引言

便(bian)攜式電(dian)子設備設計(ji)(ji)人員可以選擇(ze)(ze)各種各樣的(de)化學技(ji)術、充電(dian)器(qi)拓撲(pu)以及充電(dian)管理解決方案。選擇(ze)(ze)一款(kuan)最為(wei)合適(shi)的(de)解決方案應該(gai)是一項很簡單(dan)的(de)工(gong)作，但是在大(da)多數(shu)情況(kuang)下(xia)這(zhe)一過程(cheng)頗為(wei)復雜。設計(ji)(ji)人員需要在性能(neng)、成本、外形尺寸以及其他關(guan)鍵要求(qiu)方面找(zhao)到一個最佳平衡(heng)點。本文將為(wei)廣大(da)設計(ji)(ji)人員和系統工(gong)程(cheng)師提供一些指導(dao)和幫(bang)助以使(shi)得該(gai)選擇(ze)(ze)工(gong)作變得更為(wei)輕松。

以(yi) 3 “C”開始實(shi)現充電控制

所有(you)使用可充電(dian)電(dian)池(chi)的(de)系(xi)統設(she)計(ji)人(ren)員都需要清楚一(yi)些基(ji)礎設(she)計(ji)技術，以確保滿足下(xia)面三個關(guan)鍵的(de)要求：

1、電(dian)池(chi)(chi)安全(quan)(quan)性: 毋庸置疑，終端(duan)用戶安全(quan)(quan)是所(suo)有(you)(you)系統設計中最優先(xian)考慮的問題(ti)。大多數(shu)鋰(li)離子 (Li-Ion) 電(dian)池(chi)(chi)組和(he)鋰(li)聚合(he)物 (Li-Pol) 電(dian)池(chi)(chi)組都(dou)含有(you)(you)保護電(dian)子電(dian)路。然而，還有(you)(you)一(yi)些(xie)系統設計需(xu)要(yao)考慮的關鍵(jian)因素。其中包括(kuo)但不(bu)局限(xian)于確保在鋰(li)離子電(dian)池(chi)(chi)充(chong)電(dian)最后(hou)階段期間(jian) ?1% 的穩(wen)壓容限(xian)、安全(quan)(quan)處(chu)理深(shen)度放電(dian)電(dian)池(chi)(chi)的預處(chu)理模式、安全(quan)(quan)計時器(qi)以及電(dian)池(chi)(chi)溫(wen)度監控(kong)。

2、電(dian)池(chi)容量(liang)(liang)：所(suo)有的(de)(de)電(dian)池(chi)充(chong)電(dian)解決方案都(dou)(dou)要確保(bao)在每一(yi)次和(he)每一(yi)個(ge)充(chong)電(dian)周期(qi)都(dou)(dou)能(neng)將電(dian)池(chi)容量(liang)(liang)充(chong)至充(chong)滿狀態。過早的(de)(de)終止充(chong)電(dian)會導致(zhi)電(dian)池(chi)運行時(shi)間縮短，這是當今高功耗的(de)(de)便(bian)攜式設備所(suo)不希望的(de)(de)。

3、電(dian)池使(shi)用(yong)壽(shou)命：遵循(xun)建議的充電(dian)算(suan)法是確保終端用(yong)戶實(shi)現每(mei)個電(dian)池組最多(duo)充電(dian)周(zhou)期的重要一(yi)步(bu)。利用(yong)電(dian)池溫度和電(dian)壓限(xian)定每(mei)一(yi)次充電(dian)、預(yu)處理深(shen)度放(fang)電(dian)電(dian)池并避免(mian)過晚(wan)或非正常充電(dian)終止是最大化(hua)電(dian)池使(shi)用(yong)壽(shou)命所必須的一(yi)些步(bu)驟(zou)。

充(chong)電(dian)(dian)特性 電(dian)(dian)池安全性 電(dian)(dian)池容量 電(dian)(dian)池使用壽命

精確的(de)電壓和/或電流調節 ? ?

充電限制

（電壓和(he)溫度） ? ?

溫度(du)監控(kong) ? ? ?

預處理 ? ? ?

充電結(jie)束(shu)終止 ? ? ?

充電計時器 ?

充電狀態報告 ? ?

電(dian)池(chi)插入與(yu)去除探測 ?

最小電池泄漏 ?

短路電流限制 ?

自動再充電 ?

電池化學技術(shu)的(de)選(xuan)擇(ze)
現在(zai)系統(tong)設計人員(yuan)可以在(zai)多種電(dian)池化(hua)學技(ji)術(shu)中(zhong)進(jin)行選(xuan)擇(ze)。設計 人員(yuan)通(tong)常會(hui)根(gen)據下面(mian)的(de)(de)一些標(biao)準進(jin)行電(dian)池化(hua)學技(ji)術(shu)的(de)(de)選(xuan)擇(ze)，其中(zhong)包括：

? 能量密度

? 規格和外形尺寸

? 成本

? 使(shi)用模式和使(shi)用壽(shou)命

近年來(lai)，盡管使用(yong)(yong)鋰(li)離子電池和鋰(li)聚合物電池的(de)趨勢增(zeng)強(qiang)，但(dan)是(shi) Ni 電池化學技術仍然(ran)是(shi)諸多消費(fei)類應(ying)用(yong)(yong)一個不(bu)錯的(de)選(xuan)項(xiang)。

無論選擇(ze)何(he)種(zhong)電池化(hua)學(xue)技(ji)(ji)術，遵循每(mei)(mei)一種(zhong)電池化(hua)學(xue)技(ji)(ji)術的(de)正確充電管理(li)技(ji)(ji)術都(dou)是至關重要的(de)。這些技(ji)(ji)術將(jiang)確保電池在每(mei)(mei)一次(ci)和每(mei)(mei)個充電周期都(dou)能被充至最大容量，而不會降(jiang)低安全性或縮短電池使用壽命。

NiCd / NIMH

在(zai)一個(ge)(ge)充電(dian)(dian)(dian)周期開始之前(qian)，并且盡可能在(zai)開始快速充電(dian)(dian)(dian)之前(qian)對(dui)鎳(nie)鎘(ge) (NiCd) 電(dian)(dian)(dian)池和鎳(nie)氫 (NiMH) 電(dian)(dian)(dian)池必須要進行(xing)檢驗和調節(jie)。如(ru)果電(dian)(dian)(dian)池電(dian)(dian)(dian)壓或(huo)(huo)溫度超出(chu)了允(yun)許的(de)(de)極限是不允(yun)許進行(xing)快速充電(dian)(dian)(dian)的(de)(de)。出(chu)于安全(quan)考慮，對(dui)所有(you)“熱(re)”電(dian)(dian)(dian)池（一般高于 45?C）的(de)(de)充電(dian)(dian)(dian)工作(zuo)都(dou)會(hui)暫時終(zhong)止，直到電(dian)(dian)(dian)池冷(leng)卻到正(zheng)常(chang)工作(zuo)溫度范圍(wei)內才會(hui)再次運轉。要想處理一個(ge)(ge)“冷(leng)”電(dian)(dian)(dian)池（一般低于 10?C）或(huo)(huo)過度放(fang)電(dian)(dian)(dian)的(de)(de)電(dian)(dian)(dian)池（每(mei)節(jie)電(dian)(dian)(dian)池通常(chang)低于 1V），需要施(shi)加一個(ge)(ge)溫和的(de)(de)點滴式電(dian)(dian)(dian)流。

當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)溫度(du)(du)(du)和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓正確時(shi)(shi)快速(su)(su)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)開始(shi)。通常用 1C 或更低的(de)(de)(de)恒定電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流對 NiMH 電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。一些 NiCd 電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)可以用高達 4C 的(de)(de)(de)速(su)(su)率進行充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。采用適當(dang)的(de)(de)(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)終(zhong)止(zhi)(zhi)(zhi)來避免有害(hai)的(de)(de)(de)過充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。就鎳基可充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)而言，快速(su)(su)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)終(zhong)止(zhi)(zhi)(zhi)基于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓或溫度(du)(du)(du)。如圖 1 所示，典(dian)型的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓終(zhong)止(zhi)(zhi)(zhi)方法(fa)是峰(feng)值(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓探測，在(zai)(zai)峰(feng)值(zhi)時(shi)(shi)即每個(ge)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓在(zai)(zai) 0～-4mV 范圍內，快速(su)(su)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)被(bei)終(zhong)止(zhi)(zhi)(zhi)。基于溫度(du)(du)(du)的(de)(de)(de)快速(su)(su)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)終(zhong)止(zhi)(zhi)(zhi)方法(fa)是觀察電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)溫度(du)(du)(du)上升率 ?T/?t 來探測完全(quan)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。典(dian)型的(de)(de)(de) ?T/?t 率為 1?C/每分鐘。

鋰離子/鋰聚合(he)物電池
與 NiCd 電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)和(he)(he) NiMh 電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)相(xiang)類(lei)似，在(zai)快速充電(dian)(dian)(dian)(dian)(dian)之(zhi)前盡(jin)可能檢驗并(bing)調節鋰離(li)子(zi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)。驗證和(he)(he)處(chu)理方法(fa)與上述使用的方法(fa)相(xiang)類(lei)似。 驗證和(he)(he)預處(chu)理之(zhi)后，先用一個(ge) 1C 或更低的電(dian)(dian)(dian)(dian)(dian)流(liu)對鋰離(li)子(zi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)進行充電(dian)(dian)(dian)(dian)(dian)，直(zhi)到電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)達(da)(da)到其充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓(ya)極限為(wei)(wei)止。該充電(dian)(dian)(dian)(dian)(dian)階段通常(chang)會(hui)補充高(gao)達(da)(da) 70% 的電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)容(rong)量(liang)。然后用一個(ge)通常(chang)為(wei)(wei) 4.2V 的恒(heng)定電(dian)(dian)(dian)(dian)(dian)壓(ya)對電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)進行充電(dian)(dian)(dian)(dian)(dian)。為(wei)(wei)將安全性和(he)(he)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)容(rong)量(liang)，必須要將充電(dian)(dian)(dian)(dian)(dian)壓(ya)穩定在(zai)至少 ?1%。在(zai)此充電(dian)(dian)(dian)(dian)(dian)期間，電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)汲(ji)取的充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)逐(zhu)漸下(xia)(xia)降。就 1C 充電(dian)(dian)(dian)(dian)(dian)率而言，一旦電(dian)(dian)(dian)(dian)(dian)流(liu)電(dian)(dian)(dian)(dian)(dian)平下(xia)(xia)降到初始充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)的 10-15% 以下(xia)(xia)充電(dian)(dian)(dian)(dian)(dian)通常(chang)就會(hui)終止.

開關模式(shi)與線性(xing)充電拓撲的對比

傳統上來說，手持設備都(dou)使(shi)用線(xian)性(xing)充(chong)電拓撲。該方法(fa)具有諸(zhu)多優勢：低實施成本(ben)、設計簡捷以及(ji)無高頻開關的(de)(de)無噪聲運行。但(dan)是，線(xian)性(xing)拓撲會(hui)增加系(xi)統功(gong)耗(hao)，尤(you)其是當電池容(rong)量更高引(yin)起的(de)(de)充(chong)電率(lv)增加的(de)(de)時(shi)候(hou)。如果設計人員無法(fa)管理設計的(de)(de)散熱問題，這就(jiu)會(hui)成為一個主(zhu)要(yao)缺點。

當(dang) PC USB 端口作為電(dian)源時，則(ze)會出現其他一(yi)些缺點。當(dang)今在許多便(bian)攜式設計(ji)上都具有 USB 充電(dian)選項，并且都可(ke)(ke)提供高達 500mA 的充電(dian)率(lv)。就線性解決(jue)方(fang)案而言，由(you)于其效率(lv)較低，可(ke)(ke)以(yi)從 PC USB 傳輸(shu)的“電(dian)能”量就被大大降(jiang)低，從而導(dao)致了充電(dian)時間過長。

這就是(shi)開(kai)關(guan)(guan)模式拓(tuo)(tuo)撲有用(yong)武之(zhi)地(di)的(de)原(yuan)因。開(kai)關(guan)(guan)模式拓(tuo)(tuo)撲的(de)主要優(you)勢在(zai)(zai)于(yu)效率的(de)提高(gao)(gao)。與線性穩壓器(qi)不同，電源(yuan)開(kai)關(guan)(guan)（或多個開(kai)關(guan)(guan)）在(zai)(zai)飽和的(de)區域(yu)內運行(xing)，其(qi)大(da)大(da)降(jiang)低了總體(ti)損耗(hao)。降(jiang)壓轉換器(qi)中(zhong)功率損耗(hao)的(de)主要包括(kuo)開(kai)關(guan)(guan)損耗(hao)（在(zai)(zai)電源(yuan)開(kai)關(guan)(guan)中(zhong)）以及濾波電感中(zhong)的(de) DC 損耗(hao)。根據設(she)計參數(shu)的(de)不同，在(zai)(zai)這些(xie)應用(yong)中(zhong)出現效率大(da)大(da)高(gao)(gao)于(yu) 95% 的(de)情況就不足為(wei)奇了。

當人(ren)們聽到(dao)開關模式這(zhe)(zhe)個術語時大(da)(da)多數人(ren)都會想到(dao)大(da)(da)型(xing) IC、大(da)(da) PowerFET 以及超大(da)(da)型(xing)電(dian)(dian)感! 事實上(shang)，雖然對(dui)于處理數十(shi)安培電(dian)(dian)流的應用(yong)而言確實是(shi)這(zhe)(zhe)樣，但是(shi)對(dui)于手持設備(bei)的新(xin)(xin)一代解(jie)(jie)決(jue)方案而言情況(kuang)就不一樣了(le)(le)(le)。新(xin)(xin)一代單體(ti)鋰(li)離子開關模式充電(dian)(dian)器采用(yong)了(le)(le)(le)最(zui)高(gao)級別(bie)的芯(xin)片集(ji)(ji)成，高(gao)于 1MHz 的使用(yong)頻(pin)率以最(zui)小化電(dian)(dian)感尺(chi)寸。圖(tu) 1 說明了(le)(le)(le)當今市場上(shang)已開始銷(xiao)售的此類(lei)解(jie)(jie)決(jue)方案。該硅芯(xin)片的尺(chi)寸不到(dao) 4 mm2，其(qi)集(ji)(ji)成了(le)(le)(le)高(gao)側和低側 PowerFET。由于采用(yong)了(le)(le)(le) 3MHz 開關頻(pin)率，該解(jie)(jie)決(jue)方案要求(qiu)一個小型(xing) 1uH 電(dian)(dian)感， 其(qi)外形(xing)尺(chi)寸僅為(wei)：2mm x 2.5mm x 1.2mm (WxLxH)。

充電器的選擇

電池充電器工具使得(de)設計人(ren)員選擇正確的(de)充電器的(de)過(guo)程更輕松(song)。