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(ben)文討論使用C8051F310器(qi)件設(she)計鋰(li)離子電(dian)(dian)池(chi)智能(neng)充電(dian)(dian)器(qi)的(de)(de)(de)。利用PWM脈寬調(diao)制產生可用軟件控制的(de)(de)(de)充電(dian)(dian)電(dian)(dian)源(yuan)，以(yi)適應不同階(jie)段(duan)的(de)(de)(de)充電(dian)(dian)電(dian)(dian)流(liu)的(de)(de)(de)要(yao)求。溫度(du)傳(chuan)感器(qi)對電(dian)(dian)池(chi)溫度(du)進行監測，并通過(guo)AD轉換和相(xiang)關計算檢測電(dian)(dian)池(chi)充電(dian)(dian)電(dian)(dian)壓和電(dian)(dian)流(liu)，以(yi)判斷電(dian)(dian)池(chi)到達哪個階(jie)段(duan)。使電(dian)(dian)池(chi)具(ju)有更長的(de)(de)(de)使用壽命，更有效(xiao)的(de)(de)(de)充電(dian)(dian)方(fang)法。

　　設計過程

　　1 充電原理

　　電(dian)池(chi)(chi)(chi)的(de)特性唯一(yi)地決(jue)定(ding)其安全性能和充(chong)電(dian)的(de)效率。電(dian)池(chi)(chi)(chi)的(de)最佳充(chong)電(dian)方(fang)法是由電(dian)池(chi)(chi)(chi)的(de)化學成(cheng)分決(jue)定(ding)的(de)（鋰離子、鎳氫、鎳鎘還是SLA電(dian)池(chi)(chi)(chi)等）。盡管如此，大多數充(chong)電(dian)方(fang)案(an)都包含下面的(de)三個階(jie)段(duan)：

低電流調節階段
恒流階段
恒(heng)壓階段/充電終止

　　所有(you)電(dian)(dian)(dian)(dian)池都(dou)是通過向自(zi)身傳輸(shu)電(dian)(dian)(dian)(dian)能(neng)的(de)(de)(de)方(fang)法(fa)進行充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)(de)(de)，一(yi)節(jie)電(dian)(dian)(dian)(dian)池的(de)(de)(de)最大充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)取決于(yu)電(dian)(dian)(dian)(dian)池的(de)(de)(de)額定容(rong)量（C）例(li)如，一(yi)節(jie)容(rong)量為1000mAh的(de)(de)(de)電(dian)(dian)(dian)(dian)池在充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)為1000mA時，可(ke)以充(chong)(chong)電(dian)(dian)(dian)(dian)1C(電(dian)(dian)(dian)(dian)池容(rong)量的(de)(de)(de)1倍)也可(ke)以用1/50C(20mA)或更低的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)給(gei)電(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)。盡管如此，這只是一(yi)個普(pu)通的(de)(de)(de)低電(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)方(fang)式(shi)，不(bu)適(shi)用于(yu)要求(qiu)短(duan)充(chong)(chong)電(dian)(dian)(dian)(dian)時間的(de)(de)(de)快速充(chong)(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電(dian)池電(dian)壓保持在恒定值，同時檢測最低電(dian)流。鎳鎘、NiCd電(dian)池用電(dian)壓或溫度的變化(hua)率來決定充電(dian)的結束時間(jian)。

　　充電(dian)(dian)(dian)時(shi)(shi)部分電(dian)(dian)(dian)能被(bei)(bei)轉(zhuan)換成(cheng)熱(re)能，直(zhi)至電(dian)(dian)(dian)池(chi)充滿。而充滿后，所有(you)的(de)(de)電(dian)(dian)(dian)能將全(quan)部被(bei)(bei)轉(zhuan)換成(cheng)熱(re)能。如果此(ci)時(shi)(shi)不終止(zhi)充電(dian)(dian)(dian)，電(dian)(dian)(dian)池(chi)就會被(bei)(bei)損(sun)壞或燒毀。快(kuai)速(su)充電(dian)(dian)(dian)器電(dian)(dian)(dian)池(chi)（完全(quan)充滿的(de)(de)時(shi)(shi)間小于兩小時(shi)(shi)的(de)(de)充電(dian)(dian)(dian)器）則可以解決這個問(wen)題(ti)，因(yin)為這些充電(dian)(dian)(dian)器是使用高(gao)充電(dian)(dian)(dian)電(dian)(dian)(dian)流來縮(suo)短充電(dian)(dian)(dian)時(shi)(shi)間的(de)(de)。因(yin)此(ci)，對于鋰離(li)子電(dian)(dian)(dian)池(chi)來說,監測它的(de)(de)溫度是至關重要的(de)(de)，因(yin)為電(dian)(dian)(dian)池(chi)在(zai)過充電(dian)(dian)(dian)時(shi)(shi)會發生爆裂，在(zai)所有(you)的(de)(de)充電(dian)(dian)(dian)階段都應(ying)該隨時(shi)(shi)監測溫度的(de)(de)變化，并且在(zai)溫度超過最(zui)大設定值時(shi)(shi)立(li)即(ji)停止(zhi)充電(dian)(dian)(dian)。

　　2 總體設計

　　充(chong)電(dian)電(dian)路(lu)由(you)三部(bu)(bu)(bu)(bu)分(fen)：控(kong)制(zhi)部(bu)(bu)(bu)(bu)分(fen)，檢測部(bu)(bu)(bu)(bu)分(fen)及充(chong)電(dian)部(bu)(bu)(bu)(bu)分(fen)組成。如圖1所(suo)示，采用(yong)F310單片機(ji)進行充(chong)電(dian)控(kong)制(zhi)，單片機(ji)本(ben)身具有脈寬調制(zhi)PWM型開(kai)關穩壓電(dian)源(yuan)所(suo)需的全部(bu)(bu)(bu)(bu)功能，具有10位A/D轉換器。利用(yong)單片機(ji)A/D端口，構(gou)成電(dian)池電(dian)壓，電(dian)流，溫度檢測電(dian)路(lu)。

圖1 鋰(li)離子電池充電模塊圖

　　單片(pian)機通過電(dian)(dian)壓(ya)反(fan)饋(kui)和電(dian)(dian)流反(fan)饋(kui)信(xin)號，直接利用PWM輸出將數字電(dian)(dian)壓(ya)信(xin)號并(bing)轉化成模擬電(dian)(dian)壓(ya)信(xin)號，能夠保證控(kong)制精度。

　　3 控制部分電路(lu)設計(ji)

　　C8051F310單(dan)片機

　　①模擬外設

　　a.10位(wei)ADC：轉(zhuan)換速度(du)可(ke)達(da)200ks/s,可(ke)多達(da)21或17個外部單端(duan)或差分輸入(ru)，VREF可(ke)在外部引腳(jiao)或VDD中選擇，內置(zhi)溫度(du)傳感(gan)器（±3℃），外部轉(zhuan)換啟動輸入(ru)；

　　b.兩個(ge)模擬(ni)比較器(qi)：可(ke)(ke)編程回差電壓和響應時間，可(ke)(ke)配(pei)置為中斷或復位源，小電流（〈0.5μA）。

　　②供電電壓

　　a.典型工作(zuo)電流：5mA、25MHz；

　　b.典型停機(ji)電流：0.1μA；

　　c.溫度范(fan)圍：-40～+85℃。

　　③高(gao)速8051微控制(zhi)器內(nei)核

　　a.流水線指令(ling)結構(gou)：70%的(de)指令(ling)的(de)執行時(shi)間為一個或兩個系(xi)統(tong)時(shi)鐘周(zhou)期；

　　b.速度可達25MI/s（時鐘(zhong)頻率為25MHz時）；

　　c.擴(kuo)展(zhan)的中(zhong)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(ya)；

　　b.4個通用16位(wei)計(ji)數器/定時器；

　　c.16位可(ke)編(bian)程計數器(qi)/定(ding)時器(qi)陣列（PCA），有5個捕捉/比較模塊；

　　d.使用PCA或定時器和外部時鐘源的實(shi)時時鐘方式。

　　控制電(dian)(dian)路中如圖2所示，P0.3口(kou)提供充(chong)(chong)電(dian)(dian)電(dian)(dian)源，P0.6口(kou)檢測充(chong)(chong)電(dian)(dian)電(dian)(dian)壓的大小(xiao)，P0.5口(kou)檢測充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)的大小(xiao)，P0.4口(kou)檢測電(dian)(dian)池的溫度。

圖2 控制電路接線(xian)圖

　　充電(dian)電(dian)流由單片機脈寬調制PWM產生，充電(dian)電(dian)流由AD轉(zhuan)換(huan)再(zai)經過計算(suan)得出。

4 充電部(bu)分(fen)及檢測部(bu)分(fen)電路設計

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

圖3 充電電路(lu)與(yu)檢測電路(lu)圖

　　①充電過程曲線

　　如圖4所(suo)示(shi)，充(chong)(chong)電(dian)過程由預充(chong)(chong)狀(zhuang)態(tai)(tai)，恒(heng)流充(chong)(chong)電(dian)狀(zhuang)態(tai)(tai)和恒(heng)壓(ya)充(chong)(chong)電(dian)狀(zhuang)態(tai)(tai)組成。

圖(tu)4 鋰電池(chi)充電曲線

　　②快速轉換器

　　實現漸(jian)弱終止充電(dian)(dian)(dian)器(qi)(qi)的最經濟的方(fang)法就是用(yong)一個(ge)快速(su)轉(zhuan)換(huan)器(qi)(qi)。快速(su)轉(zhuan)換(huan)器(qi)(qi)是用(yong)一個(ge)電(dian)(dian)(dian)感和/或一個(ge)變壓(ya)器(qi)(qi)（需要隔離的時候用(yong)變壓(ya)器(qi)(qi)）作(zuo)為(wei)能量(liang)存儲單(dan)元以離散的能量(liang)包的形(xing)式將能量(liang)從輸(shu)入傳(chuan)輸(shu)至輸(shu)出的開關調(diao)節器(qi)(qi)反饋電(dian)(dian)(dian)路，通過(guo)晶體(ti)管來(lai)調(diao)節能量(liang)的傳(chuan)輸(shu)，同(tong)時也作(zuo)為(wei)過(guo)濾開關，以確保電(dian)(dian)(dian)壓(ya)或電(dian)(dian)(dian)流在負(fu)載(zai)時保持恒定。

　　快速(su)調節器的(de)(de)操作是(shi)通過(guo)控制一個晶體管開(kai)關(guan)的(de)(de)占空比(bi)來實現的(de)(de)。占空比(bi)會自動增加(jia)以(yi)使電池流入(ru)更多的(de)(de)電流。當(dang)VBATT

a 開關閉合

b 開關打開
圖5 快速轉換器操作

　　③電感的確定

　　電(dian)(dian)(dian)(dian)感(gan)(gan)(gan)對(dui)交流(liu)電(dian)(dian)(dian)(dian)是有阻礙作用的(de)。在(zai)交流(liu)電(dian)(dian)(dian)(dian)頻率一定(ding)(ding)的(de)情況下，電(dian)(dian)(dian)(dian)感(gan)(gan)(gan)量(liang)越大(da)，對(dui)交流(liu)電(dian)(dian)(dian)(dian)的(de)阻礙能力(li)越強(qiang)，電(dian)(dian)(dian)(dian)感(gan)(gan)(gan)量(liang)越小(xiao)，其阻礙能力(li)越小(xiao)。另外(wai)，在(zai)電(dian)(dian)(dian)(dian)感(gan)(gan)(gan)量(liang)一定(ding)(ding)的(de)情況下，交流(liu)電(dian)(dian)(dian)(dian)的(de)頻率越高，電(dian)(dian)(dian)(dian)感(gan)(gan)(gan)對(dui)交流(liu)電(dian)(dian)(dian)(dian)的(de)阻礙能力(li)越大(da)，頻率越低(di)，電(dian)(dian)(dian)(dian)感(gan)(gan)(gan)對(dui)交流(liu)電(dian)(dian)(dian)(dian)的(de)阻礙能力(li)越小(xiao)。也就是說，電(dian)(dian)(dian)(dian)感(gan)(gan)(gan)有阻止交流(liu)電(dian)(dian)(dian)(dian)通過的(de)特性(xing)。

　　其工作原(yuan)理是(shi)這樣(yang)的(de)：當(dang)負(fu)載(zai)(zai)兩(liang)端(duan)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)要(yao)降(jiang)低(di)時，通(tong)過(guo)(guo)MOSFET場(chang)效應管(guan)的(de)開關作用(yong)，外部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)進行(xing)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)并達到(dao)所需的(de)額定電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)。當(dang)負(fu)載(zai)(zai)兩(liang)端(duan)地電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)升(sheng)高(gao)時，通(tong)過(guo)(guo)MOSFET場(chang)效應管(guan)的(de)開關作用(yong)，外部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)斷開，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)釋放出剛(gang)才充入的(de)能(neng)量，這時電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)就變成了(le)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)繼續對負(fu)載(zai)(zai)供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。隨(sui)著電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)上存儲的(de)能(neng)量地消耗。負(fu)載(zai)(zai)兩(liang)端(duan)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)開始逐(zhu)漸降(jiang)低(di)，外部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)通(tong)過(guo)(guo)MOSFET場(chang)效應管(guan)的(de)開關作用(yong)又(you)要(yao)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。依次類推(tui)在(zai)不(bu)(bu)斷的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)和放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)過(guo)(guo)程中形(xing)成了(le)一種穩定的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，永(yong)遠使(shi)負(fu)載(zai)(zai)兩(liang)端(duan)地電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)不(bu)(bu)會升(sheng)高(gao)也不(bu)(bu)會降(jiang)低(di)，這就是(shi)開關電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)最大優勢。

　　要確定(ding)快速轉換器中電(dian)感的大(da)小首先(xian)應假(jia)定(ding)晶體管(guan)的占空(kong)比(bi)為50%，因為此時的轉換器操作操作效率最高。占空(kong)比(bi)由方(fang)程式(shi)1給出：

　　（其中T是PWM的周期在程序(xu)示例中T=10.5s）

　　占空比(bi)=ton/T（1）

　　至此就可以選擇(ze)一(yi)個PWM的(de)(de)轉換頻(pin)率（如方程式(shi)2所示）PWM的(de)(de)轉換頻(pin)率越(yue)大，則電感的(de)(de)值越(yue)小，也越(yue)節約成本。

　　我的(de)示例(li)代碼配(pei)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(zhuan)換速率。

　　L=（Vi-Vsat-Voton）/2Iomax（2）

　　現在我(wo)們可(ke)以(yi)計算電(dian)感的(de)大小了，假(jia)定充電(dian)電(dian)壓Vi的(de)值(zhi)(zhi)(zhi)為(wei)15V，飽和電(dian)壓Vsat的(de)值(zhi)(zhi)(zhi)為(wei)0.5V，需要獲得的(de)輸(shu)出電(dian)壓值(zhi)(zhi)(zhi)為(wei)4.2V,并且最大輸(shu)出電(dian)流IＯMAX為(wei)1500mA，那么，電(dian)感的(de)值(zhi)(zhi)(zhi)至少應選為(wei)18H。

　　需要注意的是：在本(ben)電路中的電容(rong)(rong)僅僅是一個紋(wen)波(bo)衰(shuai)減器，因為紋(wen)波(bo)與電容(rong)(rong)的大(da)小成反比(bi)例關系，所以電容(rong)(rong)的值越大(da)，衰(shuai)減效(xiao)果越好(hao)。