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)測量(liang)精度，可(ke)很好的(de)(de)控制(zhi)充(chong)電(dian)(dian)電(dian)(dian)流的(de)(de)大(da)小，適時(shi)的(de)(de)調整，并可(ke)根據充(chong)電(dian)(dian)的(de)(de)狀態判(pan)斷充(chong)電(dian)(dian)的(de)(de)時(shi)間(jian)，及時(shi)終止充(chong)電(dian)(dian)，以避(bi)免(mian)電(dian)(dian)池的(de)(de)過充(chong)。

　　本文討論使用C8051F310器件(jian)設計鋰(li)離子電(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)器的(de)(de)。利用PWM脈寬調(diao)制產生可用軟件(jian)控制的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)源，以適應不同階段的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)要求(qiu)。溫(wen)度傳感(gan)器對(dui)電(dian)(dian)(dian)(dian)(dian)池溫(wen)度進行監測，并通過AD轉換和(he)相關計算檢測電(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓和(he)電(dian)(dian)(dian)(dian)(dian)流(liu)，以判斷(duan)電(dian)(dian)(dian)(dian)(dian)池到達(da)哪(na)個階段。使電(dian)(dian)(dian)(dian)(dian)池具有更長的(de)(de)使用壽(shou)命，更有效的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)方法。

　　設計過程

　　1 充電原理

　　電(dian)(dian)池(chi)的(de)(de)特(te)性(xing)唯一(yi)地決定(ding)其安全性(xing)能和充(chong)電(dian)(dian)的(de)(de)效率。電(dian)(dian)池(chi)的(de)(de)最佳(jia)充(chong)電(dian)(dian)方(fang)法(fa)是由電(dian)(dian)池(chi)的(de)(de)化學成分決定(ding)的(de)(de)（鋰(li)離子、鎳(nie)氫、鎳(nie)鎘還(huan)是SLA電(dian)(dian)池(chi)等(deng)）。盡管如此，大多數充(chong)電(dian)(dian)方(fang)案都包含(han)下面的(de)(de)三(san)個階(jie)段(duan)：

　　● 低電流調節(jie)階段

　　● 恒流階段

　　● 恒壓階(jie)段/充電終止(zhi)

　　所有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)都(dou)是通過向自(zi)身(shen)傳輸電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)能的(de)方(fang)法(fa)進行充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)，一(yi)(yi)節電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)最(zui)大充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)取決于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)額定(ding)容(rong)量（C）例如，一(yi)(yi)節容(rong)量為1000mAh的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)在充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)為1000mA時，可(ke)以(yi)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)1C（電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)容(rong)量的(de)1倍）也可(ke)以(yi)用1/50C（20mA）或更低的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。盡管(guan)如此，這只是一(yi)(yi)個(ge)普(pu)通的(de)低電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)方(fang)式，不(bu)適用于要求短(duan)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時間的(de)快速充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)方(fang)案。

　　現在使用的大多數充電器在給電(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)時都(dou)是(shi)(shi)既使用低電(dian)(dian)流(liu)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)方(fang)(fang)式又使用額定(ding)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)的(de)方(fang)(fang)法，即容積充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)，低充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)通(tong)常(chang)(chang)使用在充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)的(de)初始階(jie)(jie)段。在這一(yi)階(jie)(jie)段，需要將會導致充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)過(guo)程(cheng)終止的(de)芯片初期的(de)自熱(re)效(xiao)應減小到最(zui)低程(cheng)度(du)，容積充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)通(tong)常(chang)(chang)用在充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)的(de)中級(ji)階(jie)(jie)段，電(dian)(dian)池(chi)(chi)的(de)大(da)部(bu)分能(neng)量(liang)都(dou)是(shi)(shi)在這一(yi)階(jie)(jie)段存儲的(de)。在電(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)的(de)最(zui)后階(jie)(jie)段，通(tong)常(chang)(chang)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)時間的(de)絕大(da)部(bu)分都(dou)是(shi)(shi)消耗在這一(yi)階(jie)(jie)段，可以通(tong)過(guo)監測電(dian)(dian)流(liu)、電(dian)(dian)壓或兩者的(de)值(zhi)來決定(ding)何時結束(shu)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)。同(tong)樣(yang)，結束(shu)方(fang)(fang)案依(yi)賴于電(dian)(dian)池(chi)(chi)的(de)化(hua)學特性(xing)，例(li)如：大(da)多數鋰(li)離子電(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)器(qi)都(dou)是(shi)(shi)將電(dian)(dian)池(chi)(chi)電(dian)(dian)壓保持(chi)在恒定(ding)值(zhi)，同(tong)時檢(jian)測最(zui)低電(dian)(dian)流(liu)。鎳鎘、NiCd電(dian)(dian)池(chi)(chi)用電(dian)(dian)壓或溫度(du)的(de)變化(hua)率(lv)來決定(ding)充(chong)(chong)(chong)(chong)(chong)電(dian)(dian)的(de)結束(shu)時間。

　　圖1 鋰離子電池充電模塊圖

　　充(chong)電(dian)時部分(fen)電(dian)能被(bei)轉換(huan)成熱能，直(zhi)至電(dian)池充(chong)滿(man)。而充(chong)滿(man)后，所(suo)有(you)的(de)(de)電(dian)能將全(quan)部被(bei)轉換(huan)成熱能。如果此時不終止充(chong)電(dian)，電(dian)池就會被(bei)損(sun)壞(huai)或燒毀。快速充(chong)電(dian)器電(dian)池（完(wan)全(quan)充(chong)滿(man)的(de)(de)時間小于(yu)兩小時的(de)(de)充(chong)電(dian)器）則可以解決這個(ge)問題(ti)，因(yin)為(wei)這些充(chong)電(dian)器是(shi)使用高充(chong)電(dian)電(dian)流來縮短充(chong)電(dian)時間的(de)(de)。因(yin)此，對于(yu)鋰離子電(dian)池來說，監測它的(de)(de)溫(wen)度是(shi)至關(guan)重要的(de)(de)，因(yin)為(wei)電(dian)池在(zai)(zai)(zai)過(guo)充(chong)電(dian)時會發生爆裂(lie)，在(zai)(zai)(zai)所(suo)有(you)的(de)(de)充(chong)電(dian)階段都應(ying)該隨時監測溫(wen)度的(de)(de)變(bian)化，并且在(zai)(zai)(zai)溫(wen)度超過(guo)最大設定(ding)值時立即停止充(chong)電(dian)。

　　2 總體設計

　　充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)路(lu)由三部(bu)分：控制(zhi)部(bu)分，檢測部(bu)分及充(chong)(chong)電(dian)(dian)(dian)部(bu)分組(zu)成。如圖(tu)1所示，采(cai)用F310單片機(ji)進行充(chong)(chong)電(dian)(dian)(dian)控制(zhi)，單片機(ji)本身(shen)具有脈寬調制(zhi)PWM型開關穩壓(ya)電(dian)(dian)(dian)源(yuan)所需的全部(bu)功能，具有10位(wei)A/D轉(zhuan)換器。利(li)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(liu)，溫(wen)度檢測電(dian)(dian)(dian)路(lu)。

　　單片機通過電壓反饋(kui)和電流(liu)反饋(kui)信號，直接利用PWM輸(shu)出將數字電壓信號并轉化成(cheng)模擬(ni)電壓信號，能夠保(bao)證控制精度。

　　3 控制部分電(dian)路設計

　　C8051F310單(dan)片機

　　①模擬外設

　　a.10位(wei)ADC：轉換速度(du)可(ke)達(da)200ks/s,可(ke)多(duo)達(da)21或(huo)17個(ge)外部單端(duan)或(huo)差分(fen)輸入(ru)，VREF可(ke)在外部引腳或(huo)VDD中(zhong)選(xuan)擇，內置溫度(du)傳感器（±3℃），外部轉換啟動輸入(ru)；

　　b.兩個模擬比較(jiao)器(qi)：可(ke)編程回差電壓和響應(ying)時間(jian)，可(ke)配置為中斷(duan)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(ji)電(dian)流：0.1μA；

　　c.溫度范(fan)圍：-40～+85℃。

　　③高速8051微控(kong)制器(qi)內核

　　a.流水線指令結構(gou)：70%的指令的執行(xing)時間為一個或兩個系統時鐘周期；

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

　　c.擴展的中(zhong)斷系統。

　　④數字外設

　　a.29/25個端口(kou)I/O：所有(you)的口(kou)線均耐5V電壓；

　　b.4個通用16位計數器/定時(shi)器；

　　c.16位(wei)可編程計數器/定(ding)時器陣列(lie)（PCA），有5個捕(bu)捉/比(bi)較(jiao)模(mo)塊；

　　d.使(shi)用PCA或(huo)定時(shi)器和(he)外部時(shi)鐘源的實時(shi)時(shi)鐘方(fang)式(shi)。

　　控制(zhi)電(dian)(dian)路(lu)中如(ru)圖2所示，P0.3口(kou)提供充電(dian)(dian)電(dian)(dian)源，P0.6口(kou)檢(jian)測充電(dian)(dian)電(dian)(dian)壓(ya)的大小，P0.5口(kou)檢(jian)測充電(dian)(dian)電(dian)(dian)流(liu)的大小，P0.4口(kou)檢(jian)測電(dian)(dian)池的溫度(du)。

　　充電(dian)電(dian)流由(you)單片機脈寬(kuan)調制PWM產生，充電(dian)電(dian)流由(you)AD轉換再經過(guo)計算得出。

　　4 充電部分及檢(jian)測部分電路設計

　　圖(tu)2 控制電路接線圖(tu)

　　圖(tu)3 充電電路與檢測電路圖(tu)

　　圖3為充電(dian)電(dian)路與檢測(ce)電(dian)路圖。

　　①充電過程曲線

　　圖4 鋰電池充電曲線

　　如圖4所示，充電過程由(you)預(yu)充狀態(tai)，恒(heng)流充電狀態(tai)和恒(heng)壓充電狀態(tai)組成。

　　②快速轉換器

　　實現漸弱終止充電器的(de)最經(jing)濟的(de)方法就(jiu)是用一個快(kuai)速(su)轉(zhuan)換(huan)器(qi)(qi)(qi)。快(kuai)速(su)轉(zhuan)換(huan)器(qi)(qi)(qi)是用一個電感和/或一個變壓(ya)(ya)器(qi)(qi)(qi)（需要隔離(li)的(de)時(shi)候用變壓(ya)(ya)器(qi)(qi)(qi)）作為能量存儲單元以離(li)散的(de)能量包(bao)的(de)形式將能量從(cong)輸(shu)入(ru)傳(chuan)輸(shu)至(zhi)輸(shu)出(chu)的(de)開關調節器(qi)(qi)(qi)反(fan)饋電路，通過晶體管(guan)來調節能量的(de)傳(chuan)輸(shu)，同時(shi)也作為過濾開關，以確(que)保電壓(ya)(ya)或電流在(zai)負載時(shi)保持恒定。

　　如(ru)圖a開關閉合

　　如圖b開關打開

　　快速調(diao)節器的(de)操(cao)作(zuo)是通(tong)過控制一個晶體管(guan)開關的(de)占空比(bi)來實現的(de)。占空比(bi)會(hui)自動(dong)增加以使電池流入更多(duo)的(de)電流。當VBATT

　　③電感的確定

　　電(dian)(dian)(dian)感對(dui)(dui)交流(liu)(liu)(liu)電(dian)(dian)(dian)是(shi)有阻(zu)礙(ai)作用的(de)(de)。在(zai)交流(liu)(liu)(liu)電(dian)(dian)(dian)頻率一定的(de)(de)情況(kuang)下，電(dian)(dian)(dian)感量(liang)越(yue)(yue)(yue)(yue)大，對(dui)(dui)交流(liu)(liu)(liu)電(dian)(dian)(dian)的(de)(de)阻(zu)礙(ai)能(neng)力(li)(li)(li)越(yue)(yue)(yue)(yue)強，電(dian)(dian)(dian)感量(liang)越(yue)(yue)(yue)(yue)小(xiao)(xiao)，其阻(zu)礙(ai)能(neng)力(li)(li)(li)越(yue)(yue)(yue)(yue)小(xiao)(xiao)。另外，在(zai)電(dian)(dian)(dian)感量(liang)一定的(de)(de)情況(kuang)下，交流(liu)(liu)(liu)電(dian)(dian)(dian)的(de)(de)頻率越(yue)(yue)(yue)(yue)高，電(dian)(dian)(dian)感對(dui)(dui)交流(liu)(liu)(liu)電(dian)(dian)(dian)的(de)(de)阻(zu)礙(ai)能(neng)力(li)(li)(li)越(yue)(yue)(yue)(yue)大，頻率越(yue)(yue)(yue)(yue)低(di)，電(dian)(dian)(dian)感對(dui)(dui)交流(liu)(liu)(liu)電(dian)(dian)(dian)的(de)(de)阻(zu)礙(ai)能(neng)力(li)(li)(li)越(yue)(yue)(yue)(yue)小(xiao)(xiao)。也就是(shi)說，電(dian)(dian)(dian)感有阻(zu)止交流(liu)(liu)(liu)電(dian)(dian)(dian)通過的(de)(de)特性。

　　其(qi)工作原理是這樣的(de)(de)：當(dang)負(fu)載(zai)(zai)兩(liang)端(duan)(duan)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)要(yao)降(jiang)低時(shi)(shi)，通(tong)過(guo)MOSFET場(chang)效應管(guan)的(de)(de)開(kai)關作用(yong)，外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)進行充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)并達到所需的(de)(de)額定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)。當(dang)負(fu)載(zai)(zai)兩(liang)端(duan)(duan)地(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)升(sheng)高時(shi)(shi)，通(tong)過(guo)MOSFET場(chang)效應管(guan)的(de)(de)開(kai)關作用(yong)，外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)斷開(kai)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)釋(shi)放(fang)(fang)出剛才充(chong)入的(de)(de)能(neng)量(liang)，這時(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)就變成(cheng)(cheng)了電(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)。隨著電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感(gan)上存儲的(de)(de)能(neng)量(liang)地(di)消耗。負(fu)載(zai)(zai)兩(liang)端(duan)(duan)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)開(kai)始逐漸降(jiang)低，外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)通(tong)過(guo)MOSFET場(chang)效應管(guan)的(de)(de)開(kai)關作用(yong)又要(yao)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。依次類推在不斷的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)和放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)過(guo)程中(zhong)形成(cheng)(cheng)了一種穩定(ding)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)，永遠使(shi)負(fu)載(zai)(zai)兩(liang)端(duan)(duan)地(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)不會(hui)升(sheng)高也不會(hui)降(jiang)低，這就是開(kai)關電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)最大優勢。

　　要(yao)確定(ding)快(kuai)速轉(zhuan)換(huan)器中電感(gan)的大小首先應假定(ding)晶體管(guan)的占空比為50%，因(yin)為此時(shi)的轉(zhuan)換(huan)器操作(zuo)操作(zuo)效率(lv)最(zui)高(gao)。占空比由(you)方(fang)程式1給出：

　　（其中T是PWM的周期在程序示例(li)中T=10.5s）

　　占(zhan)空比=ton/T （1）

　　至(zhi)此(ci)就可以選擇一個PWM的轉換頻率(lv)(lv)（如(ru)方程式(shi)2所示）PWM的轉換頻率(lv)(lv)越(yue)(yue)大，則電感的值越(yue)(yue)小，也(ye)越(yue)(yue)節約成本。

　　我的(de)示例代碼(ma)配置F310的(de)8位硬件PWM是使用內部24.5MHz主時(shi)鐘(zhong)的(de)256分頻(pin)來產(chan)生一個95.7kHz的(de)轉(zhuan)換速率。

　　L=（Vi-Vsat-Voton）/2Iomax （2）

　　現(xian)在我們(men)可以計(ji)算(suan)電(dian)(dian)(dian)感(gan)的大小了，假定充電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)Vi的值(zhi)為(wei)(wei)15V，飽(bao)和電(dian)(dian)(dian)壓(ya)Vsat的值(zhi)為(wei)(wei)0.5V，需要(yao)獲(huo)得的輸出電(dian)(dian)(dian)壓(ya)值(zhi)為(wei)(wei)4.2V,并且最大輸出電(dian)(dian)(dian)流IＯMAX為(wei)(wei)1500mA，那么，電(dian)(dian)(dian)感(gan)的值(zhi)至(zhi)少應(ying)選為(wei)(wei)18H。

　　需要注意的是：在(zai)本電路中的電容(rong)僅僅是一個紋波(bo)衰(shuai)減器(qi)，因為(wei)紋波(bo)與(yu)電容(rong)的大小成反比例關(guan)系，所以電容(rong)的值(zhi)越(yue)大，衰(shuai)減效(xiao)果越(yue)好。