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(shi)用(yong)(yong)C8051F310器件設計鋰離(li)子電(dian)(dian)(dian)池(chi)智(zhi)能充(chong)(chong)(chong)電(dian)(dian)(dian)器的。利用(yong)(yong)PWM脈寬調制產生可(ke)用(yong)(yong)軟件控制的充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)源，以適(shi)應不同階段的充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)的要求。溫度傳(chuan)感(gan)器對電(dian)(dian)(dian)池(chi)溫度進行監測，并通(tong)過AD轉(zhuan)換和(he)相關計算檢測電(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓和(he)電(dian)(dian)(dian)流(liu)，以判斷電(dian)(dian)(dian)池(chi)到(dao)達(da)哪個階段。使(shi)電(dian)(dian)(dian)池(chi)具(ju)有(you)更長的使(shi)用(yong)(yong)壽命，更有(you)效的充(chong)(chong)(chong)電(dian)(dian)(dian)方法(fa)。

　　設計過程

　　1 充電原理

　　電(dian)(dian)池(chi)的(de)(de)特(te)性(xing)(xing)唯一地決定(ding)其安(an)全(quan)性(xing)(xing)能(neng)和(he)充電(dian)(dian)的(de)(de)效率(lv)。電(dian)(dian)池(chi)的(de)(de)最佳(jia)充電(dian)(dian)方法是(shi)由電(dian)(dian)池(chi)的(de)(de)化學成分決定(ding)的(de)(de)（鋰離子(zi)、鎳(nie)氫(qing)、鎳(nie)鎘(ge)還(huan)是(shi)SLA電(dian)(dian)池(chi)等）。盡管如(ru)此，大(da)多(duo)數(shu)充電(dian)(dian)方案都包含下面的(de)(de)三個階段：

低電流調節階段
恒流階段
恒(heng)壓階段/充電終止

　　所有電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)都是通過向自(zi)身(shen)傳輸電(dian)(dian)(dian)(dian)(dian)(dian)能的(de)(de)(de)(de)(de)方法進行充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)(de)，一(yi)節電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)(de)最(zui)大充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)取決于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)(de)額定容(rong)量（C）例如，一(yi)節容(rong)量為(wei)1000mAh的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)在充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)為(wei)1000mA時(shi)，可以(yi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)1C(電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)容(rong)量的(de)(de)(de)(de)(de)1倍)也可以(yi)用1/50C(20mA)或更低的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)給電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。盡管如此，這只是一(yi)個普通的(de)(de)(de)(de)(de)低電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)方式，不適(shi)用于(yu)要(yao)求短(duan)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)間的(de)(de)(de)(de)(de)快(kuai)速充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)方案。

　　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)池電(dian)壓保持在恒定(ding)值(zhi)，同(tong)時(shi)檢測(ce)最低電(dian)流。鎳(nie)鎘、NiCd電(dian)池用電(dian)壓或溫度的變化率來決定(ding)充電(dian)的結束時(shi)間。

　　充(chong)(chong)(chong)電(dian)時(shi)(shi)部分電(dian)能被(bei)轉換(huan)成(cheng)熱(re)能，直至電(dian)池(chi)充(chong)(chong)(chong)滿(man)(man)。而(er)充(chong)(chong)(chong)滿(man)(man)后，所有的(de)(de)電(dian)能將(jiang)全(quan)部被(bei)轉換(huan)成(cheng)熱(re)能。如果此時(shi)(shi)不終(zhong)止充(chong)(chong)(chong)電(dian)，電(dian)池(chi)就會被(bei)損壞或燒毀(hui)。快(kuai)速充(chong)(chong)(chong)電(dian)器(qi)電(dian)池(chi)（完全(quan)充(chong)(chong)(chong)滿(man)(man)的(de)(de)時(shi)(shi)間(jian)小于兩小時(shi)(shi)的(de)(de)充(chong)(chong)(chong)電(dian)器(qi)）則可以解決這個問題，因(yin)為這些(xie)充(chong)(chong)(chong)電(dian)器(qi)是使用高充(chong)(chong)(chong)電(dian)電(dian)流來縮短充(chong)(chong)(chong)電(dian)時(shi)(shi)間(jian)的(de)(de)。因(yin)此，對于鋰離子電(dian)池(chi)來說,監測它的(de)(de)溫(wen)度是至關重(zhong)要的(de)(de)，因(yin)為電(dian)池(chi)在(zai)過(guo)充(chong)(chong)(chong)電(dian)時(shi)(shi)會發生爆裂(lie)，在(zai)所有的(de)(de)充(chong)(chong)(chong)電(dian)階段都應該隨(sui)時(shi)(shi)監測溫(wen)度的(de)(de)變化，并(bing)且在(zai)溫(wen)度超過(guo)最大設定值時(shi)(shi)立即停(ting)止充(chong)(chong)(chong)電(dian)。

　　2 總體設計

　　充電(dian)(dian)電(dian)(dian)路由三部分：控制部分，檢測部分及充電(dian)(dian)部分組成。如圖(tu)1所示(shi)，采用F310單片(pian)(pian)機(ji)(ji)進行充電(dian)(dian)控制，單片(pian)(pian)機(ji)(ji)本身(shen)具(ju)有脈寬(kuan)調制PWM型開關穩壓電(dian)(dian)源所需的全(quan)部功能，具(ju)有10位(wei)A/D轉(zhuan)換(huan)器(qi)。利用單片(pian)(pian)機(ji)(ji)A/D端口，構成電(dian)(dian)池電(dian)(dian)壓，電(dian)(dian)流(liu)，溫度檢測電(dian)(dian)路。

圖(tu)1 鋰(li)離子電池(chi)充電模塊圖(tu)

　　單片機通(tong)過電壓(ya)反饋和電流反饋信(xin)號，直接利用PWM輸出將(jiang)數字(zi)電壓(ya)信(xin)號并轉化成(cheng)模(mo)擬電壓(ya)信(xin)號，能(neng)夠(gou)保證控(kong)制精度(du)。

　　3 控制(zhi)部分電路設計

　　C8051F310單片(pian)機

　　①模擬外設

　　a.10位ADC：轉換速(su)度可(ke)達200ks/s,可(ke)多達21或(huo)17個外(wai)(wai)部(bu)單端(duan)或(huo)差分輸入，VREF可(ke)在外(wai)(wai)部(bu)引腳(jiao)或(huo)VDD中(zhong)選擇，內置溫(wen)度傳感器（±3℃），外(wai)(wai)部(bu)轉換啟動輸入；

　　b.兩個模擬比(bi)較器：可(ke)編程回差電(dian)壓和響應時間，可(ke)配置為中斷或復位源，小電(dian)流（〈0.5μA）。

　　②供電電壓

　　a.典型工作電流：5mA、25MHz；

　　b.典型停機電流：0.1μA；

　　c.溫度范圍：-40～+85℃。

　　③高速8051微控制器(qi)內核

　　a.流水線指令(ling)結構：70%的指令(ling)的執行時間為一個或兩(liang)個系統時鐘周期(qi)；

　　b.速度(du)可達(da)25MI/s（時鐘頻率(lv)為25MHz時）；

　　c.擴展的中斷(duan)系(xi)統。

　　④數字外設

　　a.29/25個(ge)端口(kou)I/O：所有(you)的(de)口(kou)線(xian)均(jun)耐5V電壓；

　　b.4個通用(yong)16位(wei)計數(shu)器/定時器；

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

　　d.使用PCA或定時(shi)器和(he)外部時(shi)鐘源的實時(shi)時(shi)鐘方式。

　　控制(zhi)電(dian)(dian)路中如圖2所示(shi)，P0.3口(kou)(kou)提(ti)供充(chong)電(dian)(dian)電(dian)(dian)源，P0.6口(kou)(kou)檢(jian)測(ce)(ce)充(chong)電(dian)(dian)電(dian)(dian)壓的大小，P0.5口(kou)(kou)檢(jian)測(ce)(ce)充(chong)電(dian)(dian)電(dian)(dian)流的大小，P0.4口(kou)(kou)檢(jian)測(ce)(ce)電(dian)(dian)池的溫度。

圖(tu)(tu)2 控制電路接線(xian)圖(tu)(tu)

　　充(chong)電(dian)電(dian)流由(you)單(dan)片機脈寬(kuan)調制(zhi)PWM產生，充(chong)電(dian)電(dian)流由(you)AD轉(zhuan)換再(zai)經過計算得(de)出。

4 充電部(bu)分(fen)及檢測部(bu)分(fen)電路設(she)計

　　圖3為充電(dian)電(dian)路(lu)與檢測電(dian)路(lu)圖。

圖3 充電(dian)(dian)(dian)電(dian)(dian)(dian)路與(yu)檢(jian)測電(dian)(dian)(dian)路圖

　　①充電過程曲線

　　如圖4所示，充(chong)電過程由(you)預充(chong)狀(zhuang)(zhuang)態(tai)，恒流充(chong)電狀(zhuang)(zhuang)態(tai)和恒壓充(chong)電狀(zhuang)(zhuang)態(tai)組(zu)成。

圖4 鋰(li)電(dian)池充(chong)電(dian)曲線

　　②快速轉換器

　　實現漸弱終止充電(dian)(dian)器(qi)(qi)的(de)(de)最經濟的(de)(de)方法就(jiu)是(shi)用(yong)(yong)一個(ge)快速(su)轉換器(qi)(qi)。快速(su)轉換器(qi)(qi)是(shi)用(yong)(yong)一個(ge)電(dian)(dian)感(gan)和/或一個(ge)變壓器(qi)(qi)（需要隔離的(de)(de)時候(hou)用(yong)(yong)變壓器(qi)(qi)）作為(wei)能量存儲(chu)單元以(yi)離散(san)的(de)(de)能量包的(de)(de)形式將能量從輸(shu)入(ru)傳輸(shu)至輸(shu)出的(de)(de)開(kai)關調節器(qi)(qi)反饋電(dian)(dian)路，通(tong)過晶(jing)體(ti)管來(lai)調節能量的(de)(de)傳輸(shu)，同時也作為(wei)過濾開(kai)關，以(yi)確保(bao)電(dian)(dian)壓或電(dian)(dian)流在負載時保(bao)持恒(heng)定。

　　快速調節器的操作是通過控制一個(ge)晶體管開關的占空比(bi)(bi)來(lai)實現(xian)的。占空比(bi)(bi)會自(zi)動增加以使(shi)電(dian)池流(liu)入更(geng)多的電(dian)流(liu)。當VBATT

a 開關閉合

b 開關打開
圖5 快(kuai)速(su)轉換器操作

　　③電感的確定

　　電(dian)(dian)(dian)感(gan)(gan)對交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)是(shi)有阻(zu)(zu)礙作用的(de)。在交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)頻(pin)(pin)率(lv)(lv)一定(ding)(ding)的(de)情況(kuang)下，電(dian)(dian)(dian)感(gan)(gan)量(liang)越(yue)大(da)，對交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)阻(zu)(zu)礙能(neng)力越(yue)強，電(dian)(dian)(dian)感(gan)(gan)量(liang)越(yue)小，其阻(zu)(zu)礙能(neng)力越(yue)小。另外，在電(dian)(dian)(dian)感(gan)(gan)量(liang)一定(ding)(ding)的(de)情況(kuang)下，交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)頻(pin)(pin)率(lv)(lv)越(yue)高，電(dian)(dian)(dian)感(gan)(gan)對交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)阻(zu)(zu)礙能(neng)力越(yue)大(da)，頻(pin)(pin)率(lv)(lv)越(yue)低(di)，電(dian)(dian)(dian)感(gan)(gan)對交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)阻(zu)(zu)礙能(neng)力越(yue)小。也就是(shi)說，電(dian)(dian)(dian)感(gan)(gan)有阻(zu)(zu)止交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)通過的(de)特性。

　　其工作(zuo)原理是這樣的(de)(de)(de)(de)：當負載兩端(duan)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)要降低(di)時，通(tong)過(guo)MOSFET場(chang)效應(ying)管的(de)(de)(de)(de)開(kai)關(guan)作(zuo)用(yong)，外部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)對電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)進(jin)行充(chong)電(dian)(dian)(dian)(dian)(dian)并達到所需的(de)(de)(de)(de)額(e)定(ding)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)。當負載兩端(duan)地(di)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)升(sheng)高(gao)時，通(tong)過(guo)MOSFET場(chang)效應(ying)管的(de)(de)(de)(de)開(kai)關(guan)作(zuo)用(yong)，外部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)供電(dian)(dian)(dian)(dian)(dian)斷開(kai)，電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)釋(shi)放(fang)出(chu)剛才充(chong)入的(de)(de)(de)(de)能(neng)量(liang)，這時電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)就變成(cheng)了電(dian)(dian)(dian)(dian)(dian)源(yuan)繼續對負載供電(dian)(dian)(dian)(dian)(dian)。隨著電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)上存儲的(de)(de)(de)(de)能(neng)量(liang)地(di)消耗(hao)。負載兩端(duan)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)開(kai)始逐漸降低(di)，外部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)通(tong)過(guo)MOSFET場(chang)效應(ying)管的(de)(de)(de)(de)開(kai)關(guan)作(zuo)用(yong)又要充(chong)電(dian)(dian)(dian)(dian)(dian)。依次類推在不斷的(de)(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)和放(fang)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)過(guo)程中(zhong)形成(cheng)了一種(zhong)穩定(ding)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，永遠使負載兩端(duan)地(di)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)不會升(sheng)高(gao)也不會降低(di)，這就是開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)最大優(you)勢(shi)。

　　要確定(ding)快(kuai)速轉換器(qi)中電感的大(da)小首先應假定(ding)晶(jing)體管的占(zhan)空比為50%，因為此時的轉換器(qi)操作操作效(xiao)率最高。占(zhan)空比由方(fang)程式1給出：

　　（其中(zhong)T是PWM的周期(qi)在程序示例中(zhong)T=10.5s）

　　占空比(bi)=ton/T（1）

　　至此就(jiu)可以選擇一個PWM的轉換頻率(lv)（如方程(cheng)式2所示）PWM的轉換頻率(lv)越(yue)大(da)，則電感的值越(yue)小，也越(yue)節約成本。

　　我(wo)的示例代碼配(pei)置F310的8位硬件(jian)PWM是使(shi)用內部24.5MHz主時鐘的256分頻來產生(sheng)一個(ge)95.7kHz的轉換(huan)速率。

　　L=（Vi-Vsat-Voton）/2Iomax（2）

　　現在我們可(ke)以計算電感的(de)大小了，假定充電電壓Vi的(de)值為15V，飽和電壓Vsat的(de)值為0.5V，需(xu)要獲(huo)得的(de)輸出電壓值為4.2V,并且最大輸出電流IＯMAX為1500mA，那么，電感的(de)值至少應選為18H。

　　需要(yao)注(zhu)意的是：在本電(dian)(dian)(dian)路中的電(dian)(dian)(dian)容僅僅是一個紋波衰減(jian)器(qi)，因(yin)為紋波與電(dian)(dian)(dian)容的大(da)小成反比例(li)關系，所以(yi)電(dian)(dian)(dian)容的值(zhi)越大(da)，衰減(jian)效(xiao)果越好(hao)。