引言

便攜(xie)式電子設備設計人(ren)員(yuan)可以(yi)選(xuan)(xuan)擇(ze)各種(zhong)各樣的(de)化學技術(shu)、充(chong)電器拓撲以(yi)及充(chong)電管理解決方(fang)案(an)。選(xuan)(xuan)擇(ze)一(yi)(yi)款最(zui)為(wei)(wei)合適的(de)解決方(fang)案(an)應該是(shi)一(yi)(yi)項很(hen)簡單的(de)工(gong)作(zuo)，但是(shi)在大多數情況下(xia)這一(yi)(yi)過(guo)程頗為(wei)(wei)復雜。設計人(ren)員(yuan)需要在性能、成(cheng)本(ben)、外形尺寸以(yi)及其他(ta)關鍵要求方(fang)面找到一(yi)(yi)個最(zui)佳(jia)平衡(heng)點。本(ben)文將(jiang)為(wei)(wei)廣大設計人(ren)員(yuan)和系統(tong)工(gong)程師提供一(yi)(yi)些指導和幫助(zhu)以(yi)使得該選(xuan)(xuan)擇(ze)工(gong)作(zuo)變得更為(wei)(wei)輕松。

以 3 “C”開始實現(xian)充(chong)電控制

所(suo)有使用可(ke)充電(dian)(dian)電(dian)(dian)池的(de)系(xi)統設(she)計(ji)人員都(dou)需要(yao)清楚一些(xie)基礎(chu)設(she)計(ji)技術，以確保滿足下面三個(ge)關鍵的(de)要(yao)求：

1、電(dian)(dian)池(chi)(chi)(chi)安(an)全性: 毋庸置(zhi)疑，終端用戶安(an)全是所有(you)系統(tong)設計(ji)中最(zui)優先考慮的(de)(de)問題。大多數鋰(li)離子 (Li-Ion) 電(dian)(dian)池(chi)(chi)(chi)組(zu)和鋰(li)聚合物 (Li-Pol) 電(dian)(dian)池(chi)(chi)(chi)組(zu)都含有(you)保護電(dian)(dian)子電(dian)(dian)路。然而，還有(you)一些(xie)系統(tong)設計(ji)需(xu)要考慮的(de)(de)關鍵因素。其中包括但不局限于確保在鋰(li)離子電(dian)(dian)池(chi)(chi)(chi)充(chong)電(dian)(dian)最(zui)后階(jie)段期間(jian) ?1% 的(de)(de)穩壓容(rong)限、安(an)全處理(li)深度(du)放電(dian)(dian)電(dian)(dian)池(chi)(chi)(chi)的(de)(de)預處理(li)模式、安(an)全計(ji)時器以及電(dian)(dian)池(chi)(chi)(chi)溫度(du)監控。

2、電池容量：所(suo)有的(de)電池充(chong)電解(jie)決方案(an)都要確(que)保在每一次和每一個充(chong)電周(zhou)期都能將(jiang)電池容量充(chong)至充(chong)滿(man)狀(zhuang)態。過早的(de)終止充(chong)電會(hui)導致電池運(yun)行時間縮短(duan)，這是當今(jin)高功耗的(de)便攜式(shi)設備所(suo)不(bu)希望的(de)。

3、電(dian)(dian)池(chi)使用(yong)(yong)壽命：遵循建議(yi)的充電(dian)(dian)算法是(shi)確保終端用(yong)(yong)戶實現(xian)每(mei)個(ge)電(dian)(dian)池(chi)組最(zui)多充電(dian)(dian)周期(qi)的重要一步。利用(yong)(yong)電(dian)(dian)池(chi)溫(wen)度(du)和(he)電(dian)(dian)壓限定每(mei)一次充電(dian)(dian)、預處(chu)理深(shen)度(du)放電(dian)(dian)電(dian)(dian)池(chi)并避(bi)免過(guo)晚或非正常充電(dian)(dian)終止(zhi)是(shi)最(zui)大(da)化電(dian)(dian)池(chi)使用(yong)(yong)壽命所必(bi)須的一些步驟。

充電特(te)性 電池(chi)安全性 電池(chi)容量 電池(chi)使用(yong)壽命(ming)

精(jing)確(que)的電壓和/或電流(liu)調節 ? ?

充電限制

（電壓和溫度） ? ?

溫度監控(kong) ? ? ?

預處理 ? ? ?

充電結束終止 ? ? ?

充電計時器 ?

充電狀態報告 ? ?

電(dian)池(chi)插入與去除探測 ?

最小電池泄漏 ?

短路電流限制 ?

自動再充電 ?

電(dian)池(chi)化學技(ji)術的選擇
現在系統(tong)設計人員可以在多種電池化學(xue)技術中進行選(xuan)擇。設計 人員通常會根據下面的一些標準(zhun)進行電池化學(xue)技術的選(xuan)擇，其中包括：

? 能量密度

? 規格和外形尺寸

? 成本

? 使(shi)用模(mo)式和使(shi)用壽命

近年來，盡管使用(yong)(yong)鋰離子電池和鋰聚(ju)合物電池的(de)趨(qu)勢增強，但是(shi) Ni 電池化學技術仍(reng)然是(shi)諸多(duo)消費類應用(yong)(yong)一個不錯的(de)選(xuan)項(xiang)。

無論選擇何種電(dian)(dian)池(chi)(chi)化學(xue)技術(shu)，遵循每一(yi)種電(dian)(dian)池(chi)(chi)化學(xue)技術(shu)的(de)正確(que)充電(dian)(dian)管理(li)技術(shu)都(dou)是至(zhi)關重要(yao)的(de)。這些技術(shu)將確(que)保(bao)電(dian)(dian)池(chi)(chi)在每一(yi)次和(he)每個充電(dian)(dian)周期都(dou)能被充至(zhi)最大容量，而不會降(jiang)低安全性或縮(suo)短電(dian)(dian)池(chi)(chi)使(shi)用壽命(ming)。

NiCd / NIMH

在一(yi)個(ge)充(chong)電(dian)周期開始之(zhi)(zhi)前，并且盡可能在開始快(kuai)速充(chong)電(dian)之(zhi)(zhi)前對鎳鎘 (NiCd) 電(dian)池(chi)(chi)和鎳氫(qing) (NiMH) 電(dian)池(chi)(chi)必(bi)須要進(jin)行(xing)檢驗和調節。如果電(dian)池(chi)(chi)電(dian)壓或(huo)溫度超出了允(yun)許的極限是不允(yun)許進(jin)行(xing)快(kuai)速充(chong)電(dian)的。出于(yu)(yu)安全考慮(lv)，對所有“熱(re)”電(dian)池(chi)(chi)（一(yi)般高于(yu)(yu) 45?C）的充(chong)電(dian)工(gong)作都會(hui)暫時終止，直到(dao)電(dian)池(chi)(chi)冷(leng)卻(que)到(dao)正常工(gong)作溫度范(fan)圍內才會(hui)再(zai)次運轉(zhuan)。要想處理一(yi)個(ge)“冷(leng)”電(dian)池(chi)(chi)（一(yi)般低于(yu)(yu) 10?C）或(huo)過度放電(dian)的電(dian)池(chi)(chi)（每節電(dian)池(chi)(chi)通常低于(yu)(yu) 1V），需要施加(jia)一(yi)個(ge)溫和的點滴式電(dian)流。

當電(dian)(dian)(dian)池(chi)(chi)(chi)溫(wen)(wen)(wen)(wen)度(du)(du)和電(dian)(dian)(dian)壓(ya)正確(que)時快速充(chong)電(dian)(dian)(dian)開始。通常用(yong) 1C 或(huo)更(geng)低的(de)(de)恒定電(dian)(dian)(dian)流對 NiMH 電(dian)(dian)(dian)池(chi)(chi)(chi)進行充(chong)電(dian)(dian)(dian)。一些 NiCd 電(dian)(dian)(dian)池(chi)(chi)(chi)可以用(yong)高(gao)達 4C 的(de)(de)速率(lv)進行充(chong)電(dian)(dian)(dian)。采用(yong)適當的(de)(de)充(chong)電(dian)(dian)(dian)終(zhong)止(zhi)來避免有害(hai)的(de)(de)過充(chong)電(dian)(dian)(dian)。就(jiu)鎳基可充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)池(chi)(chi)(chi)而言，快速充(chong)電(dian)(dian)(dian)終(zhong)止(zhi)基于電(dian)(dian)(dian)壓(ya)或(huo)溫(wen)(wen)(wen)(wen)度(du)(du)。如圖 1 所(suo)示，典型的(de)(de)電(dian)(dian)(dian)壓(ya)終(zhong)止(zhi)方法是峰(feng)值電(dian)(dian)(dian)壓(ya)探測(ce)，在峰(feng)值時即每(mei)個電(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)電(dian)(dian)(dian)壓(ya)在 0～-4mV 范圍內，快速充(chong)電(dian)(dian)(dian)被終(zhong)止(zhi)。基于溫(wen)(wen)(wen)(wen)度(du)(du)的(de)(de)快速充(chong)電(dian)(dian)(dian)終(zhong)止(zhi)方法是觀察電(dian)(dian)(dian)池(chi)(chi)(chi)溫(wen)(wen)(wen)(wen)度(du)(du)上(shang)升率(lv) ?T/?t 來探測(ce)完全充(chong)電(dian)(dian)(dian)。典型的(de)(de) ?T/?t 率(lv)為 1?C/每(mei)分(fen)鐘。

鋰離子/鋰聚合物(wu)電池(chi)
與 NiCd 電(dian)(dian)(dian)池(chi)和(he)(he) NiMh 電(dian)(dian)(dian)池(chi)相類(lei)似，在快速充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)之前盡可能檢驗并調節鋰離子電(dian)(dian)(dian)池(chi)。驗證和(he)(he)處理方(fang)法與上述使用的方(fang)法相類(lei)似。 驗證和(he)(he)預處理之后，先用一(yi)個 1C 或更(geng)低的電(dian)(dian)(dian)流(liu)(liu)對鋰離子電(dian)(dian)(dian)池(chi)進(jin)行(xing)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)，直到電(dian)(dian)(dian)池(chi)達到其充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓極限為止(zhi)。該充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)階段通常(chang)會(hui)補(bu)充(chong)(chong)(chong)(chong)高(gao)達 70% 的電(dian)(dian)(dian)池(chi)容量(liang)。然后用一(yi)個通常(chang)為 4.2V 的恒(heng)定電(dian)(dian)(dian)壓對電(dian)(dian)(dian)池(chi)進(jin)行(xing)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)。為將安全(quan)性和(he)(he)電(dian)(dian)(dian)池(chi)容量(liang)，必須要將充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)壓穩定在至少 ?1%。在此充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)期間，電(dian)(dian)(dian)池(chi)汲取(qu)的充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)逐(zhu)漸下降。就(jiu)(jiu) 1C 充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)率而言，一(yi)旦電(dian)(dian)(dian)流(liu)(liu)電(dian)(dian)(dian)平下降到初始充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)的 10-15% 以下充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)通常(chang)就(jiu)(jiu)會(hui)終止(zhi).

開關模式與線性充電拓撲的對(dui)比

傳統(tong)上來說，手持設(she)備都使用線(xian)性充(chong)電拓(tuo)撲。該方法(fa)具有諸多優勢：低(di)實施成(cheng)本、設(she)計簡捷以及無(wu)高頻開(kai)關(guan)的無(wu)噪聲運行。但是，線(xian)性拓(tuo)撲會增加(jia)系統(tong)功耗，尤(you)其是當電池容(rong)量更高引起的充(chong)電率增加(jia)的時候。如果設(she)計人員無(wu)法(fa)管理設(she)計的散(san)熱問(wen)題，這就(jiu)會成(cheng)為一個主(zhu)要缺點。

當(dang) PC USB 端口作為電(dian)源時，則會出(chu)現其他一(yi)些(xie)缺點(dian)。當(dang)今(jin)在(zai)許多(duo)便攜式設計上(shang)都(dou)具有(you) USB 充電(dian)選(xuan)項，并(bing)且都(dou)可(ke)提供(gong)高達 500mA 的充電(dian)率。就(jiu)線性解(jie)決(jue)方案而(er)言，由于其效率較(jiao)低(di)(di)，可(ke)以從(cong) PC USB 傳輸的“電(dian)能”量就(jiu)被大(da)大(da)降低(di)(di)，從(cong)而(er)導致了充電(dian)時間過長。

這(zhe)就是(shi)開(kai)關(guan)(guan)(guan)模式拓撲有用武之地的(de)(de)(de)(de)(de)原因(yin)。開(kai)關(guan)(guan)(guan)模式拓撲的(de)(de)(de)(de)(de)主要優勢在(zai)于效(xiao)(xiao)率的(de)(de)(de)(de)(de)提高。與線性(xing)穩壓器(qi)不同(tong)，電源(yuan)(yuan)開(kai)關(guan)(guan)(guan)（或多個開(kai)關(guan)(guan)(guan)）在(zai)飽和的(de)(de)(de)(de)(de)區域內(nei)運行，其大(da)大(da)降低(di)了總體損耗(hao)(hao)。降壓轉換器(qi)中(zhong)功率損耗(hao)(hao)的(de)(de)(de)(de)(de)主要包括開(kai)關(guan)(guan)(guan)損耗(hao)(hao)（在(zai)電源(yuan)(yuan)開(kai)關(guan)(guan)(guan)中(zhong)）以及濾波(bo)電感中(zhong)的(de)(de)(de)(de)(de) DC 損耗(hao)(hao)。根據設計參數的(de)(de)(de)(de)(de)不同(tong)，在(zai)這(zhe)些應用中(zhong)出(chu)現效(xiao)(xiao)率大(da)大(da)高于 95% 的(de)(de)(de)(de)(de)情況就不足為奇(qi)了。

當人們(men)聽到(dao)(dao)開(kai)(kai)關(guan)模(mo)式這個(ge)術(shu)語時(shi)大(da)多數人都會想到(dao)(dao)大(da)型(xing) IC、大(da) PowerFET 以及超大(da)型(xing)電(dian)感(gan)! 事(shi)實(shi)上，雖然對于(yu)(yu)處理(li)數十安(an)培電(dian)流的應用(yong)而言確實(shi)是這樣，但是對于(yu)(yu)手持設(she)備的新(xin)一代(dai)解決方(fang)案(an)而言情況就不(bu)一樣了。新(xin)一代(dai)單體鋰離子(zi)開(kai)(kai)關(guan)模(mo)式充電(dian)器采(cai)用(yong)了最高級別的芯(xin)片(pian)集成(cheng)(cheng)，高于(yu)(yu) 1MHz 的使(shi)用(yong)頻(pin)率(lv)以最小(xiao)化電(dian)感(gan)尺寸。圖 1 說明了當今市場(chang)上已開(kai)(kai)始銷售的此(ci)類(lei)解決方(fang)案(an)。該硅(gui)芯(xin)片(pian)的尺寸不(bu)到(dao)(dao) 4 mm2，其(qi)集成(cheng)(cheng)了高側和低側 PowerFET。由于(yu)(yu)采(cai)用(yong)了 3MHz 開(kai)(kai)關(guan)頻(pin)率(lv)，該解決方(fang)案(an)要求一個(ge)小(xiao)型(xing) 1uH 電(dian)感(gan)， 其(qi)外形尺寸僅為：2mm x 2.5mm x 1.2mm (WxLxH)。

充(chong)電器的(de)選(xuan)擇

電(dian)池充電(dian)器工具使(shi)得設計人員選(xuan)擇(ze)正確的(de)充電(dian)器的(de)過程(cheng)更輕松(song)。