隨著智能(neng)手機、平(ping)(ping)板電(dian)腦(nao)和(he)(he)攝像機等(deng)便攜設備的(de)(de)不斷普及，人(ren)們對電(dian)源(yuan)的(de)(de)要求以及對邊充電(dian)邊使(shi)用這(zhe)些(xie)設備的(de)(de)能(neng)力的(de)(de)要求與(yu)日(ri)俱(ju)增。更高的(de)(de)功率(lv)要求增加了對具有高功率(lv)密(mi)度和(he)(he)優異充電(dian)能(neng)力的(de)(de)電(dian)池(chi)(chi)(chi)的(de)(de)需求。目(mu)前，鋰離子（Li-ion）電(dian)池(chi)(chi)(chi)和(he)(he)鋰聚合物（Li-po）電(dian)池(chi)(chi)(chi)最適合當前市場對功率(lv)密(mi)度、充電(dian)能(neng)力和(he)(he)價格的(de)(de)要求。但(dan)是，有別于鉛酸、鎳氫等(deng)其他流行的(de)(de)電(dian)池(chi)(chi)(chi)技術(shu)，鋰電(dian)池(chi)(chi)(chi)技術(shu)的(de)(de)性(xing)能(neng)也最不穩定：鋰電(dian)池(chi)(chi)(chi)充放電(dian)若(ruo)管(guan)理(li)不善(shan)，將導致充電(dian)時(shi)間(jian)長、耗散功率(lv)高、效率(lv)低和(he)(he)電(dian)池(chi)(chi)(chi)壽命比平(ping)(ping)均壽命低等(deng)問題。圖1顯示了典型鋰離子電(dian)池(chi)(chi)(chi)的(de)(de)充電(dian)曲線。

　　傳統充電器相對簡單(dan)，這些充電(dian)器在小功率(lv)應(ying)用中(zhong)表現(xian)較(jiao)(jiao)好。然而，它們卻不(bu)能有效地適應(ying)充電(dian)曲線的(de)變(bian)化，比如，用戶在不(bu)同電(dian)源之間(jian)切換或(huo)者在充電(dian)期間(jian)操作(zuo)設備。另(ling)外，傳統(tong)充電(dian)器在大(da)(da)功率(lv)和大(da)(da)電(dian)流應(ying)用中(zhong)，通(tong)常效率(lv)較(jiao)(jiao)低(di)，耗(hao)散功率(lv)較(jiao)(jiao)大(da)(da)。

圖1:典(dian)型(xing)鋰(li)離子電(dian)(dian)池的充電(dian)(dian)曲線。

　　新型線性和開關充電器，比如芯源系統（MPS）公司的MP2600系列，采用電源路徑管理技術改變了充電曲線，從而能夠以更低的耗散功率更加高效地為電池/系統供電。同時，這些充電器也使系統的(de)安全性和電(dian)池的(de)使用壽命得到(dao)提高。

　　電(dian)源(yuan)管理拓撲種(zhong)類繁(fan)多，本(ben)文則重(zhong)點介紹以下三種(zhong)：電(dian)池饋電(dian)、自(zi)動(dong)選擇和動(dong)態電(dian)源(yuan)路(lu)徑(jing)。

　　電池饋電拓撲

　　電(dian)(dian)池(chi)饋(kui)電(dian)(dian)拓(tuo)撲是(shi)一種實現過程最簡單、成本最低的(de)拓(tuo)撲，這是(shi)因為其電(dian)(dian)路(lu)由充電(dian)(dian)器(qi)、電(dian)(dian)池(chi)和系統(tong)組(zu)成，如圖2所示(shi)。

圖(tu)2:電(dian)池饋(kui)電(dian)拓撲原理圖(tu)及信號圖(tu)。

　　這種(zhong)拓(tuo)撲有三個主(zhu)要特性：無論供(gong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓如(ru)何變化，系(xi)統(tong)(tong)電(dian)(dian)(dian)(dian)壓始終(zhong)等(deng)于電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓，電(dian)(dian)(dian)(dian)源系(xi)統(tong)(tong)始終(zhong)優先，以便IBATT ￡ ICHG,并且ICHG最(zui)終(zhong)限(xian)(xian)制由輸入電(dian)(dian)(dian)(dian)源提供(gong)給系(xi)統(tong)(tong)電(dian)(dian)(dian)(dian)源總(zong)線的最(zui)大(da)功率。當系(xi)統(tong)(tong)與充電(dian)(dian)(dian)(dian)器斷開時該拓(tuo)撲還可以實現最(zui)小(xiao)的耗散功率，設置ICHG從(cong)根本上限(xian)(xian)定了總(zong)輸入電(dian)(dian)(dian)(dian)流，這樣，隨著(zhu)系(xi)統(tong)(tong)電(dian)(dian)(dian)(dian)流（ISYS）的增加，充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流（IBATT）將等(deng)額(e)下降，工作波形如(ru)圖(tu)2所示(shi)。

　　遺(yi)憾的是，這(zhe)種(zhong)拓撲有如下不足之處，從(cong)而(er)限(xian)制了它在更廣應用(yong)領域的效(xiao)率和效(xiao)用(yong)：

　　在電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓太低(di)的(de)情況下，系(xi)統(tong)(tong)無(wu)法工作。電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓跌至涓流充電(dian)(dian)(dian)門限以下時，充電(dian)(dian)(dian)器將把總的(de)輸(shu)出電(dian)(dian)(dian)流限制得很低(di)。系(xi)統(tong)(tong)的(de)額外電(dian)(dian)(dian)源需求將由電(dian)(dian)(dian)池(chi)來(lai)補充，從而導致(zhi)電(dian)(dian)(dian)池(chi)能量(liang)進(jin)一(yi)步耗盡(jin)。由于(yu)系(xi)統(tong)(tong)電(dian)(dian)(dian)壓始終等于(yu)電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓，一(yi)旦電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓低(di)到系(xi)統(tong)(tong)最低(di)工作電(dian)(dian)(dian)壓以下，系(xi)統(tong)(tong)將停止工作。

　　雖然(ran)電(dian)(dian)(dian)(dian)池(chi)已(yi)具有滿電(dian)(dian)(dian)(dian)量(liang)，但是充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)無(wu)法進(jin)入EOC（結束充(chong)(chong)電(dian)(dian)(dian)(dian)）狀(zhuang)態(tai)。如果(guo)ISYS超(chao)過電(dian)(dian)(dian)(dian)池(chi)滿電(dian)(dian)(dian)(dian)量(liang)門(men)限（IBF），那(nei)么ICHG就(jiu)無(wu)法降到低于(yu)IBF,充(chong)(chong)電(dian)(dian)(dian)(dian)狀(zhuang)態(tai)始終顯示正在(zai)充(chong)(chong)電(dian)(dian)(dian)(dian)，即使(shi)電(dian)(dian)(dian)(dian)池(chi)已(yi)經具有滿電(dian)(dian)(dian)(dian)量(liang)。

　　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)，因此電(dian)(dian)池(chi)只能(neng)(neng)以(yi)低電(dian)(dian)流進行(xing)充電(dian)(dian)。此外，充電(dian)(dian)器只能(neng)(neng)在預期的有效(xiao)充電(dian)(dian)時(shi)間內工作，這樣可以(yi)避(bi)免給壞電(dian)(dian)池(chi)充電(dian)(dian)。如充電(dian)(dian)時(shi)間超出(chu)此時(shi)間段，會導致充電(dian)(dian)器誤判壞電(dian)(dian)池(chi)而停止(zhi)充電(dian)(dian)。

電源(yuan)路徑自動選(xuan)擇拓撲

　　電源路徑自動選擇(ze)拓(tuo)撲在電池直接搭載拓(tuo)撲基(ji)礎(chu)上外加(jia)了兩(liang)個開關管，使得系統(tong)電源可以根據輸入電壓的(de)變(bian)化在適配器和電池之間來回(hui)切(qie)換。拓(tuo)撲結構及工作波形如圖3所示。

圖3:電(dian)源路徑自動選擇(ze)拓撲及工(gong)作波形。

　　與(yu)電(dian)池饋(kui)電(dian)拓撲結構相比(bi)，此拓撲有(you)(you)實質性的(de)改(gai)進。它將(jiang)系(xi)統(tong)直接跟交流(liu)適配器(qi)相連，與(yu)充電(dian)器(qi)獨(du)立開(kai)來，因而能夠提供更大的(de)系(xi)統(tong)電(dian)流(liu)、更高的(de)效率(lv)并(bing)且允許系(xi)統(tong)在低(di)電(dian)池電(dian)壓下工作。此外，其價(jia)格也比(bi)較低(di)廉(lian)。然而，當適配器(qi)輸(shu)出電(dian)壓變(bian)化較大的(de)時候，系(xi)統(tong)電(dian)壓也會隨(sui)之變(bian)化，所以此拓撲要(yao)(yao)求(qiu)系(xi)統(tong)能夠接受比(bi)較寬的(de)輸(shu)入電(dian)壓變(bian)化范圍。此外，也要(yao)(yao)求(qiu)適配器(qi)具(ju)有(you)(you)更高的(de)額(e)定功(gong)率(lv)，以滿(man)足系(xi)統(tong)和充電(dian)器(qi)的(de)最大總功(gong)率(lv)需求(qiu)，以及系(xi)統(tong)負載突變(bian)時的(de)功(gong)率(lv)變(bian)化要(yao)(yao)求(qiu)。

　　圖4是(shi)采用MPS公司的(de)MP2611構(gou)成的(de)電(dian)源路徑自(zi)動選擇拓撲的(de)原理圖。為(wei)了防止出(chu)現不穩(wen)定(ding)情況(kuang)，當VBATT接(jie)近VIN時，MP2611會(hui)斷開(kai)系(xi)統(tong)(tong)與(yu)電(dian)池(chi)的(de)連接(jie)。此外，它還會(hui)在S1 （M1及M2）與(yu)S2（M3）之間插入(ru)一(yi)個消隱(yin)期，以防出(chu)現電(dian)流(liu)貫(guan)通，從而損壞系(xi)統(tong)(tong)和電(dian)池(chi)。

圖(tu)4:采用MP2611構成的電(dian)源路(lu)徑自(zi)動選擇拓撲。

　　動態電源路(lu)徑(jing)管理(li)拓撲(pu)（DPPM）

　　動態電源路徑管理（DPPM）技術采用了一套附加的(de)檢測模塊，測量(liang)系統(tong)電壓或者輸入電流(liu)，實(shi)時監測總功(gong)(gong)率需求。一旦功(gong)(gong)率需求超過(guo)(guo)預設值，通過(guo)(guo)充電器(qi)降低充電電流(liu)來保(bao)證適(shi)配器(qi)輸出功(gong)(gong)率恒(heng)定而不過(guo)(guo)載。

　　例如，基于輸入電壓的DPPM（圖5）通過比較輸入電壓與預設參考電壓來判斷輸入電流是否達到適配器的輸出電流限制。若適配器電流已經達到該限制，適配器電壓將降至預設參考電壓，然后充電器通過動態降(jiang)(jiang)低充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)來防止系統(tong)電(dian)(dian)(dian)壓繼(ji)續下(xia)降(jiang)(jiang)。只要(yao)輸(shu)入(ru)電(dian)(dian)(dian)流(liu)(liu)保持(chi)在(zai)該限(xian)制的水平或(huo)者低于該限(xian)制，就(jiu)仍然有電(dian)(dian)(dian)流(liu)(liu)向電(dian)(dian)(dian)池充電(dian)(dian)(dian)。然而(er)，由系統(tong)電(dian)(dian)(dian)壓下(xia)降(jiang)(jiang)引起的不穩定(ding)或(huo)噪聲使(shi)得這種(zhong)基于電(dian)(dian)(dian)壓的DPPM結構不適合應用在(zai)某(mou)些對噪聲敏感的場合，比如(ru)音頻(pin)設備。

圖5:基于輸入電壓的動態電源路徑(jing)管理。

基于輸入(ru)(ru)電(dian)(dian)(dian)流的(de)(de)DPPM（圖6）采用檢(jian)測電(dian)(dian)(dian)阻來評估輸入(ru)(ru)電(dian)(dian)(dian)流，當(dang)輸入(ru)(ru)電(dian)(dian)(dian)流達到預設電(dian)(dian)(dian)流門限時，通過動態降低電(dian)(dian)(dian)池電(dian)(dian)(dian)流來防止適配(pei)器(qi)過載或系統電(dian)(dian)(dian)壓下降。這樣就保證了(le)(le)系統電(dian)(dian)(dian)壓的(de)(de)穩(wen)定(ding)，降低了(le)(le)適配(pei)器(qi)的(de)(de)額外功率要求。同時，該拓撲還具備電(dian)(dian)(dian)池反(fan)向(xiang)補充供電(dian)(dian)(dian)的(de)(de)能力。

圖6:基(ji)于輸入電流(liu)的動(dong)態電源路徑管理。

　　有些充電(dian)(dian)(dian)器(qi)（例如(ru)MPS公司的(de)(de)(de)MP2607）可以根據(ju)不同(tong)電(dian)(dian)(dian)源(yuan)要求，優化選擇(ze)不同(tong)的(de)(de)(de)動(dong)態電(dian)(dian)(dian)源(yuan)路(lu)徑管理方案。MP2607根據(ju)不同(tong)的(de)(de)(de)適配(pei)(pei)器(qi)類型，在(zai)基(ji)于(yu)(yu)輸入(ru)(ru)電(dian)(dian)(dian)壓(ya)和(he)基(ji)于(yu)(yu)輸入(ru)(ru)電(dian)(dian)(dian)流(liu)的(de)(de)(de)DPPM兩(liang)種拓(tuo)撲之間(jian)進行智(zhi)能選擇(ze)。若輸入(ru)(ru)是交(jiao)流(liu)適配(pei)(pei)器(qi)，MP2607采用基(ji)于(yu)(yu)輸入(ru)(ru)電(dian)(dian)(dian)壓(ya)的(de)(de)(de)DPPM技術，控制(zhi)適配(pei)(pei)器(qi)交(jiao)流(liu)電(dian)(dian)(dian)壓(ya)，使(shi)得交(jiao)流(liu)適配(pei)(pei)器(qi)可以同(tong)時為系統供(gong)電(dian)(dian)(dian)和(he)為電(dian)(dian)(dian)池充電(dian)(dian)(dian)，工作波形如(ru)圖7所示。

圖7:MP2607在交流(liu)適配器輸入時的動態(tai)電源路(lu)徑管理(li)。

　　在(zai)(zai)USB輸(shu)入模(mo)式下(xia)，MP2607采用基于輸(shu)入電(dian)流(liu)的DPPM.如圖8所示，考慮到USB提(ti)供電(dian)流(liu)能力有限(xian)，設置充電(dian)電(dian)流(liu)在(zai)(zai)USB限(xian)制電(dian)流(liu)以下(xia)。若系統負載電(dian)流(liu)大于USB限(xian)流(liu)值，電(dian)池將(jiang)反向補(bu)充供電(dian)。

圖8:MP2607在USB輸(shu)入時的(de)動(dong)態電(dian)源路徑(jing)管理。

　　總之，具有動態電源路徑管理的充電器（尤其是那些(xie)能(neng)在不同管理(li)模式之(zhi)間切換的充電器）可以為移動電子設(she)備(bei)提供更加精妙(miao)的電源解決(jue)方案，從(cong)而給用(yong)戶帶來前所未有的便利、性能(neng)和(he)效率。