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(chi)具(ju)(ju)有(you)較長的(de)(de)(de)(de)壽命。利(li)用C8051F310單片機(ji)設計的(de)(de)(de)(de)智能充(chong)(chong)電器，具(ju)(ju)有(you)較高的(de)(de)(de)(de)測量(liang)精度，可很好的(de)(de)(de)(de)控制充(chong)(chong)電電流(liu)的(de)(de)(de)(de)大(da)小，適時的(de)(de)(de)(de)調整，并(bing)可根據充(chong)(chong)電的(de)(de)(de)(de)狀態判斷充(chong)(chong)電的(de)(de)(de)(de)時間，及時終止充(chong)(chong)電，以避免(mian)電池(chi)的(de)(de)(de)(de)過充(chong)(chong)。

　　本文(wen)討(tao)論使(shi)用C8051F310器件設計鋰離子(zi)電(dian)(dian)池充(chong)(chong)電(dian)(dian)器的(de)。利用PWM脈寬調制產生可用軟件控制的(de)充(chong)(chong)電(dian)(dian)電(dian)(dian)源，以(yi)適應不(bu)同階(jie)(jie)段(duan)的(de)充(chong)(chong)電(dian)(dian)電(dian)(dian)流的(de)要(yao)求。溫(wen)度傳感器對(dui)電(dian)(dian)池溫(wen)度進行監測，并通(tong)過AD轉換(huan)和相關(guan)計算檢測電(dian)(dian)池充(chong)(chong)電(dian)(dian)電(dian)(dian)壓和電(dian)(dian)流，以(yi)判(pan)斷電(dian)(dian)池到達哪個階(jie)(jie)段(duan)。使(shi)電(dian)(dian)池具有(you)更(geng)長的(de)使(shi)用壽命，更(geng)有(you)效的(de)充(chong)(chong)電(dian)(dian)方法。

　　設計過程

　　1 充電原理

　　電(dian)池(chi)的(de)特性唯一地決定其安(an)全性能和充電(dian)的(de)效率(lv)。電(dian)池(chi)的(de)最佳充電(dian)方法是(shi)由電(dian)池(chi)的(de)化學成分決定的(de)（鋰離子、鎳氫、鎳鎘還是(shi)SLA電(dian)池(chi)等）。盡管如此，大多數充電(dian)方案(an)都包(bao)含下面(mian)的(de)三個階段：

　　● 低電流調節階段
　　● 恒流階段
　　● 恒壓(ya)階(jie)段(duan)/充電終止

　　所有電(dian)池都是通(tong)過向(xiang)自身(shen)傳輸電(dian)能的(de)方法進行(xing)充電(dian)的(de)，一(yi)節電(dian)池的(de)最大(da)充電(dian)電(dian)流(liu)取決于電(dian)池的(de)額定容(rong)量(liang)（C）例如，一(yi)節容(rong)量(liang)為1000mAh的(de)電(dian)池在充電(dian)電(dian)流(liu)為1000mA時，可以(yi)充電(dian)1C(電(dian)池容(rong)量(liang)的(de)1倍)也可以(yi)用1/50C(20mA)或(huo)更低的(de)電(dian)流(liu)給(gei)電(dian)池充電(dian)。盡管如此，這只是一(yi)個普通(tong)的(de)低電(dian)流(liu)充電(dian)方式，不(bu)適(shi)用于要求(qiu)短充電(dian)時間的(de)快速充電(dian)方案。

　　現在(zai)(zai)使(shi)用(yong)(yong)的(de)(de)大(da)多(duo)數充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)在(zai)(zai)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)都(dou)是既使(shi)用(yong)(yong)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)方式又(you)使(shi)用(yong)(yong)額定(ding)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流的(de)(de)方法，即容積(ji)(ji)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，低(di)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流通(tong)(tong)常(chang)(chang)使(shi)用(yong)(yong)在(zai)(zai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)初始階(jie)段(duan)(duan)。在(zai)(zai)這一階(jie)段(duan)(duan)，需(xu)要將會導致充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過程終止的(de)(de)芯片初期的(de)(de)自(zi)熱(re)效(xiao)應減小到最(zui)低(di)程度，容積(ji)(ji)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)通(tong)(tong)常(chang)(chang)用(yong)(yong)在(zai)(zai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)中級階(jie)段(duan)(duan)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)大(da)部分(fen)能(neng)量都(dou)是在(zai)(zai)這一階(jie)段(duan)(duan)存儲的(de)(de)。在(zai)(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)最(zui)后階(jie)段(duan)(duan)，通(tong)(tong)常(chang)(chang)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)間的(de)(de)絕大(da)部分(fen)都(dou)是消耗在(zai)(zai)這一階(jie)段(duan)(duan)，可(ke)以(yi)通(tong)(tong)過監測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)或兩者的(de)(de)值來決定(ding)何時(shi)結束(shu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。同樣，結束(shu)方案依賴于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)化學特性，例如：大(da)多(duo)數鋰離子(zi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)都(dou)是將電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)保(bao)持在(zai)(zai)恒定(ding)值，同時(shi)檢測最(zui)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流。鎳鎘、NiCd電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)用(yong)(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)或溫度的(de)(de)變(bian)化率(lv)來決定(ding)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)結束(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(ta)的溫(wen)度是至關重要的，因(yin)為(wei)電(dian)(dian)池在過(guo)充(chong)電(dian)(dian)時會發生爆裂，在所有的充(chong)電(dian)(dian)階(jie)段都應該(gai)隨時監測溫(wen)度的變化，并(bing)且在溫(wen)度超過(guo)最大設定值時立即(ji)停止充(chong)電(dian)(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(pian)機A/D端口，構成(cheng)電池(chi)電壓，電流，溫(wen)度檢(jian)測電路。

　　單(dan)片機通過電壓反饋和電流反饋信(xin)號，直接利用PWM輸出將數字(zi)電壓信(xin)號并轉化(hua)成模(mo)擬電壓信(xin)號，能夠保證控(kong)制精度。

　　3 控制部分(fen)電路設計 

　　C8051F310單(dan)片(pian)機

　　①模擬外設

　　a.10位ADC：轉換速度可(ke)達200ks/s,可(ke)多(duo)達21或(huo)17個(ge)外部單端或(huo)差分輸(shu)入，VREF可(ke)在外部引腳(jiao)或(huo)VDD中選擇，內(nei)置溫度傳感(gan)器(qi)（±3℃），外部轉換啟動輸(shu)入；

　　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(nei)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(kuo)展的(de)中斷系(xi)統。

　　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.使用PCA或定時(shi)(shi)器和外部時(shi)(shi)鐘源的(de)實時(shi)(shi)時(shi)(shi)鐘方式。

　　控(kong)制(zhi)電(dian)(dian)路中如(ru)圖2所示(shi)，P0.3口提供充電(dian)(dian)電(dian)(dian)源，P0.6口檢(jian)(jian)測(ce)充電(dian)(dian)電(dian)(dian)壓的大(da)(da)小，P0.5口檢(jian)(jian)測(ce)充電(dian)(dian)電(dian)(dian)流的大(da)(da)小，P0.4口檢(jian)(jian)測(ce)電(dian)(dian)池的溫度。

　　充(chong)電(dian)電(dian)流(liu)由(you)單(dan)片機(ji)脈(mo)寬調制PWM產生(sheng)，充(chong)電(dian)電(dian)流(liu)由(you)AD轉(zhuan)換(huan)再(zai)經過計算得(de)出。

　　4 充電部(bu)分及檢測(ce)部(bu)分電路(lu)設計

　　②快速轉換器

　　實現漸弱終止(zhi)充電(dian)器(qi)的(de)最經濟的(de)方(fang)法就是用一個快速轉(zhuan)(zhuan)換器(qi)。快速轉(zhuan)(zhuan)換器(qi)是用一個電(dian)感和/或一個變壓(ya)器(qi)（需要(yao)隔離(li)的(de)時候用變壓(ya)器(qi)）作為能量(liang)存儲單元以離(li)散的(de)能量(liang)包的(de)形(xing)式將(jiang)能量(liang)從輸入傳輸至輸出的(de)開關調節器(qi)反饋電(dian)路，通(tong)過(guo)晶體管來調節能量(liang)的(de)傳輸，同時也作為過(guo)濾開關，以確保(bao)電(dian)壓(ya)或電(dian)流在負載時保(bao)持恒定。

　　快速調(diao)節(jie)器的(de)操(cao)作是通(tong)過控制一個晶(jing)體管開(kai)關的(de)占空比(bi)來實現的(de)。占空比(bi)會自動增加(jia)以使電池流入更多(duo)的(de)電流。當VBATT

　　③電感的確定

　　電(dian)感對(dui)(dui)交流(liu)電(dian)是有(you)阻(zu)(zu)礙作用(yong)的(de)(de)。在交流(liu)電(dian)頻率一定的(de)(de)情況(kuang)下(xia)，電(dian)感量越(yue)大，對(dui)(dui)交流(liu)電(dian)的(de)(de)阻(zu)(zu)礙能(neng)力越(yue)強??一定的(de)(de)情況(kuang)下(xia)，交流(liu)電(dian)的(de)(de)頻率越(yue)高，電(dian)感對(dui)(dui)交流(liu)電(dian)的(de)(de)阻(zu)(zu)礙能(neng)力越(yue)大，頻率越(yue)低，電(dian)感對(dui)(dui)交流(liu)電(dian)的(de)(de)阻(zu)(zu)礙能(neng)力越(yue)小(xiao)。也就是說，電(dian)感有(you)阻(zu)(zu)止(zhi)交流(liu)電(dian)通過的(de)(de)特性。

　　其(qi)工作原理是這樣的(de)(de)(de)(de)：當負(fu)載(zai)(zai)兩(liang)端的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓要(yao)(yao)降(jiang)(jiang)低(di)(di)時(shi)，通(tong)過(guo)MOSFET場(chang)效(xiao)應管的(de)(de)(de)(de)開(kai)關(guan)(guan)作用(yong)，外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)對電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)進行充(chong)電(dian)(dian)(dian)(dian)(dian)并(bing)達到所需(xu)的(de)(de)(de)(de)額(e)定電(dian)(dian)(dian)(dian)(dian)壓。當負(fu)載(zai)(zai)兩(liang)端地電(dian)(dian)(dian)(dian)(dian)壓升高時(shi)，通(tong)過(guo)MOSFET場(chang)效(xiao)應管的(de)(de)(de)(de)開(kai)關(guan)(guan)作用(yong)，外(wai)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)釋放(fang)出剛才(cai)充(chong)入的(de)(de)(de)(de)能(neng)量，這時(shi)電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)就變成(cheng)了電(dian)(dian)(dian)(dian)(dian)源(yuan)繼續(xu)對負(fu)載(zai)(zai)供電(dian)(dian)(dian)(dian)(dian)。隨著電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)上存(cun)儲的(de)(de)(de)(de)能(neng)量地消耗。負(fu)載(zai)(zai)兩(liang)端的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓開(kai)始(shi)逐(zhu)漸降(jiang)(jiang)低(di)(di)，外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)通(tong)過(guo)MOSFET場(chang)效(xiao)應管的(de)(de)(de)(de)開(kai)關(guan)(guan)作用(yong)又要(yao)(yao)充(chong)電(dian)(dian)(dian)(dian)(dian)。依次類(lei)推在不(bu)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(cheng)中(zhong)形成(cheng)了一種穩定的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓，永遠(yuan)使負(fu)載(zai)(zai)兩(liang)端地電(dian)(dian)(dian)(dian)(dian)壓不(bu)會(hui)升高也不(bu)會(hui)降(jiang)(jiang)低(di)(di)，這就是開(kai)關(guan)(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)最(zui)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的周期在程序(xu)示例中T=10.5s）

　　占空比=ton/T （1）

　　至此(ci)就可(ke)以選(xuan)擇一個PWM的(de)轉換頻率（如方程式(shi)2所示）PWM的(de)轉換頻率越(yue)(yue)大(da)，則(ze)電感的(de)值越(yue)(yue)小，也越(yue)(yue)節約成本。

　　我的(de)示(shi)例(li)代碼配(pei)置F310的(de)8位硬(ying)件PWM是使用內部24.5MHz主時鐘的(de)256分頻(pin)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。
需要注意(yi)的(de)是：在本(ben)電路中的(de)電容(rong)僅僅是一個紋波衰減器，因為紋波與電容(rong)的(de)大(da)小成反比例(li)關系，所以電容(rong)的(de)值(zhi)越大(da)，衰減效(xiao)果越好(hao)。