大(da)值(zhi)。例如，假設電(dian)(dian)池電(dian)(dian)壓(ya)為(wei)2.5V，則(ze)對(dui)應的功(gong)(gong)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)溫度限制(zhi)的(de)條件下將以(yi)最大充(chong)電(dian)電(dian)流(liu)對電(dian)池充(chong)電(dian)，直到(dao)電(dian)池電(dian)壓達到(dao)內部設置的(de)4.2V