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(wen)討論(lun)使(shi)用(yong)C8051F310器件(jian)設計鋰離子電(dian)(dian)(dian)(dian)池(chi)智能充(chong)電(dian)(dian)(dian)(dian)器的(de)(de)。利用(yong)PWM脈(mo)寬調制(zhi)產生可用(yong)軟件(jian)控制(zhi)的(de)(de)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源，以(yi)適應不同(tong)階段的(de)(de)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流的(de)(de)要求。溫度傳感器對電(dian)(dian)(dian)(dian)池(chi)溫度進行監測(ce)，并通過(guo)AD轉換和相關計算(suan)檢測(ce)電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓和電(dian)(dian)(dian)(dian)流，以(yi)判斷電(dian)(dian)(dian)(dian)池(chi)到達哪個階段。使(shi)電(dian)(dian)(dian)(dian)池(chi)具有(you)更長的(de)(de)使(shi)用(yong)壽命，更有(you)效的(de)(de)充(chong)電(dian)(dian)(dian)(dian)方法。

　　設計過程

　　1 充電原理

　　電(dian)(dian)池的(de)特性唯(wei)一地決定其安全性能和充電(dian)(dian)的(de)效率。電(dian)(dian)池的(de)最佳充電(dian)(dian)方法是(shi)由電(dian)(dian)池的(de)化學成分決定的(de)（鋰離子、鎳氫、鎳鎘(ge)還(huan)是(shi)SLA電(dian)(dian)池等）。盡(jin)管(guan)如(ru)此，大(da)多數(shu)充電(dian)(dian)方案都包(bao)含下面的(de)三個(ge)階段：

低電流調節階段
恒流階段
恒壓(ya)階段/充(chong)電終止(zhi)

　　所有電(dian)(dian)(dian)(dian)池(chi)(chi)都是通過(guo)向自身傳輸電(dian)(dian)(dian)(dian)能(neng)的(de)(de)(de)(de)方(fang)法(fa)進(jin)行(xing)充電(dian)(dian)(dian)(dian)的(de)(de)(de)(de)，一節電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)最大充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)取(qu)決于(yu)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)額定(ding)容量（C）例(li)如(ru)，一節容量為(wei)1000mAh的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)在充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)為(wei)1000mA時，可以(yi)充電(dian)(dian)(dian)(dian)1C(電(dian)(dian)(dian)(dian)池(chi)(chi)容量的(de)(de)(de)(de)1倍(bei))也可以(yi)用1/50C(20mA)或更低的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)給電(dian)(dian)(dian)(dian)池(chi)(chi)充電(dian)(dian)(dian)(dian)。盡管如(ru)此，這只是一個普通的(de)(de)(de)(de)低電(dian)(dian)(dian)(dian)流(liu)充電(dian)(dian)(dian)(dian)方(fang)式，不適用于(yu)要求短充電(dian)(dian)(dian)(dian)時間的(de)(de)(de)(de)快速充電(dian)(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)池電(dian)壓(ya)保持(chi)在恒(heng)定值，同時檢測(ce)最低(di)電(dian)流。鎳鎘、NiCd電(dian)池用(yong)電(dian)壓(ya)或溫度的(de)變化率(lv)來決定充電(dian)的(de)結束時間。

　　充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)(shi)部分電(dian)(dian)(dian)(dian)(dian)(dian)能(neng)(neng)被轉(zhuan)(zhuan)換成(cheng)熱(re)能(neng)(neng)，直(zhi)至電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)滿(man)。而充(chong)(chong)(chong)滿(man)后，所有(you)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)能(neng)(neng)將全部被轉(zhuan)(zhuan)換成(cheng)熱(re)能(neng)(neng)。如果(guo)此(ci)時(shi)(shi)(shi)不終止充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)就會被損壞(huai)或燒毀(hui)。快速充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)（完全充(chong)(chong)(chong)滿(man)的(de)時(shi)(shi)(shi)間小于兩小時(shi)(shi)(shi)的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)）則可以解(jie)決(jue)這個問題(ti)，因為這些充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器(qi)是使用(yong)高充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流來縮短充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)(shi)間的(de)。因此(ci)，對(dui)于鋰離子電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)來說,監測(ce)它的(de)溫度是至關重要的(de)，因為電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)在(zai)過充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)(shi)會發生爆裂，在(zai)所有(you)的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)階段都應該(gai)隨時(shi)(shi)(shi)監測(ce)溫度的(de)變化，并且在(zai)溫度超過最大設定值時(shi)(shi)(shi)立即停(ting)止充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。

　　2 總體設計

　　充(chong)(chong)電(dian)(dian)電(dian)(dian)路由(you)三部(bu)(bu)分(fen)：控(kong)制部(bu)(bu)分(fen)，檢測部(bu)(bu)分(fen)及充(chong)(chong)電(dian)(dian)部(bu)(bu)分(fen)組成(cheng)。如圖1所(suo)示，采用(yong)F310單片機(ji)進行(xing)充(chong)(chong)電(dian)(dian)控(kong)制，單片機(ji)本(ben)身具有(you)(you)脈寬調制PWM型(xing)開關穩(wen)壓(ya)電(dian)(dian)源所(suo)需的全部(bu)(bu)功能，具有(you)(you)10位A/D轉換器。利用(yong)單片機(ji)A/D端(duan)口，構(gou)成(cheng)電(dian)(dian)池電(dian)(dian)壓(ya)，電(dian)(dian)流(liu)，溫度檢測電(dian)(dian)路。

圖1 鋰離子(zi)電池充電模塊圖

　　單(dan)片機通過電(dian)(dian)壓(ya)反(fan)饋(kui)和(he)電(dian)(dian)流反(fan)饋(kui)信號(hao)，直接利用PWM輸出將數字(zi)電(dian)(dian)壓(ya)信號(hao)并轉化成模擬電(dian)(dian)壓(ya)信號(hao)，能夠保證控制精度。

　　3 控(kong)制部分電路設計

　　C8051F310單片機

　　①模擬外設

　　a.10位ADC：轉(zhuan)換(huan)速度可達200ks/s,可多達21或(huo)17個(ge)外部單端或(huo)差分(fen)輸入(ru)，VREF可在外部引腳或(huo)VDD中選擇，內置溫度傳感器（±3℃），外部轉(zhuan)換(huan)啟動(dong)輸入(ru)；

　　b.兩個模(mo)擬比較器(qi)：可編程回差電(dian)壓和響應時間，可配置為中斷或復位(wei)源，小電(dian)流（〈0.5μA）。

　　②供電電壓

　　a.典型工(gong)作電流：5mA、25MHz；

　　b.典型停(ting)機電流(liu)：0.1μA；

　　c.溫度范(fan)圍(wei)：-40～+85℃。

　　③高速8051微控制器(qi)內核(he)

　　a.流水線指令結構：70%的指令的執行時間為一(yi)個或兩(liang)個系統(tong)時鐘周期；

　　b.速度可(ke)達25MI/s（時鐘(zhong)頻率為25MHz時）；

　　c.擴(kuo)展(zhan)的(de)中斷系統。

　　④數字外設

　　a.29/25個端口I/O：所(suo)有的口線均耐5V電(dian)壓；

　　b.4個(ge)通(tong)用16位計數器(qi)/定時器(qi)；

　　c.16位可編(bian)程(cheng)計數(shu)器(qi)/定(ding)時(shi)器(qi)陣列（PCA），有5個(ge)捕捉/比較模塊；

　　d.使用PCA或定時器和外(wai)部時鐘(zhong)源(yuan)的實時時鐘(zhong)方式。

　　控制電(dian)路中如圖2所示，P0.3口(kou)提供充電(dian)電(dian)源(yuan)，P0.6口(kou)檢測(ce)充電(dian)電(dian)壓的(de)大(da)小，P0.5口(kou)檢測(ce)充電(dian)電(dian)流的(de)大(da)小，P0.4口(kou)檢測(ce)電(dian)池的(de)溫度(du)。

圖2 控制電路(lu)接線圖

　　充電電流(liu)(liu)由單片機脈寬調制(zhi)PWM產(chan)生，充電電流(liu)(liu)由AD轉(zhuan)換再經過計算得出。

4 充電部分及檢測部分電路設計

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

圖3 充電電路與檢測電路圖

　　①充電過程曲線

　　如(ru)圖4所(suo)示，充(chong)電過程(cheng)由預(yu)充(chong)狀態(tai)，恒流充(chong)電狀態(tai)和(he)恒壓充(chong)電狀態(tai)組成。

圖4 鋰電池充電曲線

　　②快速轉換器

　　實現漸弱終止充電(dian)器(qi)的(de)最經(jing)濟的(de)方法就是(shi)用一(yi)個(ge)快速(su)轉換(huan)器(qi)。快速(su)轉換(huan)器(qi)是(shi)用一(yi)個(ge)電(dian)感和/或(huo)一(yi)個(ge)變(bian)壓器(qi)（需要(yao)隔(ge)離的(de)時候用變(bian)壓器(qi)）作(zuo)為能量(liang)存儲單(dan)元(yuan)以離散(san)的(de)能量(liang)包的(de)形式(shi)將能量(liang)從(cong)輸(shu)入傳(chuan)(chuan)輸(shu)至輸(shu)出的(de)開關調節器(qi)反饋電(dian)路，通過(guo)晶體(ti)管(guan)來調節能量(liang)的(de)傳(chuan)(chuan)輸(shu)，同時也作(zuo)為過(guo)濾開關，以確(que)保電(dian)壓或(huo)電(dian)流在負(fu)載時保持恒定(ding)。

　　快速(su)調節器的(de)操作是通過控(kong)制一個晶體管開關的(de)占空比(bi)來實現的(de)。占空比(bi)會(hui)自(zi)動增加(jia)以使電池流入更多的(de)電流。當(dang)VBATT

a 開關閉合

b 開關打開
圖5 快(kuai)速(su)轉換器(qi)操作(zuo)

　　③電感的確定

　　電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)對交(jiao)(jiao)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)是有(you)阻(zu)(zu)礙(ai)作(zuo)用的(de)。在交(jiao)(jiao)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)頻(pin)(pin)率一定的(de)情(qing)況下(xia)(xia)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)量越(yue)大，對交(jiao)(jiao)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)阻(zu)(zu)礙(ai)能力(li)(li)越(yue)強(qiang)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)量越(yue)小，其阻(zu)(zu)礙(ai)能力(li)(li)越(yue)小。另外，在電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)量一定的(de)情(qing)況下(xia)(xia)，交(jiao)(jiao)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)頻(pin)(pin)率越(yue)高(gao)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)對交(jiao)(jiao)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)阻(zu)(zu)礙(ai)能力(li)(li)越(yue)大，頻(pin)(pin)率越(yue)低，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)對交(jiao)(jiao)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)阻(zu)(zu)礙(ai)能力(li)(li)越(yue)小。也就是說，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)有(you)阻(zu)(zu)止交(jiao)(jiao)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)通過的(de)特性。

　　其工(gong)作(zuo)原理(li)是(shi)這(zhe)(zhe)(zhe)樣的(de)(de)：當負(fu)(fu)載(zai)兩(liang)端(duan)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)要(yao)降(jiang)低時(shi)，通(tong)過MOSFET場(chang)(chang)效(xiao)應管的(de)(de)開(kai)關(guan)(guan)(guan)作(zuo)用(yong)，外部電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)對電(dian)(dian)(dian)(dian)(dian)(dian)感(gan)進行充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)并達(da)到所需(xu)的(de)(de)額定電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)。當負(fu)(fu)載(zai)兩(liang)端(duan)地(di)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)升高(gao)時(shi)，通(tong)過MOSFET場(chang)(chang)效(xiao)應管的(de)(de)開(kai)關(guan)(guan)(guan)作(zuo)用(yong)，外部電(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)釋放(fang)出剛才充(chong)入的(de)(de)能量(liang)，這(zhe)(zhe)(zhe)時(shi)電(dian)(dian)(dian)(dian)(dian)(dian)感(gan)就變成(cheng)了電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)繼續對負(fu)(fu)載(zai)供電(dian)(dian)(dian)(dian)(dian)(dian)。隨著電(dian)(dian)(dian)(dian)(dian)(dian)感(gan)上存儲的(de)(de)能量(liang)地(di)消耗。負(fu)(fu)載(zai)兩(liang)端(duan)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)開(kai)始逐漸降(jiang)低，外部電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)通(tong)過MOSFET場(chang)(chang)效(xiao)應管的(de)(de)開(kai)關(guan)(guan)(guan)作(zuo)用(yong)又要(yao)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。依次類推在(zai)不(bu)斷的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)和放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)過程中形成(cheng)了一種穩定的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，永遠(yuan)使負(fu)(fu)載(zai)兩(liang)端(duan)地(di)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)不(bu)會升高(gao)也不(bu)會降(jiang)低，這(zhe)(zhe)(zhe)就是(shi)開(kai)關(guan)(guan)(guan)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)最大優勢。

　　要(yao)確定快速(su)轉換器中電感的(de)大(da)小(xiao)首先應假定晶體管的(de)占空(kong)比為50%，因為此時(shi)的(de)轉換器操(cao)作操(cao)作效率最(zui)高。占空(kong)比由方(fang)程式1給出(chu)：

　　（其中T是PWM的周期在程(cheng)序示(shi)例中T=10.5s）

　　占(zhan)空比(bi)=ton/T（1）

　　至此就可(ke)以選擇(ze)一個PWM的轉換頻率(lv)（如方程式2所(suo)示）PWM的轉換頻率(lv)越(yue)大，則(ze)電感的值越(yue)小，也(ye)越(yue)節約成本。

　　我(wo)的(de)示例代(dai)碼(ma)配置F310的(de)8位硬(ying)件PWM是使用內部24.5MHz主時鐘的(de)256分(fen)頻來產(chan)生一個95.7kHz的(de)轉換速(su)率(lv)。

　　L=（Vi-Vsat-Voton）/2Iomax（2）

　　現在我們可(ke)以計算電(dian)感(gan)(gan)的(de)(de)大(da)(da)小(xiao)了，假定充電(dian)電(dian)壓Vi的(de)(de)值為(wei)15V，飽和電(dian)壓Vsat的(de)(de)值為(wei)0.5V，需要獲(huo)得的(de)(de)輸(shu)出(chu)(chu)電(dian)壓值為(wei)4.2V,并且最大(da)(da)輸(shu)出(chu)(chu)電(dian)流IＯMAX為(wei)1500mA，那(nei)么，電(dian)感(gan)(gan)的(de)(de)值至少應(ying)選為(wei)18H。

　　需要(yao)注意的(de)(de)是(shi)：在本(ben)電(dian)路中(zhong)的(de)(de)電(dian)容(rong)(rong)僅(jin)僅(jin)是(shi)一個(ge)紋(wen)波(bo)衰減器，因(yin)為紋(wen)波(bo)與電(dian)容(rong)(rong)的(de)(de)大(da)小成反比(bi)例(li)關(guan)系，所以(yi)電(dian)容(rong)(rong)的(de)(de)值(zhi)越(yue)大(da)，衰減效(xiao)果越(yue)好。