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)池(chi)具(ju)有(you)較長的(de)(de)壽命(ming)。利用C8051F310單片(pian)機(ji)設計的(de)(de)智能充(chong)電(dian)(dian)器，具(ju)有(you)較高的(de)(de)測量精度，可很好(hao)的(de)(de)控制(zhi)充(chong)電(dian)(dian)電(dian)(dian)流的(de)(de)大小，適(shi)時的(de)(de)調整，并可根據充(chong)電(dian)(dian)的(de)(de)狀態判斷(duan)充(chong)電(dian)(dian)的(de)(de)時間，及時終(zhong)止充(chong)電(dian)(dian)，以避免電(dian)(dian)池(chi)的(de)(de)過充(chong)。

　　本文討論使用(yong)C8051F310器(qi)件設計(ji)鋰離子電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)器(qi)的(de)(de)。利用(yong)PWM脈寬調制(zhi)產生可用(yong)軟件控制(zhi)的(de)(de)充電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)，以適應(ying)不同階(jie)段的(de)(de)充電(dian)(dian)(dian)電(dian)(dian)(dian)流的(de)(de)要求。溫(wen)(wen)度傳(chuan)感器(qi)對電(dian)(dian)(dian)池(chi)溫(wen)(wen)度進(jin)行監測(ce)，并(bing)通過(guo)AD轉換和相關計(ji)算檢測(ce)電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)電(dian)(dian)(dian)壓和電(dian)(dian)(dian)流，以判斷電(dian)(dian)(dian)池(chi)到達(da)哪個階(jie)段。使電(dian)(dian)(dian)池(chi)具有更(geng)(geng)長的(de)(de)使用(yong)壽命(ming)，更(geng)(geng)有效的(de)(de)充電(dian)(dian)(dian)方法。

　　設計過程

　　1 充電原理

　　電(dian)池的特性唯一(yi)地決(jue)定其安全性能和充電(dian)的效率。電(dian)池的最佳充電(dian)方法(fa)是由電(dian)池的化學成分(fen)決(jue)定的（鋰離子、鎳氫(qing)、鎳鎘還是SLA電(dian)池等）。盡(jin)管如此(ci)，大多數充電(dian)方案都包(bao)含下面的三個(ge)階(jie)段：

　　● 低電流調節階段
　　● 恒流階段
　　● 恒壓階段/充電終(zhong)止

　　所有電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)都是(shi)通過向自身(shen)傳輸電(dian)(dian)(dian)(dian)(dian)能的(de)(de)方(fang)法進行充電(dian)(dian)(dian)(dian)(dian)的(de)(de)，一節(jie)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)最大充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流取決(jue)于電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)額定容量（C）例(li)如，一節(jie)容量為(wei)1000mAh的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)在充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流為(wei)1000mA時，可以充電(dian)(dian)(dian)(dian)(dian)1C(電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)容量的(de)(de)1倍)也可以用1/50C(20mA)或更低的(de)(de)電(dian)(dian)(dian)(dian)(dian)流給電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充電(dian)(dian)(dian)(dian)(dian)。盡管如此(ci)，這只是(shi)一個(ge)普(pu)通的(de)(de)低電(dian)(dian)(dian)(dian)(dian)流充電(dian)(dian)(dian)(dian)(dian)方(fang)式，不適用于要求短充電(dian)(dian)(dian)(dian)(dian)時間的(de)(de)快速充電(dian)(dian)(dian)(dian)(dian)方(fang)案(an)。

　　現(xian)在使(shi)(shi)用(yong)的(de)(de)大(da)多數(shu)(shu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器在給電(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時都(dou)是(shi)既(ji)使(shi)(shi)用(yong)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)流充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)方(fang)式又使(shi)(shi)用(yong)額定(ding)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)(de)方(fang)法，即容積(ji)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，低(di)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流通常(chang)使(shi)(shi)用(yong)在充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)初始(shi)階段(duan)。在這(zhe)一(yi)階段(duan)，需要將會導致充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過程終(zhong)止的(de)(de)芯片初期的(de)(de)自熱(re)效應減小到最低(di)程度，容積(ji)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)通常(chang)用(yong)在充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)中級階段(duan)，電(dian)(dian)(dian)(dian)(dian)(dian)池的(de)(de)大(da)部(bu)分(fen)能量(liang)都(dou)是(shi)在這(zhe)一(yi)階段(duan)存儲(chu)的(de)(de)。在電(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)最后階段(duan)，通常(chang)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時間(jian)的(de)(de)絕大(da)部(bu)分(fen)都(dou)是(shi)消(xiao)耗在這(zhe)一(yi)階段(duan)，可以通過監測電(dian)(dian)(dian)(dian)(dian)(dian)流、電(dian)(dian)(dian)(dian)(dian)(dian)壓或兩者的(de)(de)值來決(jue)定(ding)何時結(jie)束充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。同樣，結(jie)束方(fang)案(an)依賴于電(dian)(dian)(dian)(dian)(dian)(dian)池的(de)(de)化學特(te)性，例如：大(da)多數(shu)(shu)鋰離(li)子電(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器都(dou)是(shi)將電(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)壓保持在恒定(ding)值，同時檢測最低(di)電(dian)(dian)(dian)(dian)(dian)(dian)流。鎳鎘、NiCd電(dian)(dian)(dian)(dian)(dian)(dian)池用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)壓或溫度的(de)(de)變化率(lv)來決(jue)定(ding)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)結(jie)束時間(jian)。

      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(lai)說,監測它的溫度是至關重要的，因為(wei)電池在過(guo)充(chong)電時會發(fa)生爆裂，在所有的充(chong)電階段都應該(gai)隨時監測溫度的變化，并且在溫度超過(guo)最大(da)設定值時立即停止充(chong)電。

　　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(yong)單片機(ji)A/D端(duan)口，構成電池電壓(ya)，電流(liu)，溫度檢測電路。

　　單(dan)片機通過電壓(ya)反饋和電流反饋信號，直接利(li)用PWM輸出將數字(zi)電壓(ya)信號并轉化成(cheng)模(mo)擬電壓(ya)信號，能夠(gou)保證控制精度。

　　3 控制部分(fen)電路(lu)設計 

　　C8051F310單片機

　　①模擬外設

　　a.10位ADC：轉換(huan)速度可(ke)達200ks/s,可(ke)多達21或17個(ge)外(wai)部(bu)單(dan)端或差分輸(shu)入，VREF可(ke)在外(wai)部(bu)引腳或VDD中選擇，內(nei)置溫度傳感器（±3℃），外(wai)部(bu)轉換(huan)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(wen)度范圍：-40～+85℃。

　　③高速8051微(wei)控制器內核(he)

　　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(huo)定時(shi)器(qi)和(he)外部時(shi)鐘源的實(shi)時(shi)時(shi)鐘方(fang)式。

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

　　充電電流由(you)單(dan)片機脈寬調(diao)制PWM產生，充電電流由(you)AD轉換再(zai)經過計算得出(chu)。

　　4 充(chong)電部(bu)分及檢測部(bu)分電路(lu)設計

　　②快速轉換器

　　實現漸弱終止充(chong)電(dian)器(qi)的(de)最經濟(ji)的(de)方法(fa)就是用(yong)(yong)一(yi)個(ge)(ge)快速轉(zhuan)換(huan)器(qi)。快速轉(zhuan)換(huan)器(qi)是用(yong)(yong)一(yi)個(ge)(ge)電(dian)感和(he)/或(huo)一(yi)個(ge)(ge)變(bian)壓(ya)(ya)器(qi)（需要隔離的(de)時(shi)候用(yong)(yong)變(bian)壓(ya)(ya)器(qi)）作(zuo)為能(neng)量存儲單元(yuan)以離散的(de)能(neng)量包(bao)的(de)形式將能(neng)量從輸(shu)入(ru)傳輸(shu)至輸(shu)出的(de)開(kai)關(guan)調節(jie)器(qi)反饋電(dian)路，通過晶體管來調節(jie)能(neng)量的(de)傳輸(shu)，同(tong)時(shi)也作(zuo)為過濾開(kai)關(guan)，以確保電(dian)壓(ya)(ya)或(huo)電(dian)流(liu)在負(fu)載時(shi)保持恒定。

　　快速調節器的(de)操作是通過控制一(yi)個晶體管開關的(de)占空比來實現的(de)。占空比會自動增(zeng)加以(yi)使電池流入更多的(de)電流。當VBATT

　　③電感的確定

　　電(dian)感(gan)(gan)對交(jiao)(jiao)流(liu)(liu)電(dian)是(shi)有阻礙(ai)(ai)作用的(de)。在(zai)交(jiao)(jiao)流(liu)(liu)電(dian)頻率一(yi)定(ding)(ding)的(de)情況(kuang)下，電(dian)感(gan)(gan)量越(yue)大，對交(jiao)(jiao)流(liu)(liu)電(dian)的(de)阻礙(ai)(ai)能力越(yue)強??一(yi)定(ding)(ding)的(de)情況(kuang)下，交(jiao)(jiao)流(liu)(liu)電(dian)的(de)頻率越(yue)高，電(dian)感(gan)(gan)對交(jiao)(jiao)流(liu)(liu)電(dian)的(de)阻礙(ai)(ai)能力越(yue)大，頻率越(yue)低(di)，電(dian)感(gan)(gan)對交(jiao)(jiao)流(liu)(liu)電(dian)的(de)阻礙(ai)(ai)能力越(yue)小(xiao)。也就是(shi)說，電(dian)感(gan)(gan)有阻止交(jiao)(jiao)流(liu)(liu)電(dian)通(tong)過的(de)特性。

　　其(qi)工作原(yuan)理是這樣的(de)(de)：當負載(zai)兩(liang)(liang)端(duan)(duan)的(de)(de)電(dian)(dian)(dian)(dian)壓(ya)(ya)要(yao)降(jiang)低(di)時，通(tong)過(guo)(guo)MOSFET場(chang)(chang)效(xiao)應管(guan)的(de)(de)開(kai)(kai)關作用，外部(bu)(bu)電(dian)(dian)(dian)(dian)源(yuan)對(dui)電(dian)(dian)(dian)(dian)感(gan)進行充(chong)電(dian)(dian)(dian)(dian)并達(da)到所需的(de)(de)額定(ding)電(dian)(dian)(dian)(dian)壓(ya)(ya)。當負載(zai)兩(liang)(liang)端(duan)(duan)地(di)電(dian)(dian)(dian)(dian)壓(ya)(ya)升高時，通(tong)過(guo)(guo)MOSFET場(chang)(chang)效(xiao)應管(guan)的(de)(de)開(kai)(kai)關作用，外部(bu)(bu)電(dian)(dian)(dian)(dian)源(yuan)供電(dian)(dian)(dian)(dian)斷開(kai)(kai)，電(dian)(dian)(dian)(dian)感(gan)釋放出剛(gang)才充(chong)入的(de)(de)能(neng)量，這時電(dian)(dian)(dian)(dian)感(gan)就變成了電(dian)(dian)(dian)(dian)源(yuan)繼(ji)續對(dui)負載(zai)供電(dian)(dian)(dian)(dian)。隨著(zhu)電(dian)(dian)(dian)(dian)感(gan)上存儲的(de)(de)能(neng)量地(di)消耗。負載(zai)兩(liang)(liang)端(duan)(duan)的(de)(de)電(dian)(dian)(dian)(dian)壓(ya)(ya)開(kai)(kai)始(shi)逐(zhu)漸降(jiang)低(di)，外部(bu)(bu)電(dian)(dian)(dian)(dian)源(yuan)通(tong)過(guo)(guo)MOSFET場(chang)(chang)效(xiao)應管(guan)的(de)(de)開(kai)(kai)關作用又要(yao)充(chong)電(dian)(dian)(dian)(dian)。依次類推在不斷的(de)(de)充(chong)電(dian)(dian)(dian)(dian)和放電(dian)(dian)(dian)(dian)的(de)(de)過(guo)(guo)程中(zhong)形成了一種(zhong)穩(wen)定(ding)的(de)(de)電(dian)(dian)(dian)(dian)壓(ya)(ya)，永遠(yuan)使(shi)負載(zai)兩(liang)(liang)端(duan)(duan)地(di)電(dian)(dian)(dian)(dian)壓(ya)(ya)不會升高也不會降(jiang)低(di)，這就是開(kai)(kai)關電(dian)(dian)(dian)(dian)源(yuan)的(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(ge)PWM的(de)轉(zhuan)換頻率（如方程式(shi)2所示）PWM的(de)轉(zhuan)換頻率越(yue)(yue)大，則電感的(de)值越(yue)(yue)小，也(ye)越(yue)(yue)節約(yue)成本(ben)。

　　我(wo)的(de)示例(li)代碼配置(zhi)F310的(de)8位硬件PWM是使用內部24.5MHz主時鐘的(de)256分頻來產生一個(ge)95.7kHz的(de)轉換速率(lv)。

　　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)的是：在(zai)本電路(lu)中(zhong)的電容(rong)僅僅是一個紋波(bo)(bo)衰(shuai)減器，因為紋波(bo)(bo)與電容(rong)的大(da)小成反比例關系，所以電容(rong)的值越大(da)，衰(shuai)減效果(guo)越好(hao)。