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)C8051F310器(qi)件設計鋰離子(zi)電(dian)(dian)(dian)池(chi)智(zhi)能(neng)充(chong)電(dian)(dian)(dian)器(qi)的。利用(yong)PWM脈寬調制產生可用(yong)軟件控(kong)制的充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)，以適應不同階(jie)段的充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流的要求。溫度(du)(du)傳感器(qi)對(dui)電(dian)(dian)(dian)池(chi)溫度(du)(du)進行監(jian)測，并通過AD轉換(huan)和(he)相關計算(suan)檢測電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓和(he)電(dian)(dian)(dian)流，以判(pan)斷電(dian)(dian)(dian)池(chi)到達哪個階(jie)段。使(shi)電(dian)(dian)(dian)池(chi)具有更長的使(shi)用(yong)壽(shou)命，更有效(xiao)的充(chong)電(dian)(dian)(dian)方(fang)法。

　　設計過程

　　1 充電原理

　　電(dian)(dian)(dian)池的(de)(de)特性唯一地(di)決定其安全(quan)性能和充電(dian)(dian)(dian)的(de)(de)效率(lv)。電(dian)(dian)(dian)池的(de)(de)最(zui)佳充電(dian)(dian)(dian)方(fang)法是由電(dian)(dian)(dian)池的(de)(de)化學成分決定的(de)(de)（鋰離子、鎳氫(qing)、鎳鎘(ge)還是SLA電(dian)(dian)(dian)池等）。盡管如此，大多數(shu)充電(dian)(dian)(dian)方(fang)案(an)都包含下面的(de)(de)三個(ge)階段(duan)：

低電流調節階段
恒流階段
恒壓階(jie)段/充電終止

　　所(suo)有電(dian)(dian)(dian)(dian)池(chi)(chi)都(dou)是通(tong)過向自(zi)身(shen)傳輸電(dian)(dian)(dian)(dian)能的方法進(jin)行充(chong)(chong)電(dian)(dian)(dian)(dian)的，一(yi)(yi)節電(dian)(dian)(dian)(dian)池(chi)(chi)的最大充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流取決于電(dian)(dian)(dian)(dian)池(chi)(chi)的額定容(rong)(rong)量（C）例(li)如，一(yi)(yi)節容(rong)(rong)量為1000mAh的電(dian)(dian)(dian)(dian)池(chi)(chi)在充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流為1000mA時，可(ke)以(yi)充(chong)(chong)電(dian)(dian)(dian)(dian)1C(電(dian)(dian)(dian)(dian)池(chi)(chi)容(rong)(rong)量的1倍)也(ye)可(ke)以(yi)用(yong)1/50C(20mA)或更(geng)低的電(dian)(dian)(dian)(dian)流給電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)。盡管如此(ci)，這只是一(yi)(yi)個普通(tong)的低電(dian)(dian)(dian)(dian)流充(chong)(chong)電(dian)(dian)(dian)(dian)方式，不(bu)適用(yong)于要求短充(chong)(chong)電(dian)(dian)(dian)(dian)時間的快(kuai)速充(chong)(chong)電(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(chi)電(dian)壓保(bao)持在恒定值(zhi)，同(tong)時檢測(ce)最低電(dian)流(liu)。鎳鎘、NiCd電(dian)池(chi)用電(dian)壓或溫度的變化率來決定充電(dian)的結束時間(jian)。

　　充(chong)(chong)(chong)(chong)電(dian)(dian)時部分電(dian)(dian)能被轉(zhuan)換(huan)成熱(re)能，直至電(dian)(dian)池充(chong)(chong)(chong)(chong)滿(man)(man)。而充(chong)(chong)(chong)(chong)滿(man)(man)后，所有的(de)(de)電(dian)(dian)能將全部被轉(zhuan)換(huan)成熱(re)能。如(ru)果此(ci)時不終止充(chong)(chong)(chong)(chong)電(dian)(dian)，電(dian)(dian)池就(jiu)會(hui)被損壞或燒(shao)毀。快速充(chong)(chong)(chong)(chong)電(dian)(dian)器電(dian)(dian)池（完全充(chong)(chong)(chong)(chong)滿(man)(man)的(de)(de)時間小于兩小時的(de)(de)充(chong)(chong)(chong)(chong)電(dian)(dian)器）則可(ke)以解決這(zhe)個問(wen)題，因(yin)(yin)為(wei)這(zhe)些(xie)充(chong)(chong)(chong)(chong)電(dian)(dian)器是使用高(gao)充(chong)(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流來(lai)縮短充(chong)(chong)(chong)(chong)電(dian)(dian)時間的(de)(de)。因(yin)(yin)此(ci)，對于鋰離(li)子電(dian)(dian)池來(lai)說,監測它的(de)(de)溫度(du)是至關重要的(de)(de)，因(yin)(yin)為(wei)電(dian)(dian)池在過充(chong)(chong)(chong)(chong)電(dian)(dian)時會(hui)發生爆裂，在所有的(de)(de)充(chong)(chong)(chong)(chong)電(dian)(dian)階段都應該隨時監測溫度(du)的(de)(de)變化，并且在溫度(du)超(chao)過最大(da)設定值時立即停止充(chong)(chong)(chong)(chong)電(dian)(dian)。

　　2 總體設計

　　充電(dian)電(dian)路由三部(bu)分：控制(zhi)部(bu)分，檢(jian)測部(bu)分及充電(dian)部(bu)分組成(cheng)。如圖(tu)1所示(shi)，采用F310單片機進(jin)行充電(dian)控制(zhi)，單片機本身具有(you)脈寬調制(zhi)PWM型開(kai)關穩壓電(dian)源所需的全部(bu)功能，具有(you)10位(wei)A/D轉換(huan)器。利(li)用單片機A/D端口，構(gou)成(cheng)電(dian)池電(dian)壓，電(dian)流，溫度檢(jian)測電(dian)路。

圖(tu)1 鋰(li)離子電(dian)池(chi)充(chong)電(dian)模塊圖(tu)

　　單片機通過電(dian)(dian)壓反饋(kui)和電(dian)(dian)流(liu)反饋(kui)信號，直接(jie)利用(yong)PWM輸出(chu)將數字電(dian)(dian)壓信號并(bing)轉化成模擬電(dian)(dian)壓信號，能夠保證控制精度(du)。

　　3 控制部分電(dian)路設計(ji)

　　C8051F310單片機

　　①模擬外設

　　a.10位ADC：轉(zhuan)換(huan)速度可(ke)達200ks/s,可(ke)多達21或17個外部(bu)(bu)單端或差分輸入(ru)(ru)，VREF可(ke)在外部(bu)(bu)引腳或VDD中選擇，內置溫度傳感器(qi)（±3℃），外部(bu)(bu)轉(zhuan)換(huan)啟動輸入(ru)(ru)；

　　b.兩個模擬比較(jiao)器：可(ke)編程回差電(dian)壓和響應(ying)時間，可(ke)配置為中斷或(huo)復位(wei)源，小電(dian)流（〈0.5μA）。

　　②供電電壓

　　a.典(dian)型工作(zuo)電流：5mA、25MHz；

　　b.典型停機電流：0.1μA；

　　c.溫度(du)范圍(wei)：-40～+85℃。

　　③高速(su)8051微(wei)控制(zhi)器內核

　　a.流(liu)水線指令結構：70%的(de)指令的(de)執行時(shi)間為一個或兩個系(xi)統時(shi)鐘周期(qi)；

　　b.速度可達25MI/s（時鐘頻率為(wei)25MHz時）；

　　c.擴展的(de)中斷系統。

　　④數字外設

　　a.29/25個端口I/O：所(suo)有(you)的口線均耐(nai)5V電壓(ya)；

　　b.4個通用16位計數器/定時器；

　　c.16位可編程計數器(qi)/定(ding)時器(qi)陣列(lie)（PCA），有(you)5個(ge)捕(bu)捉(zhuo)/比較(jiao)模塊(kuai)；

　　d.使用PCA或定時(shi)(shi)(shi)器和外(wai)部時(shi)(shi)(shi)鐘(zhong)源的實(shi)時(shi)(shi)(shi)時(shi)(shi)(shi)鐘(zhong)方式(shi)。

　　控制電(dian)(dian)(dian)路中如圖2所示，P0.3口(kou)提供充電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)，P0.6口(kou)檢(jian)測(ce)(ce)充電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)的(de)大小，P0.5口(kou)檢(jian)測(ce)(ce)充電(dian)(dian)(dian)電(dian)(dian)(dian)流的(de)大小，P0.4口(kou)檢(jian)測(ce)(ce)電(dian)(dian)(dian)池的(de)溫度。

圖(tu)2 控(kong)制(zhi)電路接線(xian)圖(tu)

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

4 充電部分(fen)及檢測部分(fen)電路設計

　　圖(tu)3為充(chong)電電路與檢測電路圖(tu)。

圖3 充電(dian)電(dian)路與檢測(ce)電(dian)路圖

　　①充電過程曲線

　　如圖(tu)4所(suo)示，充(chong)電(dian)過程由預(yu)充(chong)狀態，恒流充(chong)電(dian)狀態和恒壓充(chong)電(dian)狀態組成。

圖4 鋰電池充電曲(qu)線(xian)

　　②快速轉換器

　　實現漸(jian)弱終止充(chong)電(dian)器(qi)(qi)的最經濟(ji)的方法就(jiu)是用(yong)一(yi)(yi)個(ge)快(kuai)速轉(zhuan)換器(qi)(qi)。快(kuai)速轉(zhuan)換器(qi)(qi)是用(yong)一(yi)(yi)個(ge)電(dian)感和(he)/或(huo)一(yi)(yi)個(ge)變(bian)壓(ya)器(qi)(qi)（需要隔離(li)(li)的時(shi)候用(yong)變(bian)壓(ya)器(qi)(qi)）作為(wei)能量(liang)存儲單元以(yi)離(li)(li)散(san)的能量(liang)包的形式(shi)將能量(liang)從輸入(ru)傳(chuan)輸至輸出的開(kai)關調節(jie)器(qi)(qi)反饋電(dian)路，通過晶體管來調節(jie)能量(liang)的傳(chuan)輸，同時(shi)也(ye)作為(wei)過濾開(kai)關，以(yi)確保電(dian)壓(ya)或(huo)電(dian)流在負載時(shi)保持恒定(ding)。

　　快速(su)調節(jie)器的操作是通(tong)過控(kong)制一個晶(jing)體管開關的占空比來(lai)實現的。占空比會自動增加以使電池流入(ru)更多的電流。當VBATT

a 開關閉合

b 開關打開
圖5 快速(su)轉換器操作(zuo)

　　③電感的確定

　　電(dian)(dian)(dian)感對交(jiao)流電(dian)(dian)(dian)是(shi)有阻(zu)礙作用的(de)。在交(jiao)流電(dian)(dian)(dian)頻(pin)(pin)率(lv)一(yi)定的(de)情況下，電(dian)(dian)(dian)感量(liang)越(yue)(yue)大，對交(jiao)流電(dian)(dian)(dian)的(de)阻(zu)礙能力(li)越(yue)(yue)強，電(dian)(dian)(dian)感量(liang)越(yue)(yue)小(xiao)，其阻(zu)礙能力(li)越(yue)(yue)小(xiao)。另(ling)外，在電(dian)(dian)(dian)感量(liang)一(yi)定的(de)情況下，交(jiao)流電(dian)(dian)(dian)的(de)頻(pin)(pin)率(lv)越(yue)(yue)高(gao)，電(dian)(dian)(dian)感對交(jiao)流電(dian)(dian)(dian)的(de)阻(zu)礙能力(li)越(yue)(yue)大，頻(pin)(pin)率(lv)越(yue)(yue)低，電(dian)(dian)(dian)感對交(jiao)流電(dian)(dian)(dian)的(de)阻(zu)礙能力(li)越(yue)(yue)小(xiao)。也(ye)就是(shi)說，電(dian)(dian)(dian)感有阻(zu)止交(jiao)流電(dian)(dian)(dian)通過的(de)特性。

　　其工作原理是這(zhe)樣的(de)(de)(de)：當負載(zai)兩端的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)要降(jiang)低時(shi)，通(tong)過(guo)MOSFET場(chang)效應(ying)管(guan)的(de)(de)(de)開關(guan)(guan)作用，外部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)對(dui)電(dian)(dian)(dian)(dian)(dian)感(gan)進行(xing)充(chong)電(dian)(dian)(dian)(dian)(dian)并達到(dao)所(suo)需的(de)(de)(de)額定電(dian)(dian)(dian)(dian)(dian)壓(ya)。當負載(zai)兩端地電(dian)(dian)(dian)(dian)(dian)壓(ya)升高時(shi)，通(tong)過(guo)MOSFET場(chang)效應(ying)管(guan)的(de)(de)(de)開關(guan)(guan)作用，外部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)供電(dian)(dian)(dian)(dian)(dian)斷開，電(dian)(dian)(dian)(dian)(dian)感(gan)釋放(fang)出剛才充(chong)入的(de)(de)(de)能量，這(zhe)時(shi)電(dian)(dian)(dian)(dian)(dian)感(gan)就(jiu)變成(cheng)了電(dian)(dian)(dian)(dian)(dian)源(yuan)繼續對(dui)負載(zai)供電(dian)(dian)(dian)(dian)(dian)。隨著電(dian)(dian)(dian)(dian)(dian)感(gan)上存儲的(de)(de)(de)能量地消耗(hao)。負載(zai)兩端的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)開始逐漸降(jiang)低，外部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)通(tong)過(guo)MOSFET場(chang)效應(ying)管(guan)的(de)(de)(de)開關(guan)(guan)作用又(you)要充(chong)電(dian)(dian)(dian)(dian)(dian)。依次類推(tui)在不(bu)斷的(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)和放(fang)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)過(guo)程中形(xing)成(cheng)了一種穩定的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)，永遠(yuan)使負載(zai)兩端地電(dian)(dian)(dian)(dian)(dian)壓(ya)不(bu)會升高也不(bu)會降(jiang)低，這(zhe)就(jiu)是開關(guan)(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)最大優(you)勢(shi)。

　　要確定(ding)快速轉換(huan)器中電感的大小首先應假定(ding)晶體管的占空比為50%，因為此時(shi)的轉換(huan)器操作操作效(xiao)率最高。占空比由(you)方程式1給出：

　　（其中T是PWM的(de)周期在程序示例中T=10.5s）

　　占空比(bi)=ton/T（1）

　　至此(ci)就可以選擇(ze)一個PWM的轉換頻(pin)率（如(ru)方程式2所示）PWM的轉換頻(pin)率越(yue)(yue)大，則電感的值(zhi)越(yue)(yue)小，也越(yue)(yue)節約(yue)成本(ben)。

　　我的(de)示例代碼配置F310的(de)8位硬件PWM是使用內(nei)部24.5MHz主(zhu)時鐘(zhong)的(de)256分頻來(lai)產生(sheng)一個95.7kHz的(de)轉換(huan)速率(lv)。

　　L=（Vi-Vsat-Voton）/2Iomax（2）

　　現(xian)在我(wo)們可以(yi)計算電(dian)(dian)感的大小了(le)，假定充電(dian)(dian)電(dian)(dian)壓(ya)Vi的值(zhi)(zhi)(zhi)為(wei)(wei)15V，飽和電(dian)(dian)壓(ya)Vsat的值(zhi)(zhi)(zhi)為(wei)(wei)0.5V，需要獲得(de)的輸出電(dian)(dian)壓(ya)值(zhi)(zhi)(zhi)為(wei)(wei)4.2V,并且最(zui)大輸出電(dian)(dian)流IＯMAX為(wei)(wei)1500mA，那么，電(dian)(dian)感的值(zhi)(zhi)(zhi)至(zhi)少(shao)應選為(wei)(wei)18H。

　　需要注意的是：在本電路中(zhong)的電容(rong)僅(jin)僅(jin)是一個紋(wen)波衰減器(qi)，因為紋(wen)波與電容(rong)的大(da)小成(cheng)反(fan)比例關(guan)系，所以電容(rong)的值(zhi)越大(da)，衰減效果越好。