隨著(zhu)智(zhi)能(neng)(neng)手機(ji)、平(ping)板電(dian)(dian)(dian)(dian)腦(nao)和攝像機(ji)等便攜(xie)設備的(de)(de)不斷普及，人(ren)們(men)對電(dian)(dian)(dian)(dian)源的(de)(de)要求以及對邊充(chong)電(dian)(dian)(dian)(dian)邊使用(yong)這些設備的(de)(de)能(neng)(neng)力(li)的(de)(de)要求與日俱增。更高(gao)的(de)(de)功率(lv)要求增加了對具(ju)有高(gao)功率(lv)密(mi)度和優(you)異充(chong)電(dian)(dian)(dian)(dian)能(neng)(neng)力(li)的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)需求。目前(qian)，鋰離子(zi)（Li-ion）電(dian)(dian)(dian)(dian)池(chi)(chi)和鋰聚(ju)合物（Li-po）電(dian)(dian)(dian)(dian)池(chi)(chi)最適合當前(qian)市場對功率(lv)密(mi)度、充(chong)電(dian)(dian)(dian)(dian)能(neng)(neng)力(li)和價格的(de)(de)要求。但是，有別(bie)于鉛酸、鎳氫等其他流(liu)行的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)技術(shu)，鋰電(dian)(dian)(dian)(dian)池(chi)(chi)技術(shu)的(de)(de)性能(neng)(neng)也最不穩定：鋰電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)放(fang)電(dian)(dian)(dian)(dian)若管理(li)不善，將導致充(chong)電(dian)(dian)(dian)(dian)時間長、耗散功率(lv)高(gao)、效(xiao)率(lv)低和電(dian)(dian)(dian)(dian)池(chi)(chi)壽(shou)命(ming)比(bi)平(ping)均壽(shou)命(ming)低等問題。圖1顯示(shi)了典(dian)型(xing)鋰離子(zi)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)充(chong)電(dian)(dian)(dian)(dian)曲線(xian)。

　　傳統充電器相對簡單(dan)，這些充電(dian)器(qi)在小(xiao)功(gong)率(lv)應用中表現(xian)較好。然(ran)而，它們卻不(bu)(bu)能有(you)效地適應充電(dian)曲(qu)線(xian)的變化，比如，用戶(hu)在不(bu)(bu)同電(dian)源之間(jian)切換(huan)或者在充電(dian)期間(jian)操作(zuo)設(she)備。另外，傳統(tong)充電(dian)器(qi)在大(da)功(gong)率(lv)和(he)大(da)電(dian)流(liu)應用中，通常效率(lv)較低，耗散(san)功(gong)率(lv)較大(da)。

圖1:典型鋰離子電池的充電曲線(xian)。

　　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(he)電(dian)池的(de)使用壽命得到(dao)提高。

　　電(dian)源管理拓撲種類繁多，本文則重點介紹(shao)以下三(san)種：電(dian)池饋電(dian)、自(zi)動(dong)選擇和動(dong)態電(dian)源路(lu)徑。

　　電池饋電拓撲

　　電(dian)池(chi)饋電(dian)拓(tuo)撲(pu)是(shi)一種實現過程最簡(jian)單、成本最低的拓(tuo)撲(pu)，這是(shi)因為其(qi)電(dian)路由充電(dian)器、電(dian)池(chi)和系統組成，如圖(tu)2所示。

圖2:電池饋電拓撲原理圖及信號(hao)圖。

　　這種拓撲有三個主要(yao)特性：無論供電(dian)(dian)電(dian)(dian)壓(ya)如(ru)何變(bian)化，系統(tong)(tong)電(dian)(dian)壓(ya)始(shi)終(zhong)等(deng)于(yu)電(dian)(dian)池電(dian)(dian)壓(ya)，電(dian)(dian)源系統(tong)(tong)始(shi)終(zhong)優先，以(yi)便IBATT ￡ ICHG,并且ICHG最(zui)終(zhong)限(xian)(xian)制(zhi)由(you)輸入電(dian)(dian)源提供給系統(tong)(tong)電(dian)(dian)源總線的(de)最(zui)大功率。當(dang)系統(tong)(tong)與充(chong)電(dian)(dian)器斷(duan)開時該拓撲還可以(yi)實現最(zui)小的(de)耗(hao)散功率，設置(zhi)ICHG從根(gen)本上(shang)限(xian)(xian)定了總輸入電(dian)(dian)流，這樣，隨著系統(tong)(tong)電(dian)(dian)流（ISYS）的(de)增加(jia)，充(chong)電(dian)(dian)電(dian)(dian)流（IBATT）將(jiang)等(deng)額下(xia)降(jiang)，工作波(bo)形(xing)如(ru)圖2所示。

　　遺憾(han)的是，這種拓撲有如下不足(zu)之(zhi)處(chu)，從而限制了它在更廣應用領域的效(xiao)率(lv)和效(xiao)用：

　　在電池(chi)電壓太(tai)低(di)(di)(di)的情況下，系(xi)統無法工(gong)作。電池(chi)電壓跌至涓流充(chong)電門(men)限(xian)以(yi)(yi)下時(shi)，充(chong)電器將(jiang)(jiang)把(ba)總的輸出電流限(xian)制得很低(di)(di)(di)。系(xi)統的額外電源(yuan)需求將(jiang)(jiang)由(you)電池(chi)來(lai)補充(chong)，從而導(dao)致電池(chi)能量進(jin)一步耗盡。由(you)于系(xi)統電壓始終等(deng)于電池(chi)電壓，一旦電池(chi)電壓低(di)(di)(di)到(dao)系(xi)統最低(di)(di)(di)工(gong)作電壓以(yi)(yi)下，系(xi)統將(jiang)(jiang)停止工(gong)作。

　　雖(sui)然電(dian)(dian)池(chi)已(yi)具有(you)滿電(dian)(dian)量，但是充(chong)電(dian)(dian)器(qi)無法進入EOC（結束充(chong)電(dian)(dian)）狀態。如果ISYS超過電(dian)(dian)池(chi)滿電(dian)(dian)量門(men)限（IBF），那(nei)么ICHG就無法降到低于IBF,充(chong)電(dian)(dian)狀態始(shi)終顯示正在(zai)充(chong)電(dian)(dian)，即使電(dian)(dian)池(chi)已(yi)經具有(you)滿電(dian)(dian)量。

　　電(dian)(dian)池(chi)無法充(chong)滿(man)。由于系統優(you)先于電(dian)(dian)池(chi)供電(dian)(dian)，因此(ci)電(dian)(dian)池(chi)只能以(yi)低(di)電(dian)(dian)流進行充(chong)電(dian)(dian)。此(ci)外，充(chong)電(dian)(dian)器(qi)只能在預期的有效充(chong)電(dian)(dian)時(shi)間(jian)內工作，這樣可以(yi)避免給(gei)壞(huai)電(dian)(dian)池(chi)充(chong)電(dian)(dian)。如充(chong)電(dian)(dian)時(shi)間(jian)超出此(ci)時(shi)間(jian)段，會導(dao)致(zhi)充(chong)電(dian)(dian)器(qi)誤判壞(huai)電(dian)(dian)池(chi)而停止(zhi)充(chong)電(dian)(dian)。

電(dian)源路徑自動(dong)選(xuan)擇拓撲(pu)

　　電(dian)(dian)源路徑自動(dong)選擇拓撲(pu)在電(dian)(dian)池直(zhi)接搭載拓撲(pu)基礎(chu)上外(wai)加了兩個開(kai)關管(guan)，使(shi)得系統電(dian)(dian)源可以根據(ju)輸入電(dian)(dian)壓(ya)的(de)變化在適配器和(he)電(dian)(dian)池之(zhi)間(jian)來回(hui)切換。拓撲(pu)結構(gou)及工作(zuo)波形如圖3所(suo)示。

圖(tu)3:電源(yuan)路徑自動選擇拓撲及工作波形。

　　與(yu)電(dian)(dian)池(chi)饋電(dian)(dian)拓(tuo)撲(pu)結構相比(bi)，此拓(tuo)撲(pu)有(you)實(shi)質性的(de)(de)(de)(de)改進。它(ta)將系(xi)(xi)統(tong)(tong)直接跟交流適配(pei)器(qi)相連(lian)，與(yu)充(chong)電(dian)(dian)器(qi)獨立開來，因而能(neng)夠(gou)提供更大(da)的(de)(de)(de)(de)系(xi)(xi)統(tong)(tong)電(dian)(dian)流、更高的(de)(de)(de)(de)效率并(bing)且允許系(xi)(xi)統(tong)(tong)在低(di)電(dian)(dian)池(chi)電(dian)(dian)壓下工作。此外，其價(jia)格也(ye)比(bi)較(jiao)低(di)廉。然而，當適配(pei)器(qi)輸(shu)出(chu)電(dian)(dian)壓變(bian)化(hua)(hua)較(jiao)大(da)的(de)(de)(de)(de)時(shi)候(hou)，系(xi)(xi)統(tong)(tong)電(dian)(dian)壓也(ye)會隨之變(bian)化(hua)(hua)，所(suo)以此拓(tuo)撲(pu)要(yao)求(qiu)系(xi)(xi)統(tong)(tong)能(neng)夠(gou)接受比(bi)較(jiao)寬的(de)(de)(de)(de)輸(shu)入電(dian)(dian)壓變(bian)化(hua)(hua)范圍。此外，也(ye)要(yao)求(qiu)適配(pei)器(qi)具有(you)更高的(de)(de)(de)(de)額(e)定功(gong)率，以滿足系(xi)(xi)統(tong)(tong)和充(chong)電(dian)(dian)器(qi)的(de)(de)(de)(de)最大(da)總功(gong)率需求(qiu)，以及系(xi)(xi)統(tong)(tong)負載(zai)突變(bian)時(shi)的(de)(de)(de)(de)功(gong)率變(bian)化(hua)(hua)要(yao)求(qiu)。

　　圖4是(shi)采用MPS公司的(de)MP2611構(gou)成的(de)電(dian)源路徑自動選(xuan)擇拓撲的(de)原理圖。為了防止出(chu)現(xian)不(bu)穩定情況，當(dang)VBATT接(jie)近(jin)VIN時，MP2611會(hui)斷開(kai)系統與電(dian)池的(de)連接(jie)。此外，它還會(hui)在S1 （M1及M2）與S2（M3）之間(jian)插入一(yi)個消隱期(qi)，以防出(chu)現(xian)電(dian)流貫通(tong)，從而損壞(huai)系統和電(dian)池。

圖4:采用(yong)MP2611構成的電源(yuan)路徑自動(dong)選擇拓撲。

　　動(dong)態(tai)電源(yuan)路徑管理(li)拓撲（DPPM）

　　動(dong)態電(dian)(dian)(dian)源路徑管(guan)理（DPPM）技術采用(yong)了一(yi)套附加的(de)檢測(ce)模塊(kuai)，測(ce)量系統電(dian)(dian)(dian)壓或(huo)者輸入(ru)電(dian)(dian)(dian)流，實時監測(ce)總(zong)功率(lv)需求(qiu)。一(yi)旦功率(lv)需求(qiu)超(chao)過預設(she)值，通過充(chong)電(dian)(dian)(dian)器(qi)降(jiang)低充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流來保證適配器(qi)輸出(chu)功率(lv)恒(heng)定(ding)而(er)不(bu)過載。

　　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(dong)態降低充電(dian)(dian)電(dian)(dian)流(liu)(liu)來防止系統電(dian)(dian)壓繼續下降。只(zhi)要(yao)輸入電(dian)(dian)流(liu)(liu)保持在該限(xian)制的水平或(huo)者低于該限(xian)制，就仍然有(you)電(dian)(dian)流(liu)(liu)向電(dian)(dian)池充電(dian)(dian)。然而，由系統電(dian)(dian)壓下降引起的不(bu)穩定(ding)或(huo)噪(zao)聲使得(de)這種基(ji)于電(dian)(dian)壓的DPPM結構不(bu)適合(he)應用在某(mou)些對噪(zao)聲敏感(gan)的場(chang)合(he)，比如音頻(pin)設(she)備。

圖5:基于輸入電(dian)壓的動態電(dian)源路(lu)徑管理。

基于輸入(ru)(ru)電(dian)(dian)流(liu)的(de)DPPM（圖6）采用檢(jian)測電(dian)(dian)阻來評(ping)估輸入(ru)(ru)電(dian)(dian)流(liu)，當輸入(ru)(ru)電(dian)(dian)流(liu)達到預(yu)設電(dian)(dian)流(liu)門限時(shi)，通過(guo)動態降低電(dian)(dian)池(chi)電(dian)(dian)流(liu)來防止適(shi)配器(qi)(qi)過(guo)載或系(xi)統電(dian)(dian)壓下(xia)降。這樣就保證了系(xi)統電(dian)(dian)壓的(de)穩定，降低了適(shi)配器(qi)(qi)的(de)額(e)外(wai)功率要求。同時(shi)，該拓撲(pu)還具備電(dian)(dian)池(chi)反向(xiang)補充供電(dian)(dian)的(de)能力。

圖6:基于輸入電流的動態電源路徑管理。

　　有些充電(dian)器（例(li)如MPS公司的MP2607）可(ke)(ke)以根據不同電(dian)源(yuan)要求，優(you)化選擇(ze)不同的動態電(dian)源(yuan)路徑(jing)管理方案。MP2607根據不同的適(shi)(shi)配(pei)器類型，在基(ji)于輸(shu)入(ru)電(dian)壓(ya)和基(ji)于輸(shu)入(ru)電(dian)流的DPPM兩種(zhong)拓撲(pu)之間進行智能(neng)選擇(ze)。若輸(shu)入(ru)是交流適(shi)(shi)配(pei)器，MP2607采(cai)用基(ji)于輸(shu)入(ru)電(dian)壓(ya)的DPPM技(ji)術，控制適(shi)(shi)配(pei)器交流電(dian)壓(ya)，使得交流適(shi)(shi)配(pei)器可(ke)(ke)以同時為系統供電(dian)和為電(dian)池充電(dian)，工作波形(xing)如圖(tu)7所示(shi)。

圖7:MP2607在交流適配器輸入時的(de)動(dong)態(tai)電源路(lu)徑管理(li)。

　　在USB輸入(ru)(ru)模(mo)式下(xia)，MP2607采用基于輸入(ru)(ru)電(dian)流的DPPM.如(ru)圖8所示，考慮到(dao)USB提供電(dian)流能力有限(xian)，設置充電(dian)電(dian)流在USB限(xian)制電(dian)流以下(xia)。若系(xi)統負載電(dian)流大(da)于USB限(xian)流值，電(dian)池將反向補充供電(dian)。

圖(tu)8:MP2607在USB輸入時的動態電源(yuan)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)在不同管理模(mo)式之間切(qie)換的(de)充(chong)電(dian)器）可以為(wei)移(yi)動電(dian)子設備提供更加精妙的(de)電(dian)源(yuan)解決(jue)方案，從而給用戶帶來前所未有的(de)便利、性能(neng)和(he)效率(lv)。