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C8051F310器件(jian)設計鋰離子電(dian)(dian)(dian)(dian)池智能充(chong)電(dian)(dian)(dian)(dian)器的(de)(de)。利用PWM脈寬調(diao)制產(chan)生可用軟件(jian)控(kong)制的(de)(de)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源，以(yi)適應不同階段的(de)(de)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流的(de)(de)要求(qiu)。溫度傳感(gan)器對電(dian)(dian)(dian)(dian)池溫度進行監測，并通(tong)過(guo)AD轉換和相關計算檢測電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓和電(dian)(dian)(dian)(dian)流，以(yi)判(pan)斷電(dian)(dian)(dian)(dian)池到達哪個階段。使(shi)電(dian)(dian)(dian)(dian)池具有(you)更長(chang)的(de)(de)使(shi)用壽命，更有(you)效的(de)(de)充(chong)電(dian)(dian)(dian)(dian)方(fang)法。

　　設計過程

　　1 充電原理

　　電池的(de)特性(xing)(xing)唯(wei)一(yi)地(di)決定其安全(quan)性(xing)(xing)能和(he)充電的(de)效率。電池的(de)最佳充電方(fang)法是(shi)由電池的(de)化學成(cheng)分決定的(de)（鋰離子、鎳(nie)氫、鎳(nie)鎘還是(shi)SLA電池等）。盡管如此，大(da)多數充電方(fang)案都包含下面的(de)三個階段：

低電流調節階段
恒流階段
恒壓(ya)階(jie)段/充電終止

　　所有電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)都是通過向自身傳輸(shu)電(dian)(dian)(dian)(dian)能(neng)的(de)(de)方(fang)法進(jin)行充(chong)電(dian)(dian)(dian)(dian)的(de)(de)，一節電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)最大充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)取決于電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)額定容量（C）例(li)如，一節容量為1000mAh的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)在充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)為1000mA時，可以充(chong)電(dian)(dian)(dian)(dian)1C(電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)容量的(de)(de)1倍)也可以用(yong)1/50C(20mA)或更低的(de)(de)電(dian)(dian)(dian)(dian)流(liu)給電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)。盡(jin)管(guan)如此(ci)，這只是一個普通的(de)(de)低電(dian)(dian)(dian)(dian)流(liu)充(chong)電(dian)(dian)(dian)(dian)方(fang)式，不適用(yong)于要求短充(chong)電(dian)(dian)(dian)(dian)時間的(de)(de)快速充(chong)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(jiang)電(dian)池電(dian)壓保持(chi)在恒定值，同時檢測最(zui)低(di)電(dian)流。鎳鎘(ge)、NiCd電(dian)池用電(dian)壓或溫度的變化率來決定充電(dian)的結束時間。

　　充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)部分電(dian)(dian)(dian)(dian)能被轉(zhuan)換成熱能，直(zhi)至電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)(chong)滿。而充(chong)(chong)(chong)(chong)滿后(hou)，所(suo)(suo)有的(de)(de)(de)電(dian)(dian)(dian)(dian)能將全(quan)部被轉(zhuan)換成熱能。如果此時(shi)不終止充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)池(chi)就會被損壞或燒毀(hui)。快速充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)電(dian)(dian)(dian)(dian)池(chi)（完全(quan)充(chong)(chong)(chong)(chong)滿的(de)(de)(de)時(shi)間小于兩小時(shi)的(de)(de)(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)）則可(ke)以解決這個問題，因(yin)為(wei)這些充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)是使(shi)用高充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流來縮短(duan)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)間的(de)(de)(de)。因(yin)此，對于鋰離子電(dian)(dian)(dian)(dian)池(chi)來說,監測(ce)它(ta)的(de)(de)(de)溫(wen)度是至關(guan)重要的(de)(de)(de)，因(yin)為(wei)電(dian)(dian)(dian)(dian)池(chi)在(zai)(zai)過充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)會發生爆裂，在(zai)(zai)所(suo)(suo)有的(de)(de)(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)階段都應該隨(sui)時(shi)監測(ce)溫(wen)度的(de)(de)(de)變化，并且在(zai)(zai)溫(wen)度超(chao)過最大設定值時(shi)立即停止充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)。

　　2 總體設計

　　充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)路由三部(bu)分(fen)：控制(zhi)部(bu)分(fen)，檢(jian)測(ce)部(bu)分(fen)及充(chong)電(dian)(dian)(dian)部(bu)分(fen)組成。如圖1所(suo)示，采用F310單片機(ji)進行充(chong)電(dian)(dian)(dian)控制(zhi)，單片機(ji)本身(shen)具有(you)脈(mo)寬(kuan)調制(zhi)PWM型開關穩壓(ya)電(dian)(dian)(dian)源所(suo)需的全部(bu)功能，具有(you)10位A/D轉換器。利用單片機(ji)A/D端口，構成電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)，電(dian)(dian)(dian)流，溫(wen)度檢(jian)測(ce)電(dian)(dian)(dian)路。

圖1 鋰離子電池(chi)充(chong)電模塊(kuai)圖

　　單片(pian)機通過電(dian)壓(ya)反(fan)饋(kui)和電(dian)流反(fan)饋(kui)信號，直接利用PWM輸出將數字電(dian)壓(ya)信號并轉化成(cheng)模擬電(dian)壓(ya)信號，能夠(gou)保(bao)證控制精(jing)度。

　　3 控制部分電路(lu)設計

　　C8051F310單(dan)片機

　　①模擬外設

　　a.10位ADC：轉換速度(du)可達200ks/s,可多達21或17個外(wai)部單端或差(cha)分輸入，VREF可在外(wai)部引腳(jiao)或VDD中選擇，內置溫度(du)傳感器（±3℃），外(wai)部轉換啟動輸入；

　　b.兩個模擬比較器：可(ke)(ke)編程(cheng)回差電(dian)壓和響應(ying)時(shi)間，可(ke)(ke)配置(zhi)為中斷或復(fu)位源，小電(dian)流（〈0.5μA）。

　　②供電電壓

　　a.典(dian)型工(gong)作(zuo)電流：5mA、25MHz；

　　b.典型停(ting)機電流：0.1μA；

　　c.溫(wen)度范圍(wei)：-40～+85℃。

　　③高速8051微控制(zhi)器內核(he)

　　a.流(liu)水線指令(ling)結構：70%的指令(ling)的執行時間(jian)為(wei)一個或兩個系統時鐘周期；

　　b.速度可達(da)25MI/s（時鐘頻率為25MHz時）；

　　c.擴展的(de)中(zhong)斷系統。

　　④數字外設

　　a.29/25個端(duan)口I/O：所(suo)有的口線均耐5V電壓；

　　b.4個通用(yong)16位計數(shu)器/定時(shi)器；

　　c.16位可編程計數器/定時(shi)器陣列(lie)（PCA），有5個捕捉/比較模塊；

　　d.使用PCA或定(ding)時(shi)器和(he)外(wai)部時(shi)鐘(zhong)源的實時(shi)時(shi)鐘(zhong)方式。

　　控制電(dian)路中如圖2所示，P0.3口(kou)提(ti)供(gong)充(chong)(chong)電(dian)電(dian)源(yuan)，P0.6口(kou)檢測充(chong)(chong)電(dian)電(dian)壓的大(da)小(xiao)，P0.5口(kou)檢測充(chong)(chong)電(dian)電(dian)流的大(da)小(xiao)，P0.4口(kou)檢測電(dian)池(chi)的溫度。

圖2 控(kong)制(zhi)電路接線圖

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

4 充電(dian)(dian)部分(fen)及檢測(ce)部分(fen)電(dian)(dian)路設計

　　圖3為(wei)充電(dian)電(dian)路與檢測電(dian)路圖。

圖(tu)3 充電(dian)電(dian)路與檢測電(dian)路圖(tu)

　　①充電過程曲線

　　如圖4所示(shi)，充電(dian)過(guo)程由預充狀態，恒流充電(dian)狀態和恒壓充電(dian)狀態組(zu)成。

圖(tu)4 鋰(li)電池充電曲線

　　②快速轉換器

　　實現漸弱終止充電(dian)器(qi)(qi)的最經(jing)濟的方法就是用(yong)一(yi)個(ge)(ge)快速轉換(huan)器(qi)(qi)。快速轉換(huan)器(qi)(qi)是用(yong)一(yi)個(ge)(ge)電(dian)感和/或(huo)一(yi)個(ge)(ge)變壓器(qi)(qi)（需要(yao)隔離(li)的時(shi)候用(yong)變壓器(qi)(qi)）作為能量(liang)(liang)存儲單元以離(li)散的能量(liang)(liang)包的形(xing)式(shi)將能量(liang)(liang)從輸入(ru)傳輸至(zhi)輸出的開關調節器(qi)(qi)反饋電(dian)路，通過晶體(ti)管來調節能量(liang)(liang)的傳輸，同時(shi)也作為過濾開關，以確保電(dian)壓或(huo)電(dian)流在負載時(shi)保持恒定。

　　快速調節(jie)器的(de)(de)操作是(shi)通過控制一個晶(jing)體(ti)管(guan)開關的(de)(de)占(zhan)(zhan)空(kong)比(bi)來實現的(de)(de)。占(zhan)(zhan)空(kong)比(bi)會自動增加以使電(dian)池(chi)流入(ru)更多的(de)(de)電(dian)流。當(dang)VBATT

a 開關閉合

b 開關打開
圖5 快速(su)轉換器操作

　　③電感的確定

　　電(dian)(dian)(dian)感(gan)對(dui)(dui)交(jiao)流(liu)(liu)電(dian)(dian)(dian)是有阻(zu)(zu)礙(ai)作用的(de)。在交(jiao)流(liu)(liu)電(dian)(dian)(dian)頻(pin)率一(yi)定的(de)情(qing)況下，電(dian)(dian)(dian)感(gan)量越大，對(dui)(dui)交(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)阻(zu)(zu)礙(ai)能力越強，電(dian)(dian)(dian)感(gan)量越小，其阻(zu)(zu)礙(ai)能力越小。另外，在電(dian)(dian)(dian)感(gan)量一(yi)定的(de)情(qing)況下，交(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)頻(pin)率越高，電(dian)(dian)(dian)感(gan)對(dui)(dui)交(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)阻(zu)(zu)礙(ai)能力越大，頻(pin)率越低，電(dian)(dian)(dian)感(gan)對(dui)(dui)交(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)阻(zu)(zu)礙(ai)能力越小。也就是說，電(dian)(dian)(dian)感(gan)有阻(zu)(zu)止交(jiao)流(liu)(liu)電(dian)(dian)(dian)通(tong)過的(de)特(te)性。

　　其工(gong)作(zuo)(zuo)原理是這樣的(de)(de)(de)：當負(fu)載兩(liang)端(duan)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)要(yao)降低時(shi)(shi)，通過MOSFET場(chang)效應管的(de)(de)(de)開(kai)關作(zuo)(zuo)用(yong)，外(wai)(wai)部電(dian)(dian)(dian)(dian)(dian)源對(dui)(dui)電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)進(jin)行充(chong)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)載兩(liang)端(duan)地(di)(di)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)升高時(shi)(shi)，通過MOSFET場(chang)效應管的(de)(de)(de)開(kai)關作(zuo)(zuo)用(yong)，外(wai)(wai)部電(dian)(dian)(dian)(dian)(dian)源供電(dian)(dian)(dian)(dian)(dian)斷開(kai)，電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)釋(shi)放(fang)出剛才(cai)充(chong)入的(de)(de)(de)能(neng)量(liang)，這時(shi)(shi)電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)就(jiu)(jiu)變(bian)成了(le)電(dian)(dian)(dian)(dian)(dian)源繼續對(dui)(dui)負(fu)載供電(dian)(dian)(dian)(dian)(dian)。隨著(zhu)電(dian)(dian)(dian)(dian)(dian)感(gan)(gan)(gan)上(shang)存儲(chu)的(de)(de)(de)能(neng)量(liang)地(di)(di)消(xiao)耗。負(fu)載兩(liang)端(duan)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)開(kai)始逐(zhu)漸降低，外(wai)(wai)部電(dian)(dian)(dian)(dian)(dian)源通過MOSFET場(chang)效應管的(de)(de)(de)開(kai)關作(zuo)(zuo)用(yong)又要(yao)充(chong)電(dian)(dian)(dian)(dian)(dian)。依(yi)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)過程中形(xing)成了(le)一種穩定的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，永遠使(shi)負(fu)載兩(liang)端(duan)地(di)(di)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)不(bu)會(hui)升高也不(bu)會(hui)降低，這就(jiu)(jiu)是開(kai)關電(dian)(dian)(dian)(dian)(dian)源的(de)(de)(de)最大優勢。

　　要確定(ding)快速轉換器中電感的(de)大小首(shou)先應(ying)假定(ding)晶體管(guan)的(de)占(zhan)空比為50%，因為此時的(de)轉換器操作操作效(xiao)率最高。占(zhan)空比由(you)方(fang)程式1給(gei)出：

　　（其中T是PWM的周期(qi)在(zai)程(cheng)序示例中T=10.5s）

　　占空比=ton/T（1）

　　至(zhi)此就可以選擇(ze)一(yi)個PWM的(de)轉換頻(pin)率（如方程式2所(suo)示）PWM的(de)轉換頻(pin)率越(yue)大，則電感的(de)值越(yue)小，也(ye)越(yue)節約成本。

　　我的(de)示(shi)例代(dai)碼配(pei)置F310的(de)8位硬件PWM是使用內部24.5MHz主(zhu)時(shi)鐘的(de)256分頻來產生一個95.7kHz的(de)轉換(huan)速率(lv)。

　　L=（Vi-Vsat-Voton）/2Iomax（2）

　　現(xian)在(zai)我們可以計算電(dian)(dian)感(gan)的大小了，假定充電(dian)(dian)電(dian)(dian)壓(ya)Vi的值為15V，飽和電(dian)(dian)壓(ya)Vsat的值為0.5V，需要獲得的輸出(chu)電(dian)(dian)壓(ya)值為4.2V,并且最大輸出(chu)電(dian)(dian)流IＯMAX為1500mA，那么，電(dian)(dian)感(gan)的值至少應(ying)選為18H。

　　需要(yao)注意的是(shi)：在(zai)本電路中的電容僅(jin)(jin)僅(jin)(jin)是(shi)一(yi)個紋(wen)波(bo)(bo)衰減器，因為(wei)紋(wen)波(bo)(bo)與電容的大小成反比例關系，所(suo)以電容的值越(yue)大，衰減效果越(yue)好。