鋰(li)離子(Li-ion)電(dian)池(chi)(chi)(chi)和(he)(he)鋰(li)聚合物(Li-po)電(dian)池(chi)(chi)(chi)最適合當前市(shi)場對功(gong)率(lv)密(mi)度、充電(dian)能力和(he)(he)價格的(de)要求。但是，有別于鉛酸(suan)、鎳氫等其他(ta)流行(xing)的(de)電(dian)池(chi)(chi)(chi)技術，鋰(li)電(dian)池(chi)(chi)(chi)技術的(de)性能也(ye)最不穩定：鋰(li)電(dian)池(chi)(chi)(chi)充放(fang)電(dian)若管理不善，將導致充電(dian)時間長(chang)、耗散功(gong)率(lv)高、效率(lv)低和(he)(he)電(dian)池(chi)(chi)(chi)壽命比平均壽命低等問題。圖1顯示了典型鋰(li)離子電(dian)池(chi)(chi)(chi)的(de)充電(dian)曲線。

　　傳統充電器相對簡(jian)單，這些充電(dian)(dian)器在(zai)小功(gong)率應用中表現(xian)較好。然而，它(ta)們(men)卻不(bu)能有效地適應充電(dian)(dian)曲線的變(bian)化，比如，用戶在(zai)不(bu)同電(dian)(dian)源(yuan)之間切(qie)換或者在(zai)充電(dian)(dian)期間操(cao)作設備。另外，傳統充電(dian)(dian)器在(zai)大功(gong)率和(he)大電(dian)(dian)流應用中，通(tong)常(chang)效率較低，耗散功(gong)率較大。

　　

 

　　圖1:典型鋰離子電池的充(chong)電曲線。

　　新型線性和開關充電器，比如芯源系統(MPS)公司的(de)MP2600系列，采用(yong)電源路徑管(guan)理技術改變了充(chong)(chong)電曲線，從而能(neng)夠以更低的(de)耗散功(gong)率更加高效地為電池/系統供電。同(tong)時，這些充(chong)(chong)電器也(ye)使系統的(de)安全性和電池的(de)使用(yong)壽(shou)命得到提高。

　　電源管理(li)拓撲種(zhong)類繁多(duo)，本文(wen)則重點(dian)介紹以下三(san)種(zhong)：電池饋電、自動選擇(ze)和動態電源路徑。

　　電池饋電拓撲

　　電(dian)(dian)池饋電(dian)(dian)拓(tuo)撲(pu)是(shi)一種實現過程最簡單、成本最低的拓(tuo)撲(pu)，這(zhe)是(shi)因(yin)為(wei)其電(dian)(dian)路由充電(dian)(dian)器、電(dian)(dian)池和系統組成，如(ru)圖2所示(shi)。

　　

 

　　圖2:電(dian)池饋電(dian)拓(tuo)撲原理圖及(ji)信(xin)號圖。

　　這種拓撲(pu)有三個(ge)主(zhu)要(yao)特性：無(wu)論(lun)供電(dian)(dian)(dian)電(dian)(dian)(dian)壓如何變化，系(xi)(xi)(xi)統(tong)電(dian)(dian)(dian)壓始終(zhong)(zhong)等于電(dian)(dian)(dian)池電(dian)(dian)(dian)壓，電(dian)(dian)(dian)源系(xi)(xi)(xi)統(tong)始終(zhong)(zhong)優先(xian)，以便IBATT ￡ ICHG,并且ICHG最(zui)終(zhong)(zhong)限(xian)制由輸(shu)(shu)入電(dian)(dian)(dian)源提供給系(xi)(xi)(xi)統(tong)電(dian)(dian)(dian)源總線的(de)最(zui)大功(gong)率。當系(xi)(xi)(xi)統(tong)與(yu)充(chong)電(dian)(dian)(dian)器斷開(kai)時該拓撲(pu)還可以實(shi)現(xian)最(zui)小的(de)耗散功(gong)率，設(she)置ICHG從根(gen)本上(shang)限(xian)定了總輸(shu)(shu)入電(dian)(dian)(dian)流，這樣，隨著系(xi)(xi)(xi)統(tong)電(dian)(dian)(dian)流(ISYS)的(de)增(zeng)加，充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(IBATT)將等額下降，工(gong)作(zuo)波形如圖2所示。

　　遺憾的是，這(zhe)種拓撲有如下不(bu)足之處，從而限制了它(ta)在更廣應用(yong)領(ling)域的效率和效用(yong)：

　　在電(dian)(dian)池(chi)電(dian)(dian)壓(ya)太低(di)的(de)(de)情(qing)況下，系統無法(fa)工作(zuo)。電(dian)(dian)池(chi)電(dian)(dian)壓(ya)跌至涓流充(chong)(chong)電(dian)(dian)門限以下時(shi)，充(chong)(chong)電(dian)(dian)器將(jiang)把總的(de)(de)輸(shu)出電(dian)(dian)流限制得很低(di)。系統的(de)(de)額(e)外電(dian)(dian)源需求將(jiang)由電(dian)(dian)池(chi)來補充(chong)(chong)，從而導致電(dian)(dian)池(chi)能量進一步耗盡。由于(yu)系統電(dian)(dian)壓(ya)始終等于(yu)電(dian)(dian)池(chi)電(dian)(dian)壓(ya)，一旦電(dian)(dian)池(chi)電(dian)(dian)壓(ya)低(di)到系統最低(di)工作(zuo)電(dian)(dian)壓(ya)以下，系統將(jiang)停止(zhi)工作(zuo)。

　　雖然(ran)電(dian)(dian)(dian)池已具有(you)滿(man)電(dian)(dian)(dian)量，但是充(chong)電(dian)(dian)(dian)器無(wu)法進入EOC(結束充(chong)電(dian)(dian)(dian))狀態。如果ISYS超過電(dian)(dian)(dian)池滿(man)電(dian)(dian)(dian)量門限(IBF)，那么ICHG就無(wu)法降到低(di)于IBF,充(chong)電(dian)(dian)(dian)狀態始終顯(xian)示正在(zai)充(chong)電(dian)(dian)(dian)，即使電(dian)(dian)(dian)池已經具有(you)滿(man)電(dian)(dian)(dian)量。

　　電(dian)(dian)池(chi)無法充滿。由于(yu)系統優先于(yu)電(dian)(dian)池(chi)供電(dian)(dian)，因此(ci)電(dian)(dian)池(chi)只能以(yi)低電(dian)(dian)流進行(xing)充電(dian)(dian)。此(ci)外，充電(dian)(dian)器只能在預期的(de)有效(xiao)充電(dian)(dian)時(shi)間(jian)內工作，這樣可(ke)以(yi)避免給壞電(dian)(dian)池(chi)充電(dian)(dian)。如充電(dian)(dian)時(shi)間(jian)超出此(ci)時(shi)間(jian)段(duan)，會導致充電(dian)(dian)器誤判壞電(dian)(dian)池(chi)而停止充電(dian)(dian)。

　　電源(yuan)路(lu)徑(jing)自動(dong)選擇拓(tuo)撲

　　電(dian)源路徑自動選擇拓撲在電(dian)池直接搭(da)載拓撲基礎上外(wai)加了兩(liang)個開(kai)關管，使得(de)系統電(dian)源可以根據輸入(ru)電(dian)壓的變化在適配器和電(dian)池之間(jian)來回(hui)切換。拓撲結構及工作波形如圖3所示(shi)。

　　

 

　　圖3:電源路徑自動選擇拓撲及工作(zuo)波(bo)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需求，以及系統負載突(tu)變(bian)(bian)時的功率變(bian)(bian)化要求。

　　圖4是采用MPS公(gong)司(si)的(de)MP2611構成的(de)電源路徑(jing)自動選(xuan)擇拓(tuo)撲的(de)原理(li)圖。為了防止(zhi)出現(xian)不穩定情況，當VBATT接近VIN時，MP2611會斷開系統(tong)與(yu)電池的(de)連(lian)接。此外，它還會在S1 (M1及M2)與(yu)S2(M3)之(zhi)間插入一個(ge)消隱期(qi)，以防出現(xian)電流貫通，從而損壞系統(tong)和電池。

　　

 

　　圖4:采用MP2611構成的(de)電(dian)源路徑自動選擇拓撲(pu)。

   動態(tai)電源路徑管理拓撲(pu)(DPPM)

 

　　動態電(dian)(dian)源路徑管理(DPPM)技術采用了一套附加的檢(jian)測模塊，測量系統電(dian)(dian)壓或(huo)者輸入(ru)電(dian)(dian)流(liu)(liu)，實時監測總(zong)功率需(xu)求。一旦功率需(xu)求超過預(yu)設值(zhi)，通過充(chong)(chong)電(dian)(dian)器降低充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)來保證適(shi)配器輸出功率恒(heng)定而不過載。

　　例(li)如(ru)，基于輸(shu)入電(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)DPPM(圖5)通過比(bi)較(jiao)輸(shu)入電(dian)(dian)(dian)(dian)(dian)壓(ya)與預設參考電(dian)(dian)(dian)(dian)(dian)壓(ya)來判斷輸(shu)入電(dian)(dian)(dian)(dian)(dian)流(liu)是否達到(dao)適(shi)配器的(de)(de)輸(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)流(liu)限制(zhi)。若適(shi)配器電(dian)(dian)(dian)(dian)(dian)流(liu)已經達到(dao)該(gai)(gai)限制(zhi)，適(shi)配器電(dian)(dian)(dian)(dian)(dian)壓(ya)將(jiang)降(jiang)(jiang)至(zhi)預設參考電(dian)(dian)(dian)(dian)(dian)壓(ya)，然(ran)后充(chong)電(dian)(dian)(dian)(dian)(dian)器通過動態降(jiang)(jiang)低充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)來防止(zhi)系統電(dian)(dian)(dian)(dian)(dian)壓(ya)繼續下降(jiang)(jiang)。只要輸(shu)入電(dian)(dian)(dian)(dian)(dian)流(liu)保持(chi)在該(gai)(gai)限制(zhi)的(de)(de)水平或者低于該(gai)(gai)限制(zhi)，就仍然(ran)有電(dian)(dian)(dian)(dian)(dian)流(liu)向電(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)。然(ran)而，由(you)系統電(dian)(dian)(dian)(dian)(dian)壓(ya)下降(jiang)(jiang)引起的(de)(de)不穩定或噪聲使(shi)得這種基于電(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)(de)DPPM結構不適(shi)合應用在某些對噪聲敏感的(de)(de)場合，比(bi)如(ru)音頻設備。

　　

 

　　圖5:基于(yu)輸入電壓(ya)的動態電源(yuan)路徑管理。

　　基于輸入電(dian)流(liu)的DPPM(圖6)采用檢(jian)測(ce)電(dian)阻來(lai)評估輸入電(dian)流(liu)，當輸入電(dian)流(liu)達到預設(she)電(dian)流(liu)門限時(shi)，通(tong)過(guo)動態降低電(dian)池電(dian)流(liu)來(lai)防(fang)止適配器過(guo)載(zai)或(huo)系統電(dian)壓下(xia)降。這樣就保證了系統電(dian)壓的穩定，降低了適配器的額外功(gong)率(lv)要求。同時(shi)，該拓撲還具備電(dian)池反向補充供(gong)電(dian)的能力(li)。

　　

 

　　圖6:基于輸入(ru)電流的動態電源路徑管(guan)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，工作波形(xing)如圖7所示。

　　

 

　　圖(tu)7:MP2607在交流適配器輸入時的動態(tai)電源路徑(jing)管理。

　　在(zai)USB輸入模式下，MP2607采用基于輸入電(dian)(dian)(dian)(dian)流(liu)的DPPM.如圖8所示，考慮到USB提(ti)供(gong)電(dian)(dian)(dian)(dian)流(liu)能(neng)力有(you)限，設(she)置充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)在(zai)USB限制電(dian)(dian)(dian)(dian)流(liu)以下。若系統負載(zai)電(dian)(dian)(dian)(dian)流(liu)大于USB限流(liu)值(zhi)，電(dian)(dian)(dian)(dian)池將(jiang)反向補(bu)充供(gong)電(dian)(dian)(dian)(dian)。

　　

 

　　圖8:MP2607在USB輸入時的(de)動(dong)態電源(yuan)路徑管理(li)。

　　總之，具有動態電源路徑管理的充電器(尤其是那些能在不同管(guan)理模(mo)式(shi)之(zhi)間切換的(de)充電器)可以為移動電子設備提供更加(jia)精妙(miao)的(de)電源解決方案，從而給用(yong)戶(hu)帶來前所未(wei)有的(de)便利、性能和效率。