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(shi)電(dian)(dian)(dian)池具(ju)有較(jiao)長的(de)壽命。利用C8051F310單片機(ji)設計(ji)的(de)智能充(chong)電(dian)(dian)(dian)器，具(ju)有較(jiao)高的(de)測量精度，可很(hen)好的(de)控(kong)制充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流的(de)大小，適時的(de)調整，并可根(gen)據充(chong)電(dian)(dian)(dian)的(de)狀態(tai)判斷充(chong)電(dian)(dian)(dian)的(de)時間，及時終止充(chong)電(dian)(dian)(dian)，以(yi)避免電(dian)(dian)(dian)池的(de)過充(chong)。

　　本文(wen)討論使用(yong)C8051F310器件設計鋰(li)離子電(dian)(dian)(dian)(dian)池(chi)(chi)充電(dian)(dian)(dian)(dian)器的。利用(yong)PWM脈寬調制產生可用(yong)軟(ruan)件控制的充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源，以適應不同(tong)階(jie)段的充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)的要(yao)求。溫(wen)度傳感器對電(dian)(dian)(dian)(dian)池(chi)(chi)溫(wen)度進行(xing)監(jian)測，并通過AD轉(zhuan)換和相關計算檢測電(dian)(dian)(dian)(dian)池(chi)(chi)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓和電(dian)(dian)(dian)(dian)流(liu)，以判斷電(dian)(dian)(dian)(dian)池(chi)(chi)到達哪個階(jie)段。使電(dian)(dian)(dian)(dian)池(chi)(chi)具有(you)更長的使用(yong)壽(shou)命(ming)，更有(you)效的充電(dian)(dian)(dian)(dian)方(fang)法。

　　設計過程

　　1 充電原理

　　電(dian)(dian)池的(de)(de)特性唯一地決(jue)(jue)定其安全性能和充(chong)電(dian)(dian)的(de)(de)效率。電(dian)(dian)池的(de)(de)最佳充(chong)電(dian)(dian)方法是由電(dian)(dian)池的(de)(de)化學(xue)成(cheng)分決(jue)(jue)定的(de)(de)（鋰離子、鎳氫(qing)、鎳鎘(ge)還是SLA電(dian)(dian)池等）。盡(jin)管如此，大多數充(chong)電(dian)(dian)方案(an)都包(bao)含下面的(de)(de)三(san)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)池(chi)都是(shi)通過向自身傳(chuan)輸電(dian)(dian)能的(de)(de)(de)方法進行充(chong)(chong)電(dian)(dian)的(de)(de)(de)，一節(jie)(jie)電(dian)(dian)池(chi)的(de)(de)(de)最大充(chong)(chong)電(dian)(dian)電(dian)(dian)流取決于電(dian)(dian)池(chi)的(de)(de)(de)額定(ding)容(rong)(rong)量（C）例(li)如，一節(jie)(jie)容(rong)(rong)量為1000mAh的(de)(de)(de)電(dian)(dian)池(chi)在(zai)充(chong)(chong)電(dian)(dian)電(dian)(dian)流為1000mA時，可以充(chong)(chong)電(dian)(dian)1C(電(dian)(dian)池(chi)容(rong)(rong)量的(de)(de)(de)1倍)也(ye)可以用(yong)(yong)1/50C(20mA)或更低(di)的(de)(de)(de)電(dian)(dian)流給電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)。盡管如此，這只是(shi)一個普通的(de)(de)(de)低(di)電(dian)(dian)流充(chong)(chong)電(dian)(dian)方式(shi)，不適用(yong)(yong)于要求短充(chong)(chong)電(dian)(dian)時間的(de)(de)(de)快速充(chong)(chong)電(dian)(dian)方案。

　　現在(zai)使(shi)用(yong)(yong)(yong)的(de)(de)(de)大(da)多數(shu)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)在(zai)給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)都(dou)是(shi)既使(shi)用(yong)(yong)(yong)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)方(fang)式又使(shi)用(yong)(yong)(yong)額定(ding)(ding)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)方(fang)法，即容積充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，低(di)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)通常使(shi)用(yong)(yong)(yong)在(zai)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)初始階(jie)段。在(zai)這(zhe)(zhe)一(yi)階(jie)段，需要將(jiang)會導致充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程終止的(de)(de)(de)芯片初期的(de)(de)(de)自熱效(xiao)應(ying)減小(xiao)到最低(di)程度，容積充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)通常用(yong)(yong)(yong)在(zai)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)中級階(jie)段，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)大(da)部分(fen)能量都(dou)是(shi)在(zai)這(zhe)(zhe)一(yi)階(jie)段存(cun)儲的(de)(de)(de)。在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)最后階(jie)段，通常充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)間的(de)(de)(de)絕大(da)部分(fen)都(dou)是(shi)消耗在(zai)這(zhe)(zhe)一(yi)階(jie)段，可以通過(guo)監測(ce)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓或兩者的(de)(de)(de)值來(lai)決(jue)定(ding)(ding)何時(shi)結束(shu)(shu)(shu)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。同樣(yang)，結束(shu)(shu)(shu)方(fang)案依賴(lai)于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)化(hua)學特性，例如(ru)：大(da)多數(shu)鋰離子電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)都(dou)是(shi)將(jiang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓保持在(zai)恒定(ding)(ding)值，同時(shi)檢測(ce)最低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)。鎳鎘、NiCd電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)用(yong)(yong)(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓或溫度的(de)(de)(de)變化(hua)率來(lai)決(jue)定(ding)(ding)充(chong)(chong)(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)結束(shu)(shu)(shu)時(shi)間。

      充電時部分電能被轉換成熱能，直至電池充滿。而充滿后，所有的電能將全部被轉換成熱能。如果此時不終止充電，電池就會被損壞或燒毀。快速充電器電池（完全充滿的時間小于兩小時的充電器）則可以解決這個問題，因為這些充電器是使用高充電電流來縮短充電時間的。因此，對于鋰離子電池來說,監測它的(de)(de)溫(wen)度(du)是至關(guan)重要的(de)(de)，因為電(dian)池在過充電(dian)時會發生爆裂，在所有的(de)(de)充電(dian)階段都應該隨(sui)時監測溫(wen)度(du)的(de)(de)變化，并且在溫(wen)度(du)超過最大設定值時立即停止充電(dian)。

　　2 總體設計 
　
　　充電電路由三部分：控制部分，檢測部分及充電部分組成。如圖1所示，采用F310單片機進行充電控制，單片機本身具有脈寬調制PWM型開關穩壓電源所需的全部功能，具有10位A/D轉換器。利用單片機A/D端(duan)口，構成電池電壓，電流，溫度檢測電路(lu)。

　　單片(pian)機通(tong)過(guo)電(dian)壓(ya)反(fan)(fan)饋(kui)和電(dian)流反(fan)(fan)饋(kui)信號，直接利用PWM輸(shu)出(chu)將數(shu)字電(dian)壓(ya)信號并轉化成(cheng)模擬電(dian)壓(ya)信號，能夠(gou)保(bao)證控(kong)制精度。

　　3 控制(zhi)部分電路設計 

　　C8051F310單片機

　　①模擬外設

　　a.10位ADC：轉(zhuan)換速度(du)可(ke)(ke)達(da)200ks/s,可(ke)(ke)多達(da)21或(huo)17個(ge)外部單(dan)端(duan)或(huo)差(cha)分輸(shu)入(ru)，VREF可(ke)(ke)在外部引腳或(huo)VDD中選(xuan)擇(ze)，內(nei)置溫度(du)傳感器（±3℃），外部轉(zhuan)換啟(qi)動(dong)輸(shu)入(ru)；

　　b.兩個模擬比較器：可編程回差電壓和響應時間，可配置為中斷或復位源，小電流（〈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微控制器內核

　　a.流水線指令結構：70%的指令的執行時間為一個或兩個系統時鐘周期；
　　b.速度可達25MI/s（時鐘頻率為25MHz時）；
　　c.擴展的中斷系統(tong)。

　　④數字外設

　　a.29/25個端口I/O：所有的口線均耐5V電壓；
　　b.4個通用16位計數器/定時器；
　　c.16位可編程計數器/定時器陣列（PCA），有5個捕捉/比較模塊；
　　d.使(shi)用PCA或定時器和(he)外部時鐘源的實(shi)時時鐘方式。

　　控制電(dian)路中如圖(tu)2所示，P0.3口(kou)(kou)提(ti)供充(chong)電(dian)電(dian)源(yuan)，P0.6口(kou)(kou)檢(jian)測充(chong)電(dian)電(dian)壓的大小(xiao)，P0.5口(kou)(kou)檢(jian)測充(chong)電(dian)電(dian)流(liu)的大小(xiao)，P0.4口(kou)(kou)檢(jian)測電(dian)池的溫度。

　　充電電流由單片機脈寬(kuan)調制PWM產生，充電電流由AD轉(zhuan)換再經(jing)過計算得出。

　　4 充電(dian)部(bu)分(fen)及檢測部(bu)分(fen)電(dian)路設計

　　②快速轉換器

　　實現漸弱(ruo)終止(zhi)充電(dian)器(qi)的(de)最經濟的(de)方法(fa)就是(shi)用(yong)一個(ge)快速轉(zhuan)換器(qi)。快速轉(zhuan)換器(qi)是(shi)用(yong)一個(ge)電(dian)感和/或一個(ge)變壓器(qi)（需要隔(ge)離(li)的(de)時(shi)候用(yong)變壓器(qi)）作為能量存儲單元以離(li)散的(de)能量包的(de)形式將能量從輸入傳(chuan)輸至輸出(chu)的(de)開關調節器(qi)反饋電(dian)路，通過晶體管(guan)來調節能量的(de)傳(chuan)輸，同(tong)時(shi)也作為過濾開關，以確保電(dian)壓或電(dian)流(liu)在負(fu)載時(shi)保持恒(heng)定(ding)。

　　快速調(diao)節(jie)器(qi)的(de)(de)操作是(shi)通過(guo)控(kong)制一(yi)個晶體管開(kai)關的(de)(de)占空比來實現的(de)(de)。占空比會自動增加以使電(dian)池流(liu)入更多的(de)(de)電(dian)流(liu)。當VBATT

　　③電感的確定

　　電(dian)(dian)(dian)(dian)感對交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)是(shi)有(you)阻(zu)礙(ai)作用的。在交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)頻率一定的情況下，電(dian)(dian)(dian)(dian)感量越(yue)大，對交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)的阻(zu)礙(ai)能力(li)越(yue)強??一定的情況下，交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)的頻率越(yue)高，電(dian)(dian)(dian)(dian)感對交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)的阻(zu)礙(ai)能力(li)越(yue)大，頻率越(yue)低，電(dian)(dian)(dian)(dian)感對交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)的阻(zu)礙(ai)能力(li)越(yue)小。也就是(shi)說，電(dian)(dian)(dian)(dian)感有(you)阻(zu)止交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)通過的特性。

　　其工作(zuo)原(yuan)理是(shi)這樣的(de)(de)(de)：當負(fu)(fu)載兩(liang)端(duan)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)要降(jiang)(jiang)低(di)時，通過(guo)MOSFET場(chang)效應管的(de)(de)(de)開關作(zuo)用，外部電(dian)(dian)(dian)(dian)(dian)源對電(dian)(dian)(dian)(dian)(dian)感進行充電(dian)(dian)(dian)(dian)(dian)并達到所需的(de)(de)(de)額定電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)。當負(fu)(fu)載兩(liang)端(duan)地(di)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)升(sheng)高(gao)時，通過(guo)MOSFET場(chang)效應管的(de)(de)(de)開關作(zuo)用，外部電(dian)(dian)(dian)(dian)(dian)源供電(dian)(dian)(dian)(dian)(dian)斷(duan)(duan)開，電(dian)(dian)(dian)(dian)(dian)感釋放(fang)出剛才充入的(de)(de)(de)能(neng)量，這時電(dian)(dian)(dian)(dian)(dian)感就(jiu)變成了(le)電(dian)(dian)(dian)(dian)(dian)源繼續(xu)對負(fu)(fu)載供電(dian)(dian)(dian)(dian)(dian)。隨著電(dian)(dian)(dian)(dian)(dian)感上(shang)存儲(chu)的(de)(de)(de)能(neng)量地(di)消耗。負(fu)(fu)載兩(liang)端(duan)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)開始逐(zhu)漸降(jiang)(jiang)低(di)，外部電(dian)(dian)(dian)(dian)(dian)源通過(guo)MOSFET場(chang)效應管的(de)(de)(de)開關作(zuo)用又要充電(dian)(dian)(dian)(dian)(dian)。依(yi)次(ci)類推在不斷(duan)(duan)的(de)(de)(de)充電(dian)(dian)(dian)(dian)(dian)和(he)放(fang)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)過(guo)程中形成了(le)一(yi)種穩(wen)定的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，永遠使負(fu)(fu)載兩(liang)端(duan)地(di)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)不會升(sheng)高(gao)也不會降(jiang)(jiang)低(di)，這就(jiu)是(shi)開關電(dian)(dian)(dian)(dian)(dian)源的(de)(de)(de)最大優勢。

　　要確定快速轉換器中電感的大小首先應假定晶體管的占空比為50%，因為此時的轉換器操作操作效率最高。占空比由方程式1給出：
　　（其中T是PWM的周(zhou)期在(zai)程序示例中T=10.5s）

　　占空(kong)比=ton/T （1）

　　至此就可以選擇(ze)一(yi)個PWM的轉換(huan)頻率（如方程式2所示）PWM的轉換(huan)頻率越大(da)，則電(dian)感的值越小，也越節(jie)約成(cheng)本。

　　我(wo)的(de)示(shi)例代碼配置F310的(de)8位硬件PWM是使用內部24.5MHz主(zhu)時鐘的(de)256分頻來產生(sheng)一個95.7kHz的(de)轉換速率。

　　L=（Vi-Vsat-Voton）/2Iomax （2）

　　現在我們可以計算電感的大小了，假定充電電壓Vi的值為15V，飽和電壓Vsat的值為0.5V，需要獲得的輸出電壓值為4.2V,并且最大輸出電流IＯMAX為1500mA，那么，電感的值至少應選為18H。
需要注(zhu)意的是：在(zai)本電路中的電容僅僅是一(yi)個紋波衰減器，因為紋波與電容的大(da)小(xiao)成反比例關系，所以電容的值(zhi)越大(da)，衰減效(xiao)果越好。