隨著智(zhi)能(neng)手(shou)機、平板電腦和(he)攝像機等(deng)便攜(xie)設(she)備的不斷普及，人們對(dui)(dui)電源的要(yao)(yao)求以(yi)及對(dui)(dui)邊充(chong)(chong)電邊使(shi)用(yong)這些(xie)設(she)備的能(neng)力的要(yao)(yao)求與日俱增。更(geng)高的功率(lv)要(yao)(yao)求增加了對(dui)(dui)具有高功率(lv)密(mi)度(du)和(he)優異(yi)充(chong)(chong)電能(neng)力的電池(chi)(chi)的需求。目前，鋰離子（Li-ion）電池(chi)(chi)和(he)鋰聚合物（Li-po）電池(chi)(chi)最(zui)適(shi)合當前市場對(dui)(dui)功率(lv)密(mi)度(du)、充(chong)(chong)電能(neng)力和(he)價格的要(yao)(yao)求。但是(shi)，有別于(yu)鉛酸、鎳氫等(deng)其(qi)他流行(xing)的電池(chi)(chi)技(ji)術(shu)，鋰電池(chi)(chi)技(ji)術(shu)的性能(neng)也最(zui)不穩定：鋰電池(chi)(chi)充(chong)(chong)放電若(ruo)管理不善(shan)，將(jiang)導(dao)致充(chong)(chong)電時間長、耗(hao)散功率(lv)高、效(xiao)率(lv)低和(he)電池(chi)(chi)壽命比平均壽命低等(deng)問題。圖1顯示了典型鋰離子電池(chi)(chi)的充(chong)(chong)電曲線。

　　傳(chuan)統充(chong)電(dian)(dian)器相對(dui)簡單，這些充(chong)電(dian)(dian)器在(zai)(zai)小功(gong)率(lv)(lv)應(ying)(ying)用(yong)中(zhong)表(biao)現較(jiao)好。然而，它(ta)們卻不(bu)能有效地適應(ying)(ying)充(chong)電(dian)(dian)曲線的(de)變(bian)化，比(bi)如，用(yong)戶(hu)在(zai)(zai)不(bu)同電(dian)(dian)源之間切換或者(zhe)在(zai)(zai)充(chong)電(dian)(dian)期間操作設備(bei)。另(ling)外，傳(chuan)統充(chong)電(dian)(dian)器在(zai)(zai)大(da)功(gong)率(lv)(lv)和大(da)電(dian)(dian)流應(ying)(ying)用(yong)中(zhong)，通常效率(lv)(lv)較(jiao)低，耗散(san)功(gong)率(lv)(lv)較(jiao)大(da)。

圖1:典(dian)型(xing)鋰離(li)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(tong)（MPS）公司(si)的(de)MP2600系列(lie)，采用電(dian)源路徑管理技術改變了充電(dian)曲(qu)線，從而能夠以更低的(de)耗散功(gong)率更加(jia)高效地為電(dian)池/系統(tong)供電(dian)。同(tong)時，這(zhe)些充電(dian)器也使系統(tong)的(de)安全性和電(dian)池的(de)使用壽命得到(dao)提高。

　　電源管理(li)拓撲種(zhong)類繁(fan)多，本文則重點介(jie)紹以下三種(zhong)：電池饋(kui)電、自動(dong)選擇和動(dong)態(tai)電源路(lu)徑。

　　電池饋電拓撲

　　電池(chi)饋電拓(tuo)撲是一種實現過程最簡單(dan)、成本(ben)最低的拓(tuo)撲，這是因為其(qi)電路由充電器、電池(chi)和系(xi)統組成，如圖(tu)2所示。

圖(tu)2:電(dian)池(chi)饋電(dian)拓撲(pu)原理圖(tu)及信(xin)號圖(tu)。

　　這(zhe)種拓撲有三個主要(yao)特性：無論供(gong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓如何變化，系統電(dian)(dian)(dian)(dian)(dian)壓始(shi)終等于(yu)電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓，電(dian)(dian)(dian)(dian)(dian)源(yuan)系統始(shi)終優(you)先(xian)，以(yi)便IBATT ￡ ICHG,并且ICHG最終限制(zhi)由輸入電(dian)(dian)(dian)(dian)(dian)源(yuan)提供(gong)給系統電(dian)(dian)(dian)(dian)(dian)源(yuan)總線的(de)最大功(gong)率。當系統與充(chong)電(dian)(dian)(dian)(dian)(dian)器斷開時(shi)該拓撲還可(ke)以(yi)實現(xian)最小的(de)耗散(san)功(gong)率，設置ICHG從根本上(shang)限定(ding)了總輸入電(dian)(dian)(dian)(dian)(dian)流，這(zhe)樣，隨著系統電(dian)(dian)(dian)(dian)(dian)流（ISYS）的(de)增加，充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流（IBATT）將等額下降(jiang)，工作波形如圖(tu)2所示。

　　遺憾(han)的是，這(zhe)種拓撲有如(ru)下不足之處，從而限制了它在更(geng)廣(guang)應(ying)用(yong)領域的效(xiao)率和(he)效(xiao)用(yong)：

　　在(zai)電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(ya)太低(di)的情況下(xia)，系統無法工作。電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(ya)跌至涓流充(chong)電(dian)(dian)(dian)(dian)門限以下(xia)時，充(chong)電(dian)(dian)(dian)(dian)器將(jiang)把總的輸(shu)出電(dian)(dian)(dian)(dian)流限制得(de)很低(di)。系統的額外電(dian)(dian)(dian)(dian)源需求將(jiang)由(you)電(dian)(dian)(dian)(dian)池(chi)來補充(chong)，從而導致電(dian)(dian)(dian)(dian)池(chi)能量(liang)進一(yi)(yi)步耗盡。由(you)于系統電(dian)(dian)(dian)(dian)壓(ya)始終(zhong)等于電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(ya)，一(yi)(yi)旦電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(ya)低(di)到系統最低(di)工作電(dian)(dian)(dian)(dian)壓(ya)以下(xia)，系統將(jiang)停止(zhi)工作。

　　雖(sui)然電(dian)池已具有(you)滿(man)電(dian)量(liang)(liang)，但是(shi)充電(dian)器無法進(jin)入EOC（結(jie)束充電(dian)）狀(zhuang)態。如(ru)果ISYS超(chao)過電(dian)池滿(man)電(dian)量(liang)(liang)門限（IBF），那(nei)么ICHG就無法降到低于IBF,充電(dian)狀(zhuang)態始終顯示正在充電(dian)，即使(shi)電(dian)池已經具有(you)滿(man)電(dian)量(liang)(liang)。

　　電(dian)(dian)(dian)(dian)池無法充(chong)(chong)滿(man)。由于系統優先于電(dian)(dian)(dian)(dian)池供電(dian)(dian)(dian)(dian)，因(yin)此電(dian)(dian)(dian)(dian)池只(zhi)能以低電(dian)(dian)(dian)(dian)流進行(xing)充(chong)(chong)電(dian)(dian)(dian)(dian)。此外(wai)，充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)只(zhi)能在(zai)預期的有效充(chong)(chong)電(dian)(dian)(dian)(dian)時間(jian)內(nei)工作，這樣可以避免給壞電(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)。如充(chong)(chong)電(dian)(dian)(dian)(dian)時間(jian)超出(chu)此時間(jian)段(duan)，會(hui)導致充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)誤判壞電(dian)(dian)(dian)(dian)池而停(ting)止充(chong)(chong)電(dian)(dian)(dian)(dian)。

電源路徑自動選擇拓撲

　　電(dian)(dian)源(yuan)路徑自動選擇拓(tuo)撲在電(dian)(dian)池(chi)直接搭載(zai)拓(tuo)撲基礎上外(wai)加(jia)了兩個開關管，使得系統電(dian)(dian)源(yuan)可以根據(ju)輸入電(dian)(dian)壓的變化在適配器和(he)電(dian)(dian)池(chi)之(zhi)間(jian)來回切換(huan)。拓(tuo)撲結構及工作波形如圖(tu)3所示。

圖3:電源路徑自動選擇(ze)拓(tuo)撲及工作波(bo)形。

　　與(yu)電(dian)池饋(kui)電(dian)拓(tuo)撲(pu)結(jie)構相(xiang)比(bi)，此(ci)拓(tuo)撲(pu)有實質性(xing)的(de)(de)改進。它將系(xi)(xi)統(tong)(tong)直接跟(gen)交流(liu)適配器(qi)(qi)相(xiang)連，與(yu)充電(dian)器(qi)(qi)獨立開(kai)來，因而能夠提供更大(da)的(de)(de)系(xi)(xi)統(tong)(tong)電(dian)流(liu)、更高的(de)(de)效(xiao)率(lv)并且允許(xu)系(xi)(xi)統(tong)(tong)在低(di)(di)電(dian)池電(dian)壓(ya)下工作。此(ci)外(wai)，其價格也(ye)比(bi)較(jiao)(jiao)低(di)(di)廉。然而，當適配器(qi)(qi)輸出(chu)電(dian)壓(ya)變(bian)化(hua)(hua)較(jiao)(jiao)大(da)的(de)(de)時候，系(xi)(xi)統(tong)(tong)電(dian)壓(ya)也(ye)會(hui)隨(sui)之變(bian)化(hua)(hua)，所以(yi)此(ci)拓(tuo)撲(pu)要(yao)求(qiu)系(xi)(xi)統(tong)(tong)能夠接受比(bi)較(jiao)(jiao)寬的(de)(de)輸入(ru)電(dian)壓(ya)變(bian)化(hua)(hua)范(fan)圍。此(ci)外(wai)，也(ye)要(yao)求(qiu)適配器(qi)(qi)具有更高的(de)(de)額定功(gong)率(lv)，以(yi)滿足系(xi)(xi)統(tong)(tong)和充電(dian)器(qi)(qi)的(de)(de)最大(da)總功(gong)率(lv)需求(qiu)，以(yi)及系(xi)(xi)統(tong)(tong)負載突變(bian)時的(de)(de)功(gong)率(lv)變(bian)化(hua)(hua)要(yao)求(qiu)。

　　圖(tu)4是采(cai)用MPS公司的MP2611構成的電源路徑自動選擇拓撲(pu)的原理圖(tu)。為(wei)了(le)防止出(chu)現不穩(wen)定情況，當VBATT接近(jin)VIN時，MP2611會斷(duan)開系(xi)統(tong)與(yu)電池(chi)的連接。此外，它還(huan)會在S1 （M1及M2）與(yu)S2（M3）之間(jian)插入(ru)一個(ge)消(xiao)隱期(qi)，以防出(chu)現電流貫通(tong)，從而損壞系(xi)統(tong)和電池(chi)。

圖4:采用MP2611構成的電源(yuan)路徑自動選擇拓撲。

　　動態電源路徑管理(li)拓(tuo)撲（DPPM）

　　動態電(dian)(dian)源路徑管理(li)（DPPM）技(ji)術采用了一套(tao)附加的檢測(ce)模塊，測(ce)量系統電(dian)(dian)壓(ya)或者輸入電(dian)(dian)流，實時監(jian)測(ce)總功(gong)率(lv)(lv)(lv)需(xu)求(qiu)。一旦功(gong)率(lv)(lv)(lv)需(xu)求(qiu)超(chao)過預設值，通過充(chong)電(dian)(dian)器降低充(chong)電(dian)(dian)電(dian)(dian)流來保證適(shi)配器輸出(chu)功(gong)率(lv)(lv)(lv)恒定而不(bu)過載。

　　例(li)如，基(ji)于(yu)輸(shu)入(ru)電(dian)壓(ya)的DPPM（圖(tu)5）通過比較輸(shu)入(ru)電(dian)壓(ya)與預(yu)設參(can)考電(dian)壓(ya)來判斷輸(shu)入(ru)電(dian)流(liu)(liu)是否達到適(shi)(shi)配器的輸(shu)出電(dian)流(liu)(liu)限(xian)制(zhi)(zhi)。若(ruo)適(shi)(shi)配器電(dian)流(liu)(liu)已經達到該限(xian)制(zhi)(zhi)，適(shi)(shi)配器電(dian)壓(ya)將降(jiang)(jiang)至(zhi)預(yu)設參(can)考電(dian)壓(ya)，然(ran)(ran)后充(chong)電(dian)器通過動態降(jiang)(jiang)低充(chong)電(dian)電(dian)流(liu)(liu)來防止系統電(dian)壓(ya)繼(ji)續下(xia)降(jiang)(jiang)。只要(yao)輸(shu)入(ru)電(dian)流(liu)(liu)保持在該限(xian)制(zhi)(zhi)的水平或者(zhe)低于(yu)該限(xian)制(zhi)(zhi)，就仍然(ran)(ran)有電(dian)流(liu)(liu)向電(dian)池充(chong)電(dian)。然(ran)(ran)而，由系統電(dian)壓(ya)下(xia)降(jiang)(jiang)引起的不穩定或噪(zao)聲使得這種(zhong)基(ji)于(yu)電(dian)壓(ya)的DPPM結構(gou)不適(shi)(shi)合應用在某些對噪(zao)聲敏感的場合，比如音(yin)頻設備。

圖5:基于輸(shu)入(ru)電壓的(de)動態電源路徑管理。

基于(yu)輸(shu)入電(dian)(dian)流(liu)的(de)(de)(de)DPPM（圖6）采用檢測電(dian)(dian)阻來評估輸(shu)入電(dian)(dian)流(liu)，當輸(shu)入電(dian)(dian)流(liu)達到預設電(dian)(dian)流(liu)門(men)限時(shi)，通過動態(tai)降(jiang)低電(dian)(dian)池電(dian)(dian)流(liu)來防止適(shi)配(pei)器(qi)過載或系(xi)(xi)統電(dian)(dian)壓(ya)下(xia)降(jiang)。這樣就保(bao)證了系(xi)(xi)統電(dian)(dian)壓(ya)的(de)(de)(de)穩定(ding)，降(jiang)低了適(shi)配(pei)器(qi)的(de)(de)(de)額外功率(lv)要求。同時(shi)，該拓撲還(huan)具備(bei)電(dian)(dian)池反(fan)向補充供電(dian)(dian)的(de)(de)(de)能力。

圖6:基于輸入(ru)電(dian)流的動態電(dian)源路徑管理。

　　有些充(chong)電(dian)(dian)器(qi)（例如MPS公司的MP2607）可以根據不同電(dian)(dian)源(yuan)要(yao)求(qiu)，優化(hua)選擇不同的動態電(dian)(dian)源(yuan)路(lu)徑管(guan)理方案。MP2607根據不同的適(shi)(shi)配器(qi)類(lei)型，在(zai)基(ji)于輸(shu)入(ru)電(dian)(dian)壓(ya)和基(ji)于輸(shu)入(ru)電(dian)(dian)流(liu)的DPPM兩(liang)種拓撲之間進行智能(neng)選擇。若輸(shu)入(ru)是交(jiao)流(liu)適(shi)(shi)配器(qi)，MP2607采(cai)用基(ji)于輸(shu)入(ru)電(dian)(dian)壓(ya)的DPPM技術(shu)，控(kong)制適(shi)(shi)配器(qi)交(jiao)流(liu)電(dian)(dian)壓(ya)，使得交(jiao)流(liu)適(shi)(shi)配器(qi)可以同時為(wei)系統供(gong)電(dian)(dian)和為(wei)電(dian)(dian)池充(chong)電(dian)(dian)，工作(zuo)波(bo)形如圖7所(suo)示。

圖7:MP2607在交流適配器(qi)輸入(ru)時的(de)動態電源路徑(jing)管理。

　　在USB輸(shu)入(ru)模式下，MP2607采用基于輸(shu)入(ru)電流的DPPM.如圖(tu)8所示，考慮到USB提供(gong)(gong)電流能力(li)有限，設置充電電流在USB限制電流以(yi)下。若系統負載(zai)電流大(da)于USB限流值，電池(chi)將(jiang)反向(xiang)補(bu)充供(gong)(gong)電。

圖8:MP2607在(zai)USB輸入時的動(dong)態電源路徑管理。

　　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管理模式之間切換的充電器）可以為移動電子設備提供更加精妙的電源解決方(fang)案，從而給用戶帶來(lai)前(qian)所未(wei)有的便利、性(xing)能和效率。