隨(sui)著(zhu)智能(neng)手(shou)機、平(ping)板(ban)電(dian)(dian)(dian)(dian)腦(nao)和攝像機等便攜設(she)備(bei)的(de)(de)不斷普及(ji)，人們對電(dian)(dian)(dian)(dian)源(yuan)的(de)(de)要(yao)求(qiu)以(yi)及(ji)對邊充電(dian)(dian)(dian)(dian)邊使用這些設(she)備(bei)的(de)(de)能(neng)力的(de)(de)要(yao)求(qiu)與(yu)日俱(ju)增。更高(gao)的(de)(de)功率(lv)要(yao)求(qiu)增加了(le)對具(ju)有高(gao)功率(lv)密度(du)和優異(yi)充電(dian)(dian)(dian)(dian)能(neng)力的(de)(de)電(dian)(dian)(dian)(dian)池(chi)的(de)(de)需求(qiu)。目前(qian)，鋰(li)離子（Li-ion）電(dian)(dian)(dian)(dian)池(chi)和鋰(li)聚合物(wu)（Li-po）電(dian)(dian)(dian)(dian)池(chi)最適(shi)合當(dang)前(qian)市(shi)場(chang)對功率(lv)密度(du)、充電(dian)(dian)(dian)(dian)能(neng)力和價(jia)格的(de)(de)要(yao)求(qiu)。但(dan)是，有別(bie)于(yu)鉛酸(suan)、鎳氫等其他流行的(de)(de)電(dian)(dian)(dian)(dian)池(chi)技術，鋰(li)電(dian)(dian)(dian)(dian)池(chi)技術的(de)(de)性(xing)能(neng)也(ye)最不穩定：鋰(li)電(dian)(dian)(dian)(dian)池(chi)充放電(dian)(dian)(dian)(dian)若(ruo)管理不善，將(jiang)導(dao)致(zhi)充電(dian)(dian)(dian)(dian)時間長、耗散功率(lv)高(gao)、效率(lv)低(di)和電(dian)(dian)(dian)(dian)池(chi)壽命(ming)比(bi)平(ping)均壽命(ming)低(di)等問題。圖1顯(xian)示了(le)典型鋰(li)離子電(dian)(dian)(dian)(dian)池(chi)的(de)(de)充電(dian)(dian)(dian)(dian)曲線(xian)。

　　傳統充電器相對簡單，這(zhe)些充電器在(zai)小(xiao)功(gong)率應用中表現較(jiao)(jiao)好。然而，它們卻不能有效地適應充電曲線的變化，比如，用戶(hu)在(zai)不同電源之間切換或者在(zai)充電期間操作設(she)備。另外(wai)，傳(chuan)統充電器在(zai)大功(gong)率和大電流應用中，通常效率較(jiao)(jiao)低(di)，耗(hao)散功(gong)率較(jiao)(jiao)大。

圖(tu)1:典型鋰離子電(dian)池的充(chong)電(dian)曲(qu)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安全(quan)性和電(dian)池的使用壽(shou)命(ming)得(de)到提高(gao)。

　　電(dian)(dian)源管理拓撲(pu)種(zhong)類繁多(duo)，本(ben)文(wen)則重點介紹以下三(san)種(zhong)：電(dian)(dian)池(chi)饋電(dian)(dian)、自動選擇(ze)和(he)動態電(dian)(dian)源路徑。

　　電池饋電拓撲

　　電池饋電拓撲是一種(zhong)實(shi)現過程最(zui)簡單(dan)、成本最(zui)低的拓撲，這是因為其電路由(you)充電器、電池和(he)系統組成，如(ru)圖2所(suo)示。

圖2:電池饋電拓撲原理圖及信號圖。

　　這種拓撲有三(san)個主要特性：無(wu)論供電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓如何變化，系統(tong)(tong)(tong)電(dian)(dian)(dian)(dian)壓始終(zhong)等(deng)于(yu)電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓，電(dian)(dian)(dian)(dian)源系統(tong)(tong)(tong)始終(zhong)優先，以便IBATT ￡ ICHG,并且ICHG最(zui)終(zhong)限制(zhi)由輸入(ru)電(dian)(dian)(dian)(dian)源提供給(gei)系統(tong)(tong)(tong)電(dian)(dian)(dian)(dian)源總線的最(zui)大功率。當(dang)系統(tong)(tong)(tong)與充電(dian)(dian)(dian)(dian)器斷開時該拓撲還可(ke)以實現(xian)最(zui)小的耗散(san)功率，設置(zhi)ICHG從根(gen)本上限定(ding)了總輸入(ru)電(dian)(dian)(dian)(dian)流，這樣，隨著系統(tong)(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)額下(xia)降，工作波形如圖2所示。

　　遺憾的是，這種拓撲有如下不足之處，從而限制(zhi)了它在更廣應用(yong)領域的效率和效用(yong)：

　　在電(dian)(dian)池(chi)(chi)電(dian)(dian)壓太低(di)的(de)情況下(xia)，系統(tong)無法工(gong)作(zuo)。電(dian)(dian)池(chi)(chi)電(dian)(dian)壓跌至涓流充(chong)電(dian)(dian)門(men)限以(yi)下(xia)時，充(chong)電(dian)(dian)器將(jiang)把總(zong)的(de)輸出電(dian)(dian)流限制得很(hen)低(di)。系統(tong)的(de)額外電(dian)(dian)源需求將(jiang)由(you)(you)電(dian)(dian)池(chi)(chi)來(lai)補充(chong)，從而導致電(dian)(dian)池(chi)(chi)能量(liang)進一步耗盡。由(you)(you)于系統(tong)電(dian)(dian)壓始終(zhong)等于電(dian)(dian)池(chi)(chi)電(dian)(dian)壓，一旦電(dian)(dian)池(chi)(chi)電(dian)(dian)壓低(di)到系統(tong)最低(di)工(gong)作(zuo)電(dian)(dian)壓以(yi)下(xia)，系統(tong)將(jiang)停(ting)止(zhi)工(gong)作(zuo)。

　　雖然電(dian)(dian)(dian)(dian)(dian)池(chi)已具有滿電(dian)(dian)(dian)(dian)(dian)量，但(dan)是充電(dian)(dian)(dian)(dian)(dian)器無法進入EOC（結束充電(dian)(dian)(dian)(dian)(dian)）狀態。如果(guo)ISYS超過電(dian)(dian)(dian)(dian)(dian)池(chi)滿電(dian)(dian)(dian)(dian)(dian)量門(men)限（IBF），那么ICHG就無法降到低于IBF,充電(dian)(dian)(dian)(dian)(dian)狀態始(shi)終顯示正在(zai)充電(dian)(dian)(dian)(dian)(dian)，即(ji)使電(dian)(dian)(dian)(dian)(dian)池(chi)已經具有滿電(dian)(dian)(dian)(dian)(dian)量。

　　電(dian)(dian)(dian)池無法充(chong)滿。由于系統優先(xian)于電(dian)(dian)(dian)池供電(dian)(dian)(dian)，因(yin)此電(dian)(dian)(dian)池只能以低(di)電(dian)(dian)(dian)流進行充(chong)電(dian)(dian)(dian)。此外，充(chong)電(dian)(dian)(dian)器只能在預期(qi)的有效充(chong)電(dian)(dian)(dian)時(shi)間(jian)內(nei)工作(zuo)，這(zhe)樣可以避(bi)免(mian)給(gei)壞電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)。如充(chong)電(dian)(dian)(dian)時(shi)間(jian)超(chao)出此時(shi)間(jian)段，會導致充(chong)電(dian)(dian)(dian)器誤判(pan)壞電(dian)(dian)(dian)池而停止充(chong)電(dian)(dian)(dian)。

電源路徑自動選擇拓撲

　　電源(yuan)路(lu)徑自動(dong)選擇(ze)拓(tuo)撲(pu)在電池(chi)直接搭載拓(tuo)撲(pu)基礎上(shang)外加(jia)了兩個開關管(guan)，使(shi)得系(xi)統(tong)電源(yuan)可(ke)以(yi)根(gen)據輸(shu)入電壓的變化(hua)在適(shi)配器和(he)電池(chi)之(zhi)間來回(hui)切換(huan)。拓(tuo)撲(pu)結構(gou)及工作(zuo)波(bo)形如圖3所示(shi)。

圖3:電源(yuan)路徑自動選(xuan)擇拓撲及(ji)工(gong)作波形(xing)。

　　與電(dian)(dian)(dian)池(chi)饋電(dian)(dian)(dian)拓(tuo)撲(pu)(pu)結(jie)構相比(bi)，此拓(tuo)撲(pu)(pu)有實質性的(de)(de)(de)改進。它(ta)將系(xi)(xi)統(tong)(tong)(tong)直接(jie)(jie)跟交流(liu)適配(pei)(pei)器(qi)(qi)(qi)相連，與充(chong)電(dian)(dian)(dian)器(qi)(qi)(qi)獨立(li)開來，因而能夠(gou)提(ti)供(gong)更大的(de)(de)(de)系(xi)(xi)統(tong)(tong)(tong)電(dian)(dian)(dian)流(liu)、更高的(de)(de)(de)效(xiao)率并且允許系(xi)(xi)統(tong)(tong)(tong)在(zai)低電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(ya)(ya)(ya)下工作(zuo)。此外，其價格也(ye)比(bi)較低廉。然而，當適配(pei)(pei)器(qi)(qi)(qi)輸出電(dian)(dian)(dian)壓(ya)(ya)(ya)變(bian)化(hua)較大的(de)(de)(de)時候(hou)，系(xi)(xi)統(tong)(tong)(tong)電(dian)(dian)(dian)壓(ya)(ya)(ya)也(ye)會隨(sui)之變(bian)化(hua)，所以此拓(tuo)撲(pu)(pu)要(yao)求系(xi)(xi)統(tong)(tong)(tong)能夠(gou)接(jie)(jie)受比(bi)較寬的(de)(de)(de)輸入電(dian)(dian)(dian)壓(ya)(ya)(ya)變(bian)化(hua)范圍(wei)。此外，也(ye)要(yao)求適配(pei)(pei)器(qi)(qi)(qi)具有更高的(de)(de)(de)額定功率，以滿足系(xi)(xi)統(tong)(tong)(tong)和充(chong)電(dian)(dian)(dian)器(qi)(qi)(qi)的(de)(de)(de)最大總功率需求，以及(ji)系(xi)(xi)統(tong)(tong)(tong)負(fu)載突變(bian)時的(de)(de)(de)功率變(bian)化(hua)要(yao)求。

　　圖4是采用MPS公司的(de)MP2611構(gou)成(cheng)的(de)電源路徑自動(dong)選擇拓撲的(de)原理圖。為了(le)防止出現(xian)(xian)不穩(wen)定情(qing)況(kuang)，當VBATT接(jie)近VIN時，MP2611會斷開系(xi)統與電池(chi)的(de)連接(jie)。此(ci)外，它還會在S1 （M1及M2）與S2（M3）之間插入一個消隱(yin)期，以防出現(xian)(xian)電流貫通，從而損壞系(xi)統和(he)電池(chi)。

圖(tu)4:采(cai)用MP2611構成的電源路(lu)徑自(zi)動選(xuan)擇(ze)拓撲。

　　動態電源路(lu)徑管理拓撲（DPPM）

　　動(dong)態電(dian)源(yuan)路徑(jing)管理（DPPM）技術采用了一套附加的檢測(ce)模塊(kuai)，測(ce)量系(xi)統電(dian)壓(ya)或者輸(shu)(shu)入(ru)電(dian)流(liu)，實時監測(ce)總(zong)功率需求。一旦功率需求超過預設(she)值，通過充電(dian)器降低充電(dian)電(dian)流(liu)來保證適配器輸(shu)(shu)出功率恒(heng)定而不過載。

　　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，然后充電器通過動態降低(di)充電(dian)(dian)電(dian)(dian)流(liu)來防(fang)止系統電(dian)(dian)壓(ya)(ya)繼續(xu)下(xia)降。只(zhi)要(yao)輸入(ru)電(dian)(dian)流(liu)保(bao)持(chi)在(zai)該(gai)(gai)限(xian)制的水平或者低(di)于該(gai)(gai)限(xian)制，就仍然有(you)電(dian)(dian)流(liu)向(xiang)電(dian)(dian)池充電(dian)(dian)。然而，由系統電(dian)(dian)壓(ya)(ya)下(xia)降引起的不(bu)穩定或噪聲使得這種基(ji)于電(dian)(dian)壓(ya)(ya)的DPPM結(jie)構不(bu)適合應(ying)用在(zai)某些(xie)對噪聲敏感的場合，比如音(yin)頻(pin)設備。

圖(tu)5:基于輸入(ru)電(dian)壓(ya)的動(dong)態電(dian)源路徑(jing)管理。

基于輸(shu)入電(dian)(dian)(dian)流的DPPM（圖(tu)6）采用檢測電(dian)(dian)(dian)阻來評估輸(shu)入電(dian)(dian)(dian)流，當輸(shu)入電(dian)(dian)(dian)流達到預設(she)電(dian)(dian)(dian)流門限時，通過動(dong)態降低(di)電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)流來防止適配器過載或(huo)系(xi)統(tong)電(dian)(dian)(dian)壓(ya)下(xia)降。這樣就保證了系(xi)統(tong)電(dian)(dian)(dian)壓(ya)的穩定，降低(di)了適配器的額外(wai)功(gong)率(lv)要求(qiu)。同時，該(gai)拓撲(pu)還(huan)具備電(dian)(dian)(dian)池(chi)反向補充(chong)供電(dian)(dian)(dian)的能(neng)力。

圖(tu)6:基于輸入電流的動態電源路徑(jing)管理。

　　有些(xie)充電(dian)(dian)器(qi)（例如(ru)MPS公司(si)的(de)(de)(de)MP2607）可以根據不(bu)同電(dian)(dian)源(yuan)要求，優化選擇(ze)不(bu)同的(de)(de)(de)動(dong)態電(dian)(dian)源(yuan)路徑(jing)管(guan)理方案。MP2607根據不(bu)同的(de)(de)(de)適(shi)配器(qi)類(lei)型(xing)，在(zai)基(ji)于(yu)輸(shu)入電(dian)(dian)壓(ya)(ya)和基(ji)于(yu)輸(shu)入電(dian)(dian)流(liu)的(de)(de)(de)DPPM兩種拓(tuo)撲(pu)之間(jian)進行智能(neng)選擇(ze)。若輸(shu)入是交流(liu)適(shi)配器(qi)，MP2607采用基(ji)于(yu)輸(shu)入電(dian)(dian)壓(ya)(ya)的(de)(de)(de)DPPM技術(shu)，控制適(shi)配器(qi)交流(liu)電(dian)(dian)壓(ya)(ya)，使得交流(liu)適(shi)配器(qi)可以同時為(wei)(wei)系統供電(dian)(dian)和為(wei)(wei)電(dian)(dian)池充電(dian)(dian)，工作波(bo)形如(ru)圖(tu)7所示。

圖7:MP2607在交流適配器輸(shu)入(ru)時的動態電源路(lu)徑管理。

　　在USB輸入模(mo)式下，MP2607采用基于(yu)輸入電流(liu)的DPPM.如圖8所示，考(kao)慮到(dao)USB提供(gong)(gong)電流(liu)能力(li)有限(xian)(xian)，設置充(chong)電電流(liu)在USB限(xian)(xian)制電流(liu)以(yi)下。若系統(tong)負載電流(liu)大于(yu)USB限(xian)(xian)流(liu)值，電池將反向(xiang)補(bu)充(chong)供(gong)(gong)電。

圖(tu)8:MP2607在USB輸入時(shi)的(de)動態電源路徑管(guan)理。

　　總之，具有動態電源路徑管理的充電器（尤(you)其是(shi)那些能在不同管(guan)理(li)模(mo)式之間(jian)切換的(de)充電(dian)(dian)器）可以為(wei)移動電(dian)(dian)子設備提供更加(jia)精妙的(de)電(dian)(dian)源解決方案(an)，從而給用(yong)戶帶來(lai)前所未有的(de)便利、性(xing)能和效率(lv)。