鋰(li)離(li)子(zi)(Li-ion)電(dian)(dian)池(chi)和(he)鋰(li)聚合(he)物(Li-po)電(dian)(dian)池(chi)最(zui)適合(he)當前市場對功(gong)(gong)率(lv)密度、充電(dian)(dian)能力和(he)價格的(de)要求。但(dan)是，有別于鉛(qian)酸、鎳氫等其他流行的(de)電(dian)(dian)池(chi)技術(shu)，鋰(li)電(dian)(dian)池(chi)技術(shu)的(de)性能也最(zui)不(bu)穩(wen)定：鋰(li)電(dian)(dian)池(chi)充放電(dian)(dian)若管理(li)不(bu)善，將導致充電(dian)(dian)時間長(chang)、耗散功(gong)(gong)率(lv)高、效率(lv)低(di)和(he)電(dian)(dian)池(chi)壽(shou)命比平均壽(shou)命低(di)等問題。圖1顯示了典型鋰(li)離(li)子(zi)電(dian)(dian)池(chi)的(de)充電(dian)(dian)曲線。

　　傳統充電器相對簡單，這些充電(dian)器在(zai)小功(gong)(gong)率(lv)應(ying)(ying)用中(zhong)表現(xian)較好。然而，它們卻不(bu)能有效地適應(ying)(ying)充電(dian)曲線的變化(hua)，比(bi)如，用戶在(zai)不(bu)同(tong)電(dian)源(yuan)之間切換或者(zhe)在(zai)充電(dian)期間操作設(she)備(bei)。另外，傳統充電(dian)器在(zai)大功(gong)(gong)率(lv)和(he)大電(dian)流應(ying)(ying)用中(zhong)，通常效率(lv)較低(di)，耗散功(gong)(gong)率(lv)較大。

　　

 

　　圖1:典型鋰離子(zi)電池的充(chong)電曲線。

　　新型線性和開關充電器，比如(ru)芯(xin)源系統(tong)(tong)(MPS)公司(si)的(de)MP2600系列(lie)，采用電源路(lu)徑管(guan)理技術改變了充電曲線(xian)，從(cong)而(er)能夠(gou)以更(geng)低的(de)耗散功率更(geng)加高效地為電池/系統(tong)(tong)供電。同(tong)時，這些充電器也使系統(tong)(tong)的(de)安(an)全(quan)性和電池的(de)使用壽命得到提高。

　　電源管理拓撲種類(lei)繁多，本文則重(zhong)點介紹以下(xia)三種：電池(chi)饋(kui)電、自動選(xuan)擇和動態電源路徑。

　　電池饋電拓撲

　　電(dian)池饋電(dian)拓撲是一種實現過程(cheng)最簡單、成(cheng)本最低的拓撲，這是因為其電(dian)路由充(chong)電(dian)器、電(dian)池和(he)系統(tong)組成(cheng)，如圖2所(suo)示(shi)。

　　

 

　　圖(tu)(tu)2:電池饋電拓撲(pu)原理圖(tu)(tu)及(ji)信號圖(tu)(tu)。

　　這種(zhong)拓撲有(you)三(san)個主要特(te)性：無論供電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓如何變化(hua)，系統(tong)(tong)電(dian)(dian)(dian)(dian)壓始終(zhong)等于電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓，電(dian)(dian)(dian)(dian)源(yuan)系統(tong)(tong)始終(zhong)優先，以便(bian)IBATT ￡ ICHG,并且ICHG最終(zhong)限制由輸入電(dian)(dian)(dian)(dian)源(yuan)提(ti)供給(gei)系統(tong)(tong)電(dian)(dian)(dian)(dian)源(yuan)總(zong)線的最大功(gong)率。當(dang)系統(tong)(tong)與充(chong)電(dian)(dian)(dian)(dian)器斷(duan)開時該(gai)拓撲還可(ke)以實現最小的耗散功(gong)率，設置ICHG從(cong)根本上限定了總(zong)輸入電(dian)(dian)(dian)(dian)流(liu)，這樣，隨著系統(tong)(tong)電(dian)(dian)(dian)(dian)流(liu)(ISYS)的增(zeng)加，充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(IBATT)將等額下降，工作波形如圖2所(suo)示。

　　遺憾的(de)是，這(zhe)種拓撲有如(ru)下不足之處(chu)，從(cong)而限制了它在更(geng)廣應用(yong)領域的(de)效(xiao)率和(he)效(xiao)用(yong)：

　　在電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)太低(di)(di)的情(qing)況下(xia)，系(xi)統無法工作。電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)跌(die)至涓流充電(dian)(dian)(dian)(dian)(dian)(dian)門限以(yi)下(xia)時，充電(dian)(dian)(dian)(dian)(dian)(dian)器將把總的輸出電(dian)(dian)(dian)(dian)(dian)(dian)流限制得很低(di)(di)。系(xi)統的額(e)外電(dian)(dian)(dian)(dian)(dian)(dian)源需求將由電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)來補(bu)充，從而導(dao)致電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)能量進一步耗(hao)盡。由于系(xi)統電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)始終(zhong)等于電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，一旦電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低(di)(di)到系(xi)統最低(di)(di)工作電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)以(yi)下(xia)，系(xi)統將停止工作。

　　雖然(ran)電(dian)(dian)池已(yi)具有(you)滿(man)電(dian)(dian)量(liang)，但是充(chong)電(dian)(dian)器(qi)無法(fa)進入EOC(結(jie)束充(chong)電(dian)(dian))狀(zhuang)態。如(ru)果ISYS超過(guo)電(dian)(dian)池滿(man)電(dian)(dian)量(liang)門限(IBF)，那么(me)ICHG就無法(fa)降(jiang)到低于IBF,充(chong)電(dian)(dian)狀(zhuang)態始終顯(xian)示正在(zai)充(chong)電(dian)(dian)，即使(shi)電(dian)(dian)池已(yi)經具有(you)滿(man)電(dian)(dian)量(liang)。

　　電(dian)(dian)(dian)池(chi)無法充(chong)滿(man)。由于(yu)系(xi)統(tong)優先于(yu)電(dian)(dian)(dian)池(chi)供電(dian)(dian)(dian)，因此(ci)電(dian)(dian)(dian)池(chi)只(zhi)能以低電(dian)(dian)(dian)流進行充(chong)電(dian)(dian)(dian)。此(ci)外，充(chong)電(dian)(dian)(dian)器(qi)(qi)只(zhi)能在預期的有效充(chong)電(dian)(dian)(dian)時間(jian)內工作，這樣可以避免(mian)給壞(huai)(huai)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)。如充(chong)電(dian)(dian)(dian)時間(jian)超(chao)出此(ci)時間(jian)段，會導致充(chong)電(dian)(dian)(dian)器(qi)(qi)誤判壞(huai)(huai)電(dian)(dian)(dian)池(chi)而停止充(chong)電(dian)(dian)(dian)。

　　電(dian)源路徑自動選擇拓撲

　　電源(yuan)(yuan)路徑自動(dong)選擇拓(tuo)撲(pu)在電池(chi)(chi)直接搭(da)載拓(tuo)撲(pu)基礎(chu)上(shang)外加了兩個(ge)開關管，使得系統電源(yuan)(yuan)可(ke)以根據輸(shu)入電壓的變化在適配器和電池(chi)(chi)之間來(lai)回切換。拓(tuo)撲(pu)結構及工作波形如圖(tu)3所示。

　　

 

　　圖3:電源路徑自(zi)動(dong)選(xuan)擇(ze)拓撲及(ji)工作波形(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(zui)大總功率需求(qiu)(qiu)，以及(ji)系統(tong)負載(zai)突變時的功率變化要求(qiu)(qiu)。

　　圖(tu)4是采用MPS公(gong)司的(de)(de)MP2611構成的(de)(de)電源路(lu)徑自動選擇拓撲的(de)(de)原理圖(tu)。為了防止出現不穩(wen)定情況，當VBATT接(jie)近VIN時，MP2611會(hui)斷(duan)開系統(tong)與電池的(de)(de)連接(jie)。此外，它還會(hui)在S1 (M1及M2)與S2(M3)之間插入(ru)一個消隱(yin)期，以防出現電流貫通，從而損壞(huai)系統(tong)和電池。

　　

 

　　圖4:采用MP2611構(gou)成的(de)電源(yuan)路(lu)徑自動選(xuan)擇拓撲。

   動(dong)態電源(yuan)路徑管理拓撲(DPPM)

 

　　動態電(dian)源路徑管理(DPPM)技術采用(yong)了一套附加的檢測模塊，測量系統電(dian)壓或者輸入(ru)電(dian)流(liu)，實時監測總功(gong)率(lv)需求(qiu)。一旦功(gong)率(lv)需求(qiu)超過預設值，通(tong)過充電(dian)器(qi)降低充電(dian)電(dian)流(liu)來保證適配(pei)器(qi)輸出功(gong)率(lv)恒定而不過載(zai)。

　　例如(ru)，基于輸入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)DPPM(圖5)通(tong)(tong)過(guo)比(bi)較輸入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)與(yu)預(yu)設(she)參(can)考(kao)(kao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)來判斷輸入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)是否達(da)到適(shi)配(pei)(pei)器(qi)(qi)的(de)輸出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)限(xian)(xian)制(zhi)(zhi)。若適(shi)配(pei)(pei)器(qi)(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)已經達(da)到該(gai)(gai)限(xian)(xian)制(zhi)(zhi)，適(shi)配(pei)(pei)器(qi)(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)將降至預(yu)設(she)參(can)考(kao)(kao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，然(ran)后充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)通(tong)(tong)過(guo)動態降低充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)來防(fang)止系統電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)繼續下降。只要輸入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)保持在該(gai)(gai)限(xian)(xian)制(zhi)(zhi)的(de)水平(ping)或者低于該(gai)(gai)限(xian)(xian)制(zhi)(zhi)，就仍然(ran)有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)向(xiang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。然(ran)而，由系統電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)下降引起的(de)不(bu)穩(wen)定或噪(zao)聲使得這種基于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)DPPM結構不(bu)適(shi)合應用(yong)在某(mou)些(xie)對(dui)噪(zao)聲敏感的(de)場合，比(bi)如(ru)音頻(pin)設(she)備(bei)。

　　

 

　　圖5:基于輸入電壓的動態(tai)電源路徑管理(li)。

　　基(ji)于輸入(ru)電流的(de)(de)DPPM(圖6)采用檢(jian)測電阻來評估輸入(ru)電流，當(dang)輸入(ru)電流達到預設電流門限時(shi)，通過動態(tai)降(jiang)低(di)電池(chi)電流來防止適(shi)配器過載或系(xi)(xi)統電壓下降(jiang)。這樣就保證了系(xi)(xi)統電壓的(de)(de)穩(wen)定，降(jiang)低(di)了適(shi)配器的(de)(de)額外(wai)功率(lv)要求。同時(shi)，該拓(tuo)撲還具備電池(chi)反向補充(chong)供電的(de)(de)能力。

　　

 

　　圖6:基于輸入電流的動態(tai)電源路徑管(guan)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(gong)作波形如圖7所示。

　　

 

　　圖7:MP2607在交流適配器(qi)輸入時(shi)的動態電源路徑管理。

　　在(zai)USB輸入模(mo)式下，MP2607采用基于輸入電(dian)(dian)流(liu)(liu)(liu)(liu)的DPPM.如(ru)圖8所示，考慮(lv)到USB提供電(dian)(dian)流(liu)(liu)(liu)(liu)能力有限，設置(zhi)充(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)(liu)(liu)在(zai)USB限制電(dian)(dian)流(liu)(liu)(liu)(liu)以下。若系統負(fu)載電(dian)(dian)流(liu)(liu)(liu)(liu)大于USB限流(liu)(liu)(liu)(liu)值，電(dian)(dian)池將反向補充(chong)供電(dian)(dian)。

　　

 

　　圖8:MP2607在USB輸入時(shi)的動(dong)態電源路(lu)徑管理(li)。

　　總之，具有動態電源路徑管理的充電器(尤其是那些(xie)能在不同管(guan)理模式(shi)之(zhi)間切換(huan)的充電(dian)器)可(ke)以(yi)為移動電(dian)子設(she)備提供更加精(jing)妙的電(dian)源(yuan)解決方案，從而(er)給用(yong)戶帶來前(qian)所未有(you)的便利、性能和效率。