引言

便攜(xie)式電(dian)子(zi)設(she)備設(she)計人(ren)員可以(yi)選擇(ze)各種各樣的化學技(ji)術(shu)、充(chong)(chong)電(dian)器拓撲(pu)以(yi)及充(chong)(chong)電(dian)管(guan)理解決(jue)方(fang)案(an)。選擇(ze)一(yi)款最(zui)為合適(shi)的解決(jue)方(fang)案(an)應該(gai)是一(yi)項(xiang)很簡(jian)單(dan)的工作，但(dan)是在大多數情況下這一(yi)過(guo)程頗為復雜(za)。設(she)計人(ren)員需要在性(xing)能、成本(ben)、外形尺寸以(yi)及其他關鍵要求方(fang)面找到一(yi)個最(zui)佳平衡點。本(ben)文將為廣大設(she)計人(ren)員和系統(tong)工程師提供一(yi)些指導和幫助以(yi)使得該(gai)選擇(ze)工作變得更為輕松(song)。

以(yi) 3 “C”開始(shi)實現充電控制

所有使用可充電(dian)電(dian)池(chi)的系統設(she)計(ji)人員都需要清楚(chu)一(yi)些(xie)基礎(chu)設(she)計(ji)技術(shu)，以確保滿足下面(mian)三(san)個關鍵的要求：

1、電(dian)(dian)(dian)池(chi)安全(quan)(quan)性(xing): 毋庸置(zhi)疑，終端用戶安全(quan)(quan)是所有(you)系(xi)統設(she)計(ji)中最優先考(kao)慮的問題。大多數鋰(li)離(li)(li)子(zi) (Li-Ion) 電(dian)(dian)(dian)池(chi)組(zu)和鋰(li)聚合物 (Li-Pol) 電(dian)(dian)(dian)池(chi)組(zu)都含有(you)保(bao)護電(dian)(dian)(dian)子(zi)電(dian)(dian)(dian)路。然而(er)，還(huan)有(you)一些(xie)系(xi)統設(she)計(ji)需要(yao)考(kao)慮的關鍵因素。其中包括但不局限于確保(bao)在鋰(li)離(li)(li)子(zi)電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)最后階段期間 ?1% 的穩壓(ya)容限、安全(quan)(quan)處理深度放電(dian)(dian)(dian)電(dian)(dian)(dian)池(chi)的預處理模式、安全(quan)(quan)計(ji)時器以及電(dian)(dian)(dian)池(chi)溫度監控。

2、電(dian)(dian)池(chi)容(rong)量：所(suo)有(you)的電(dian)(dian)池(chi)充(chong)電(dian)(dian)解決方案都(dou)要確保在每一次和每一個充(chong)電(dian)(dian)周期(qi)都(dou)能將(jiang)電(dian)(dian)池(chi)容(rong)量充(chong)至充(chong)滿狀態。過早(zao)的終止(zhi)充(chong)電(dian)(dian)會導致電(dian)(dian)池(chi)運(yun)行時間縮短，這(zhe)是當(dang)今高(gao)功耗的便攜式設備所(suo)不希望的。

3、電(dian)(dian)池(chi)使用壽命(ming)：遵(zun)循(xun)建議的充(chong)電(dian)(dian)算法是(shi)確保終端(duan)用戶實(shi)現每(mei)個(ge)電(dian)(dian)池(chi)組(zu)最多充(chong)電(dian)(dian)周期(qi)的重要一(yi)(yi)(yi)步。利(li)用電(dian)(dian)池(chi)溫度和電(dian)(dian)壓限定每(mei)一(yi)(yi)(yi)次(ci)充(chong)電(dian)(dian)、預處理(li)深度放電(dian)(dian)電(dian)(dian)池(chi)并避免過晚或(huo)非正常充(chong)電(dian)(dian)終止是(shi)最大(da)化電(dian)(dian)池(chi)使用壽命(ming)所必須的一(yi)(yi)(yi)些步驟。

充電(dian)特(te)性 電(dian)池安全性 電(dian)池容量 電(dian)池使(shi)用(yong)壽(shou)命

精確的(de)電(dian)壓(ya)和/或電(dian)流調節 ? ?

充電限制

（電壓(ya)和溫度） ? ?

溫度監控 ? ? ?

預處理 ? ? ?

充(chong)電(dian)結束終止 ? ? ?

充電計時器 ?

充電狀態報告 ? ?

電池插入(ru)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(xue)技(ji)術的選擇(ze)
現(xian)在系統設計人員可(ke)以(yi)在多(duo)種電池化學(xue)技(ji)術中(zhong)進行選擇。設計 人員通常會根據下面的(de)一些標準進行電池化學(xue)技(ji)術的(de)選擇，其中(zhong)包括：

? 能量密度

? 規格和外形尺寸

? 成本

? 使用模式和使用壽命

近年來，盡管使用鋰離子電(dian)池和(he)鋰聚(ju)合物電(dian)池的(de)趨勢增強，但(dan)是 Ni 電(dian)池化學技術(shu)仍然是諸多(duo)消費類(lei)應用一個(ge)不錯(cuo)的(de)選項。

無(wu)論(lun)選擇何種(zhong)電池化(hua)學技術，遵循每一(yi)種(zhong)電池化(hua)學技術的正確充電管理技術都是至(zhi)關重要的。這些技術將確保電池在(zai)每一(yi)次和每個充電周(zhou)期都能被(bei)充至(zhi)最(zui)大容量，而(er)不會降(jiang)低(di)安全性或(huo)縮短(duan)電池使用壽命。

NiCd / NIMH

在一(yi)(yi)個(ge)充(chong)(chong)電(dian)(dian)(dian)周期(qi)開始(shi)(shi)之前，并(bing)且盡可(ke)能在開始(shi)(shi)快速充(chong)(chong)電(dian)(dian)(dian)之前對鎳鎘 (NiCd) 電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)和鎳氫 (NiMH) 電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)必須要進行檢(jian)驗和調節。如果電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)電(dian)(dian)(dian)壓或(huo)(huo)溫度(du)超出了(le)允許(xu)(xu)的(de)(de)極限是不允許(xu)(xu)進行快速充(chong)(chong)電(dian)(dian)(dian)的(de)(de)。出于安全(quan)考慮，對所有“熱”電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)（一(yi)(yi)般高于 45?C）的(de)(de)充(chong)(chong)電(dian)(dian)(dian)工作都會(hui)暫(zan)時終止，直到(dao)電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)冷卻(que)到(dao)正常工作溫度(du)范圍內(nei)才(cai)會(hui)再(zai)次運轉。要想處理(li)一(yi)(yi)個(ge)“冷”電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)（一(yi)(yi)般低于 10?C）或(huo)(huo)過度(du)放電(dian)(dian)(dian)的(de)(de)電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)（每節電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)通常低于 1V），需要施加(jia)一(yi)(yi)個(ge)溫和的(de)(de)點(dian)滴(di)式電(dian)(dian)(dian)流。

當電(dian)(dian)(dian)(dian)池(chi)溫(wen)度(du)和電(dian)(dian)(dian)(dian)壓正確(que)時快(kuai)速充(chong)電(dian)(dian)(dian)(dian)開始。通常(chang)用 1C 或更(geng)低的(de)(de)(de)恒定(ding)電(dian)(dian)(dian)(dian)流對 NiMH 電(dian)(dian)(dian)(dian)池(chi)進行(xing)充(chong)電(dian)(dian)(dian)(dian)。一些(xie) NiCd 電(dian)(dian)(dian)(dian)池(chi)可以用高達 4C 的(de)(de)(de)速率進行(xing)充(chong)電(dian)(dian)(dian)(dian)。采用適(shi)當的(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)終(zhong)止來避免(mian)有(you)害的(de)(de)(de)過充(chong)電(dian)(dian)(dian)(dian)。就鎳(nie)基可充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)而言，快(kuai)速充(chong)電(dian)(dian)(dian)(dian)終(zhong)止基于電(dian)(dian)(dian)(dian)壓或溫(wen)度(du)。如圖 1 所示，典型(xing)的(de)(de)(de)電(dian)(dian)(dian)(dian)壓終(zhong)止方法是(shi)峰值(zhi)電(dian)(dian)(dian)(dian)壓探(tan)測，在峰值(zhi)時即(ji)每(mei)個電(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)電(dian)(dian)(dian)(dian)壓在 0～-4mV 范圍(wei)內(nei)，快(kuai)速充(chong)電(dian)(dian)(dian)(dian)被終(zhong)止。基于溫(wen)度(du)的(de)(de)(de)快(kuai)速充(chong)電(dian)(dian)(dian)(dian)終(zhong)止方法是(shi)觀察電(dian)(dian)(dian)(dian)池(chi)溫(wen)度(du)上(shang)升(sheng)率 ?T/?t 來探(tan)測完全充(chong)電(dian)(dian)(dian)(dian)。典型(xing)的(de)(de)(de) ?T/?t 率為 1?C/每(mei)分鐘(zhong)。

鋰(li)離(li)子/鋰(li)聚合(he)物電池
與 NiCd 電(dian)(dian)(dian)(dian)池(chi)(chi)和(he) NiMh 電(dian)(dian)(dian)(dian)池(chi)(chi)相(xiang)類似(si)，在(zai)快(kuai)速充(chong)電(dian)(dian)(dian)(dian)之前盡可能(neng)檢驗(yan)并調節鋰離(li)子電(dian)(dian)(dian)(dian)池(chi)(chi)。驗(yan)證和(he)處理方法(fa)與上述(shu)使用的(de)方法(fa)相(xiang)類似(si)。 驗(yan)證和(he)預處理之后，先用一個 1C 或(huo)更低的(de)電(dian)(dian)(dian)(dian)流對鋰離(li)子電(dian)(dian)(dian)(dian)池(chi)(chi)進(jin)行充(chong)電(dian)(dian)(dian)(dian)，直到(dao)(dao)電(dian)(dian)(dian)(dian)池(chi)(chi)達到(dao)(dao)其充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)極限為止。該充(chong)電(dian)(dian)(dian)(dian)階段通常(chang)會補充(chong)高達 70% 的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)容量。然后用一個通常(chang)為 4.2V 的(de)恒定電(dian)(dian)(dian)(dian)壓(ya)對電(dian)(dian)(dian)(dian)池(chi)(chi)進(jin)行充(chong)電(dian)(dian)(dian)(dian)。為將安(an)全(quan)性和(he)電(dian)(dian)(dian)(dian)池(chi)(chi)容量，必須要將充(chong)電(dian)(dian)(dian)(dian)壓(ya)穩定在(zai)至少 ?1%。在(zai)此充(chong)電(dian)(dian)(dian)(dian)期間(jian)，電(dian)(dian)(dian)(dian)池(chi)(chi)汲取的(de)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流逐(zhu)漸下降(jiang)。就(jiu)(jiu) 1C 充(chong)電(dian)(dian)(dian)(dian)率(lv)而言，一旦電(dian)(dian)(dian)(dian)流電(dian)(dian)(dian)(dian)平(ping)下降(jiang)到(dao)(dao)初始(shi)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流的(de) 10-15% 以(yi)下充(chong)電(dian)(dian)(dian)(dian)通常(chang)就(jiu)(jiu)會終止.

開關(guan)模式與線性充電拓撲的對(dui)比

傳統上來說，手持設備(bei)都使用線(xian)(xian)性(xing)充(chong)電(dian)拓(tuo)撲。該方(fang)法具有諸多(duo)優勢：低實施成(cheng)(cheng)本、設計(ji)(ji)簡捷以及無高(gao)頻開關的(de)無噪聲運行。但是，線(xian)(xian)性(xing)拓(tuo)撲會增(zeng)加系(xi)統功(gong)耗(hao)，尤其是當電(dian)池容量(liang)更(geng)高(gao)引起的(de)充(chong)電(dian)率增(zeng)加的(de)時(shi)候。如果設計(ji)(ji)人員無法管(guan)理設計(ji)(ji)的(de)散熱問(wen)題，這就會成(cheng)(cheng)為一(yi)個主(zhu)要缺(que)點。

當 PC USB 端口作為電(dian)源(yuan)時，則會出現其他一些缺點。當今在許(xu)多便攜式設計上都(dou)具有(you) USB 充(chong)電(dian)選項，并且都(dou)可提供高達 500mA 的(de)充(chong)電(dian)率(lv)。就線性解決(jue)方案(an)而言(yan)，由于其效率(lv)較低，可以(yi)從(cong) PC USB 傳輸的(de)“電(dian)能”量就被大大降低，從(cong)而導(dao)致了充(chong)電(dian)時間(jian)過長。

這就是開關(guan)(guan)模(mo)(mo)式拓撲(pu)有用武之地的原(yuan)因。開關(guan)(guan)模(mo)(mo)式拓撲(pu)的主要(yao)優(you)勢在于效(xiao)率的提(ti)高。與線性穩壓器(qi)不同，電(dian)源開關(guan)(guan)（或多個開關(guan)(guan)）在飽(bao)和的區域內運行，其大(da)大(da)降低了總體損耗。降壓轉換器(qi)中功率損耗的主要(yao)包(bao)括開關(guan)(guan)損耗（在電(dian)源開關(guan)(guan)中）以及濾波(bo)電(dian)感中的 DC 損耗。根據設計(ji)參數的不同，在這些(xie)應用中出(chu)現(xian)效(xiao)率大(da)大(da)高于 95% 的情(qing)況就不足為奇了。

當人(ren)(ren)們聽到開(kai)關(guan)模式這個(ge)術語時大(da)多數(shu)人(ren)(ren)都會想到大(da)型 IC、大(da) PowerFET 以及(ji)超大(da)型電(dian)感(gan)! 事(shi)實上(shang)，雖(sui)然對(dui)于(yu)(yu)處理數(shu)十安(an)培電(dian)流的應用而言確實是這樣，但(dan)是對(dui)于(yu)(yu)手持(chi)設備的新一(yi)代解(jie)(jie)決(jue)方(fang)案(an)而言情況就(jiu)不一(yi)樣了(le)。新一(yi)代單體鋰離(li)子開(kai)關(guan)模式充電(dian)器采用了(le)最(zui)高級別的芯(xin)(xin)片集(ji)成，高于(yu)(yu) 1MHz 的使用頻率(lv)以最(zui)小化電(dian)感(gan)尺(chi)寸。圖 1 說(shuo)明了(le)當今市(shi)場上(shang)已開(kai)始銷售(shou)的此類解(jie)(jie)決(jue)方(fang)案(an)。該硅芯(xin)(xin)片的尺(chi)寸不到 4 mm2，其(qi)集(ji)成了(le)高側和低側 PowerFET。由于(yu)(yu)采用了(le) 3MHz 開(kai)關(guan)頻率(lv)，該解(jie)(jie)決(jue)方(fang)案(an)要求一(yi)個(ge)小型 1uH 電(dian)感(gan)， 其(qi)外形(xing)尺(chi)寸僅(jin)為：2mm x 2.5mm x 1.2mm (WxLxH)。

充電器的選擇

電(dian)池充電(dian)器工具使得(de)設計人員選(xuan)擇正(zheng)確的充電(dian)器的過程更輕松。