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(ju)有(you)較(jiao)長(chang)的壽命。利用(yong)C8051F310單片(pian)機設計(ji)的智能充(chong)(chong)電器，具(ju)有(you)較(jiao)高的測(ce)量精度，可很好(hao)的控制(zhi)充(chong)(chong)電電流的大小，適(shi)時(shi)的調整(zheng)，并可根據充(chong)(chong)電的狀態判斷(duan)充(chong)(chong)電的時(shi)間，及時(shi)終止充(chong)(chong)電，以避免電池的過充(chong)(chong)。

　　本文(wen)討論(lun)使(shi)(shi)用(yong)(yong)C8051F310器件(jian)設計(ji)鋰離子電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器的。利用(yong)(yong)PWM脈寬調制產生可用(yong)(yong)軟件(jian)控制的充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源，以適應不(bu)同(tong)階段的充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的要求(qiu)。溫(wen)度傳感器對電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)溫(wen)度進行(xing)監(jian)測，并通過AD轉換和相關計(ji)算(suan)檢(jian)測電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)和電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，以判斷電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)到達哪個階段。使(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)具(ju)有更長(chang)的使(shi)(shi)用(yong)(yong)壽命，更有效的充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)方法。

　　設計過程

　　1 充電原理

　　電池(chi)的(de)(de)特性唯(wei)一地決定其安全性能和充(chong)電的(de)(de)效率(lv)。電池(chi)的(de)(de)最(zui)佳充(chong)電方法是(shi)由電池(chi)的(de)(de)化(hua)學成(cheng)分決定的(de)(de)（鋰離(li)子、鎳(nie)氫、鎳(nie)鎘還是(shi)SLA電池(chi)等）。盡管如(ru)此，大多(duo)數充(chong)電方案都包含下(xia)面的(de)(de)三個階段：

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

　　所(suo)有(you)電(dian)(dian)(dian)(dian)(dian)池都是通過(guo)向(xiang)自身傳輸電(dian)(dian)(dian)(dian)(dian)能的(de)(de)(de)方法進行充(chong)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)，一(yi)(yi)節電(dian)(dian)(dian)(dian)(dian)池的(de)(de)(de)最(zui)大充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流取決于電(dian)(dian)(dian)(dian)(dian)池的(de)(de)(de)額定(ding)容量(liang)（C）例(li)如，一(yi)(yi)節容量(liang)為(wei)1000mAh的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)池在(zai)充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流為(wei)1000mA時(shi)，可以充(chong)電(dian)(dian)(dian)(dian)(dian)1C(電(dian)(dian)(dian)(dian)(dian)池容量(liang)的(de)(de)(de)1倍)也可以用1/50C(20mA)或(huo)更低(di)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流給電(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)。盡管如此，這(zhe)只是一(yi)(yi)個普通的(de)(de)(de)低(di)電(dian)(dian)(dian)(dian)(dian)流充(chong)電(dian)(dian)(dian)(dian)(dian)方式，不適用于要求(qiu)短充(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)間的(de)(de)(de)快速充(chong)電(dian)(dian)(dian)(dian)(dian)方案。

　　現在(zai)(zai)使(shi)(shi)用(yong)的(de)(de)(de)(de)(de)大(da)(da)多數充(chong)(chong)電(dian)(dian)(dian)器(qi)在(zai)(zai)給電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)時(shi)(shi)都(dou)是(shi)既使(shi)(shi)用(yong)低(di)電(dian)(dian)(dian)流充(chong)(chong)電(dian)(dian)(dian)方(fang)(fang)式又使(shi)(shi)用(yong)額定(ding)(ding)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流的(de)(de)(de)(de)(de)方(fang)(fang)法(fa)，即容(rong)(rong)積充(chong)(chong)電(dian)(dian)(dian)，低(di)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流通(tong)(tong)常使(shi)(shi)用(yong)在(zai)(zai)充(chong)(chong)電(dian)(dian)(dian)的(de)(de)(de)(de)(de)初(chu)始階(jie)段(duan)。在(zai)(zai)這(zhe)一(yi)階(jie)段(duan)，需要將(jiang)會導致充(chong)(chong)電(dian)(dian)(dian)過程終止的(de)(de)(de)(de)(de)芯(xin)片初(chu)期的(de)(de)(de)(de)(de)自熱效應減(jian)小到最(zui)(zui)低(di)程度，容(rong)(rong)積充(chong)(chong)電(dian)(dian)(dian)通(tong)(tong)常用(yong)在(zai)(zai)充(chong)(chong)電(dian)(dian)(dian)的(de)(de)(de)(de)(de)中級階(jie)段(duan)，電(dian)(dian)(dian)池(chi)的(de)(de)(de)(de)(de)大(da)(da)部分能(neng)量都(dou)是(shi)在(zai)(zai)這(zhe)一(yi)階(jie)段(duan)存儲的(de)(de)(de)(de)(de)。在(zai)(zai)電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)的(de)(de)(de)(de)(de)最(zui)(zui)后階(jie)段(duan)，通(tong)(tong)常充(chong)(chong)電(dian)(dian)(dian)時(shi)(shi)間的(de)(de)(de)(de)(de)絕(jue)大(da)(da)部分都(dou)是(shi)消耗在(zai)(zai)這(zhe)一(yi)階(jie)段(duan)，可以通(tong)(tong)過監(jian)測(ce)(ce)電(dian)(dian)(dian)流、電(dian)(dian)(dian)壓(ya)或兩者的(de)(de)(de)(de)(de)值(zhi)來決定(ding)(ding)何(he)時(shi)(shi)結(jie)束(shu)充(chong)(chong)電(dian)(dian)(dian)。同(tong)樣(yang)，結(jie)束(shu)方(fang)(fang)案依賴于電(dian)(dian)(dian)池(chi)的(de)(de)(de)(de)(de)化(hua)學特(te)性，例如：大(da)(da)多數鋰離子電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)器(qi)都(dou)是(shi)將(jiang)電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(ya)保持在(zai)(zai)恒定(ding)(ding)值(zhi)，同(tong)時(shi)(shi)檢測(ce)(ce)最(zui)(zui)低(di)電(dian)(dian)(dian)流。鎳鎘、NiCd電(dian)(dian)(dian)池(chi)用(yong)電(dian)(dian)(dian)壓(ya)或溫度的(de)(de)(de)(de)(de)變化(hua)率來決定(ding)(ding)充(chong)(chong)電(dian)(dian)(dian)的(de)(de)(de)(de)(de)結(jie)束(shu)時(shi)(shi)間。

      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(shuo),監(jian)測(ce)它的(de)溫度是至關重要的(de)，因為電(dian)池在(zai)過(guo)充電(dian)時(shi)會發生爆裂，在(zai)所有的(de)充電(dian)階段都應該隨時(shi)監(jian)測(ce)溫度的(de)變化，并且在(zai)溫度超過(guo)最大設定值時(shi)立即停止充電(dian)。

　　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(yong)單片機A/D端口，構成電(dian)(dian)池電(dian)(dian)壓，電(dian)(dian)流，溫度檢測電(dian)(dian)路。

　　單片機通過電壓(ya)反(fan)饋(kui)和電流(liu)反(fan)饋(kui)信號(hao)，直(zhi)接利用PWM輸出將數字電壓(ya)信號(hao)并(bing)轉(zhuan)化成模擬電壓(ya)信號(hao)，能夠(gou)保證(zheng)控(kong)制精(jing)度。

　　3 控制部分(fen)電路設計 

　　C8051F310單(dan)片機

　　①模擬外設

　　a.10位ADC：轉換(huan)速度(du)可達(da)200ks/s,可多達(da)21或(huo)17個外部單端或(huo)差分輸入，VREF可在外部引腳或(huo)VDD中(zhong)選擇，內置(zhi)溫度(du)傳感器（±3℃），外部轉換(huan)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(kong)制(zhi)器內核(he)

　　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.擴展(zhan)的中斷系(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或定時(shi)(shi)器和外部時(shi)(shi)鐘(zhong)源的實(shi)時(shi)(shi)時(shi)(shi)鐘(zhong)方式。

　　控制電(dian)路中如圖2所示，P0.3口提供充電(dian)電(dian)源，P0.6口檢(jian)測(ce)充電(dian)電(dian)壓的(de)大(da)小(xiao)，P0.5口檢(jian)測(ce)充電(dian)電(dian)流的(de)大(da)小(xiao)，P0.4口檢(jian)測(ce)電(dian)池(chi)的(de)溫度(du)。

　　充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)由單(dan)片機(ji)脈(mo)寬調制PWM產生(sheng)，充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)由AD轉換再經過計算得出。

　　4 充(chong)電部(bu)分(fen)及檢測部(bu)分(fen)電路設計

　　②快速轉換器

　　實(shi)現漸弱終止(zhi)充電器的最(zui)經濟(ji)的方法就是(shi)(shi)用(yong)(yong)一個快(kuai)速轉換(huan)器。快(kuai)速轉換(huan)器是(shi)(shi)用(yong)(yong)一個電感和/或一個變壓器（需要隔離的時(shi)候用(yong)(yong)變壓器）作(zuo)為(wei)能(neng)量(liang)存(cun)儲單元(yuan)以離散的能(neng)量(liang)包的形式將能(neng)量(liang)從輸(shu)入傳輸(shu)至輸(shu)出的開關調(diao)節器反饋電路，通過(guo)晶體管(guan)來(lai)調(diao)節能(neng)量(liang)的傳輸(shu)，同時(shi)也(ye)作(zuo)為(wei)過(guo)濾開關，以確(que)保電壓或電流在負載時(shi)保持恒定。

　　快速調(diao)節器(qi)的(de)(de)(de)(de)操作(zuo)是通過控制一個晶體管開關(guan)的(de)(de)(de)(de)占空比來實現的(de)(de)(de)(de)。占空比會自動(dong)增加以使電(dian)池流(liu)入更多的(de)(de)(de)(de)電(dian)流(liu)。當VBATT

　　③電感的確定

　　電(dian)(dian)(dian)(dian)(dian)感對交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)是有阻(zu)礙作用的(de)。在交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)頻率(lv)一定的(de)情況下，電(dian)(dian)(dian)(dian)(dian)感量越大，對交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)的(de)阻(zu)礙能力(li)越強??一定的(de)情況下，交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)的(de)頻率(lv)越高，電(dian)(dian)(dian)(dian)(dian)感對交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)的(de)阻(zu)礙能力(li)越大，頻率(lv)越低，電(dian)(dian)(dian)(dian)(dian)感對交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)的(de)阻(zu)礙能力(li)越小(xiao)。也就是說，電(dian)(dian)(dian)(dian)(dian)感有阻(zu)止交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)通過的(de)特性。

　　其工作(zuo)原理是這樣(yang)的(de)(de)：當負載(zai)(zai)兩(liang)(liang)端的(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)要降低(di)(di)時，通過MOSFET場效(xiao)(xiao)應管(guan)的(de)(de)開(kai)關(guan)作(zuo)用，外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)對(dui)電(dian)(dian)(dian)(dian)(dian)感(gan)進行充電(dian)(dian)(dian)(dian)(dian)并達(da)到所需的(de)(de)額定電(dian)(dian)(dian)(dian)(dian)壓(ya)。當負載(zai)(zai)兩(liang)(liang)端地(di)電(dian)(dian)(dian)(dian)(dian)壓(ya)升高(gao)時，通過MOSFET場效(xiao)(xiao)應管(guan)的(de)(de)開(kai)關(guan)作(zuo)用，外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)供(gong)電(dian)(dian)(dian)(dian)(dian)斷開(kai)，電(dian)(dian)(dian)(dian)(dian)感(gan)釋放(fang)出剛(gang)才充入的(de)(de)能量(liang)，這時電(dian)(dian)(dian)(dian)(dian)感(gan)就(jiu)變成(cheng)了(le)電(dian)(dian)(dian)(dian)(dian)源(yuan)繼續對(dui)負載(zai)(zai)供(gong)電(dian)(dian)(dian)(dian)(dian)。隨著電(dian)(dian)(dian)(dian)(dian)感(gan)上(shang)存儲的(de)(de)能量(liang)地(di)消(xiao)耗。負載(zai)(zai)兩(liang)(liang)端的(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)開(kai)始逐(zhu)漸降低(di)(di)，外(wai)部(bu)電(dian)(dian)(dian)(dian)(dian)源(yuan)通過MOSFET場效(xiao)(xiao)應管(guan)的(de)(de)開(kai)關(guan)作(zuo)用又要充電(dian)(dian)(dian)(dian)(dian)。依(yi)次類推在(zai)不斷的(de)(de)充電(dian)(dian)(dian)(dian)(dian)和放(fang)電(dian)(dian)(dian)(dian)(dian)的(de)(de)過程中形成(cheng)了(le)一種(zhong)穩定的(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)，永遠使負載(zai)(zai)兩(liang)(liang)端地(di)電(dian)(dian)(dian)(dian)(dian)壓(ya)不會(hui)升高(gao)也不會(hui)降低(di)(di)，這就(jiu)是開(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)最(zui)大優(you)勢(shi)。

　　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(zhong)T是PWM的周期(qi)在程序示例(li)中(zhong)T=10.5s）

　　占空比=ton/T （1）

　　至此就可以選(xuan)擇一個PWM的轉換頻率（如方(fang)程式2所示）PWM的轉換頻率越(yue)(yue)(yue)大(da)，則(ze)電感的值越(yue)(yue)(yue)小，也(ye)越(yue)(yue)(yue)節約成(cheng)本。

　　我(wo)的示例代(dai)碼配置F310的8位硬件(jian)PWM是使用(yong)內部(bu)24.5MHz主時(shi)鐘的256分頻來(lai)產(chan)生(sheng)一(yi)個95.7kHz的轉換速率(lv)。

　　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(de)是：在本電(dian)路中的(de)電(dian)容(rong)僅僅是一(yi)個紋(wen)波衰減(jian)器，因為紋(wen)波與電(dian)容(rong)的(de)大(da)小(xiao)成反比例關(guan)系，所以電(dian)容(rong)的(de)值越大(da)，衰減(jian)效果越好。