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)同化學類型的電池對充電器(qi)的要求(qiu)   

    通常(chang)快(kuai)(kuai)速充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)比(bi)涓(juan)流(liu)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)更受歡迎，但(dan)快(kuai)(kuai)速充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路的(de)(de)(de)(de)要求(qiu)也復雜，鎳(nie)氫或(huo)鎳(nie)鎘電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)(de)快(kuai)(kuai)速充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)技術(shu)與其它電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)也是不同(tong)的(de)(de)(de)(de)。鎳(nie)鎘和鎳(nie)氫電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)通常(chang)在(zai)恒(heng)流(liu)狀態下快(kuai)(kuai)充(chong)(chong)(chong)(chong)，而(er)不是恒(heng)壓(ya)狀態下。快(kuai)(kuai)充(chong)(chong)(chong)(chong)終止(zhi)檢測(ce)基于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)和溫度的(de)(de)(de)(de)變化率，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)還(huan)應(ying)具(ju)備過壓(ya)保護和過熱保護功能。Li+和鉛(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)必須保證作用到電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)上的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)最大值(zhi)在(zai)規定(ding)的(de)(de)(de)(de)范圍內，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)維持在(zai)最大單節電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)下降到一個較低(di)值(zhi)時，充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)終止(zhi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。Li+和鉛(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)的(de)(de)(de)(de)區(qu)別在(zai)于(yu)所(suo)(suo)允許的(de)(de)(de)(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)、最大電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，另外鉛(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)一般具(ju)有浮充(chong)(chong)(chong)(chong)能力(浮充(chong)(chong)(chong)(chong)是為了(le)補充(chong)(chong)(chong)(chong)鉛(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)(de)自放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，而(er)對一個已經完全充(chong)(chong)(chong)(chong)滿的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)繼(ji)續輸入(ru)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)技術(shu))，Li+電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)(de)自放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)非常(chang)低(di)，所(suo)(suo)以(yi)不需要浮充(chong)(chong)(chong)(chong)。    

    Li+電(dian)池    

    為便攜式(shi)產(chan)品(pin)選擇電(dian)(dian)(dian)池時，最重要的(de)(de)是(shi)高能量密度、尺(chi)寸、重量和(he)價(jia)格。迄今為止，Li+電(dian)(dian)(dian)池在(zai)最為流行的(de)(de)電(dian)(dian)(dian)池中(zhong)能夠提供最高的(de)(de)體(ti)積和(he)能量密度，但(dan)其每(mei)瓦(wa)時的(de)(de)成本也較(jiao)高。鉛(qian)酸電(dian)(dian)(dian)池的(de)(de)每(mei)瓦(wa)時成本最低，但(dan)比較(jiao)笨重。本文以(yi)Li+電(dian)(dian)(dian)池為例討論充(chong)電(dian)(dian)(dian)器的(de)(de)設計，它(ta)在(zai)便攜式(shi)產(chan)品(pin)中(zhong)已經被普遍使用。我們選擇780mA的(de)(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流和(he)4.2V的(de)(de)終止電(dian)(dian)(dian)壓。 

 通用(yong)輸入交流電(dian)(dian)壓的離(li)線式Li+電(dian)(dian)池充電(dian)(dian)器。    

    所示充電(dian)器(qi)無需微處理器(qi)干預(yu)，輸(shu)入(ru)電(dian)源可以采用(yong)全球范圍的(de)(de)任(ren)何交流電(dian)源，省去了(le)大體積(ji)60Hz變壓(ya)器(qi)，而且可提供單節(jie)Li+電(dian)池(chi)所要(yao)求(qiu)的(de)(de)精確的(de)(de)充電(dian)電(dian)壓(ya)和(he)電(dian)流。充電(dian)器(qi)IC(U4)集成了(le)全面(mian)的(de)(de)保(bao)護功能(電(dian)壓(ya)、電(dian)流和(he)自保(bao)護)，確保(bao)Li+電(dian)池(chi)的(de)(de)安全充電(dian)。    

    假設Li+電(dian)(dian)池(chi)(chi)帶有(you)過(guo)流、過(guo)壓和過(guo)熱(re)保護，這些保護特性(xing)在電(dian)(dian)池(chi)(chi)包里(li)是(shi)必需的，因為充(chong)電(dian)(dian)期間一旦電(dian)(dian)路出現故障(zhang)，Li+電(dian)(dian)池(chi)(chi)將存在很大的危險(xian)性(xing)，過(guo)流、過(guo)壓或溫度過(guo)高都有(you)可能造成Li+電(dian)(dian)池(chi)(chi)爆炸。    

    電路描述     

    包括兩顆主器(qi)件(U1和(he)U4)、精(jing)密基準(U3)和(he)光(guang)耦(ou)(U2)。U1是離(li)線(xian)式(shi)開關(guan)控(kong)制(zhi)器(qi)，配(pei)合(he)隔離(li)變(bian)壓(ya)器(qi)、光(guang)耦(ou)和(he)基準產(chan)生隔離(li)的穩(wen)壓(ya)直(zhi)流(liu)輸出。直(zhi)流(liu)電(dian)(dian)(dian)壓(ya)供給電(dian)(dian)(dian)池充電(dian)(dian)(dian)器(qi)(U4)，U4提(ti)供電(dian)(dian)(dian)流(liu)限制(zhi)、電(dian)(dian)(dian)壓(ya)調節、電(dian)(dian)(dian)池充電(dian)(dian)(dian)和(he)充電(dian)(dian)(dian)指示(shi)等功能。本方案中，U4是一款簡單的線(xian)性充電(dian)(dian)(dian)器(qi)，內置調整管，結合(he)其熱控(kong)制(zhi)環路(lu)提(ti)供快速充電(dian)(dian)(dian)。    

    MAX5022的(de)特性(xing)     

    U1(MAX5022)在寬輸(shu)入(ru)(ru)(ru)范(fan)圍的應用中很容易設計，本文所(suo)(suo)提供的方(fang)案要求(qiu)能夠滿(man)足全球各地的交(jiao)流電(dian)(dian)(dian)源(yuan)規(gui)格，這(zhe)里(li)假設通(tong)用的輸(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)壓范(fan)圍為85VAC至265VAC。MAX5022的輸(shu)入(ru)(ru)(ru)范(fan)圍指標以(yi)及評估板電(dian)(dian)(dian)路(lu)的輸(shu)入(ru)(ru)(ru)范(fan)圍恰好滿(man)足這(zhe)一(yi)需(xu)求(qiu)。對(dui)于所(suo)(suo)示充電(dian)(dian)(dian)器的電(dian)(dian)(dian)源(yuan)端MAX5022評估板不需(xu)要作任何修改，隔離端只需(xu)對(dui)評估板的電(dian)(dian)(dian)阻值稍作修改。    

    對于(yu)更(geng)大功(gong)(gong)率的應用，只(zhi)需(xu)選(xuan)取功(gong)(gong)率較大的開(kai)關管(guan)和能夠(gou)處理更(geng)大功(gong)(gong)率的變壓(ya)(ya)器(qi)(qi)(qi)即可(ke)。圖(tu)1所示電(dian)(dian)路要(yao)(yao)求(qiu)充電(dian)(dian)電(dian)(dian)流為(wei)780mA，最(zui)大電(dian)(dian)池電(dian)(dian)壓(ya)(ya)為(wei)4.2V。對充電(dian)(dian)電(dian)(dian)源的要(yao)(yao)求(qiu)與(yu)MAX5022評(ping)估(gu)板(ban)(ban)所提供(gong)的輸出相吻合：5V@1A，因此，不需(xu)要(yao)(yao)更(geng)換評(ping)估(gu)板(ban)(ban)的晶(jing)體(ti)管(guan)和變壓(ya)(ya)器(qi)(qi)(qi)。U4采用SOT23封(feng)裝，所以，充電(dian)(dian)器(qi)(qi)(qi)的尺(chi)寸在很大程度上取決于(yu)應用對充電(dian)(dian)電(dian)(dian)源的需(xu)求(qiu)。變壓(ya)(ya)器(qi)(qi)(qi)是(shi)電(dian)(dian)路中尺(chi)寸最(zui)大的元件，由于(yu)開(kai)關控(kong)制器(qi)(qi)(qi)的工作頻率大于(yu)250kHz，允許(xu)系統選(xuan)用小尺(chi)寸的變壓(ya)(ya)器(qi)(qi)(qi)。     

    上電(dian)(dian)(dian)(dian)(dian)時，在(zai)開關(guan)控(kong)制(zhi)器工作之前，U1調節器直接通(tong)過泄漏電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)R1、R2從整流(liu)通(tong)路吸取少量的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)，兩(liang)個(ge)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)阻(zu)(zu)值(zhi)保證每個(ge)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)上的(de)(de)(de)壓降不(bu)會(hui)超出每個(ge)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)的(de)(de)(de)容限，Vin引(yin)腳(jiao)電(dian)(dian)(dian)(dian)(dian)壓不(bu)會(hui)超出其(qi)28V額定(ding)值(zhi)(30V為絕對(dui)最大值(zhi))，U1在(zai)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)壓達到(dao)24V時開始開關(guan)操作，并吸取更大的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(高于R1、R2所能(neng)(neng)(neng)提供的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu))，在(zai)變壓器副邊(bian)線圈能(neng)(neng)(neng)夠提供足夠的(de)(de)(de)能(neng)(neng)(neng)量之前，額外的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)由Vin引(yin)腳(jiao)的(de)(de)(de)旁路電(dian)(dian)(dian)(dian)(dian)容供給。這種處理方式能(neng)(neng)(neng)夠適合較寬的(de)(de)(de)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)壓范圍(wei)，對(dui)效率的(de)(de)(de)影響也很小(xiao)(xiao)，這是因為在(zai)啟動過程中(zhong)只需極小(xiao)(xiao)的(de)(de)(de)供電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(典型值(zhi)為50uA)。   

    為了(le)防止U1的(de)Vin引腳(jiao)出現過(guo)壓(ya)，可以(yi)在Vin與地之間接(jie)一(yi)個26V至30V的(de)齊納管，電壓(ya)值(zhi)需要高于欠壓(ya)鎖存電壓(ya)的(de)最大(da)值(zhi)，低于該引腳(jiao)所允許的(de)最大(da)絕對(dui)電壓(ya)。如果器件沒有(you)啟動正(zheng)常(chang)的(de)開關操(cao)作，則(ze)可認為電路發生了(le)某些問題，所以(yi)，這一(yi)保護措施對(dui)于U1來說并不是(shi)必需的(de)。     

    U1是一(yi)款電(dian)流(liu)(liu)模式PWM控制(zhi)器，具有(you)逐周期限流(liu)(liu)電(dian)路，必要時其占(zhan)空比可(ke)以提高到(dao)75%，非常適合(he)圖(tu)1所示的反激拓撲(pu)。原邊(bian)開關電(dian)流(liu)(liu)檢(jian)測采用尺寸為1206的1.78Ω電(dian)阻(zu)(R7)，該電(dian)阻(zu)限制(zhi)了變(bian)壓器原邊(bian)的最(zui)大電(dian)流(liu)(liu)。固定開關頻率和最(zui)大占(zhan)空比限制(zhi)使(shi)得最(zui)大限流(liu)(liu)具有(you)輸(shu)出短(duan)路保護(hu)功能。   

    一旦短路輸出造成電路達到了上(shang)述限制條(tiao)件，第(di)三(san)組線(xian)圈將無(wu)法提供10V以上(shang)的(de)電壓(ya)(UVLO的(de)低(di)電壓(ya)門限)，U1將再次進入(ru)啟動狀(zhuang)態，停止開關操作(zuo)(zuo)。短路故障解除后(hou)系統(tong)會自動恢復正常的(de)工作(zuo)(zuo)狀(zhuang)態。   

    電壓調(diao)節   

    變壓器副邊的電(dian)(dian)(dian)壓經(jing)過整流、濾波(bo)，然(ran)后由R4、R5分壓在并聯型穩壓器U3的調節(jie)點產生1.24V(對應于4.5V輸(shu)出(chu))的反饋電(dian)(dian)(dian)壓。為(wei)保證電(dian)(dian)(dian)池充電(dian)(dian)(dian)器正常工作，4.5V是(shi)最低(di)電(dian)(dian)(dian)壓(包括(kuo)容差(cha))。因為(wei)充電(dian)(dian)(dian)器采用的是(shi)線(xian)性(xing)結構，充電(dian)(dian)(dian)效率與輸(shu)入(ru)、輸(shu)出(chu)電(dian)(dian)(dian)壓的差(cha)值成反比，用最低(di)電(dian)(dian)(dian)壓為(wei)充電(dian)(dian)(dian)器供(gong)電(dian)(dian)(dian)有助于降低(di)功(gong)率損(sun)耗。   

    當調節(jie)(jie)點電(dian)(dian)(dian)壓(ya)高于(yu)1.24V時，并聯型(xing)穩(wen)壓(ya)器(qi)將吸入(ru)(ru)電(dian)(dian)(dian)流(liu)，導(dao)通光(guang)耦LED，原邊的(de)(de)(de)光(guang)敏晶(jing)(jing)體管(guan)將處于(yu)發(fa)光(guang)狀態。U1的(de)(de)(de)OPTO輸(shu)入(ru)(ru)引(yin)腳用于(yu)直接連接光(guang)敏晶(jing)(jing)體管(guan)，以極其(qi)簡單的(de)(de)(de)方式構成(cheng)閉合環路。光(guang)敏晶(jing)(jing)體管(guan)導(dao)通時，OPTO引(yin)腳被拉低，內部比較器(qi)在(zai)(zai)它的(de)(de)(de)一個輸(shu)入(ru)(ru)端檢(jian)測到較低的(de)(de)(de)電(dian)(dian)(dian)壓(ya)，比較器(qi)的(de)(de)(de)另(ling)一輸(shu)入(ru)(ru)電(dian)(dian)(dian)流(liu)檢(jian)測引(yin)腳(CS)的(de)(de)(de)峰(feng)值(zhi)電(dian)(dian)(dian)壓(ya)，OPTO引(yin)腳的(de)(de)(de)低電(dian)(dian)(dian)壓(ya)將在(zai)(zai)每個周期直接限制功率(lv)MOSFETN1的(de)(de)(de)峰(feng)值(zhi)電(dian)(dian)(dian)流(liu)。由于(yu)U1是一個PWM控制器(qi)，電(dian)(dian)(dian)流(liu)限制使得電(dian)(dian)(dian)壓(ya)調節(jie)(jie)受作用在(zai)(zai)N1上的(de)(de)(de)占(zhan)空比(導(dao)通時間與斷開時間的(de)(de)(de)比值(zhi))的(de)(de)(de)影響(xiang)，環路穩(wen)定(ding)性通過調節(jie)(jie)R11和(he)C12來保證(zheng)。R10和(he)C5(連接在(zai)(zai)U3的(de)(de)(de)第(di)3和(he)第(di)4引(yin)腳)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(te)點    

    U4是一款用于單節Li+電池充電、功能完備的充電器，采用線性充(chong)電(dian)(dian)(dian)(dian)模式，內(nei)(nei)置調整管(guan)和電(dian)(dian)(dian)(dian)流(liu)(liu)檢測電(dian)(dian)(dian)(dian)路。另外，它還集成(cheng)了(le)一個反向抑制二極管(guan)，在去掉輸(shu)入電(dian)(dian)(dian)(dian)源時(shi)可防止電(dian)(dian)(dian)(dian)池(chi)(chi)方向放(fang)電(dian)(dian)(dian)(dian)。接(jie)入一個深度放(fang)電(dian)(dian)(dian)(dian)的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)時(shi)，U4能夠檢測到低電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)(低于2.5V)，這樣(yang)，U4將首先啟動(dong)涓(juan)流(liu)(liu)充(chong)電(dian)(dian)(dian)(dian)過程，在快充(chong)周期的(de)1/10時(shi)間段對電(dian)(dian)(dian)(dian)池(chi)(chi)進行涓(juan)流(liu)(liu)充(chong)電(dian)(dian)(dian)(dian)，直到電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)上(shang)升到2.5V以上(shang)。在涓(juan)流(liu)(liu)充(chong)電(dian)(dian)(dian)(dian)到快速(su)充(chong)電(dian)(dian)(dian)(dian)轉換時(shi)，軟啟動(dong)電(dian)(dian)(dian)(dian)路迫使充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)在3ms時(shi)間內(nei)(nei)緩(huan)慢上(shang)升，避免(mian)較(jiao)大的(de)浪涌(yong)電(dian)(dian)(dian)(dian)流(liu)(liu)拉(la)低輸(shu)入電(dian)(dian)(dian)(dian)源。    

   上述(shu)功能的(de)實施不需要微控(kong)制器(qi)的(de)監(jian)管，而且，U4還(huan)具有可編程的(de)溫度限制功能，我們會(hui)在下面(mian)就這一(yi)點(dian)進行詳(xiang)細(xi)討論。用(yong)一(yi)個電(dian)(dian)阻設(she)置最大充電(dian)(dian)電(dian)(dian)流(liu)(liu)，電(dian)(dian)阻兩端的(de)電(dian)(dian)壓與(yu)充電(dian)(dian)電(dian)(dian)流(liu)(liu)成正(zheng)比，通過監(jian)視(shi)該電(dian)(dian)壓即可連續(xu)跟(gen)蹤充電(dian)(dian)電(dian)(dian)流(liu)(liu)，更為復雜的(de)系統也可以采(cai)用(yong)ADC跟(gen)蹤監(jian)視(shi)充電(dian)(dian)電(dian)(dian)流(liu)(liu)。    

    Maxim還提(ti)供(gong)有另(ling)一(yi)款與MAX1507非常(chang)相似的(de)充電器―MAX1555，這款IC能(neng)夠在沒有交流電源(yuan)的(de)情況(kuang)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(ge)低(di)阻(zu)電(dian)(dian)壓(ya)源連接，充電(dian)(dian)電(dian)(dian)流(liu)將(jiang)(jiang)不受任何(he)限制，這(zhe)種(zhong)狀況會(hui)對電(dian)(dian)池及其(qi)周圍(wei)環境造成災(zai)難性(xing)的(de)(de)損害(hai)，從(cong)Li+電(dian)(dian)池的(de)(de)安(an)全性(xing)考慮，必須將(jiang)(jiang)其(qi)充電(dian)(dian)電(dian)(dian)流(liu)限制在(zai)額, 定范圍(wei)以(yi)內(nei)。U4根據連接在(zai)ISET(第(di)5引腳)的(de)(de)電(dian)(dian)阻(zu)限制充電(dian)(dian)電(dian)(dian)流(liu)，圖1電(dian)(dian)路中選用(yong)了一個(ge)1.87kΩ的(de)(de)電(dian)(dian)阻(zu)，將(jiang)(jiang)最大電(dian)(dian)流(liu)設置在(zai)780mA: 

    Ifast=1461V/Rset=1461/1870≈780mA 

    電池(chi)電壓最(zui)(zui)小時，由(you)于(yu)輸(shu)入(ru)穩定(ding)在4.5V，U4輸(shu)入(ru)與輸(shu)出的壓差(cha)最(zui)(zui)大，如果此時電池(chi)是以(yi)最(zui)(zui)大電流(liu)充電，U4功耗(hao)將達到最(zui)(zui)大值(zhi)。例如，假設電池(chi)電壓為2.5V，則對應的功耗(hao)為：  

    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)的條件下將以最大充(chong)(chong)電(dian)(dian)電(dian)(dian)流對電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)，直(zhi)到電(dian)(dian)池(chi)電(dian)(dian)壓(ya)達(da)到內部設(she)置的4.2V