鋰(li)(li)(li)離子(Li-ion)電(dian)(dian)池(chi)(chi)和(he)鋰(li)(li)(li)聚合物(wu)(Li-po)電(dian)(dian)池(chi)(chi)最(zui)(zui)適合當前市(shi)場對功率(lv)密度、充(chong)電(dian)(dian)能(neng)(neng)力和(he)價格的(de)要求。但(dan)是(shi)，有別于鉛酸(suan)、鎳氫等其他流行的(de)電(dian)(dian)池(chi)(chi)技術，鋰(li)(li)(li)電(dian)(dian)池(chi)(chi)技術的(de)性(xing)能(neng)(neng)也最(zui)(zui)不穩(wen)定：鋰(li)(li)(li)電(dian)(dian)池(chi)(chi)充(chong)放電(dian)(dian)若管理不善，將導(dao)致充(chong)電(dian)(dian)時間(jian)長、耗(hao)散(san)功率(lv)高、效率(lv)低和(he)電(dian)(dian)池(chi)(chi)壽命(ming)比平均壽命(ming)低等問題。圖1顯示了典(dian)型鋰(li)(li)(li)離子電(dian)(dian)池(chi)(chi)的(de)充(chong)電(dian)(dian)曲線。

　　傳統充電器相對簡(jian)單(dan)，這些充(chong)電器(qi)在(zai)(zai)小功率(lv)(lv)(lv)(lv)應用中表(biao)現較(jiao)好。然而，它們(men)卻不(bu)能(neng)有效地適(shi)應充(chong)電曲線的變化，比如(ru)，用戶在(zai)(zai)不(bu)同電源之間切換或者在(zai)(zai)充(chong)電期(qi)間操作(zuo)設備。另外，傳統(tong)充(chong)電器(qi)在(zai)(zai)大(da)功率(lv)(lv)(lv)(lv)和大(da)電流應用中，通常效率(lv)(lv)(lv)(lv)較(jiao)低，耗散功率(lv)(lv)(lv)(lv)較(jiao)大(da)。

　　

 

　　圖1:典(dian)型鋰離子電池的充電曲線。

　　新型線性和開關充電器，比如芯(xin)源(yuan)系(xi)統(tong)(MPS)公司的(de)(de)MP2600系(xi)列，采用電(dian)源(yuan)路徑管理技術改(gai)變(bian)了(le)充電(dian)曲線，從而(er)能夠以更低的(de)(de)耗散功率(lv)更加(jia)高效地為電(dian)池/系(xi)統(tong)供電(dian)。同時，這些充電(dian)器也使系(xi)統(tong)的(de)(de)安全(quan)性和電(dian)池的(de)(de)使用壽命(ming)得到提高。

　　電(dian)源(yuan)管(guan)理拓(tuo)撲種(zhong)類繁(fan)多，本文(wen)則重點介紹(shao)以下三種(zhong)：電(dian)池(chi)饋電(dian)、自動(dong)選擇(ze)和動(dong)態(tai)電(dian)源(yuan)路徑。

　　電池饋電拓撲

　　電(dian)池饋(kui)電(dian)拓撲是(shi)一種(zhong)實現過程最簡單、成(cheng)本最低的拓撲，這是(shi)因(yin)為其電(dian)路由充電(dian)器、電(dian)池和系統(tong)組成(cheng)，如圖2所示。

　　

 

　　圖(tu)2:電池(chi)饋電拓撲原理(li)圖(tu)及信(xin)號圖(tu)。

　　這種拓(tuo)撲(pu)有三個主要特性：無論(lun)供(gong)電(dian)(dian)電(dian)(dian)壓(ya)如何(he)變化，系統(tong)電(dian)(dian)壓(ya)始(shi)終(zhong)等于電(dian)(dian)池電(dian)(dian)壓(ya)，電(dian)(dian)源系統(tong)始(shi)終(zhong)優先，以便IBATT ￡ ICHG,并且ICHG最終(zhong)限制由輸入電(dian)(dian)源提供(gong)給系統(tong)電(dian)(dian)源總(zong)線的最大功率。當系統(tong)與充(chong)電(dian)(dian)器斷開時該拓(tuo)撲(pu)還(huan)可以實現最小的耗散功率，設置ICHG從根本上限定了總(zong)輸入電(dian)(dian)流(liu)，這樣(yang)，隨(sui)著(zhu)系統(tong)電(dian)(dian)流(liu)(ISYS)的增(zeng)加，充(chong)電(dian)(dian)電(dian)(dian)流(liu)(IBATT)將(jiang)等額下(xia)降，工作波形如圖2所示。

　　遺憾的(de)是，這種(zhong)拓撲有如下(xia)不足之(zhi)處，從(cong)而(er)限制了它在更廣應(ying)用(yong)領域的(de)效(xiao)率和效(xiao)用(yong)：

　　在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)太低(di)的情況下，系(xi)(xi)統(tong)無法工(gong)作。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)跌至(zhi)涓流充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)門限以下時，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器將(jiang)把(ba)總的輸出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流限制(zhi)得很低(di)。系(xi)(xi)統(tong)的額(e)外電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源需求將(jiang)由電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)來補(bu)充(chong)(chong)，從而(er)導致(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)能(neng)量進一步耗盡。由于(yu)系(xi)(xi)統(tong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)始終(zhong)等于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，一旦電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低(di)到(dao)系(xi)(xi)統(tong)最低(di)工(gong)作電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)以下，系(xi)(xi)統(tong)將(jiang)停止工(gong)作。

　　雖(sui)然電(dian)(dian)池(chi)(chi)(chi)已(yi)具有滿電(dian)(dian)量(liang)，但是充電(dian)(dian)器無法進(jin)入EOC(結束充電(dian)(dian))狀態(tai)。如果ISYS超過(guo)電(dian)(dian)池(chi)(chi)(chi)滿電(dian)(dian)量(liang)門限(IBF)，那么ICHG就無法降到低(di)于IBF,充電(dian)(dian)狀態(tai)始終顯示(shi)正在充電(dian)(dian)，即(ji)使(shi)電(dian)(dian)池(chi)(chi)(chi)已(yi)經具有滿電(dian)(dian)量(liang)。

　　電池(chi)無法充(chong)滿。由于系(xi)統優先于電池(chi)供電，因此(ci)電池(chi)只(zhi)能(neng)以(yi)低電流進行充(chong)電。此(ci)外，充(chong)電器只(zhi)能(neng)在預期的有效充(chong)電時(shi)間內(nei)工(gong)作(zuo)，這樣可以(yi)避(bi)免給壞電池(chi)充(chong)電。如(ru)充(chong)電時(shi)間超出此(ci)時(shi)間段，會(hui)導致充(chong)電器誤(wu)判(pan)壞電池(chi)而(er)停止充(chong)電。

　　電源(yuan)路徑(jing)自(zi)動選擇拓撲

　　電(dian)(dian)源路(lu)徑自動選擇(ze)拓(tuo)撲在電(dian)(dian)池直接搭(da)載(zai)拓(tuo)撲基礎上外(wai)加了兩(liang)個開關管，使得系統電(dian)(dian)源可(ke)以根(gen)據輸入電(dian)(dian)壓(ya)的(de)變(bian)化(hua)在適配器和電(dian)(dian)池之間來回切(qie)換。拓(tuo)撲結構及(ji)工作波形如(ru)圖(tu)3所示。

　　

 

　　圖3:電(dian)源路徑自動(dong)選擇拓(tuo)撲及(ji)工(gong)作波形。

　　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(zui)大總功(gong)(gong)率(lv)需求，以及(ji)系(xi)統負載突變時的功(gong)(gong)率(lv)變化要求。

　　圖4是采用MPS公(gong)司的MP2611構成(cheng)的電(dian)(dian)源(yuan)路徑自動選擇拓撲的原理圖。為了(le)防止出(chu)(chu)現不穩定情況，當VBATT接近VIN時，MP2611會(hui)斷(duan)開系統(tong)與電(dian)(dian)池的連接。此外，它(ta)還會(hui)在S1 (M1及M2)與S2(M3)之(zhi)間(jian)插入一個消隱期，以防出(chu)(chu)現電(dian)(dian)流(liu)貫通，從而損壞系統(tong)和(he)電(dian)(dian)池。

　　

 

　　圖4:采用MP2611構成(cheng)的(de)電源路徑自(zi)動選(xuan)擇拓撲(pu)。

   動態(tai)電源路徑管理拓(tuo)撲(DPPM)

 

　　動(dong)態電(dian)源路(lu)徑管理(li)(DPPM)技術采用了一套附(fu)加的檢測模塊，測量系統電(dian)壓或者輸(shu)入電(dian)流，實時監測總功率(lv)需(xu)求(qiu)。一旦功率(lv)需(xu)求(qiu)超過預設值，通(tong)過充電(dian)器降(jiang)低(di)充電(dian)電(dian)流來(lai)保證適(shi)配器輸(shu)出功率(lv)恒定而不過載。

　　例如，基(ji)于輸入(ru)電(dian)壓(ya)(ya)(ya)(ya)的(de)DPPM(圖(tu)5)通過比較輸入(ru)電(dian)壓(ya)(ya)(ya)(ya)與預設參考電(dian)壓(ya)(ya)(ya)(ya)來判斷(duan)輸入(ru)電(dian)流是否達到適(shi)配器(qi)(qi)的(de)輸出電(dian)流限(xian)制(zhi)。若(ruo)適(shi)配器(qi)(qi)電(dian)流已經達到該(gai)限(xian)制(zhi)，適(shi)配器(qi)(qi)電(dian)壓(ya)(ya)(ya)(ya)將(jiang)降(jiang)至預設參考電(dian)壓(ya)(ya)(ya)(ya)，然后充(chong)電(dian)器(qi)(qi)通過動態降(jiang)低充(chong)電(dian)電(dian)流來防止系(xi)統電(dian)壓(ya)(ya)(ya)(ya)繼續下降(jiang)。只要(yao)輸入(ru)電(dian)流保持(chi)在(zai)該(gai)限(xian)制(zhi)的(de)水平(ping)或者低于該(gai)限(xian)制(zhi)，就仍然有電(dian)流向電(dian)池(chi)充(chong)電(dian)。然而，由系(xi)統電(dian)壓(ya)(ya)(ya)(ya)下降(jiang)引起的(de)不穩定或噪聲使(shi)得這種基(ji)于電(dian)壓(ya)(ya)(ya)(ya)的(de)DPPM結構不適(shi)合應用在(zai)某些對(dui)噪聲敏感的(de)場合，比如音頻(pin)設備(bei)。

　　

 

　　圖5:基于輸入(ru)電壓的動態電源路徑管理(li)。

　　基(ji)于輸(shu)入電(dian)(dian)(dian)流(liu)的DPPM(圖6)采(cai)用檢測電(dian)(dian)(dian)阻來評估輸(shu)入電(dian)(dian)(dian)流(liu)，當(dang)輸(shu)入電(dian)(dian)(dian)流(liu)達(da)到預設電(dian)(dian)(dian)流(liu)門限時，通(tong)過動態降(jiang)低電(dian)(dian)(dian)池電(dian)(dian)(dian)流(liu)來防(fang)止適配(pei)器(qi)過載或(huo)系(xi)統電(dian)(dian)(dian)壓下降(jiang)。這樣就保證了系(xi)統電(dian)(dian)(dian)壓的穩定，降(jiang)低了適配(pei)器(qi)的額外功率要求。同時，該拓撲還具備電(dian)(dian)(dian)池反(fan)向補充供電(dian)(dian)(dian)的能力。

　　

 

　　圖6:基于輸入電(dian)(dian)流(liu)的動態電(dian)(dian)源路(lu)徑管理(li)。

　　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(zuo)波形如圖7所示。

　　

 

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

　　在(zai)(zai)USB輸入模式下，MP2607采用基于(yu)輸入電(dian)流(liu)(liu)(liu)(liu)的(de)DPPM.如圖8所示，考慮到USB提(ti)供電(dian)流(liu)(liu)(liu)(liu)能力有限，設置充電(dian)電(dian)流(liu)(liu)(liu)(liu)在(zai)(zai)USB限制(zhi)電(dian)流(liu)(liu)(liu)(liu)以下。若系統(tong)負載(zai)電(dian)流(liu)(liu)(liu)(liu)大于(yu)USB限流(liu)(liu)(liu)(liu)值，電(dian)池將反(fan)向補充供電(dian)。

　　

 

　　圖8:MP2607在USB輸入時的動態電源路(lu)徑管理。

　　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(tong)管理模式之間切換的充(chong)電(dian)器)可以為移動電(dian)子設備(bei)提(ti)供更加精妙的電(dian)源解決方(fang)案，從而給用戶(hu)帶來(lai)前(qian)所未有的便利、性能和效率。