鋰(li)(li)離子(Li-ion)電(dian)(dian)(dian)池(chi)和(he)鋰(li)(li)聚合物(Li-po)電(dian)(dian)(dian)池(chi)最(zui)適合當前市場對功(gong)率(lv)密度、充電(dian)(dian)(dian)能(neng)力和(he)價格的(de)要(yao)求(qiu)。但是，有別于(yu)鉛(qian)酸、鎳(nie)氫(qing)等(deng)其他流行的(de)電(dian)(dian)(dian)池(chi)技(ji)術(shu)，鋰(li)(li)電(dian)(dian)(dian)池(chi)技(ji)術(shu)的(de)性能(neng)也最(zui)不穩(wen)定(ding)：鋰(li)(li)電(dian)(dian)(dian)池(chi)充放電(dian)(dian)(dian)若(ruo)管理不善，將導(dao)致充電(dian)(dian)(dian)時間長、耗散功(gong)率(lv)高、效率(lv)低和(he)電(dian)(dian)(dian)池(chi)壽命比平均(jun)壽命低等(deng)問題。圖1顯示了典型鋰(li)(li)離子電(dian)(dian)(dian)池(chi)的(de)充電(dian)(dian)(dian)曲線(xian)。

　　傳統充電器相對(dui)簡單(dan)，這些充(chong)(chong)(chong)電器在(zai)小功率應(ying)用(yong)中(zhong)表(biao)現較(jiao)好。然而，它們卻不能有效(xiao)地適(shi)應(ying)充(chong)(chong)(chong)電曲線(xian)的變化，比(bi)如，用(yong)戶(hu)在(zai)不同(tong)電源(yuan)之間(jian)切換(huan)或者在(zai)充(chong)(chong)(chong)電期間(jian)操(cao)作設備。另外，傳(chuan)統充(chong)(chong)(chong)電器在(zai)大功率和(he)大電流應(ying)用(yong)中(zhong)，通常效(xiao)率較(jiao)低，耗散功率較(jiao)大。

　　

 

　　圖1:典型鋰離子電池的充電曲線。

　　新型線性和開關充電器，比如芯源系統(tong)(MPS)公司的(de)MP2600系列，采(cai)用電源路徑管(guan)理(li)技術(shu)改(gai)變(bian)了充電曲線，從而能夠以更低(di)的(de)耗散功率更加(jia)高效地(di)為電池(chi)/系統(tong)供(gong)電。同時(shi)，這些充電器也使(shi)系統(tong)的(de)安(an)全性和電池(chi)的(de)使(shi)用壽命得(de)到提(ti)高。

　　電源管理(li)拓(tuo)撲種(zhong)類(lei)繁多，本文則重點介紹(shao)以(yi)下三種(zhong)：電池饋電、自動(dong)選擇和(he)動(dong)態(tai)電源路徑。

　　電池饋電拓撲

　　電(dian)池饋電(dian)拓(tuo)撲是一種實現過程最簡單、成本最低的拓(tuo)撲，這是因為(wei)其電(dian)路由充電(dian)器、電(dian)池和(he)系統組成，如圖(tu)2所示。

　　

 

　　圖2:電池饋電拓撲原(yuan)理圖及信號圖。

　　這(zhe)種(zhong)拓(tuo)撲有三個主要特性：無論供(gong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)如何變(bian)化，系(xi)統(tong)(tong)電(dian)(dian)(dian)(dian)壓(ya)始(shi)終(zhong)等于電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)，電(dian)(dian)(dian)(dian)源(yuan)(yuan)系(xi)統(tong)(tong)始(shi)終(zhong)優先，以(yi)便(bian)IBATT ￡ ICHG,并(bing)且ICHG最終(zhong)限制由輸入電(dian)(dian)(dian)(dian)源(yuan)(yuan)提供(gong)給系(xi)統(tong)(tong)電(dian)(dian)(dian)(dian)源(yuan)(yuan)總線的最大功率。當(dang)系(xi)統(tong)(tong)與充(chong)電(dian)(dian)(dian)(dian)器(qi)斷(duan)開(kai)時該拓(tuo)撲還(huan)可(ke)以(yi)實現最小的耗散功率，設置(zhi)ICHG從(cong)根本上(shang)限定了(le)總輸入電(dian)(dian)(dian)(dian)流(liu)，這(zhe)樣，隨著系(xi)統(tong)(tong)電(dian)(dian)(dian)(dian)流(liu)(ISYS)的增加，充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(IBATT)將等額下降，工作波(bo)形如圖2所示。

　　遺憾的是，這種(zhong)拓(tuo)撲有(you)如下不足之(zhi)處(chu)，從而限制了它在更廣應用領域的效(xiao)率和效(xiao)用：

　　在電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)太(tai)低(di)(di)的情況下(xia)，系(xi)統(tong)無法工作(zuo)(zuo)。電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)跌至涓流充電(dian)(dian)(dian)門限以下(xia)時，充電(dian)(dian)(dian)器(qi)將(jiang)把總的輸出電(dian)(dian)(dian)流限制得很低(di)(di)。系(xi)統(tong)的額外電(dian)(dian)(dian)源需求將(jiang)由(you)電(dian)(dian)(dian)池來補充，從而導致電(dian)(dian)(dian)池能量進(jin)一(yi)(yi)步(bu)耗盡(jin)。由(you)于(yu)系(xi)統(tong)電(dian)(dian)(dian)壓(ya)始終等于(yu)電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)，一(yi)(yi)旦電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)低(di)(di)到(dao)系(xi)統(tong)最低(di)(di)工作(zuo)(zuo)電(dian)(dian)(dian)壓(ya)以下(xia)，系(xi)統(tong)將(jiang)停止(zhi)工作(zuo)(zuo)。

　　雖然電(dian)池(chi)已(yi)具有(you)滿電(dian)量，但是(shi)充(chong)電(dian)器無法(fa)(fa)進入EOC(結束充(chong)電(dian))狀態。如果ISYS超過電(dian)池(chi)滿電(dian)量門(men)限(IBF)，那(nei)么(me)ICHG就(jiu)無法(fa)(fa)降到(dao)低于(yu)IBF,充(chong)電(dian)狀態始終顯示正在(zai)充(chong)電(dian)，即使電(dian)池(chi)已(yi)經具有(you)滿電(dian)量。

　　電(dian)(dian)池無(wu)法充滿。由于(yu)系統優先于(yu)電(dian)(dian)池供電(dian)(dian)，因此(ci)電(dian)(dian)池只(zhi)能以低(di)電(dian)(dian)流進行(xing)充電(dian)(dian)。此(ci)外，充電(dian)(dian)器(qi)只(zhi)能在預(yu)期的有效充電(dian)(dian)時間內工作，這(zhe)樣可以避免給壞電(dian)(dian)池充電(dian)(dian)。如充電(dian)(dian)時間超出(chu)此(ci)時間段，會導致(zhi)充電(dian)(dian)器(qi)誤判壞電(dian)(dian)池而(er)停止充電(dian)(dian)。

　　電源路徑(jing)自動選(xuan)擇拓撲

　　電(dian)源路徑自動選擇拓撲在電(dian)池直接(jie)搭載拓撲基礎(chu)上外加(jia)了兩個開關(guan)管，使得系統電(dian)源可以根據輸入(ru)電(dian)壓的變化(hua)在適配器和電(dian)池之間來(lai)回切換。拓撲結構及工作波形如(ru)圖3所示。

　　

 

　　圖3:電源(yuan)路徑自動選擇拓撲及工作(zuo)波形。

　　與電池饋電拓撲結構相比，此拓撲有實質性的改進。它將系統直接跟交流適配器相連，與充電器獨立開來，因而能夠提供更大的系統電流、更高的效率并且允許系統在低電池電壓下工作。此外，其價格也比較低廉。然而，當適配器輸出電壓變化較大的時候，系統電壓也會隨之變化，所以此拓撲要求系統能夠接受比較寬的輸入電壓變化范圍。此外，也要求適配器具有更高的額定功率，以滿足系統和充電器的最大總功率(lv)需求，以及(ji)系統(tong)負載突變(bian)時的功率(lv)變(bian)化(hua)要求。

　　圖(tu)4是采用MPS公司的MP2611構成的電源(yuan)路(lu)徑自(zi)動選擇拓撲的原(yuan)理圖(tu)。為了防止出現(xian)不穩定(ding)情況，當VBATT接近VIN時，MP2611會(hui)斷(duan)開系統(tong)與電池(chi)的連接。此外，它還會(hui)在S1 (M1及M2)與S2(M3)之(zhi)間插(cha)入一個消隱期，以防出現(xian)電流貫通，從而損壞(huai)系統(tong)和電池(chi)。

　　

 

　　圖4:采用MP2611構成的電(dian)源路徑自動選擇拓(tuo)撲。

   動態電(dian)源路徑管理拓撲(DPPM)

 

　　動態電(dian)(dian)源(yuan)路徑管(guan)理(DPPM)技術采(cai)用(yong)了一套附加(jia)的檢(jian)測模(mo)塊(kuai)，測量系(xi)統(tong)電(dian)(dian)壓或者輸入電(dian)(dian)流(liu)，實時監測總(zong)功率需(xu)求。一旦功率需(xu)求超過預設(she)值，通(tong)過充電(dian)(dian)器(qi)降低充電(dian)(dian)電(dian)(dian)流(liu)來保(bao)證適配器(qi)輸出功率恒(heng)定而不過載(zai)。

　　例如，基于(yu)(yu)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)DPPM(圖5)通過比(bi)較輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)與預設(she)參考電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)來判斷輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)是否(fou)達到(dao)適配(pei)器的(de)輸(shu)出電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)限制(zhi)(zhi)(zhi)。若適配(pei)器電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)已經達到(dao)該(gai)(gai)限制(zhi)(zhi)(zhi)，適配(pei)器電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)將降至預設(she)參考電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，然(ran)后充電(dian)(dian)(dian)(dian)(dian)(dian)器通過動態降低充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)來防止系統電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)繼(ji)續下降。只要輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)保持在(zai)該(gai)(gai)限制(zhi)(zhi)(zhi)的(de)水平或者(zhe)低于(yu)(yu)該(gai)(gai)限制(zhi)(zhi)(zhi)，就仍然(ran)有(you)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)向電(dian)(dian)(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)(dian)(dian)。然(ran)而，由系統電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)下降引起的(de)不穩定(ding)或噪聲(sheng)使得這種(zhong)基于(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)DPPM結構不適合應用在(zai)某些對噪聲(sheng)敏感的(de)場合，比(bi)如音頻設(she)備。

　　

 

　　圖5:基于輸入電壓的動態電源路徑管理。

　　基于輸(shu)入電(dian)(dian)流(liu)的(de)DPPM(圖(tu)6)采用檢測電(dian)(dian)阻來(lai)評估輸(shu)入電(dian)(dian)流(liu)，當輸(shu)入電(dian)(dian)流(liu)達到(dao)預(yu)設電(dian)(dian)流(liu)門限時，通過動態降(jiang)(jiang)低電(dian)(dian)池電(dian)(dian)流(liu)來(lai)防止適配器過載或系統電(dian)(dian)壓(ya)(ya)下(xia)降(jiang)(jiang)。這(zhe)樣就(jiu)保證了系統電(dian)(dian)壓(ya)(ya)的(de)穩定，降(jiang)(jiang)低了適配器的(de)額(e)外功(gong)率要求(qiu)。同時，該拓撲還具(ju)備(bei)電(dian)(dian)池反向補充供電(dian)(dian)的(de)能力。

　　

 

　　圖6:基于(yu)輸入電流的動(dong)態(tai)電源路徑管理。

　　有些充電器(例如MPS公司的MP2607)可以根據不同電源要求，優化選擇不同的動態電源路徑管理方案。MP2607根據不同的適配器類型，在基于輸入電壓和基于輸入電流的DPPM兩種拓撲之間進行智能選擇。若輸入是交流適配器，MP2607采用基于輸入電壓的DPPM技術，控制適配器交流電壓，使得交流適配器可以同時為系統供電和為電池充電，工(gong)作波形如圖7所示。

　　

 

　　圖7:MP2607在交流適配器(qi)輸(shu)入時的動態電源路徑管(guan)理(li)。

　　在USB輸(shu)入(ru)模式下(xia)，MP2607采用基(ji)于(yu)(yu)輸(shu)入(ru)電流(liu)(liu)的(de)DPPM.如圖8所示，考慮到USB提供電流(liu)(liu)能力有限，設置充(chong)電電流(liu)(liu)在USB限制電流(liu)(liu)以下(xia)。若系(xi)統負(fu)載(zai)電流(liu)(liu)大于(yu)(yu)USB限流(liu)(liu)值，電池將反向補充(chong)供電。

　　

 

　　圖8:MP2607在USB輸入時的動態電源(yuan)路徑管理。

　　總之，具有動態電源路徑管理的充電器(尤其是那(nei)些能在不同(tong)管(guan)理模式之間切換(huan)的(de)(de)充電器)可以為移動電子設備提供更加精妙的(de)(de)電源解決方案，從而給用戶帶來前(qian)所未(wei)有的(de)(de)便利、性能和效率(lv)。