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(lei)型(xing)的電池(chi)對充電器(qi)的要求   

    通常(chang)快(kuai)速(su)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)比涓流(liu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)更受歡迎(ying)，但快(kuai)速(su)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)的(de)(de)要求也復雜，鎳(nie)氫(qing)或鎳(nie)鎘電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)快(kuai)速(su)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)技(ji)術(shu)(shu)與其它(ta)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)也是不同的(de)(de)。鎳(nie)鎘和(he)鎳(nie)氫(qing)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)通常(chang)在(zai)恒(heng)流(liu)狀態(tai)下快(kuai)充(chong)，而不是恒(heng)壓(ya)(ya)狀態(tai)下。快(kuai)充(chong)終(zhong)止檢測基于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)和(he)溫度(du)的(de)(de)變化率，充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)還應具(ju)備(bei)過(guo)壓(ya)(ya)保(bao)護(hu)和(he)過(guo)熱保(bao)護(hu)功能。Li+和(he)鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)必(bi)須保(bao)證作用(yong)到(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)上的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)和(he)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)最大值(zhi)在(zai)規定的(de)(de)范圍內，當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)維持在(zai)最大單(dan)節電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)下降到(dao)一個較低值(zhi)時，充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)終(zhong)止充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。Li+和(he)鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)的(de)(de)區別在(zai)于所允許的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)、最大電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，另(ling)外鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)一般具(ju)有(you)浮充(chong)能力(浮充(chong)是為(wei)了補(bu)充(chong)鉛(qian)酸電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)自放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，而對一個已經完全充(chong)滿的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)繼續輸入充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)技(ji)術(shu)(shu))，Li+電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)自放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)非(fei)常(chang)低，所以不需要浮充(chong)。    

    Li+電池(chi)    

    為(wei)便攜式(shi)產品選擇電(dian)(dian)(dian)池時，最重(zhong)要的(de)(de)(de)是高(gao)能(neng)量密度、尺寸、重(zhong)量和價(jia)格。迄(qi)今為(wei)止(zhi)，Li+電(dian)(dian)(dian)池在最為(wei)流行的(de)(de)(de)電(dian)(dian)(dian)池中(zhong)(zhong)能(neng)夠提供最高(gao)的(de)(de)(de)體積和能(neng)量密度，但其每瓦時的(de)(de)(de)成本(ben)(ben)也較(jiao)高(gao)。鉛酸(suan)電(dian)(dian)(dian)池的(de)(de)(de)每瓦時成本(ben)(ben)最低，但比較(jiao)笨重(zhong)。本(ben)(ben)文以(yi)Li+電(dian)(dian)(dian)池為(wei)例討論充(chong)電(dian)(dian)(dian)器的(de)(de)(de)設計，它在便攜式(shi)產品中(zhong)(zhong)已(yi)經被普遍使用(yong)。我(wo)們選擇780mA的(de)(de)(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流和4.2V的(de)(de)(de)終止(zhi)電(dian)(dian)(dian)壓。 

 通(tong)用輸入交流電(dian)壓的離(li)線式Li+電(dian)池(chi)充電(dian)器。    

    所(suo)示充電(dian)器(qi)(qi)無需微處理器(qi)(qi)干預，輸入電(dian)源(yuan)可以采(cai)用全球范圍的任何交流電(dian)源(yuan)，省去了(le)(le)大體積60Hz變壓器(qi)(qi)，而且(qie)可提供單(dan)節Li+電(dian)池所(suo)要求的精(jing)確的充電(dian)電(dian)壓和電(dian)流。充電(dian)器(qi)(qi)IC(U4)集成(cheng)了(le)(le)全面的保(bao)護(hu)功能(電(dian)壓、電(dian)流和自保(bao)護(hu))，確保(bao)Li+電(dian)池的安全充電(dian)。    

    假設Li+電(dian)(dian)池帶有過(guo)流(liu)、過(guo)壓和過(guo)熱保護，這些保護特性在電(dian)(dian)池包里是必需的，因為充電(dian)(dian)期(qi)間一旦電(dian)(dian)路出現(xian)故障，Li+電(dian)(dian)池將存在很大的危險(xian)性，過(guo)流(liu)、過(guo)壓或(huo)溫度過(guo)高都有可能造成Li+電(dian)(dian)池爆(bao)炸。    

    電路描述     

    包(bao)括兩顆主器(qi)(qi)件(U1和U4)、精密基準(U3)和光耦(U2)。U1是離(li)線式開關控制(zhi)器(qi)(qi)，配合(he)隔(ge)離(li)變壓器(qi)(qi)、光耦和基準產(chan)生隔(ge)離(li)的(de)穩(wen)壓直(zhi)流輸出。直(zhi)流電壓供給電池(chi)充(chong)電器(qi)(qi)(U4)，U4提供電流限制(zhi)、電壓調(diao)節(jie)、電池(chi)充(chong)電和充(chong)電指示等功能。本方案中，U4是一款簡(jian)單的(de)線性充(chong)電器(qi)(qi)，內置調(diao)整管，結合(he)其(qi)熱控制(zhi)環路提供快速充(chong)電。    

    MAX5022的特性     

    U1(MAX5022)在(zai)寬輸(shu)入(ru)(ru)范圍(wei)的(de)應用中很(hen)容易設計，本文所(suo)提供的(de)方案要(yao)求能夠滿足(zu)全球(qiu)各(ge)地的(de)交流電(dian)(dian)(dian)源(yuan)(yuan)規(gui)格，這里假(jia)設通用的(de)輸(shu)入(ru)(ru)電(dian)(dian)(dian)源(yuan)(yuan)電(dian)(dian)(dian)壓范圍(wei)為85VAC至265VAC。MAX5022的(de)輸(shu)入(ru)(ru)范圍(wei)指標以及(ji)評估板電(dian)(dian)(dian)路的(de)輸(shu)入(ru)(ru)范圍(wei)恰好滿足(zu)這一(yi)需求。對于所(suo)示(shi)充電(dian)(dian)(dian)器的(de)電(dian)(dian)(dian)源(yuan)(yuan)端MAX5022評估板不需要(yao)作任(ren)何修改，隔離端只需對評估板的(de)電(dian)(dian)(dian)阻值(zhi)稍作修改。    

    對于(yu)更(geng)(geng)大(da)(da)功(gong)(gong)率的(de)(de)應用(yong)，只需(xu)選(xuan)取(qu)功(gong)(gong)率較大(da)(da)的(de)(de)開(kai)關管(guan)和能夠處理更(geng)(geng)大(da)(da)功(gong)(gong)率的(de)(de)變壓(ya)器(qi)(qi)即可。圖1所示(shi)電(dian)路(lu)要求充(chong)(chong)電(dian)電(dian)流為780mA，最大(da)(da)電(dian)池電(dian)壓(ya)為4.2V。對充(chong)(chong)電(dian)電(dian)源的(de)(de)要求與(yu)MAX5022評估板(ban)(ban)所提供的(de)(de)輸出相吻合：5V@1A，因此，不需(xu)要更(geng)(geng)換評估板(ban)(ban)的(de)(de)晶體管(guan)和變壓(ya)器(qi)(qi)。U4采用(yong)SOT23封裝，所以，充(chong)(chong)電(dian)器(qi)(qi)的(de)(de)尺寸(cun)在(zai)很(hen)大(da)(da)程度上(shang)取(qu)決(jue)于(yu)應用(yong)對充(chong)(chong)電(dian)電(dian)源的(de)(de)需(xu)求。變壓(ya)器(qi)(qi)是電(dian)路(lu)中(zhong)尺寸(cun)最大(da)(da)的(de)(de)元件，由于(yu)開(kai)關控制器(qi)(qi)的(de)(de)工作頻率大(da)(da)于(yu)250kHz，允許系統選(xuan)用(yong)小尺寸(cun)的(de)(de)變壓(ya)器(qi)(qi)。     

    上(shang)電(dian)(dian)(dian)時，在開(kai)關(guan)控制器工作(zuo)之前(qian)，U1調(diao)節器直接通過泄漏電(dian)(dian)(dian)阻(zu)(zu)R1、R2從整流(liu)通路吸取少量(liang)的(de)(de)電(dian)(dian)(dian)流(liu)，兩(liang)個(ge)(ge)電(dian)(dian)(dian)阻(zu)(zu)阻(zu)(zu)值(zhi)保證(zheng)每個(ge)(ge)電(dian)(dian)(dian)阻(zu)(zu)上(shang)的(de)(de)壓(ya)降(jiang)不(bu)會超出每個(ge)(ge)電(dian)(dian)(dian)阻(zu)(zu)的(de)(de)容限，Vin引腳(jiao)電(dian)(dian)(dian)壓(ya)不(bu)會超出其28V額定(ding)值(zhi)(30V為絕(jue)對(dui)最大值(zhi))，U1在輸(shu)入(ru)電(dian)(dian)(dian)壓(ya)達到24V時開(kai)始開(kai)關(guan)操作(zuo)，并吸取更大的(de)(de)電(dian)(dian)(dian)流(liu)(高于R1、R2所(suo)能提供(gong)的(de)(de)電(dian)(dian)(dian)流(liu))，在變壓(ya)器副邊(bian)線圈能夠提供(gong)足夠的(de)(de)能量(liang)之前(qian)，額外的(de)(de)電(dian)(dian)(dian)流(liu)由Vin引腳(jiao)的(de)(de)旁(pang)路電(dian)(dian)(dian)容供(gong)給(gei)。這(zhe)種處理方(fang)式能夠適合較寬的(de)(de)輸(shu)入(ru)電(dian)(dian)(dian)壓(ya)范圍，對(dui)效(xiao)率的(de)(de)影響也很小，這(zhe)是因為在啟動過程中只需(xu)極小的(de)(de)供(gong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(典型值(zhi)為50uA)。   

    為(wei)了(le)防止(zhi)U1的(de)(de)Vin引(yin)腳(jiao)出現過壓(ya)，可(ke)以在Vin與地之(zhi)間接一(yi)個26V至30V的(de)(de)齊(qi)納管，電壓(ya)值需要高于(yu)欠壓(ya)鎖存電壓(ya)的(de)(de)最大值，低于(yu)該引(yin)腳(jiao)所允許的(de)(de)最大絕對(dui)電壓(ya)。如果器件沒有啟動正常(chang)的(de)(de)開關操作(zuo)，則可(ke)認為(wei)電路(lu)發生了(le)某(mou)些(xie)問題(ti)，所以，這一(yi)保護(hu)措施對(dui)于(yu)U1來說并不是必(bi)需的(de)(de)。     

    U1是一款電(dian)流模式(shi)PWM控制器(qi)，具有逐周期限(xian)(xian)流電(dian)路(lu)，必要時其占空(kong)比(bi)可以提高到75%，非常(chang)適合(he)圖1所示的(de)(de)反(fan)激拓撲。原邊開關(guan)電(dian)流檢(jian)測(ce)采用尺寸為1206的(de)(de)1.78Ω電(dian)阻(R7)，該(gai)電(dian)阻限(xian)(xian)制了變(bian)壓器(qi)原邊的(de)(de)最大(da)電(dian)流。固定開關(guan)頻率(lv)和(he)最大(da)占空(kong)比(bi)限(xian)(xian)制使得(de)最大(da)限(xian)(xian)流具有輸出短路(lu)保(bao)護功(gong)能(neng)。   

    一旦短路輸出(chu)造成(cheng)電路達到了(le)上述限制條(tiao)件，第三組線圈(quan)將無法(fa)提供10V以上的(de)(de)電壓(UVLO的(de)(de)低電壓門限)，U1將再次進(jin)入啟動(dong)狀(zhuang)態(tai)，停止(zhi)開(kai)關操作。短路故障解除后系統(tong)會自動(dong)恢復正常(chang)的(de)(de)工作狀(zhuang)態(tai)。   

    電(dian)壓調節   

    變壓(ya)(ya)(ya)器(qi)副邊的電(dian)(dian)壓(ya)(ya)(ya)經過整流、濾波(bo)，然后由R4、R5分壓(ya)(ya)(ya)在(zai)并聯型(xing)穩壓(ya)(ya)(ya)器(qi)U3的調節(jie)點產生(sheng)1.24V(對應于(yu)4.5V輸出(chu))的反饋(kui)電(dian)(dian)壓(ya)(ya)(ya)。為保證電(dian)(dian)池(chi)充(chong)電(dian)(dian)器(qi)正(zheng)常工作，4.5V是最低電(dian)(dian)壓(ya)(ya)(ya)(包(bao)括容差)。因為充(chong)電(dian)(dian)器(qi)采用(yong)的是線性(xing)結構，充(chong)電(dian)(dian)效率(lv)(lv)與輸入、輸出(chu)電(dian)(dian)壓(ya)(ya)(ya)的差值成反比，用(yong)最低電(dian)(dian)壓(ya)(ya)(ya)為充(chong)電(dian)(dian)器(qi)供電(dian)(dian)有助(zhu)于(yu)降(jiang)低功率(lv)(lv)損耗。   

    當調節(jie)點電(dian)(dian)(dian)壓(ya)高于(yu)1.24V時(shi)，并聯型(xing)穩壓(ya)器將(jiang)吸入電(dian)(dian)(dian)流，導(dao)(dao)通(tong)(tong)光(guang)(guang)(guang)耦LED，原邊(bian)的(de)(de)(de)(de)(de)光(guang)(guang)(guang)敏(min)晶(jing)體管將(jiang)處于(yu)發光(guang)(guang)(guang)狀(zhuang)態(tai)。U1的(de)(de)(de)(de)(de)OPTO輸入引腳(jiao)(jiao)用(yong)于(yu)直(zhi)接連接光(guang)(guang)(guang)敏(min)晶(jing)體管，以極其(qi)簡單(dan)的(de)(de)(de)(de)(de)方式(shi)構成閉合(he)環路(lu)。光(guang)(guang)(guang)敏(min)晶(jing)體管導(dao)(dao)通(tong)(tong)時(shi)，OPTO引腳(jiao)(jiao)被拉低，內(nei)部比(bi)(bi)較(jiao)器在它的(de)(de)(de)(de)(de)一(yi)個(ge)輸入端檢測到較(jiao)低的(de)(de)(de)(de)(de)電(dian)(dian)(dian)壓(ya)，比(bi)(bi)較(jiao)器的(de)(de)(de)(de)(de)另一(yi)輸入電(dian)(dian)(dian)流檢測引腳(jiao)(jiao)(CS)的(de)(de)(de)(de)(de)峰值電(dian)(dian)(dian)壓(ya)，OPTO引腳(jiao)(jiao)的(de)(de)(de)(de)(de)低電(dian)(dian)(dian)壓(ya)將(jiang)在每個(ge)周期直(zhi)接限制(zhi)功率MOSFETN1的(de)(de)(de)(de)(de)峰值電(dian)(dian)(dian)流。由于(yu)U1是一(yi)個(ge)PWM控制(zhi)器，電(dian)(dian)(dian)流限制(zhi)使得電(dian)(dian)(dian)壓(ya)調節(jie)受作用(yong)在N1上的(de)(de)(de)(de)(de)占空比(bi)(bi)(導(dao)(dao)通(tong)(tong)時(shi)間與斷開時(shi)間的(de)(de)(de)(de)(de)比(bi)(bi)值)的(de)(de)(de)(de)(de)影響，環路(lu)穩定性通(tong)(tong)過調節(jie)R11和C12來保證。R10和C5(連接在U3的(de)(de)(de)(de)(de)第3和第4引腳(jiao)(jiao))可消除穩定工作情況下(xia)的(de)(de)(de)(de)(de)噪(zao)聲干擾(rao)。    

    U4的工(gong)作特點    

    U4是一款用于單節Li+電池充電、功能完備的充電器，采用線(xian)性充(chong)電(dian)(dian)模式(shi)，內置調整管(guan)和電(dian)(dian)流(liu)檢測電(dian)(dian)路。另外(wai)，它還集(ji)成了一個反向抑(yi)制二極管(guan)，在去掉輸入電(dian)(dian)源(yuan)時(shi)可防(fang)止電(dian)(dian)池(chi)方向放電(dian)(dian)。接入一個深度放電(dian)(dian)的電(dian)(dian)池(chi)時(shi)，U4能夠檢測到(dao)低電(dian)(dian)池(chi)電(dian)(dian)壓(低于2.5V)，這樣，U4將首先啟動(dong)涓(juan)流(liu)充(chong)電(dian)(dian)過程，在快充(chong)周期的1/10時(shi)間段對電(dian)(dian)池(chi)進行(xing)涓(juan)流(liu)充(chong)電(dian)(dian)，直到(dao)電(dian)(dian)池(chi)電(dian)(dian)壓上(shang)升到(dao)2.5V以(yi)上(shang)。在涓(juan)流(liu)充(chong)電(dian)(dian)到(dao)快速(su)充(chong)電(dian)(dian)轉(zhuan)換(huan)時(shi)，軟啟動(dong)電(dian)(dian)路迫使充(chong)電(dian)(dian)電(dian)(dian)流(liu)在3ms時(shi)間內緩慢上(shang)升，避免較大的浪涌電(dian)(dian)流(liu)拉低輸入電(dian)(dian)源(yuan)。    

   上述(shu)功能的(de)實(shi)施不需(xu)要(yao)微(wei)控制器的(de)監(jian)管，而且，U4還具(ju)有可編程(cheng)的(de)溫度(du)限制功能，我們(men)會(hui)在下面(mian)就(jiu)這一(yi)點(dian)進(jin)行詳細討(tao)論。用(yong)(yong)一(yi)個電(dian)(dian)(dian)阻設置最大充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流，電(dian)(dian)(dian)阻兩端的(de)電(dian)(dian)(dian)壓與充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流成正比，通過監(jian)視(shi)該電(dian)(dian)(dian)壓即可連續(xu)跟蹤(zong)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流，更(geng)為(wei)復(fu)雜的(de)系(xi)統也可以采用(yong)(yong)ADC跟蹤(zong)監(jian)視(shi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流。    

    Maxim還提供(gong)有(you)另一(yi)款(kuan)與MAX1507非常相似的充電器―MAX1555，這款(kuan)IC能夠(gou)在沒有(you)交流電源的情況下(xia)從USB主機獲得充電電源。   

    電(dian)流(liu)調節 

    如(ru)果把(ba)Li+電(dian)(dian)池直接與一(yi)個低(di)阻(zu)電(dian)(dian)壓源連(lian)(lian)接，充電(dian)(dian)電(dian)(dian)流(liu)將(jiang)不受任何限制，這(zhe)種狀況會(hui)對電(dian)(dian)池及其(qi)周(zhou)圍(wei)環境造成災難性(xing)的(de)(de)損害，從Li+電(dian)(dian)池的(de)(de)安全性(xing)考(kao)慮(lv)，必須將(jiang)其(qi)充電(dian)(dian)電(dian)(dian)流(liu)限制在(zai)額, 定范圍(wei)以內。U4根據連(lian)(lian)接在(zai)ISET(第5引(yin)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)路中選用了(le)一(yi)個1.87kΩ的(de)(de)電(dian)(dian)阻(zu)，將(jiang)最(zui)大電(dian)(dian)流(liu)設(she)置(zhi)在(zai)780mA: 

    Ifast=1461V/Rset=1461/1870≈780mA 

    電(dian)(dian)池電(dian)(dian)壓最小時(shi)(shi)，由于輸(shu)入穩定在4.5V，U4輸(shu)入與輸(shu)出的壓差最大(da)，如(ru)果此時(shi)(shi)電(dian)(dian)池是以最大(da)電(dian)(dian)流充電(dian)(dian)，U4功(gong)耗將達到最大(da)值。例如(ru)，假(jia)設電(dian)(dian)池電(dian)(dian)壓為2.5V，則對應(ying)的功(gong)耗為：  

    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，充電器在滿足芯片溫度(du)限制的條件下將以最大充電電流(liu)對(dui)電池充電，直到電池電壓達到內部設置的4.2V