鋰離子(Li-ion)電(dian)(dian)(dian)池(chi)和(he)鋰聚合(he)物(Li-po)電(dian)(dian)(dian)池(chi)最適合(he)當前市場對功(gong)率(lv)密度、充電(dian)(dian)(dian)能力和(he)價格(ge)的(de)(de)(de)要求(qiu)。但是(shi)，有別于鉛酸、鎳氫等其他流(liu)行的(de)(de)(de)電(dian)(dian)(dian)池(chi)技(ji)術(shu)，鋰電(dian)(dian)(dian)池(chi)技(ji)術(shu)的(de)(de)(de)性(xing)能也最不穩定：鋰電(dian)(dian)(dian)池(chi)充放(fang)電(dian)(dian)(dian)若管理不善，將導致充電(dian)(dian)(dian)時間長、耗(hao)散(san)功(gong)率(lv)高、效率(lv)低和(he)電(dian)(dian)(dian)池(chi)壽命(ming)比(bi)平均壽命(ming)低等問題。圖(tu)1顯(xian)示了(le)典(dian)型鋰離子電(dian)(dian)(dian)池(chi)的(de)(de)(de)充電(dian)(dian)(dian)曲線。

　　傳統充電器相對簡單，這些充(chong)電(dian)器在小功率應(ying)用中(zhong)表現較(jiao)好。然而，它們卻(que)不能有效地適應(ying)充(chong)電(dian)曲線的(de)變化，比如，用戶在不同電(dian)源(yuan)之間切換或者(zhe)在充(chong)電(dian)期間操作設備。另(ling)外(wai)，傳統充(chong)電(dian)器在大功率和大電(dian)流應(ying)用中(zhong)，通常效率較(jiao)低，耗散功率較(jiao)大。

　　

 

　　圖1:典(dian)型鋰離子電(dian)池的充電(dian)曲(qu)線。

　　新型線性和開關充電器，比如(ru)芯源(yuan)系統(MPS)公司的MP2600系列，采(cai)用(yong)電(dian)源(yuan)路徑(jing)管理技術(shu)改變了充電(dian)曲(qu)線，從(cong)而能夠以更低(di)的耗散(san)功率更加(jia)高效地為(wei)電(dian)池/系統供電(dian)。同(tong)時(shi)，這些充電(dian)器也使(shi)系統的安(an)全性和電(dian)池的使(shi)用(yong)壽命(ming)得到提高。

　　電源管(guan)理拓撲(pu)種類繁多，本文則重點介紹以下(xia)三種：電池饋電、自動選擇和(he)動態電源路徑。

　　電池饋電拓撲

　　電池饋(kui)電拓撲是一種實現過(guo)程最簡單、成(cheng)本最低的拓撲，這是因為其電路由充(chong)電器、電池和系統組成(cheng)，如圖(tu)2所示。

　　

 

　　圖2:電(dian)池(chi)饋電(dian)拓(tuo)撲原(yuan)理(li)圖及信號(hao)圖。

　　這種拓撲(pu)有三個(ge)主(zhu)要特(te)性：無(wu)論(lun)供電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)如(ru)何變化，系(xi)(xi)統(tong)電(dian)(dian)(dian)壓(ya)始終(zhong)等(deng)于電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)，電(dian)(dian)(dian)源(yuan)系(xi)(xi)統(tong)始終(zhong)優先，以便(bian)IBATT ￡ ICHG,并且(qie)ICHG最(zui)終(zhong)限(xian)制(zhi)由輸(shu)入電(dian)(dian)(dian)源(yuan)提供給系(xi)(xi)統(tong)電(dian)(dian)(dian)源(yuan)總線的最(zui)大功(gong)率(lv)。當系(xi)(xi)統(tong)與充(chong)電(dian)(dian)(dian)器斷(duan)開(kai)時(shi)該拓撲(pu)還可(ke)以實(shi)現最(zui)小的耗散(san)功(gong)率(lv)，設置(zhi)ICHG從根本上(shang)限(xian)定(ding)了(le)總輸(shu)入電(dian)(dian)(dian)流，這樣，隨著(zhu)系(xi)(xi)統(tong)電(dian)(dian)(dian)流(ISYS)的增加，充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(IBATT)將等(deng)額下降(jiang)，工作(zuo)波形(xing)如(ru)圖2所示(shi)。

　　遺(yi)憾的是，這種拓撲有如下不足之處，從而(er)限制了它在更廣(guang)應用(yong)領域的效率(lv)和效用(yong)：

　　在電(dian)(dian)池(chi)電(dian)(dian)壓(ya)(ya)(ya)太低的情況(kuang)下，系(xi)統(tong)(tong)無法工作(zuo)。電(dian)(dian)池(chi)電(dian)(dian)壓(ya)(ya)(ya)跌至涓流充電(dian)(dian)門限(xian)以(yi)下時，充電(dian)(dian)器將把(ba)總的輸出(chu)電(dian)(dian)流限(xian)制得很低。系(xi)統(tong)(tong)的額外電(dian)(dian)源需求將由(you)電(dian)(dian)池(chi)來補充，從而導致電(dian)(dian)池(chi)能量進一(yi)步(bu)耗盡。由(you)于系(xi)統(tong)(tong)電(dian)(dian)壓(ya)(ya)(ya)始(shi)終等于電(dian)(dian)池(chi)電(dian)(dian)壓(ya)(ya)(ya)，一(yi)旦電(dian)(dian)池(chi)電(dian)(dian)壓(ya)(ya)(ya)低到系(xi)統(tong)(tong)最低工作(zuo)電(dian)(dian)壓(ya)(ya)(ya)以(yi)下，系(xi)統(tong)(tong)將停止工作(zuo)。

　　雖然電(dian)(dian)(dian)池已具有(you)滿電(dian)(dian)(dian)量，但是充(chong)電(dian)(dian)(dian)器(qi)無法進入EOC(結束充(chong)電(dian)(dian)(dian))狀態(tai)。如果ISYS超過電(dian)(dian)(dian)池滿電(dian)(dian)(dian)量門限(IBF)，那么ICHG就無法降(jiang)到低于IBF,充(chong)電(dian)(dian)(dian)狀態(tai)始終(zhong)顯示正在充(chong)電(dian)(dian)(dian)，即(ji)使電(dian)(dian)(dian)池已經(jing)具有(you)滿電(dian)(dian)(dian)量。

　　電(dian)(dian)池無法充(chong)滿(man)。由于系統(tong)優先于電(dian)(dian)池供電(dian)(dian)，因此電(dian)(dian)池只能以(yi)低電(dian)(dian)流進行(xing)充(chong)電(dian)(dian)。此外，充(chong)電(dian)(dian)器只能在(zai)預期的(de)有效(xiao)充(chong)電(dian)(dian)時間(jian)內工作，這樣可以(yi)避(bi)免給(gei)壞(huai)電(dian)(dian)池充(chong)電(dian)(dian)。如充(chong)電(dian)(dian)時間(jian)超(chao)出此時間(jian)段，會導致充(chong)電(dian)(dian)器誤(wu)判壞(huai)電(dian)(dian)池而(er)停(ting)止充(chong)電(dian)(dian)。

　　電源路徑自動選擇拓撲

　　電源路徑自動選擇拓(tuo)撲在(zai)電池直接搭(da)載拓(tuo)撲基(ji)礎上外加了兩(liang)個開關(guan)管，使得(de)系(xi)統電源可以根(gen)據輸入(ru)電壓的變化(hua)在(zai)適配器和電池之間來(lai)回(hui)切(qie)換。拓(tuo)撲結構及工作波形如(ru)圖3所(suo)示。

　　

 

　　圖3:電源路(lu)徑自動選擇拓撲(pu)及工(gong)作(zuo)波形(xing)。

　　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(zong)功率需求，以(yi)及系統負載突變(bian)時的功率變(bian)化要求。

　　圖4是采(cai)用MPS公司的(de)(de)MP2611構(gou)成(cheng)的(de)(de)電源路徑(jing)自動(dong)選(xuan)擇拓撲的(de)(de)原理圖。為(wei)了防(fang)止出現不(bu)穩定(ding)情況，當(dang)VBATT接(jie)近VIN時，MP2611會斷開系統與電池(chi)的(de)(de)連接(jie)。此外，它還會在S1 (M1及(ji)M2)與S2(M3)之間(jian)插入一個消隱期，以(yi)防(fang)出現電流貫通(tong)，從而損壞(huai)系統和電池(chi)。

　　

 

　　圖4:采用MP2611構成(cheng)的電(dian)源路徑自動選擇(ze)拓撲。

   動態(tai)電源(yuan)路徑管理拓撲(DPPM)

 

　　動態電(dian)(dian)(dian)(dian)源路徑管理(li)(DPPM)技術采用了一套附(fu)加的檢測(ce)模塊，測(ce)量系統電(dian)(dian)(dian)(dian)壓或(huo)者輸(shu)入電(dian)(dian)(dian)(dian)流，實時監測(ce)總(zong)功率需求。一旦功率需求超過(guo)預設(she)值，通過(guo)充電(dian)(dian)(dian)(dian)器(qi)降低(di)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流來保(bao)證適配器(qi)輸(shu)出功率恒定而不過(guo)載(zai)。

　　例如(ru)，基于輸(shu)(shu)入(ru)電(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)DPPM(圖5)通過(guo)比較輸(shu)(shu)入(ru)電(dian)(dian)(dian)壓(ya)(ya)與預設參考電(dian)(dian)(dian)壓(ya)(ya)來(lai)判斷(duan)輸(shu)(shu)入(ru)電(dian)(dian)(dian)流是(shi)否(fou)達(da)到適配器(qi)(qi)的(de)(de)(de)輸(shu)(shu)出電(dian)(dian)(dian)流限制。若適配器(qi)(qi)電(dian)(dian)(dian)流已經達(da)到該限制，適配器(qi)(qi)電(dian)(dian)(dian)壓(ya)(ya)將降(jiang)至預設參考電(dian)(dian)(dian)壓(ya)(ya)，然后充電(dian)(dian)(dian)器(qi)(qi)通過(guo)動(dong)態降(jiang)低充電(dian)(dian)(dian)電(dian)(dian)(dian)流來(lai)防止系統(tong)電(dian)(dian)(dian)壓(ya)(ya)繼續下(xia)降(jiang)。只要輸(shu)(shu)入(ru)電(dian)(dian)(dian)流保持(chi)在(zai)該限制的(de)(de)(de)水平(ping)或(huo)者低于該限制，就仍然有電(dian)(dian)(dian)流向電(dian)(dian)(dian)池充電(dian)(dian)(dian)。然而，由系統(tong)電(dian)(dian)(dian)壓(ya)(ya)下(xia)降(jiang)引(yin)起的(de)(de)(de)不(bu)穩定或(huo)噪(zao)(zao)聲使得(de)這種基于電(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)DPPM結構不(bu)適合(he)應(ying)用(yong)在(zai)某些(xie)對噪(zao)(zao)聲敏感的(de)(de)(de)場合(he)，比如(ru)音頻(pin)設備。

　　

 

　　圖5:基于輸入電(dian)壓(ya)的動態電(dian)源(yuan)路徑管理。

　　基(ji)于輸入電流的(de)(de)DPPM(圖6)采用檢測電阻來評(ping)估輸入電流，當輸入電流達到預設電流門限(xian)時(shi)，通過動態降低電池電流來防止適配器過載或系統電壓下(xia)降。這(zhe)樣就保證(zheng)了系統電壓的(de)(de)穩(wen)定，降低了適配器的(de)(de)額外功率要求。同時(shi)，該拓撲(pu)還具備電池反向補充供電的(de)(de)能力。

　　

 

　　圖6:基于輸入電流的動態電源路(lu)徑(jing)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(bo)形如(ru)圖7所示。

　　

 

　　圖7:MP2607在交流適配器(qi)輸入時的(de)動態(tai)電(dian)源路徑管理(li)。

　　在USB輸入模式下，MP2607采用基于(yu)輸入電流的DPPM.如圖(tu)8所(suo)示(shi)，考慮到USB提供電流能力有限(xian)，設置充電電流在USB限(xian)制電流以下。若系統(tong)負載電流大于(yu)USB限(xian)流值，電池將反(fan)向補充供電。

　　

 

　　圖8:MP2607在USB輸入時的(de)動態電源路徑管理。

　　總之，具有動態電源路徑管理的充電器(尤(you)其是那(nei)些(xie)能(neng)在不同管理(li)模式之(zhi)間切換的充電器(qi))可以為移動電子設(she)備提(ti)供更加精妙的電源解決方案，從而給用戶帶(dai)來前所未有的便利、性能(neng)和效率。