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(shi)電(dian)(dian)(dian)(dian)池(chi)具(ju)有較長的(de)(de)(de)(de)壽命。利用C8051F310單片(pian)機設計的(de)(de)(de)(de)智能充(chong)(chong)電(dian)(dian)(dian)(dian)器，具(ju)有較高的(de)(de)(de)(de)測量精(jing)度，可很好(hao)的(de)(de)(de)(de)控制充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流的(de)(de)(de)(de)大小，適時(shi)的(de)(de)(de)(de)調整，并可根據充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)(de)(de)(de)狀(zhuang)態判斷充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)(de)(de)(de)時(shi)間，及時(shi)終止(zhi)充(chong)(chong)電(dian)(dian)(dian)(dian)，以避免電(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)(de)過充(chong)(chong)。

　　本文討論使(shi)用C8051F310器件設(she)計(ji)鋰離(li)子電(dian)(dian)池充電(dian)(dian)器的(de)(de)。利用PWM脈寬(kuan)調(diao)制產生可(ke)用軟(ruan)件控制的(de)(de)充電(dian)(dian)電(dian)(dian)源，以(yi)適應不(bu)同階(jie)段的(de)(de)充電(dian)(dian)電(dian)(dian)流(liu)(liu)的(de)(de)要(yao)求。溫度(du)傳感器對電(dian)(dian)池溫度(du)進行(xing)監測(ce)，并通過AD轉(zhuan)換(huan)和相關計(ji)算檢(jian)測(ce)電(dian)(dian)池充電(dian)(dian)電(dian)(dian)壓(ya)和電(dian)(dian)流(liu)(liu)，以(yi)判斷電(dian)(dian)池到達哪個(ge)階(jie)段。使(shi)電(dian)(dian)池具有(you)更(geng)長的(de)(de)使(shi)用壽命，更(geng)有(you)效的(de)(de)充電(dian)(dian)方(fang)法。

　　設計過程

　　1 充電原理

　　電(dian)池(chi)(chi)的(de)特(te)性唯(wei)一地決(jue)定(ding)其(qi)安全性能和充電(dian)的(de)效率(lv)。電(dian)池(chi)(chi)的(de)最佳(jia)充電(dian)方法(fa)是(shi)由電(dian)池(chi)(chi)的(de)化學成分決(jue)定(ding)的(de)（鋰離子、鎳(nie)氫、鎳(nie)鎘還是(shi)SLA電(dian)池(chi)(chi)等）。盡管如此，大(da)多數充電(dian)方案都包含下面的(de)三個(ge)階段：

　　● 低電流調節階段
　　● 恒流階段
　　● 恒壓(ya)階段/充電(dian)終止

　　所有電(dian)(dian)(dian)(dian)池(chi)(chi)都是通過向自(zi)身傳輸(shu)電(dian)(dian)(dian)(dian)能的(de)方法進行充(chong)電(dian)(dian)(dian)(dian)的(de)，一(yi)節(jie)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)最大(da)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流取(qu)決(jue)于電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)額定容量(liang)（C）例如，一(yi)節(jie)容量(liang)為(wei)1000mAh的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)在充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流為(wei)1000mA時(shi)，可以充(chong)電(dian)(dian)(dian)(dian)1C(電(dian)(dian)(dian)(dian)池(chi)(chi)容量(liang)的(de)1倍)也可以用1/50C(20mA)或(huo)更低的(de)電(dian)(dian)(dian)(dian)流給電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)。盡管如此(ci)，這(zhe)只是一(yi)個普通的(de)低電(dian)(dian)(dian)(dian)流充(chong)電(dian)(dian)(dian)(dian)方式，不適用于要求短(duan)充(chong)電(dian)(dian)(dian)(dian)時(shi)間的(de)快速充(chong)電(dian)(dian)(dian)(dian)方案(an)。

　　現在(zai)(zai)(zai)(zai)使用(yong)(yong)的(de)(de)(de)(de)大(da)多(duo)(duo)數充(chong)(chong)電(dian)(dian)(dian)器在(zai)(zai)(zai)(zai)給(gei)電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)時(shi)(shi)(shi)都是(shi)既(ji)使用(yong)(yong)低(di)電(dian)(dian)(dian)流充(chong)(chong)電(dian)(dian)(dian)方(fang)(fang)式又使用(yong)(yong)額定充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流的(de)(de)(de)(de)方(fang)(fang)法，即(ji)容積充(chong)(chong)電(dian)(dian)(dian)，低(di)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流通(tong)常(chang)使用(yong)(yong)在(zai)(zai)(zai)(zai)充(chong)(chong)電(dian)(dian)(dian)的(de)(de)(de)(de)初始階(jie)段。在(zai)(zai)(zai)(zai)這(zhe)(zhe)一階(jie)段，需要將(jiang)會導(dao)致充(chong)(chong)電(dian)(dian)(dian)過程(cheng)(cheng)終止的(de)(de)(de)(de)芯片初期的(de)(de)(de)(de)自熱效應減小到(dao)最(zui)低(di)程(cheng)(cheng)度，容積充(chong)(chong)電(dian)(dian)(dian)通(tong)常(chang)用(yong)(yong)在(zai)(zai)(zai)(zai)充(chong)(chong)電(dian)(dian)(dian)的(de)(de)(de)(de)中(zhong)級階(jie)段，電(dian)(dian)(dian)池(chi)的(de)(de)(de)(de)大(da)部分(fen)能量(liang)都是(shi)在(zai)(zai)(zai)(zai)這(zhe)(zhe)一階(jie)段存(cun)儲(chu)的(de)(de)(de)(de)。在(zai)(zai)(zai)(zai)電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)的(de)(de)(de)(de)最(zui)后(hou)階(jie)段，通(tong)常(chang)充(chong)(chong)電(dian)(dian)(dian)時(shi)(shi)(shi)間(jian)的(de)(de)(de)(de)絕大(da)部分(fen)都是(shi)消耗在(zai)(zai)(zai)(zai)這(zhe)(zhe)一階(jie)段，可以通(tong)過監(jian)測電(dian)(dian)(dian)流、電(dian)(dian)(dian)壓(ya)(ya)或(huo)兩者的(de)(de)(de)(de)值(zhi)來決定何(he)時(shi)(shi)(shi)結束充(chong)(chong)電(dian)(dian)(dian)。同(tong)(tong)樣，結束方(fang)(fang)案依(yi)賴(lai)于電(dian)(dian)(dian)池(chi)的(de)(de)(de)(de)化學特性(xing)，例如(ru)：大(da)多(duo)(duo)數鋰離子電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)器都是(shi)將(jiang)電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(ya)(ya)保持在(zai)(zai)(zai)(zai)恒(heng)定值(zhi)，同(tong)(tong)時(shi)(shi)(shi)檢測最(zui)低(di)電(dian)(dian)(dian)流。鎳鎘、NiCd電(dian)(dian)(dian)池(chi)用(yong)(yong)電(dian)(dian)(dian)壓(ya)(ya)或(huo)溫度的(de)(de)(de)(de)變化率(lv)來決定充(chong)(chong)電(dian)(dian)(dian)的(de)(de)(de)(de)結束時(shi)(shi)(shi)間(jian)。

      充電時部分電能被轉換成熱能，直至電池充滿。而充滿后，所有的電能將全部被轉換成熱能。如果此時不終止充電，電池就會被損壞或燒毀。快速充電器電池（完全充滿的時間小于兩小時的充電器）則可以解決這個問題，因為這些充電器是使用高充電電流來縮短充電時間的。因此，對于鋰離子電池來說,監測它的(de)(de)溫度是至關重要的(de)(de)，因為電池在過(guo)充電時會(hui)發生爆裂，在所有的(de)(de)充電階段都應該(gai)隨時監測溫度的(de)(de)變(bian)化(hua)，并且(qie)在溫度超過(guo)最大(da)設定(ding)值時立即(ji)停止充電。

　　2 總體設計 
　
　　充電電路由三部分：控制部分，檢測部分及充電部分組成。如圖1所示，采用F310單片機進行充電控制，單片機本身具有脈寬調制PWM型開關穩壓電源所需的全部功能，具有10位A/D轉換器。利用單片機A/D端口，構成電(dian)池電(dian)壓(ya)，電(dian)流，溫(wen)度檢(jian)測(ce)電(dian)路。

　　單片(pian)機通過電(dian)壓反(fan)饋(kui)(kui)和(he)電(dian)流反(fan)饋(kui)(kui)信號，直接利用(yong)PWM輸出將數字電(dian)壓信號并轉(zhuan)化成模擬電(dian)壓信號，能夠保證控制精度。

　　3 控制部分電路設(she)計 

　　C8051F310單片機(ji)

　　①模擬外設

　　a.10位ADC：轉換速度可達200ks/s,可多達21或17個外(wai)(wai)部(bu)單端或差分輸入，VREF可在外(wai)(wai)部(bu)引腳或VDD中選擇，內置溫(wen)度傳感器(qi)（±3℃），外(wai)(wai)部(bu)轉換啟動輸入；

　　b.兩個模擬比較器：可編程回差電壓和響應時間，可配置為中斷或復位源，小電流（〈0.5μA）。
　　
　　②供電電壓

　　a.典型工作電流：5mA、25MHz；
　　b.典型停機電流：0.1μA；
　　c.溫度范圍：-40～+85℃。

　　③高速8051微控制器內核

　　a.流水線指令結構：70%的指令的執行時間為一個或兩個系統時鐘周期；
　　b.速度可達25MI/s（時鐘頻率為25MHz時）；
　　c.擴(kuo)展的中(zhong)斷系(xi)統。

　　④數字外設

　　a.29/25個端口I/O：所有的口線均耐5V電壓；
　　b.4個通用16位計數器/定時器；
　　c.16位可編程計數器/定時器陣列（PCA），有5個捕捉/比較模塊；
　　d.使用PCA或定(ding)時(shi)器和(he)外部時(shi)鐘源的實(shi)時(shi)時(shi)鐘方式(shi)。

　　控制(zhi)電(dian)路中如圖(tu)2所示(shi)，P0.3口提供充電(dian)電(dian)源，P0.6口檢(jian)(jian)測充電(dian)電(dian)壓的大小(xiao)，P0.5口檢(jian)(jian)測充電(dian)電(dian)流的大小(xiao)，P0.4口檢(jian)(jian)測電(dian)池的溫度(du)。

　　充(chong)電電流由(you)單片機(ji)脈寬調制(zhi)PWM產生，充(chong)電電流由(you)AD轉(zhuan)換(huan)再經過計(ji)算得出。

　　4 充電部分(fen)及檢測部分(fen)電路(lu)設(she)計

　　②快速轉換器

　　實現漸弱終止充電(dian)(dian)器(qi)的(de)最經(jing)濟的(de)方法(fa)就是用一個(ge)快(kuai)速(su)轉(zhuan)換器(qi)。快(kuai)速(su)轉(zhuan)換器(qi)是用一個(ge)電(dian)(dian)感和/或一個(ge)變壓(ya)器(qi)（需要(yao)隔(ge)離的(de)時候用變壓(ya)器(qi)）作(zuo)為能量存儲單元以(yi)離散的(de)能量包的(de)形(xing)式將能量從輸入(ru)傳輸至輸出的(de)開(kai)關調節(jie)器(qi)反饋電(dian)(dian)路(lu)，通過晶體管來調節(jie)能量的(de)傳輸，同(tong)時也作(zuo)為過濾開(kai)關，以(yi)確保(bao)電(dian)(dian)壓(ya)或電(dian)(dian)流(liu)在(zai)負載(zai)時保(bao)持(chi)恒定。

　　快速(su)調節器(qi)的(de)操(cao)作是(shi)通過控制一(yi)個晶體管開關的(de)占空比來實現的(de)。占空比會自(zi)動增加以使電池流(liu)入更多的(de)電流(liu)。當(dang)VBATT

　　③電感的確定

　　電(dian)(dian)(dian)感(gan)對交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)是(shi)有(you)(you)阻礙(ai)(ai)作(zuo)用的(de)(de)。在交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)頻率一定(ding)(ding)的(de)(de)情況(kuang)下，電(dian)(dian)(dian)感(gan)量越(yue)大，對交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)(de)阻礙(ai)(ai)能(neng)力(li)(li)越(yue)強??一定(ding)(ding)的(de)(de)情況(kuang)下，交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)(de)頻率越(yue)高，電(dian)(dian)(dian)感(gan)對交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)(de)阻礙(ai)(ai)能(neng)力(li)(li)越(yue)大，頻率越(yue)低(di)，電(dian)(dian)(dian)感(gan)對交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)的(de)(de)阻礙(ai)(ai)能(neng)力(li)(li)越(yue)小。也就是(shi)說，電(dian)(dian)(dian)感(gan)有(you)(you)阻止交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)通(tong)過的(de)(de)特性(xing)。

　　其工作原理(li)是(shi)這(zhe)樣的(de)(de)(de)：當負(fu)(fu)載(zai)(zai)兩(liang)端的(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya)要降(jiang)低時(shi)，通過(guo)(guo)MOSFET場效應(ying)(ying)管的(de)(de)(de)開(kai)(kai)關作用，外部(bu)(bu)電(dian)(dian)(dian)(dian)源對(dui)電(dian)(dian)(dian)(dian)感(gan)進行(xing)充電(dian)(dian)(dian)(dian)并達到所需的(de)(de)(de)額定電(dian)(dian)(dian)(dian)壓(ya)。當負(fu)(fu)載(zai)(zai)兩(liang)端地電(dian)(dian)(dian)(dian)壓(ya)升(sheng)(sheng)高(gao)時(shi)，通過(guo)(guo)MOSFET場效應(ying)(ying)管的(de)(de)(de)開(kai)(kai)關作用，外部(bu)(bu)電(dian)(dian)(dian)(dian)源供(gong)(gong)電(dian)(dian)(dian)(dian)斷(duan)開(kai)(kai)，電(dian)(dian)(dian)(dian)感(gan)釋放(fang)出剛才(cai)充入的(de)(de)(de)能量(liang)，這(zhe)時(shi)電(dian)(dian)(dian)(dian)感(gan)就變成了電(dian)(dian)(dian)(dian)源繼續對(dui)負(fu)(fu)載(zai)(zai)供(gong)(gong)電(dian)(dian)(dian)(dian)。隨(sui)著電(dian)(dian)(dian)(dian)感(gan)上存儲的(de)(de)(de)能量(liang)地消耗。負(fu)(fu)載(zai)(zai)兩(liang)端的(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya)開(kai)(kai)始逐漸降(jiang)低，外部(bu)(bu)電(dian)(dian)(dian)(dian)源通過(guo)(guo)MOSFET場效應(ying)(ying)管的(de)(de)(de)開(kai)(kai)關作用又要充電(dian)(dian)(dian)(dian)。依次類推在不斷(duan)的(de)(de)(de)充電(dian)(dian)(dian)(dian)和(he)放(fang)電(dian)(dian)(dian)(dian)的(de)(de)(de)過(guo)(guo)程(cheng)中(zhong)形成了一種穩定的(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya)，永遠使負(fu)(fu)載(zai)(zai)兩(liang)端地電(dian)(dian)(dian)(dian)壓(ya)不會(hui)升(sheng)(sheng)高(gao)也(ye)不會(hui)降(jiang)低，這(zhe)就是(shi)開(kai)(kai)關電(dian)(dian)(dian)(dian)源的(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比為50%，因為此時的轉換器操作操作效率最高。占空比由方程式1給出：
　　（其中T是PWM的周期在程(cheng)序(xu)示例中T=10.5s）

　　占空比=ton/T （1）

　　至(zhi)此就可以選擇一(yi)個(ge)PWM的(de)轉換頻率（如(ru)方程式2所示）PWM的(de)轉換頻率越大，則電(dian)感(gan)的(de)值越小，也越節約(yue)成(cheng)本。

　　我(wo)的示例代(dai)碼配置F310的8位硬件PWM是使(shi)用內部24.5MHz主(zhu)時鐘(zhong)的256分頻來(lai)產生一個95.7kHz的轉換速率。

　　L=（Vi-Vsat-Voton）/2Iomax （2）

　　現在我們可以計算電感的大小了，假定充電電壓Vi的值為15V，飽和電壓Vsat的值為0.5V，需要獲得的輸出電壓值為4.2V,并且最大輸出電流IＯMAX為1500mA，那么，電感的值至少應選為18H。
需要注意的是(shi)：在本電路中的電容(rong)僅僅是(shi)一個紋(wen)波衰減器，因為(wei)紋(wen)波與電容(rong)的大小(xiao)成反比(bi)例關(guan)系，所以電容(rong)的值越大，衰減效果越好。