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的要求(qiu)   

    通(tong)常快(kuai)速充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)比涓流充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)更(geng)受歡迎，但快(kuai)速充(chong)(chong)(chong)(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)要求也(ye)復(fu)雜，鎳氫或鎳鎘(ge)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)快(kuai)速充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)技術(shu)與其它電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)也(ye)是不(bu)同的(de)。鎳鎘(ge)和(he)鎳氫電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)通(tong)常在恒流狀態下快(kuai)充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)，而(er)不(bu)是恒壓(ya)狀態下。快(kuai)充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)終止檢測基于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)和(he)溫(wen)度的(de)變化率，充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)還應具備過壓(ya)保護和(he)過熱保護功能(neng)。Li+和(he)鉛(qian)(qian)(qian)(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)必須保證作用到(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)上的(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)流最(zui)大(da)(da)值在規定的(de)范圍(wei)內，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)維持在最(zui)大(da)(da)單節電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，充(chong)(chong)(chong)(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)流下降到(dao)一個較低(di)值時，充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)終止充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。Li+和(he)鉛(qian)(qian)(qian)(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)的(de)區(qu)別在于所允(yun)許的(de)充(chong)(chong)(chong)(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、最(zui)大(da)(da)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，另外鉛(qian)(qian)(qian)(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)一般具有浮充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)能(neng)力(li)(浮充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)是為了補(bu)充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)鉛(qian)(qian)(qian)(qian)酸(suan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)自(zi)放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，而(er)對(dui)一個已經(jing)完全充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)滿的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)繼續輸入(ru)充(chong)(chong)(chong)(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)流的(de)技術(shu))，Li+電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)自(zi)放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)非常低(di)，所以不(bu)需要浮充(chong)(chong)(chong)(chong)(chong)(chong)(chong)(chong)。    

    Li+電(dian)池    

    為(wei)便(bian)攜式產(chan)品選擇電(dian)池(chi)(chi)時，最(zui)(zui)(zui)重要的(de)(de)是高(gao)能(neng)量(liang)密度、尺寸、重量(liang)和(he)(he)價格。迄今為(wei)止，Li+電(dian)池(chi)(chi)在(zai)最(zui)(zui)(zui)為(wei)流(liu)行的(de)(de)電(dian)池(chi)(chi)中(zhong)能(neng)夠提供(gong)最(zui)(zui)(zui)高(gao)的(de)(de)體積和(he)(he)能(neng)量(liang)密度，但其每(mei)瓦時的(de)(de)成(cheng)本(ben)也(ye)較高(gao)。鉛酸(suan)電(dian)池(chi)(chi)的(de)(de)每(mei)瓦時成(cheng)本(ben)最(zui)(zui)(zui)低，但比較笨重。本(ben)文以Li+電(dian)池(chi)(chi)為(wei)例(li)討論充(chong)(chong)電(dian)器的(de)(de)設(she)計，它在(zai)便(bian)攜式產(chan)品中(zhong)已經被普遍(bian)使(shi)用。我們選擇780mA的(de)(de)充(chong)(chong)電(dian)電(dian)流(liu)和(he)(he)4.2V的(de)(de)終(zhong)止電(dian)壓。 

 通用輸入交流電壓的離(li)線式Li+電池(chi)充電器。    

   ; 所示充(chong)(chong)電(dian)(dian)(dian)(dian)器無需微處理(li)器干預，輸入(ru)電(dian)(dian)(dian)(dian)源可(ke)以采用全(quan)(quan)球(qiu)范(fan)圍的任何交流(liu)電(dian)(dian)(dian)(dian)源，省去了(le)大體積60Hz變壓(ya)器，而且可(ke)提供單節Li+電(dian)(dian)(dian)(dian)池所要求的精確的充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)和電(dian)(dian)(dian)(dian)流(liu)。充(chong)(chong)電(dian)(dian)(dian)(dian)器IC(U4)集成(cheng)了(le)全(quan)(quan)面的保護功能(電(dian)(dian)(dian)(dian)壓(ya)、電(dian)(dian)(dian)(dian)流(liu)和自保護)，確保Li+電(dian)(dian)(dian)(dian)池的安全(quan)(quan)充(chong)(chong)電(dian)(dian)(dian)(dian)。    

    假設Li+電(dian)(dian)池(chi)帶有(you)過(guo)流、過(guo)壓和過(guo)熱保護，這(zhe)些保護特(te)性(xing)在(zai)電(dian)(dian)池(chi)包里是必需的，因為充電(dian)(dian)期間(jian)一旦電(dian)(dian)路出現故障，Li+電(dian)(dian)池(chi)將存在(zai)很大的危(wei)險性(xing)，過(guo)流、過(guo)壓或溫度過(guo)高(gao)都有(you)可能造(zao)成Li+電(dian)(dian)池(chi)爆炸。    

    電路描(miao)述     

    包括兩顆主器(qi)件(U1和U4)、精密(mi)基(ji)準(U3)和光(guang)耦(ou)(U2)。U1是離線(xian)式開關控制(zhi)器(qi)，配合隔離變(bian)壓器(qi)、光(guang)耦(ou)和基(ji)準產生隔離的穩壓直流(liu)輸(shu)出。直流(liu)電(dian)(dian)(dian)壓供(gong)(gong)給(gei)電(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)器(qi)(U4)，U4提供(gong)(gong)電(dian)(dian)(dian)流(liu)限(xian)制(zhi)、電(dian)(dian)(dian)壓調(diao)節、電(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)和充(chong)(chong)(chong)電(dian)(dian)(dian)指示等功(gong)能。本(ben)方案中，U4是一款(kuan)簡單的線(xian)性充(chong)(chong)(chong)電(dian)(dian)(dian)器(qi)，內置(zhi)調(diao)整管，結合其熱(re)控制(zhi)環路(lu)提供(gong)(gong)快速充(chong)(chong)(chong)電(dian)(dian)(dian)。    

    MAX5022的特性     

    U1(MAX5022)在(zai)寬輸(shu)(shu)入(ru)范(fan)圍(wei)的(de)(de)應用中很容易設計(ji)，本文所(suo)提(ti)供的(de)(de)方案要求(qiu)能夠滿足全球(qiu)各地的(de)(de)交(jiao)流電(dian)源規格，這(zhe)里假設通用的(de)(de)輸(shu)(shu)入(ru)電(dian)源電(dian)壓(ya)范(fan)圍(wei)為85VAC至(zhi)265VAC。MAX5022的(de)(de)輸(shu)(shu)入(ru)范(fan)圍(wei)指標以及評(ping)估(gu)板(ban)電(dian)路的(de)(de)輸(shu)(shu)入(ru)范(fan)圍(wei)恰好(hao)滿足這(zhe)一需(xu)求(qiu)。對于所(suo)示充電(dian)器的(de)(de)電(dian)源端(duan)MAX5022評(ping)估(gu)板(ban)不需(xu)要作任(ren)何修(xiu)改，隔離端(duan)只需(xu)對評(ping)估(gu)板(ban)的(de)(de)電(dian)阻值稍作修(xiu)改。    

    對(dui)于(yu)(yu)更(geng)大(da)功(gong)(gong)(gong)率(lv)(lv)的應用，只需(xu)(xu)選取功(gong)(gong)(gong)率(lv)(lv)較大(da)的開關(guan)管和能(neng)夠處(chu)理更(geng)大(da)功(gong)(gong)(gong)率(lv)(lv)的變(bian)(bian)壓器(qi)(qi)(qi)即可。圖1所(suo)示電(dian)路要求(qiu)充(chong)電(dian)電(dian)流為780mA，最大(da)電(dian)池電(dian)壓為4.2V。對(dui)充(chong)電(dian)電(dian)源(yuan)(yuan)的要求(qiu)與MAX5022評估板所(suo)提供的輸出相吻合(he)：5V@1A，因此，不(bu)需(xu)(xu)要更(geng)換評估板的晶(jing)體(ti)管和變(bian)(bian)壓器(qi)(qi)(qi)。U4采用SOT23封裝，所(suo)以，充(chong)電(dian)器(qi)(qi)(qi)的尺寸(cun)在很(hen)大(da)程(cheng)度上取決于(yu)(yu)應用對(dui)充(chong)電(dian)電(dian)源(yuan)(yuan)的需(xu)(xu)求(qiu)。變(bian)(bian)壓器(qi)(qi)(qi)是電(dian)路中(zhong)尺寸(cun)最大(da)的元件，由(you)于(yu)(yu)開關(guan)控制器(qi)(qi)(qi)的工作頻率(lv)(lv)大(da)于(yu)(yu)250kHz，允許(xu)系統選用小尺寸(cun)的變(bian)(bian)壓器(qi)(qi)(qi)。     

    上(shang)電(dian)時，在(zai)(zai)開(kai)關(guan)控制器工作(zuo)(zuo)之前，U1調(diao)節器直(zhi)接(jie)通過泄漏(lou)電(dian)阻R1、R2從整(zheng)流(liu)(liu)通路吸(xi)取少量(liang)的(de)(de)(de)電(dian)流(liu)(liu)，兩個電(dian)阻阻值保證每(mei)個電(dian)阻上(shang)的(de)(de)(de)壓(ya)(ya)(ya)(ya)降不會(hui)超(chao)出每(mei)個電(dian)阻的(de)(de)(de)容限，Vin引(yin)(yin)腳電(dian)壓(ya)(ya)(ya)(ya)不會(hui)超(chao)出其28V額(e)定值(30V為絕對最大(da)值)，U1在(zai)(zai)輸(shu)(shu)入(ru)電(dian)壓(ya)(ya)(ya)(ya)達(da)到24V時開(kai)始開(kai)關(guan)操(cao)作(zuo)(zuo)，并吸(xi)取更大(da)的(de)(de)(de)電(dian)流(liu)(liu)(高(gao)于R1、R2所(suo)能提供(gong)(gong)(gong)的(de)(de)(de)電(dian)流(liu)(liu))，在(zai)(zai)變壓(ya)(ya)(ya)(ya)器副邊線圈(quan)能夠(gou)提供(gong)(gong)(gong)足(zu)夠(gou)的(de)(de)(de)能量(liang)之前，額(e)外的(de)(de)(de)電(dian)流(liu)(liu)由Vin引(yin)(yin)腳的(de)(de)(de)旁路電(dian)容供(gong)(gong)(gong)給。這種(zhong)處理方(fang)式能夠(gou)適(shi)合較寬的(de)(de)(de)輸(shu)(shu)入(ru)電(dian)壓(ya)(ya)(ya)(ya)范圍，對效率的(de)(de)(de)影響也很小，這是因為在(zai)(zai)啟(qi)動過程中(zhong)只需極小的(de)(de)(de)供(gong)(gong)(gong)電(dian)電(dian)流(liu)(liu)(典型(xing)值為50uA)。   

    為(wei)了(le)防止U1的Vin引腳出現過(guo)壓，可以(yi)在Vin與(yu)地之間接一個26V至30V的齊(qi)納管，電(dian)壓值需(xu)要高于欠壓鎖存電(dian)壓的最大值，低于該引腳所允許的最大絕對(dui)電(dian)壓。如果器件沒有啟動(dong)正常(chang)的開關操作，則可認為(wei)電(dian)路發(fa)生了(le)某些問題，所以(yi)，這一保(bao)護措施(shi)對(dui)于U1來說并不(bu)是必需(xu)的。     

    U1是一款電(dian)流(liu)模式PWM控制(zhi)器(qi)(qi)，具(ju)有逐周期限(xian)流(liu)電(dian)路，必要(yao)時(shi)其(qi)占空(kong)比(bi)可(ke)以(yi)提高到75%，非常適合圖1所示的反(fan)激拓撲。原(yuan)邊開關(guan)電(dian)流(liu)檢(jian)測采用尺寸為1206的1.78Ω電(dian)阻(R7)，該(gai)電(dian)阻限(xian)制(zhi)了(le)變壓器(qi)(qi)原(yuan)邊的最大電(dian)流(liu)。固(gu)定(ding)開關(guan)頻率(lv)和最大占空(kong)比(bi)限(xian)制(zhi)使得最大限(xian)流(liu)具(ju)有輸(shu)出(chu)短路保護(hu)功能。   

    一旦短(duan)路(lu)輸出造(zao)成(cheng)電路(lu)達到了上述限制條件，第三(san)組(zu)線圈將無(wu)法(fa)提供10V以上的電壓(UVLO的低電壓門限)，U1將再次進入啟動(dong)狀態，停止開關操作(zuo)。短(duan)路(lu)故障解除后系(xi)統會自動(dong)恢復正常的工作(zuo)狀態。   

    電壓調節(jie)   

    變壓(ya)器(qi)(qi)(qi)副邊的電(dian)壓(ya)經過整流、濾(lv)波，然后由R4、R5分壓(ya)在并聯型穩壓(ya)器(qi)(qi)(qi)U3的調節點產生1.24V(對(dui)應于4.5V輸出)的反饋電(dian)壓(ya)。為(wei)保證電(dian)池充電(dian)器(qi)(qi)(qi)正常工作(zuo)，4.5V是最低電(dian)壓(ya)(包括容差)。因為(wei)充電(dian)器(qi)(qi)(qi)采用的是線性結構(gou)，充電(dian)效率與(yu)輸入、輸出電(dian)壓(ya)的差值成反比，用最低電(dian)壓(ya)為(wei)充電(dian)器(qi)(qi)(qi)供(gong)電(dian)有助于降(jiang)低功(gong)率損耗。   

    當調(diao)節(jie)點電(dian)(dian)(dian)壓高于(yu)(yu)1.24V時，并聯(lian)型(xing)穩(wen)壓器(qi)將(jiang)(jiang)吸入(ru)電(dian)(dian)(dian)流(liu)，導通(tong)光(guang)耦(ou)LED，原邊(bian)的(de)(de)光(guang)敏晶(jing)體(ti)管將(jiang)(jiang)處于(yu)(yu)發光(guang)狀態。U1的(de)(de)OPTO輸(shu)入(ru)引(yin)腳用于(yu)(yu)直接(jie)(jie)連(lian)接(jie)(jie)光(guang)敏晶(jing)體(ti)管，以(yi)極(ji)其簡單的(de)(de)方式構成(cheng)閉合環路。光(guang)敏晶(jing)體(ti)管導通(tong)時，OPTO引(yin)腳被拉(la)低(di)(di)，內部(bu)比(bi)(bi)較(jiao)器(qi)在(zai)它的(de)(de)一個(ge)輸(shu)入(ru)端檢(jian)測(ce)到(dao)較(jiao)低(di)(di)的(de)(de)電(dian)(dian)(dian)壓，比(bi)(bi)較(jiao)器(qi)的(de)(de)另一輸(shu)入(ru)電(dian)(dian)(dian)流(liu)檢(jian)測(ce)引(yin)腳(CS)的(de)(de)峰值電(dian)(dian)(dian)壓，OPTO引(yin)腳的(de)(de)低(di)(di)電(dian)(dian)(dian)壓將(jiang)(jiang)在(zai)每個(ge)周(zhou)期直接(jie)(jie)限制(zhi)功率MOSFETN1的(de)(de)峰值電(dian)(dian)(dian)流(liu)。由于(yu)(yu)U1是一個(ge)PWM控(kong)制(zhi)器(qi)，電(dian)(dian)(dian)流(liu)限制(zhi)使得電(dian)(dian)(dian)壓調(diao)節(jie)受作(zuo)用在(zai)N1上(shang)的(de)(de)占(zhan)空(kong)比(bi)(bi)(導通(tong)時間與(yu)斷開時間的(de)(de)比(bi)(bi)值)的(de)(de)影響(xiang)，環路穩(wen)定(ding)性(xing)通(tong)過(guo)調(diao)節(jie)R11和C12來保證。R10和C5(連(lian)接(jie)(jie)在(zai)U3的(de)(de)第(di)3和第(di)4引(yin)腳)可消除穩(wen)定(ding)工作(zuo)情(qing)況下的(de)(de)噪(zao)聲干擾(rao)。    

    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)模(mo)式，內置調整管和電(dian)(dian)(dian)流(liu)檢(jian)測電(dian)(dian)(dian)路。另(ling)外，它還(huan)集成了一個反向抑制二(er)極管，在(zai)去掉(diao)輸(shu)入電(dian)(dian)(dian)源時(shi)可(ke)防(fang)止(zhi)電(dian)(dian)(dian)池(chi)(chi)方(fang)向放(fang)電(dian)(dian)(dian)。接入一個深度放(fang)電(dian)(dian)(dian)的(de)電(dian)(dian)(dian)池(chi)(chi)時(shi)，U4能夠檢(jian)測到(dao)(dao)(dao)低電(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)壓(低于2.5V)，這樣，U4將首先啟動(dong)(dong)涓流(liu)充(chong)電(dian)(dian)(dian)過(guo)程，在(zai)快(kuai)充(chong)周期的(de)1/10時(shi)間(jian)段對電(dian)(dian)(dian)池(chi)(chi)進行涓流(liu)充(chong)電(dian)(dian)(dian)，直到(dao)(dao)(dao)電(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)壓上升到(dao)(dao)(dao)2.5V以(yi)上。在(zai)涓流(liu)充(chong)電(dian)(dian)(dian)到(dao)(dao)(dao)快(kuai)速充(chong)電(dian)(dian)(dian)轉換時(shi)，軟啟動(dong)(dong)電(dian)(dian)(dian)路迫(po)使充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)在(zai)3ms時(shi)間(jian)內緩慢(man)上升，避免(mian)較大的(de)浪涌電(dian)(dian)(dian)流(liu)拉低輸(shu)入電(dian)(dian)(dian)源。    

   上述功能的(de)(de)(de)實施(shi)不需要微控制器的(de)(de)(de)監(jian)管，而且，U4還具有(you)可編程的(de)(de)(de)溫度限制功能，我們會在(zai)下(xia)面(mian)就(jiu)這一(yi)點進行(xing)詳細(xi)討論。用(yong)一(yi)個電(dian)(dian)阻設置最大充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)，電(dian)(dian)阻兩端的(de)(de)(de)電(dian)(dian)壓與充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)成(cheng)正(zheng)比，通過監(jian)視(shi)該電(dian)(dian)壓即可連續(xu)跟(gen)蹤充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)，更為復雜的(de)(de)(de)系(xi)統(tong)也可以采(cai)用(yong)ADC跟(gen)蹤監(jian)視(shi)充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)。    

    Maxim還(huan)提供有另(ling)一款與MAX1507非常相似的(de)(de)充電(dian)器―MAX1555，這(zhe)款IC能夠在沒(mei)有交(jiao)流(liu)電(dian)源(yuan)的(de)(de)情況下(xia)從USB主機獲得充電(dian)電(dian)源(yuan)。   

    電(dian)流(liu)調(diao)節 

    如(ru)果把Li+電(dian)池(chi)(chi)直接與一(yi)個低阻電(dian)壓源連接，充(chong)電(dian)電(dian)流將不受任(ren)何限制(zhi)，這種(zhong)狀況會對電(dian)池(chi)(chi)及其周(zhou)圍(wei)環境造成災(zai)難性(xing)的(de)損(sun)害，從Li+電(dian)池(chi)(chi)的(de)安全性(xing)考慮，必須將其充(chong)電(dian)電(dian)流限制(zhi)在(zai)(zai)(zai)額, 定范圍(wei)以內(nei)。U4根據連接在(zai)(zai)(zai)ISET(第5引腳)的(de)電(dian)阻限制(zhi)充(chong)電(dian)電(dian)流，圖(tu)1電(dian)路中(zhong)選用了一(yi)個1.87kΩ的(de)電(dian)阻，將最(zui)大電(dian)流設(she)置在(zai)(zai)(zai)780mA: 

  ;  Ifast=1461V/Rset=1461/1870≈780mA 

    電池(chi)電壓最(zui)小時，由于輸(shu)入穩定在4.5V，U4輸(shu)入與輸(shu)出的壓差最(zui)大，如(ru)果此時電池(chi)是以(yi)最(zui)大電流充電，U4功(gong)耗(hao)將達(da)到最(zui)大值。例(li)如(ru)，假設電池(chi)電壓為(wei)(wei)2.5V，則對應的功(gong)耗(hao)為(wei)(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，充電器在滿足芯片(pian)溫度(du)限(xian)制的條件(jian)下將以最(zui)大(da)充電(dian)(dian)電(dian)(dian)流對電(dian)(dian)池充電(dian)(dian)，直到電(dian)(dian)池電(dian)(dian)壓達到內部設置的4.2V