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(ji)鋰離子電(dian)(dian)池(chi)智能充電(dian)(dian)器(qi)的。利(li)用(yong)PWM脈寬調制(zhi)產生(sheng)可用(yong)軟件控制(zhi)的充電(dian)(dian)電(dian)(dian)源，以適應不同階段的充電(dian)(dian)電(dian)(dian)流的要求(qiu)。溫度傳感器(qi)對電(dian)(dian)池(chi)溫度進行監測，并通過AD轉換和(he)相關計(ji)算檢測電(dian)(dian)池(chi)充電(dian)(dian)電(dian)(dian)壓和(he)電(dian)(dian)流，以判斷電(dian)(dian)池(chi)到達哪個(ge)階段。使(shi)電(dian)(dian)池(chi)具有(you)更長的使(shi)用(yong)壽命(ming)，更有(you)效的充電(dian)(dian)方法。

　　設計過程

　　1 充電原理

　　電(dian)池的特(te)性唯(wei)一地決定(ding)(ding)其安全(quan)性能和充(chong)電(dian)的效率(lv)。電(dian)池的最佳充(chong)電(dian)方法(fa)是(shi)由電(dian)池的化(hua)學成分決定(ding)(ding)的（鋰離(li)子、鎳(nie)氫、鎳(nie)鎘還是(shi)SLA電(dian)池等）。盡管如(ru)此，大多數充(chong)電(dian)方案都包含下面的三個階段(duan)：

低電流調節階段
恒流階段
恒壓階段/充電終止

　　所有電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)都(dou)是通過(guo)向自身傳(chuan)輸電(dian)(dian)(dian)(dian)(dian)能的(de)方法進行充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)的(de)，一節電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)最大充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流取決于(yu)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)額定容量（C）例如，一節容量為1000mAh的(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)在(zai)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流為1000mA時(shi)，可(ke)以充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)1C(電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)容量的(de)1倍)也(ye)可(ke)以用1/50C(20mA)或(huo)更(geng)低的(de)電(dian)(dian)(dian)(dian)(dian)流給電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)。盡管如此，這只是一個普(pu)通的(de)低電(dian)(dian)(dian)(dian)(dian)流充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)方式，不適用于(yu)要求短充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)間(jian)的(de)快速(su)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)方案(an)。

　　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)(dian)池(chi)(chi)電(dian)(dian)壓保(bao)持在恒(heng)定(ding)(ding)值，同時(shi)檢(jian)測最低電(dian)(dian)流。鎳鎘、NiCd電(dian)(dian)池(chi)(chi)用電(dian)(dian)壓或溫度的(de)變(bian)化率來決定(ding)(ding)充電(dian)(dian)的(de)結束時(shi)間。

　　充(chong)電(dian)(dian)時部(bu)分電(dian)(dian)能(neng)被(bei)轉換成熱能(neng)，直(zhi)至(zhi)電(dian)(dian)池(chi)充(chong)滿(man)。而充(chong)滿(man)后(hou)，所(suo)有的(de)電(dian)(dian)能(neng)將全(quan)(quan)部(bu)被(bei)轉換成熱能(neng)。如果此時不終止(zhi)充(chong)電(dian)(dian)，電(dian)(dian)池(chi)就會(hui)被(bei)損壞(huai)或燒毀。快(kuai)速充(chong)電(dian)(dian)器電(dian)(dian)池(chi)（完全(quan)(quan)充(chong)滿(man)的(de)時間(jian)小于兩小時的(de)充(chong)電(dian)(dian)器）則可以解決這(zhe)個問題(ti)，因為這(zhe)些充(chong)電(dian)(dian)器是使(shi)用(yong)高充(chong)電(dian)(dian)電(dian)(dian)流來(lai)縮短(duan)充(chong)電(dian)(dian)時間(jian)的(de)。因此，對于鋰離子電(dian)(dian)池(chi)來(lai)說(shuo),監測它的(de)溫度(du)(du)是至(zhi)關重要的(de)，因為電(dian)(dian)池(chi)在(zai)過(guo)充(chong)電(dian)(dian)時會(hui)發(fa)生(sheng)爆裂，在(zai)所(suo)有的(de)充(chong)電(dian)(dian)階(jie)段都應(ying)該隨時監測溫度(du)(du)的(de)變(bian)化，并且在(zai)溫度(du)(du)超(chao)過(guo)最大(da)設定(ding)值時立即停止(zhi)充(chong)電(dian)(dian)。

　　2 總體設計

　　充電(dian)(dian)電(dian)(dian)路由三(san)部分(fen)：控制部分(fen)，檢(jian)測部分(fen)及充電(dian)(dian)部分(fen)組成(cheng)。如圖1所示，采用(yong)F310單(dan)(dan)片機(ji)進行充電(dian)(dian)控制，單(dan)(dan)片機(ji)本身(shen)具有脈寬(kuan)調制PWM型開(kai)關穩(wen)壓(ya)電(dian)(dian)源所需的全部功(gong)能，具有10位A/D轉換器。利用(yong)單(dan)(dan)片機(ji)A/D端(duan)口，構成(cheng)電(dian)(dian)池電(dian)(dian)壓(ya)，電(dian)(dian)流，溫度(du)檢(jian)測電(dian)(dian)路。

圖1 鋰(li)離子電池(chi)充(chong)電模塊(kuai)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(shu)出(chu)將數(shu)字(zi)電(dian)(dian)壓(ya)信(xin)號并轉(zhuan)化成模擬電(dian)(dian)壓(ya)信(xin)號，能夠保證(zheng)控制精(jing)度。

　　3 控制部(bu)分電路設計

　　C8051F310單片機

　　①模擬外設

　　a.10位ADC：轉換速(su)度(du)可(ke)達200ks/s,可(ke)多達21或(huo)17個外(wai)部單端或(huo)差分(fen)輸(shu)入，VREF可(ke)在(zai)外(wai)部引腳或(huo)VDD中選(xuan)擇，內置溫度(du)傳感器（±3℃），外(wai)部轉換啟動輸(shu)入；

　　b.兩個模擬比較(jiao)器：可(ke)編程回差(cha)電(dian)壓和響應時(shi)間，可(ke)配(pei)置為中斷或復位源(yuan)，小電(dian)流（〈0.5μA）。

　　②供電電壓

　　a.典型(xing)工作電流：5mA、25MHz；

　　b.典型停機電流：0.1μA；

　　c.溫度范(fan)圍：-40～+85℃。

　　③高速8051微控制器內核

　　a.流水(shui)線指(zhi)令結構：70%的指(zhi)令的執行(xing)時間為一個或兩個系統時鐘周(zhou)期(qi)；

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

　　c.擴展的中斷(duan)系統。

　　④數字外設

　　a.29/25個端口I/O：所有的口線均耐5V電(dian)壓；

　　b.4個通用16位計數器(qi)/定時器(qi)；

　　c.16位(wei)可編程(cheng)計(ji)數器/定時器陣列（PCA），有(you)5個捕捉/比(bi)較(jiao)模塊；

　　d.使(shi)用(yong)PCA或定(ding)時器和(he)外(wai)部時鐘源的(de)實時時鐘方式(shi)。

　　控(kong)制電(dian)(dian)路中如圖(tu)2所示，P0.3口提供充(chong)(chong)電(dian)(dian)電(dian)(dian)源(yuan)，P0.6口檢測充(chong)(chong)電(dian)(dian)電(dian)(dian)壓的(de)大小，P0.5口檢測充(chong)(chong)電(dian)(dian)電(dian)(dian)流的(de)大小，P0.4口檢測電(dian)(dian)池的(de)溫度(du)。

圖(tu)2 控(kong)制電路接線圖(tu)

　　充電(dian)(dian)電(dian)(dian)流由單(dan)片機脈寬調制PWM產生(sheng)，充電(dian)(dian)電(dian)(dian)流由AD轉(zhuan)換再經過計算得出。

4 充電部分及檢(jian)測部分電路設計

　　圖(tu)3為充(chong)電電路與檢(jian)測電路圖(tu)。

圖3 充電電路(lu)與檢(jian)測電路(lu)圖

　　①充電過程曲線

　　如圖4所示(shi)，充(chong)電過程由預充(chong)狀(zhuang)(zhuang)態(tai)，恒流(liu)充(chong)電狀(zhuang)(zhuang)態(tai)和恒壓(ya)充(chong)電狀(zhuang)(zhuang)態(tai)組成。

圖4 鋰電池充電曲線(xian)

　　②快速轉換器

　　實現漸弱終止充電(dian)(dian)(dian)器(qi)的最經濟的方法就是用(yong)一個快(kuai)速(su)轉換器(qi)。快(kuai)速(su)轉換器(qi)是用(yong)一個電(dian)(dian)(dian)感(gan)和(he)/或一個變壓器(qi)（需要隔離(li)的時候(hou)用(yong)變壓器(qi)）作為能(neng)量(liang)(liang)存儲單元(yuan)以離(li)散的能(neng)量(liang)(liang)包的形式將能(neng)量(liang)(liang)從輸(shu)(shu)入(ru)傳(chuan)輸(shu)(shu)至(zhi)輸(shu)(shu)出(chu)的開(kai)關(guan)調(diao)節器(qi)反饋電(dian)(dian)(dian)路，通過晶體管(guan)來調(diao)節能(neng)量(liang)(liang)的傳(chuan)輸(shu)(shu)，同時也作為過濾開(kai)關(guan)，以確(que)保(bao)電(dian)(dian)(dian)壓或電(dian)(dian)(dian)流在負載(zai)時保(bao)持恒定。

　　快速調節器的(de)操(cao)作是通過控制一個晶體管開關的(de)占(zhan)空(kong)比(bi)來實現的(de)。占(zhan)空(kong)比(bi)會自動增(zeng)加以(yi)使電池(chi)流入更多的(de)電流。當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)對交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)是有阻(zu)(zu)礙(ai)(ai)(ai)作用的(de)(de)(de)。在交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)頻率一(yi)定的(de)(de)(de)情(qing)況下(xia)，電(dian)(dian)(dian)(dian)感(gan)量越大(da)，對交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)的(de)(de)(de)阻(zu)(zu)礙(ai)(ai)(ai)能(neng)(neng)力(li)越強，電(dian)(dian)(dian)(dian)感(gan)量越小，其(qi)阻(zu)(zu)礙(ai)(ai)(ai)能(neng)(neng)力(li)越小。另外(wai)，在電(dian)(dian)(dian)(dian)感(gan)量一(yi)定的(de)(de)(de)情(qing)況下(xia)，交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)的(de)(de)(de)頻率越高，電(dian)(dian)(dian)(dian)感(gan)對交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)的(de)(de)(de)阻(zu)(zu)礙(ai)(ai)(ai)能(neng)(neng)力(li)越大(da)，頻率越低，電(dian)(dian)(dian)(dian)感(gan)對交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)的(de)(de)(de)阻(zu)(zu)礙(ai)(ai)(ai)能(neng)(neng)力(li)越小。也(ye)就是說(shuo)，電(dian)(dian)(dian)(dian)感(gan)有阻(zu)(zu)止交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)通(tong)過(guo)的(de)(de)(de)特(te)性。

　　其(qi)工作原理是(shi)這樣(yang)的(de)(de)(de)(de)：當(dang)負(fu)載兩端的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓要降(jiang)低時(shi)(shi)，通過(guo)MOSFET場效應(ying)管的(de)(de)(de)(de)開(kai)(kai)關(guan)作用，外(wai)部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感進行充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)并達到所需的(de)(de)(de)(de)額定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓。當(dang)負(fu)載兩端地電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓升高時(shi)(shi)，通過(guo)MOSFET場效應(ying)管的(de)(de)(de)(de)開(kai)(kai)關(guan)作用，外(wai)部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)斷(duan)開(kai)(kai)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感釋放出剛才充(chong)入的(de)(de)(de)(de)能量，這時(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感就變成了電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)繼續對負(fu)載供電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。隨著電(dian)(dian)(dian)(dian)(dian)(dian)(dian)感上存(cun)儲的(de)(de)(de)(de)能量地消(xiao)耗。負(fu)載兩端的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓開(kai)(kai)始逐漸(jian)降(jiang)低，外(wai)部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)通過(guo)MOSFET場效應(ying)管的(de)(de)(de)(de)開(kai)(kai)關(guan)作用又要充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。依次類推在不(bu)斷(duan)的(de)(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)和放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)過(guo)程中(zhong)形成了一種穩定(ding)(ding)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓，永(yong)遠(yuan)使負(fu)載兩端地電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓不(bu)會升高也不(bu)會降(jiang)低，這就是(shi)開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)最大優勢。

　　要確定快速轉換器中電感的大小首先應假定晶體管的占空(kong)比(bi)為50%，因(yin)為此時的轉換器操作(zuo)操作(zuo)效率最高。占空(kong)比(bi)由方程式(shi)1給出：

　　（其中T是PWM的周期在程序示例(li)中T=10.5s）

　　占空比=ton/T（1）

　　至此就可以選擇一個PWM的(de)轉(zhuan)(zhuan)換(huan)頻率（如方程式(shi)2所示）PWM的(de)轉(zhuan)(zhuan)換(huan)頻率越(yue)大，則電感的(de)值越(yue)小，也越(yue)節約成本。

　　我的示例代碼配置(zhi)F310的8位硬件PWM是使用內部(bu)24.5MHz主時(shi)鐘(zhong)的256分頻來產生一個95.7kHz的轉換速率。

　　L=（Vi-Vsat-Voton）/2Iomax（2）

　　現在(zai)我們可以計算電(dian)(dian)感的(de)大小了，假(jia)定充電(dian)(dian)電(dian)(dian)壓(ya)Vi的(de)值(zhi)為15V，飽和電(dian)(dian)壓(ya)Vsat的(de)值(zhi)為0.5V，需要獲得(de)的(de)輸(shu)出電(dian)(dian)壓(ya)值(zhi)為4.2V,并且(qie)最(zui)大輸(shu)出電(dian)(dian)流IＯMAX為1500mA，那么，電(dian)(dian)感的(de)值(zhi)至(zhi)少(shao)應(ying)選為18H。

　　需(xu)要注意(yi)的(de)是：在本電(dian)(dian)路(lu)中的(de)電(dian)(dian)容僅僅是一(yi)個紋(wen)波衰減器，因為紋(wen)波與電(dian)(dian)容的(de)大(da)小成反(fan)比例關系(xi)，所以(yi)電(dian)(dian)容的(de)值越大(da)，衰減效果(guo)越好。