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(de)(de)(de)測量精度，可很好的(de)(de)(de)控制充(chong)電電流(liu)的(de)(de)(de)大小，適時的(de)(de)(de)調整，并可根據充(chong)電的(de)(de)(de)狀態(tai)判斷充(chong)電的(de)(de)(de)時間，及(ji)時終止充(chong)電，以避(bi)免(mian)電池的(de)(de)(de)過充(chong)。

　　本文討論使用(yong)(yong)C8051F310器(qi)件(jian)設計(ji)鋰離子電(dian)(dian)池充(chong)(chong)電(dian)(dian)器(qi)的。利用(yong)(yong)PWM脈寬調制產(chan)生可用(yong)(yong)軟(ruan)件(jian)控(kong)制的充(chong)(chong)電(dian)(dian)電(dian)(dian)源，以適應不同階(jie)段(duan)的充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)的要求。溫度傳感器(qi)對(dui)電(dian)(dian)池溫度進行監測，并通過AD轉換和(he)(he)相(xiang)關(guan)計(ji)算檢測電(dian)(dian)池充(chong)(chong)電(dian)(dian)電(dian)(dian)壓(ya)和(he)(he)電(dian)(dian)流(liu)，以判(pan)斷電(dian)(dian)池到達哪個(ge)階(jie)段(duan)。使電(dian)(dian)池具有(you)更(geng)長的使用(yong)(yong)壽命，更(geng)有(you)效的充(chong)(chong)電(dian)(dian)方(fang)法。

　　設計過程

　　1 充電原理

　　電(dian)池的(de)特(te)性(xing)唯(wei)一地決(jue)定(ding)其安全性(xing)能和充(chong)電(dian)的(de)效率。電(dian)池的(de)最(zui)佳充(chong)電(dian)方法是由(you)電(dian)池的(de)化學(xue)成分決(jue)定(ding)的(de)（鋰離子、鎳氫、鎳鎘還是SLA電(dian)池等(deng)）。盡管(guan)如此(ci)，大(da)多數充(chong)電(dian)方案都包含(han)下(xia)面的(de)三個階段：

　　● 低電流調節階段

　　● 恒流階段

　　● 恒壓階段(duan)/充電終(zhong)止

　　所有電(dian)(dian)(dian)池(chi)(chi)(chi)都是(shi)通過向自身傳輸電(dian)(dian)(dian)能的方法(fa)進行充(chong)電(dian)(dian)(dian)的，一(yi)節電(dian)(dian)(dian)池(chi)(chi)(chi)的最(zui)大充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流取決于(yu)電(dian)(dian)(dian)池(chi)(chi)(chi)的額(e)定容量(liang)（C）例如，一(yi)節容量(liang)為1000mAh的電(dian)(dian)(dian)池(chi)(chi)(chi)在充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流為1000mA時，可(ke)以充(chong)電(dian)(dian)(dian)1C（電(dian)(dian)(dian)池(chi)(chi)(chi)容量(liang)的1倍）也可(ke)以用1/50C（20mA）或(huo)更低的電(dian)(dian)(dian)流給電(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)。盡管如此(ci)，這只(zhi)是(shi)一(yi)個普通的低電(dian)(dian)(dian)流充(chong)電(dian)(dian)(dian)方式，不適用于(yu)要求短充(chong)電(dian)(dian)(dian)時間的快速充(chong)電(dian)(dian)(dian)方案(an)。

　　現在使用的大多數充電器在(zai)(zai)給電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)(shi)都(dou)是既使(shi)用低電(dian)(dian)(dian)(dian)(dian)流充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)方式(shi)又使(shi)用額定充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流的(de)(de)(de)方法(fa)，即容積(ji)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，低充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流通常使(shi)用在(zai)(zai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)初(chu)始階段(duan)。在(zai)(zai)這(zhe)一(yi)階段(duan)，需要將會(hui)導致充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)過(guo)程(cheng)終止的(de)(de)(de)芯片初(chu)期的(de)(de)(de)自熱效應減小(xiao)到最(zui)(zui)(zui)低程(cheng)度(du)，容積(ji)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)通常用在(zai)(zai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)中級階段(duan)，電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)大(da)部分(fen)能量都(dou)是在(zai)(zai)這(zhe)一(yi)階段(duan)存儲的(de)(de)(de)。在(zai)(zai)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)最(zui)(zui)(zui)后階段(duan)，通常充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)(shi)間的(de)(de)(de)絕大(da)部分(fen)都(dou)是消耗在(zai)(zai)這(zhe)一(yi)階段(duan)，可以通過(guo)監測電(dian)(dian)(dian)(dian)(dian)流、電(dian)(dian)(dian)(dian)(dian)壓(ya)或(huo)兩者的(de)(de)(de)值來(lai)決(jue)定何時(shi)(shi)結束(shu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)。同(tong)樣，結束(shu)方案依賴于電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)化學(xue)特性，例如：大(da)多數鋰離子電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器都(dou)是將電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)保持在(zai)(zai)恒定值，同(tong)時(shi)(shi)檢測最(zui)(zui)(zui)低電(dian)(dian)(dian)(dian)(dian)流。鎳鎘(ge)、NiCd電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)用電(dian)(dian)(dian)(dian)(dian)壓(ya)或(huo)溫度(du)的(de)(de)(de)變(bian)化率來(lai)決(jue)定充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)結束(shu)時(shi)(shi)間。

　　圖1 鋰離子電池充電模塊圖

　　充(chong)電(dian)(dian)(dian)(dian)時(shi)(shi)(shi)部分電(dian)(dian)(dian)(dian)能(neng)(neng)被(bei)轉(zhuan)換(huan)成熱能(neng)(neng)，直至(zhi)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)滿。而(er)充(chong)滿后，所(suo)有的(de)電(dian)(dian)(dian)(dian)能(neng)(neng)將(jiang)全部被(bei)轉(zhuan)換(huan)成熱能(neng)(neng)。如果(guo)此(ci)時(shi)(shi)(shi)不終止充(chong)電(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)池(chi)(chi)就會被(bei)損壞或燒毀。快速充(chong)電(dian)(dian)(dian)(dian)器電(dian)(dian)(dian)(dian)池(chi)(chi)（完全充(chong)滿的(de)時(shi)(shi)(shi)間小于(yu)兩小時(shi)(shi)(shi)的(de)充(chong)電(dian)(dian)(dian)(dian)器）則可(ke)以(yi)解決這(zhe)個(ge)問題，因(yin)為(wei)這(zhe)些充(chong)電(dian)(dian)(dian)(dian)器是(shi)使用(yong)高充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)來(lai)(lai)縮(suo)短(duan)充(chong)電(dian)(dian)(dian)(dian)時(shi)(shi)(shi)間的(de)。因(yin)此(ci)，對于(yu)鋰離(li)子電(dian)(dian)(dian)(dian)池(chi)(chi)來(lai)(lai)說，監(jian)(jian)測它的(de)溫(wen)度是(shi)至(zhi)關(guan)重要的(de)，因(yin)為(wei)電(dian)(dian)(dian)(dian)池(chi)(chi)在過(guo)充(chong)電(dian)(dian)(dian)(dian)時(shi)(shi)(shi)會發(fa)生爆裂，在所(suo)有的(de)充(chong)電(dian)(dian)(dian)(dian)階(jie)段都應該隨時(shi)(shi)(shi)監(jian)(jian)測溫(wen)度的(de)變(bian)化，并且(qie)在溫(wen)度超(chao)過(guo)最大設定值(zhi)時(shi)(shi)(shi)立即停止充(chong)電(dian)(dian)(dian)(dian)。

　　2 總體設計

　　充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)路(lu)由三部(bu)分(fen)：控制(zhi)部(bu)分(fen)，檢測(ce)部(bu)分(fen)及充(chong)電(dian)(dian)(dian)部(bu)分(fen)組成。如圖1所示，采用(yong)F310單(dan)片機進行充(chong)電(dian)(dian)(dian)控制(zhi)，單(dan)片機本身具有(you)脈(mo)寬調制(zhi)PWM型開(kai)關穩壓(ya)電(dian)(dian)(dian)源所需的全(quan)部(bu)功能，具有(you)10位A/D轉換器(qi)。利(li)用(yong)單(dan)片機A/D端口(kou)，構成電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)，電(dian)(dian)(dian)流，溫(wen)度(du)檢測(ce)電(dian)(dian)(dian)路(lu)。

　　單(dan)片(pian)機通過(guo)電(dian)(dian)壓(ya)(ya)反饋(kui)和電(dian)(dian)流(liu)反饋(kui)信(xin)號(hao)，直接(jie)利用PWM輸出將數(shu)字電(dian)(dian)壓(ya)(ya)信(xin)號(hao)并轉化成模(mo)擬(ni)電(dian)(dian)壓(ya)(ya)信(xin)號(hao)，能(neng)夠保證控制精度(du)。

　　3 控(kong)制部(bu)分電路設計(ji)

　　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(huo)17個外(wai)(wai)部(bu)單端或(huo)差分(fen)輸(shu)(shu)入，VREF可(ke)在外(wai)(wai)部(bu)引腳或(huo)VDD中選(xuan)擇(ze)，內置溫(wen)度傳感器（±3℃），外(wai)(wai)部(bu)轉換(huan)啟動輸(shu)(shu)入；

　　b.兩個模(mo)擬比較器：可(ke)編(bian)程回(hui)差(cha)電壓和(he)響(xiang)應時間，可(ke)配置為中斷或復(fu)位(wei)源，小(xiao)電流（〈0.5μA）。

　　②供電電壓

　　a.典型工作電(dian)流：5mA、25MHz；

　　b.典型停機電(dian)流：0.1μA；

　　c.溫度范圍：-40～+85℃。

　　③高速(su)8051微控制器內(nei)核(he)

　　a.流(liu)水線指令結構：70%的(de)指令的(de)執(zhi)行時間(jian)為(wei)一個(ge)或(huo)兩個(ge)系統時鐘(zhong)周期(qi)；

　　b.速度可達25MI/s（時(shi)鐘頻率為25MHz時(shi)）；

　　c.擴(kuo)展的中斷系統(tong)。

　　④數字外設

　　a.29/25個端(duan)口I/O：所有的口線均耐5V電(dian)壓(ya)；

　　b.4個通用16位計數器/定(ding)時器；

　　c.16位可(ke)編程計(ji)數器(qi)/定(ding)時器(qi)陣列（PCA），有5個捕(bu)捉/比較模塊；

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

　　控制電(dian)(dian)路中(zhong)如圖2所示，P0.3口提供充(chong)電(dian)(dian)電(dian)(dian)源(yuan)，P0.6口檢(jian)測(ce)(ce)充(chong)電(dian)(dian)電(dian)(dian)壓(ya)的大小(xiao)，P0.5口檢(jian)測(ce)(ce)充(chong)電(dian)(dian)電(dian)(dian)流的大小(xiao)，P0.4口檢(jian)測(ce)(ce)電(dian)(dian)池(chi)的溫度。

　　充(chong)電(dian)電(dian)流由單片(pian)機脈寬調制PWM產生，充(chong)電(dian)電(dian)流由AD轉換再經過計算得出。

　　4 充電(dian)部(bu)分及檢測(ce)部(bu)分電(dian)路設計

　　圖(tu)2 控制(zhi)電路接線圖(tu)

　　圖3 充(chong)電(dian)電(dian)路與檢(jian)測電(dian)路圖

　　圖3為充電電路與檢測電路圖。

　　①充電過程曲線

　　圖4 鋰電池充電曲(qu)線

　　如(ru)圖4所示，充電(dian)過程由預充狀(zhuang)態(tai)，恒流充電(dian)狀(zhuang)態(tai)和(he)恒壓充電(dian)狀(zhuang)態(tai)組成。

　　②快速轉換器

　　實現漸弱終止充電器的(de)(de)最(zui)經濟的(de)(de)方法就是用(yong)一(yi)(yi)個(ge)快速轉換器(qi)(qi)。快速轉換器(qi)(qi)是用(yong)一(yi)(yi)個(ge)電(dian)感和/或一(yi)(yi)個(ge)變(bian)壓器(qi)(qi)（需要隔(ge)離的(de)(de)時(shi)候(hou)用(yong)變(bian)壓器(qi)(qi)）作(zuo)(zuo)為能量(liang)存(cun)儲單元以(yi)離散的(de)(de)能量(liang)包的(de)(de)形式將能量(liang)從(cong)輸(shu)(shu)入傳輸(shu)(shu)至輸(shu)(shu)出的(de)(de)開(kai)關調節(jie)器(qi)(qi)反饋電(dian)路，通過(guo)晶體管來調節(jie)能量(liang)的(de)(de)傳輸(shu)(shu)，同時(shi)也作(zuo)(zuo)為過(guo)濾開(kai)關，以(yi)確保電(dian)壓或電(dian)流在負載(zai)時(shi)保持恒定。

　　如圖a開關閉合(he)

　　如(ru)圖b開關(guan)打(da)開

　　快速調節(jie)器的操作是通過控(kong)制(zhi)一(yi)個晶(jing)體(ti)管開關的占空比來實現的。占空比會自動增加(jia)以使(shi)電池流入更多的電流。當VBATT

　　③電感的確定

　　電感(gan)對(dui)交流(liu)(liu)電是有阻礙作用的。在(zai)交流(liu)(liu)電頻率一(yi)定(ding)(ding)的情(qing)況(kuang)(kuang)下，電感(gan)量越(yue)(yue)(yue)大，對(dui)交流(liu)(liu)電的阻礙能(neng)力(li)越(yue)(yue)(yue)強，電感(gan)量越(yue)(yue)(yue)小，其阻礙能(neng)力(li)越(yue)(yue)(yue)小。另(ling)外，在(zai)電感(gan)量一(yi)定(ding)(ding)的情(qing)況(kuang)(kuang)下，交流(liu)(liu)電的頻率越(yue)(yue)(yue)高，電感(gan)對(dui)交流(liu)(liu)電的阻礙能(neng)力(li)越(yue)(yue)(yue)大，頻率越(yue)(yue)(yue)低，電感(gan)對(dui)交流(liu)(liu)電的阻礙能(neng)力(li)越(yue)(yue)(yue)小。也就是說，電感(gan)有阻止(zhi)交流(liu)(liu)電通過(guo)的特性(xing)。

　　其工作(zuo)原理是這(zhe)樣的(de)(de)：當負(fu)載(zai)兩端(duan)的(de)(de)電(dian)(dian)(dian)壓(ya)要降低(di)時，通過MOSFET場(chang)效(xiao)(xiao)應(ying)管(guan)的(de)(de)開(kai)關作(zuo)用(yong)，外(wai)(wai)部電(dian)(dian)(dian)源(yuan)對電(dian)(dian)(dian)感(gan)進行充(chong)(chong)電(dian)(dian)(dian)并達到所需的(de)(de)額定電(dian)(dian)(dian)壓(ya)。當負(fu)載(zai)兩端(duan)地電(dian)(dian)(dian)壓(ya)升(sheng)高時，通過MOSFET場(chang)效(xiao)(xiao)應(ying)管(guan)的(de)(de)開(kai)關作(zuo)用(yong)，外(wai)(wai)部電(dian)(dian)(dian)源(yuan)供電(dian)(dian)(dian)斷(duan)(duan)開(kai)，電(dian)(dian)(dian)感(gan)釋放(fang)出剛才充(chong)(chong)入的(de)(de)能量，這(zhe)時電(dian)(dian)(dian)感(gan)就(jiu)(jiu)變成(cheng)了電(dian)(dian)(dian)源(yuan)繼(ji)續對負(fu)載(zai)供電(dian)(dian)(dian)。隨著電(dian)(dian)(dian)感(gan)上存儲(chu)的(de)(de)能量地消耗(hao)。負(fu)載(zai)兩端(duan)的(de)(de)電(dian)(dian)(dian)壓(ya)開(kai)始逐漸降低(di)，外(wai)(wai)部電(dian)(dian)(dian)源(yuan)通過MOSFET場(chang)效(xiao)(xiao)應(ying)管(guan)的(de)(de)開(kai)關作(zuo)用(yong)又要充(chong)(chong)電(dian)(dian)(dian)。依(yi)次類推在不(bu)斷(duan)(duan)的(de)(de)充(chong)(chong)電(dian)(dian)(dian)和放(fang)電(dian)(dian)(dian)的(de)(de)過程中形成(cheng)了一(yi)種穩定的(de)(de)電(dian)(dian)(dian)壓(ya)，永遠使負(fu)載(zai)兩端(duan)地電(dian)(dian)(dian)壓(ya)不(bu)會升(sheng)高也不(bu)會降低(di)，這(zhe)就(jiu)(jiu)是開(kai)關電(dian)(dian)(dian)源(yuan)的(de)(de)最(zui)大優勢。

　　要確定快(kuai)速(su)轉換(huan)器中電(dian)感的(de)(de)大小首先應(ying)假(jia)定晶體管(guan)的(de)(de)占(zhan)空(kong)比為(wei)50%，因為(wei)此時(shi)的(de)(de)轉換(huan)器操作操作效率(lv)最高。占(zhan)空(kong)比由方程式1給出(chu)：

　　（其中(zhong)T是PWM的周期在程序示例中(zhong)T=10.5s）

　　占(zhan)空比=ton/T （1）

　　至此就可以選擇一個PWM的(de)轉換頻率（如方(fang)程式(shi)2所(suo)示）PWM的(de)轉換頻率越大，則(ze)電感(gan)的(de)值越小，也越節約成本。

　　我的示例(li)代碼配置F310的8位(wei)硬件PWM是(shi)使用(yong)內部24.5MHz主時鐘的256分頻(pin)來產生(sheng)一(yi)個95.7kHz的轉(zhuan)換速率(lv)。

　　L=（Vi-Vsat-Voton）/2Iomax （2）

　　現在我(wo)們可以(yi)計算電(dian)感(gan)的(de)(de)大小了，假(jia)定充(chong)電(dian)電(dian)壓Vi的(de)(de)值(zhi)為15V，飽和電(dian)壓Vsat的(de)(de)值(zhi)為0.5V，需要獲得的(de)(de)輸出(chu)電(dian)壓值(zhi)為4.2V,并且最大輸出(chu)電(dian)流IＯMAX為1500mA，那么，電(dian)感(gan)的(de)(de)值(zhi)至少應選(xuan)為18H。

　　需(xu)要注意的(de)(de)是：在(zai)本電路中的(de)(de)電容(rong)僅僅是一個紋波衰減器，因為紋波與(yu)電容(rong)的(de)(de)大小成反比例關系，所以電容(rong)的(de)(de)值越大，衰減效果越好。