鋰離子電池具有較高的能量重量和能量體積比，無記憶效應，可重復充電次數多，使用壽命長，價格也越來越低。一個良好的充電器可使電池具有較長的壽命。利用C8051F310單片機設計的智能充電器，具有較高的測量精度，可很好的控制充電電流的大小，適時的調整，并可根據充電的狀態判斷充電的時間，及時終止充電，以避免電池的過充。
本文討論使用(yong)C8051F310器件(jian)設計(ji)(ji)鋰離子電(dian)(dian)(dian)(dian)(dian)池(chi)智能充電(dian)(dian)(dian)(dian)(dian)器的(de)。利用(yong)PWM脈寬調(diao)制產生可用(yong)軟件(jian)控(kong)制的(de)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)源，以適應不同階(jie)段的(de)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)要求。溫(wen)度(du)傳感(gan)器對電(dian)(dian)(dian)(dian)(dian)池(chi)溫(wen)度(du)進行監測，并(bing)通過AD轉(zhuan)換和相關計(ji)(ji)算檢測電(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓和電(dian)(dian)(dian)(dian)(dian)流(liu)，以判斷電(dian)(dian)(dian)(dian)(dian)池(chi)到達哪個(ge)階(jie)段。使電(dian)(dian)(dian)(dian)(dian)池(chi)具有(you)更(geng)長(chang)的(de)使用(yong)壽(shou)命，更(geng)有(you)效的(de)充電(dian)(dian)(dian)(dian)(dian)方法(fa)。

　　設計過程

　　1 充電原理

　　電(dian)(dian)池的(de)特(te)性唯一(yi)地決(jue)定(ding)其安全性能和(he)充電(dian)(dian)的(de)效率(lv)。電(dian)(dian)池的(de)最佳充電(dian)(dian)方(fang)(fang)法是由電(dian)(dian)池的(de)化(hua)學成分決(jue)定(ding)的(de)（鋰離子、鎳氫(qing)、鎳鎘(ge)還是SLA電(dian)(dian)池等）。盡管如(ru)此，大多(duo)數(shu)充電(dian)(dian)方(fang)(fang)案(an)都(dou)包含下面的(de)三個階段：

低電流調節階段
恒流階段
恒壓(ya)階(jie)段/充電終(zhong)止

　　所有電(dian)(dian)(dian)池(chi)(chi)(chi)都(dou)是通過向自(zi)身傳(chuan)輸電(dian)(dian)(dian)能的(de)方(fang)法進行(xing)充(chong)(chong)(chong)電(dian)(dian)(dian)的(de)，一(yi)(yi)(yi)節(jie)電(dian)(dian)(dian)池(chi)(chi)(chi)的(de)最大充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)取決于(yu)電(dian)(dian)(dian)池(chi)(chi)(chi)的(de)額定容量(liang)（C）例如，一(yi)(yi)(yi)節(jie)容量(liang)為(wei)1000mAh的(de)電(dian)(dian)(dian)池(chi)(chi)(chi)在充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)為(wei)1000mA時(shi)(shi)，可以充(chong)(chong)(chong)電(dian)(dian)(dian)1C(電(dian)(dian)(dian)池(chi)(chi)(chi)容量(liang)的(de)1倍)也可以用(yong)1/50C(20mA)或更低(di)的(de)電(dian)(dian)(dian)流(liu)給(gei)電(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)。盡管如此，這只是一(yi)(yi)(yi)個(ge)普通的(de)低(di)電(dian)(dian)(dian)流(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)方(fang)式(shi)，不適用(yong)于(yu)要求短(duan)充(chong)(chong)(chong)電(dian)(dian)(dian)時(shi)(shi)間的(de)快速(su)充(chong)(chong)(chong)電(dian)(dian)(dian)方(fang)案。

　　現在使用的大多數充電器在給電池充電時都是既使用低電流充電方式又使用額定充電電流的方法，即容積充電，低充電電流通常使用在充電的初始階段。在這一階段，需要將會導致充電過程終止的芯片初期的自熱效應減小到最低程度，容積充電通常用在充電的中級階段，電池的大部分能量都是在這一階段存儲的。在電池充電的最后階段，通常充電時間的絕大部分都是消耗在這一階段，可以通過監測電流、電壓或兩者的值來決定何時結束充電。同樣，結束方案依賴于電池的化學特性，例如：大多數鋰離子電池充電器都是將電(dian)(dian)(dian)池電(dian)(dian)(dian)壓保持在恒定值，同時檢測最(zui)低(di)電(dian)(dian)(dian)流。鎳鎘、NiCd電(dian)(dian)(dian)池用(yong)電(dian)(dian)(dian)壓或溫度的(de)變化率(lv)來決定充電(dian)(dian)(dian)的(de)結束時間。

　　充(chong)電(dian)(dian)(dian)時(shi)部分電(dian)(dian)(dian)能(neng)被轉(zhuan)換(huan)成熱(re)能(neng)，直至電(dian)(dian)(dian)池(chi)充(chong)滿(man)。而充(chong)滿(man)后(hou)，所(suo)有的(de)電(dian)(dian)(dian)能(neng)將全部被轉(zhuan)換(huan)成熱(re)能(neng)。如果(guo)此(ci)時(shi)不(bu)終止(zhi)充(chong)電(dian)(dian)(dian)，電(dian)(dian)(dian)池(chi)就會被損壞或燒毀(hui)。快速充(chong)電(dian)(dian)(dian)器電(dian)(dian)(dian)池(chi)（完(wan)全充(chong)滿(man)的(de)時(shi)間(jian)小于兩小時(shi)的(de)充(chong)電(dian)(dian)(dian)器）則可(ke)以(yi)解(jie)決這個問題，因為(wei)這些(xie)充(chong)電(dian)(dian)(dian)器是使用高充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流來縮短(duan)充(chong)電(dian)(dian)(dian)時(shi)間(jian)的(de)。因此(ci)，對于鋰離子電(dian)(dian)(dian)池(chi)來說,監測它的(de)溫(wen)度是至關重要的(de)，因為(wei)電(dian)(dian)(dian)池(chi)在(zai)過充(chong)電(dian)(dian)(dian)時(shi)會發生爆裂，在(zai)所(suo)有的(de)充(chong)電(dian)(dian)(dian)階段都應該(gai)隨時(shi)監測溫(wen)度的(de)變化，并且在(zai)溫(wen)度超過最(zui)大設定(ding)值(zhi)時(shi)立即停止(zhi)充(chong)電(dian)(dian)(dian)。

　　2 總體設計

　　充(chong)電(dian)(dian)電(dian)(dian)路由三(san)部(bu)(bu)分(fen)：控制(zhi)部(bu)(bu)分(fen)，檢測(ce)部(bu)(bu)分(fen)及(ji)充(chong)電(dian)(dian)部(bu)(bu)分(fen)組成(cheng)。如圖1所(suo)示(shi)，采用F310單(dan)片機進行充(chong)電(dian)(dian)控制(zhi)，單(dan)片機本(ben)身(shen)具有脈寬調制(zhi)PWM型開關穩壓(ya)電(dian)(dian)源所(suo)需的全部(bu)(bu)功能，具有10位A/D轉換器。利用單(dan)片機A/D端(duan)口，構成(cheng)電(dian)(dian)池電(dian)(dian)壓(ya)，電(dian)(dian)流，溫(wen)度檢測(ce)電(dian)(dian)路。

圖1 鋰(li)離子電池充(chong)電模塊圖

　　單片(pian)機通(tong)過電(dian)壓反(fan)饋和電(dian)流(liu)反(fan)饋信(xin)號，直接利用PWM輸出將數字(zi)電(dian)壓信(xin)號并轉化成模擬(ni)電(dian)壓信(xin)號，能夠保(bao)證控制精度。

　　3 控制部分電路設(she)計

　　C8051F310單片(pian)機

　　①模擬外設

　　a.10位ADC：轉(zhuan)換(huan)速度可(ke)達200ks/s,可(ke)多達21或17個外部單(dan)端(duan)或差分輸入(ru)，VREF可(ke)在外部引腳或VDD中選擇(ze)，內置(zhi)溫度傳感器（±3℃），外部轉(zhuan)換(huan)啟動輸入(ru)；

　　b.兩(liang)個模擬比較器：可(ke)編程回差電壓和響應時間，可(ke)配置(zhi)為中斷或復位(wei)源，小電流(liu)（〈0.5μA）。

　　②供電電壓

　　a.典型工(gong)作電流：5mA、25MHz；

　　b.典型(xing)停機電(dian)流：0.1μA；

　　c.溫度范圍：-40～+85℃。

　　③高速8051微(wei)控制器內(nei)核(he)

　　a.流水線(xian)指(zhi)令結構：70%的指(zhi)令的執行時間(jian)為一個或兩個系統時鐘周期；

　　b.速度可(ke)達(da)25MI/s（時鐘頻(pin)率(lv)為25MHz時）；

　　c.擴展的中(zhong)斷(duan)系統。

　　④數字外設

　　a.29/25個端口I/O：所有的口線均(jun)耐5V電(dian)壓；

　　b.4個通用16位計數器(qi)/定時器(qi)；

　　c.16位可編程計(ji)數器/定時(shi)器陣(zhen)列(lie)（PCA），有5個捕捉/比較模塊；

　　d.使用PCA或(huo)定時器和(he)外部時鐘源(yuan)的(de)實時時鐘方式。

　　控制(zhi)電(dian)路中如圖2所示，P0.3口(kou)提供充電(dian)電(dian)源，P0.6口(kou)檢測充電(dian)電(dian)壓的(de)大(da)小(xiao)，P0.5口(kou)檢測充電(dian)電(dian)流的(de)大(da)小(xiao)，P0.4口(kou)檢測電(dian)池(chi)的(de)溫度。

圖2 控制電路接(jie)線圖

　　充電(dian)電(dian)流由(you)單片機(ji)脈寬調(diao)制(zhi)PWM產生，充電(dian)電(dian)流由(you)AD轉換再經過計算得(de)出。

4 充電部(bu)分及(ji)檢測部(bu)分電路設計

　　圖3為充電電路與檢測電路圖。

圖(tu)3 充電(dian)電(dian)路與檢測電(dian)路圖(tu)

　　①充電過程曲線

　　如圖4所(suo)示，充電(dian)(dian)過程由(you)預充狀(zhuang)(zhuang)態，恒(heng)流充電(dian)(dian)狀(zhuang)(zhuang)態和恒(heng)壓(ya)充電(dian)(dian)狀(zhuang)(zhuang)態組成(cheng)。

圖4 鋰(li)電池充電曲線

　　②快速轉換器

　　實現漸弱終止充電(dian)器(qi)的(de)最經濟的(de)方法(fa)就是用一個快速轉換器(qi)。快速轉換器(qi)是用一個電(dian)感(gan)和/或一個變壓器(qi)（需要隔離(li)的(de)時(shi)候用變壓器(qi)）作為(wei)能(neng)(neng)量存儲單元以離(li)散的(de)能(neng)(neng)量包的(de)形(xing)式將能(neng)(neng)量從輸(shu)入(ru)傳輸(shu)至輸(shu)出(chu)的(de)開關調(diao)(diao)節器(qi)反饋電(dian)路，通過晶體管來調(diao)(diao)節能(neng)(neng)量的(de)傳輸(shu)，同時(shi)也(ye)作為(wei)過濾開關，以確保電(dian)壓或電(dian)流在(zai)負(fu)載時(shi)保持恒定。

　　快速調節器的操作是通(tong)過控制(zhi)一個(ge)晶(jing)體(ti)管開關的占(zhan)空(kong)比來實(shi)現的。占(zhan)空(kong)比會自動增加以使電池流(liu)入更(geng)多的電流(liu)。當VBATT

a 開關閉合

b 開關打開
圖5 快速轉換器操作

　　③電感的確定

　　電(dian)(dian)感(gan)對(dui)交(jiao)(jiao)流(liu)(liu)電(dian)(dian)是(shi)有(you)(you)阻(zu)礙作用的(de)(de)。在交(jiao)(jiao)流(liu)(liu)電(dian)(dian)頻(pin)率一定的(de)(de)情況下，電(dian)(dian)感(gan)量(liang)越(yue)大，對(dui)交(jiao)(jiao)流(liu)(liu)電(dian)(dian)的(de)(de)阻(zu)礙能(neng)力(li)(li)越(yue)強，電(dian)(dian)感(gan)量(liang)越(yue)小，其阻(zu)礙能(neng)力(li)(li)越(yue)小。另外(wai)，在電(dian)(dian)感(gan)量(liang)一定的(de)(de)情況下，交(jiao)(jiao)流(liu)(liu)電(dian)(dian)的(de)(de)頻(pin)率越(yue)高，電(dian)(dian)感(gan)對(dui)交(jiao)(jiao)流(liu)(liu)電(dian)(dian)的(de)(de)阻(zu)礙能(neng)力(li)(li)越(yue)大，頻(pin)率越(yue)低，電(dian)(dian)感(gan)對(dui)交(jiao)(jiao)流(liu)(liu)電(dian)(dian)的(de)(de)阻(zu)礙能(neng)力(li)(li)越(yue)小。也就(jiu)是(shi)說，電(dian)(dian)感(gan)有(you)(you)阻(zu)止交(jiao)(jiao)流(liu)(liu)電(dian)(dian)通過的(de)(de)特性。

　　其工作(zuo)原(yuan)理是(shi)(shi)這樣的(de)(de)(de)(de)(de)：當(dang)負載(zai)(zai)(zai)兩端(duan)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓要(yao)降(jiang)(jiang)低(di)時，通(tong)過MOSFET場效(xiao)應管的(de)(de)(de)(de)(de)開(kai)關(guan)作(zuo)用(yong)，外部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)對電(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)進(jin)行充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)并達到所(suo)需的(de)(de)(de)(de)(de)額(e)定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)壓。當(dang)負載(zai)(zai)(zai)兩端(duan)地電(dian)(dian)(dian)(dian)(dian)(dian)壓升高時，通(tong)過MOSFET場效(xiao)應管的(de)(de)(de)(de)(de)開(kai)關(guan)作(zuo)用(yong)，外部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)供電(dian)(dian)(dian)(dian)(dian)(dian)斷開(kai)，電(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)釋放出剛才充(chong)入的(de)(de)(de)(de)(de)能(neng)量(liang)，這時電(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)就(jiu)變成(cheng)了(le)(le)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)繼續對負載(zai)(zai)(zai)供電(dian)(dian)(dian)(dian)(dian)(dian)。隨著電(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)上存儲的(de)(de)(de)(de)(de)能(neng)量(liang)地消耗(hao)。負載(zai)(zai)(zai)兩端(duan)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓開(kai)始逐漸降(jiang)(jiang)低(di)，外部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)通(tong)過MOSFET場效(xiao)應管的(de)(de)(de)(de)(de)開(kai)關(guan)作(zuo)用(yong)又要(yao)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。依次類(lei)推(tui)在(zai)不斷的(de)(de)(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)和放電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)(de)過程中形成(cheng)了(le)(le)一種穩定(ding)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓，永遠使(shi)負載(zai)(zai)(zai)兩端(duan)地電(dian)(dian)(dian)(dian)(dian)(dian)壓不會升高也不會降(jiang)(jiang)低(di)，這就(jiu)是(shi)(shi)開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)(de)(de)最大(da)優勢。

　　要確定(ding)快(kuai)速轉換(huan)器(qi)中電感的(de)大小首先應假(jia)定(ding)晶(jing)體(ti)管的(de)占(zhan)空比為(wei)50%，因為(wei)此時的(de)轉換(huan)器(qi)操作操作效(xiao)率最高。占(zhan)空比由方程式1給(gei)出：

　　（其中T是PWM的周期(qi)在程序示例中T=10.5s）

　　占空比=ton/T（1）

　　至此就可以選擇一個PWM的(de)轉(zhuan)換頻率（如方程式2所示）PWM的(de)轉(zhuan)換頻率越大，則電(dian)感的(de)值越小，也越節(jie)約成本。

　　我的(de)(de)示(shi)例(li)代碼配置F310的(de)(de)8位硬(ying)件PWM是(shi)使用(yong)內(nei)部24.5MHz主時鐘的(de)(de)256分頻來(lai)產生一個95.7kHz的(de)(de)轉(zhuan)換速(su)率。

　　L=（Vi-Vsat-Voton）/2Iomax（2）

　　現在我(wo)們可以計算電(dian)感(gan)的(de)(de)大小了(le)，假定充電(dian)電(dian)壓Vi的(de)(de)值(zhi)(zhi)為(wei)(wei)15V，飽和(he)電(dian)壓Vsat的(de)(de)值(zhi)(zhi)為(wei)(wei)0.5V，需要獲(huo)得的(de)(de)輸(shu)出(chu)電(dian)壓值(zhi)(zhi)為(wei)(wei)4.2V,并(bing)且最大輸(shu)出(chu)電(dian)流IＯMAX為(wei)(wei)1500mA，那么，電(dian)感(gan)的(de)(de)值(zhi)(zhi)至(zhi)少應選為(wei)(wei)18H。

　　需要注意的(de)(de)是：在本電路中的(de)(de)電容(rong)僅(jin)僅(jin)是一個紋波衰減(jian)(jian)器，因為紋波與(yu)電容(rong)的(de)(de)大(da)小成反比(bi)例關系，所以(yi)電容(rong)的(de)(de)值越(yue)(yue)大(da)，衰減(jian)(jian)效果越(yue)(yue)好。