鋰離子電池智能充電器硬件
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(gao)的(de)(de)(de)測量精度,可很好的(de)(de)(de)控制(zhi)充電(dian)電(dian)流的(de)(de)(de)大小,適時的(de)(de)(de)調整,并可根據充電(dian)的(de)(de)(de)狀態(tai)判斷充電(dian)的(de)(de)(de)時間,及時終止充電(dian),以(yi)避免電(dian)池的(de)(de)(de)過(guo)充。
本(ben)文討論使用(yong)(yong)(yong)C8051F310器件設(she)計鋰離(li)子電(dian)(dian)池(chi)充(chong)電(dian)(dian)器的(de)(de)。利用(yong)(yong)(yong)PWM脈寬調制產生可用(yong)(yong)(yong)軟件控制的(de)(de)充(chong)電(dian)(dian)電(dian)(dian)源,以適應不同階段(duan)的(de)(de)充(chong)電(dian)(dian)電(dian)(dian)流(liu)的(de)(de)要求(qiu)。溫度(du)傳感(gan)器對電(dian)(dian)池(chi)溫度(du)進行監(jian)測,并通過AD轉換(huan)和相(xiang)關計算檢測電(dian)(dian)池(chi)充(chong)電(dian)(dian)電(dian)(dian)壓(ya)和電(dian)(dian)流(liu),以判斷電(dian)(dian)池(chi)到達哪個階段(duan)。使電(dian)(dian)池(chi)具有(you)更長的(de)(de)使用(yong)(yong)(yong)壽命,更有(you)效的(de)(de)充(chong)電(dian)(dian)方法(fa)。
設計過程
1 充電原理
電池的(de)特(te)性唯一地(di)決定其安全性能和充(chong)電的(de)效率。電池的(de)最佳(jia)充(chong)電方(fang)法是(shi)由電池的(de)化學成分決定的(de)(鋰(li)離子、鎳(nie)氫(qing)、鎳(nie)鎘還是(shi)SLA電池等(deng))。盡管(guan)如此,大多數充(chong)電方(fang)案都包含下面的(de)三個階段:
● 低電流調節階段
● 恒流階段
● 恒壓階段/充(chong)電終止(zhi)
所有電(dian)(dian)(dian)(dian)池(chi)都是通過向(xiang)自(zi)身(shen)傳輸電(dian)(dian)(dian)(dian)能的(de)(de)方(fang)法進行(xing)充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)(de),一節電(dian)(dian)(dian)(dian)池(chi)的(de)(de)最大充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)取決于電(dian)(dian)(dian)(dian)池(chi)的(de)(de)額定容(rong)(rong)量(liang)(liang)(C)例(li)如,一節容(rong)(rong)量(liang)(liang)為(wei)1000mAh的(de)(de)電(dian)(dian)(dian)(dian)池(chi)在充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)為(wei)1000mA時,可以(yi)充(chong)(chong)電(dian)(dian)(dian)(dian)1C(電(dian)(dian)(dian)(dian)池(chi)容(rong)(rong)量(liang)(liang)的(de)(de)1倍)也可以(yi)用1/50C(20mA)或更(geng)低的(de)(de)電(dian)(dian)(dian)(dian)流(liu)給(gei)電(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)。盡管如此,這只是一個(ge)普(pu)通的(de)(de)低電(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)方(fang)式,不適用于要求(qiu)短充(chong)(chong)電(dian)(dian)(dian)(dian)時間的(de)(de)快速充(chong)(chong)電(dian)(dian)(dian)(dian)方(fang)案。
現在使用的大多數充電器在(zai)給電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)(shi)都(dou)(dou)是(shi)既(ji)使用(yong)低(di)電(dian)(dian)(dian)(dian)流充(chong)(chong)電(dian)(dian)(dian)(dian)方(fang)式又(you)使用(yong)額定(ding)(ding)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流的(de)方(fang)法,即容(rong)積充(chong)(chong)電(dian)(dian)(dian)(dian),低(di)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流通(tong)(tong)常使用(yong)在(zai)充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)初始階(jie)段(duan)(duan)。在(zai)這一(yi)階(jie)段(duan)(duan),需要將會(hui)導致(zhi)充(chong)(chong)電(dian)(dian)(dian)(dian)過程(cheng)終止的(de)芯片初期的(de)自熱(re)效應減小到最(zui)低(di)程(cheng)度(du),容(rong)積充(chong)(chong)電(dian)(dian)(dian)(dian)通(tong)(tong)常用(yong)在(zai)充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)中級階(jie)段(duan)(duan),電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)大部分能(neng)量都(dou)(dou)是(shi)在(zai)這一(yi)階(jie)段(duan)(duan)存儲(chu)的(de)。在(zai)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)最(zui)后階(jie)段(duan)(duan),通(tong)(tong)常充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)(shi)間的(de)絕大部分都(dou)(dou)是(shi)消耗在(zai)這一(yi)階(jie)段(duan)(duan),可以通(tong)(tong)過監測電(dian)(dian)(dian)(dian)流、電(dian)(dian)(dian)(dian)壓(ya)或(huo)兩者的(de)值來(lai)決(jue)定(ding)(ding)何時(shi)(shi)結(jie)束充(chong)(chong)電(dian)(dian)(dian)(dian)。同樣,結(jie)束方(fang)案依(yi)賴于電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)化學特性,例如:大多數鋰離子(zi)電(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)器都(dou)(dou)是(shi)將電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓(ya)保持(chi)在(zai)恒(heng)定(ding)(ding)值,同時(shi)(shi)檢測最(zui)低(di)電(dian)(dian)(dian)(dian)流。鎳鎘、NiCd電(dian)(dian)(dian)(dian)池(chi)(chi)用(yong)電(dian)(dian)(dian)(dian)壓(ya)或(huo)溫度(du)的(de)變化率來(lai)決(jue)定(ding)(ding)充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)結(jie)束時(shi)(shi)間。
圖1 鋰離子電池充電模塊圖
充電(dian)時(shi)(shi)部分電(dian)能被轉(zhuan)換(huan)成熱能,直至(zhi)電(dian)池(chi)充滿。而充滿后(hou),所有的電(dian)能將全(quan)部被轉(zhuan)換(huan)成熱能。如果(guo)此(ci)時(shi)(shi)不終止(zhi)充電(dian),電(dian)池(chi)就會被損壞或燒毀(hui)。快速充電(dian)器電(dian)池(chi)(完全(quan)充滿的時(shi)(shi)間小于兩小時(shi)(shi)的充電(dian)器)則(ze)可(ke)以解決這個問(wen)題,因(yin)為這些充電(dian)器是使用高充電(dian)電(dian)流來縮(suo)短充電(dian)時(shi)(shi)間的。因(yin)此(ci),對于鋰離(li)子電(dian)池(chi)來說(shuo),監(jian)測它(ta)的溫(wen)度是至(zhi)關(guan)重要的,因(yin)為電(dian)池(chi)在過充電(dian)時(shi)(shi)會發生爆裂(lie),在所有的充電(dian)階段都應該隨時(shi)(shi)監(jian)測溫(wen)度的變化,并且(qie)在溫(wen)度超過最大(da)設定(ding)值時(shi)(shi)立即停(ting)止(zhi)充電(dian)。
2 總體設計
充(chong)(chong)電(dian)電(dian)路由三(san)部(bu)分(fen):控制(zhi)部(bu)分(fen),檢測部(bu)分(fen)及充(chong)(chong)電(dian)部(bu)分(fen)組(zu)成。如圖1所示,采用F310單片(pian)機進行充(chong)(chong)電(dian)控制(zhi),單片(pian)機本身具有(you)脈寬(kuan)調制(zhi)PWM型開關(guan)穩壓電(dian)源所需的全部(bu)功能,具有(you)10位(wei)A/D轉換器。利用單片(pian)機A/D端口,構成電(dian)池電(dian)壓,電(dian)流(liu),溫度(du)檢測電(dian)路。
單(dan)片(pian)機(ji)通(tong)過電壓反饋和(he)電流反饋信(xin)號,直接利用(yong)PWM輸出(chu)將數(shu)字電壓信(xin)號并轉化(hua)成模擬電壓信(xin)號,能夠保證控制精度。
3 控制部分電路設計
C8051F310單(dan)片機
①模擬外設
a.10位ADC:轉換(huan)速度可(ke)達200ks/s,可(ke)多(duo)達21或(huo)17個外(wai)部(bu)單端(duan)或(huo)差分(fen)輸入,VREF可(ke)在外(wai)部(bu)引腳(jiao)或(huo)VDD中選擇(ze),內置(zhi)溫度傳感器(±3℃),外(wai)部(bu)轉換(huan)啟動(dong)輸入;
b.兩個模擬比(bi)較器(qi):可編(bian)程(cheng)回差電壓和響(xiang)應時(shi)間(jian),可配(pei)置為中(zhong)斷(duan)或復位源,小電流(〈0.5μA)。
②供電電壓
a.典型工(gong)作電流:5mA、25MHz;
b.典型(xing)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(liu)水線指令(ling)(ling)結構(gou):70%的指令(ling)(ling)的執(zhi)行時間(jian)為一個(ge)或兩個(ge)系(xi)統時鐘(zhong)周(zhou)期(qi);
b.速(su)度可(ke)達25MI/s(時(shi)(shi)鐘頻率為(wei)25MHz時(shi)(shi));
c.擴展(zhan)的中(zhong)斷系(xi)統。
④數字外設
a.29/25個端口(kou)I/O:所有的(de)口(kou)線均耐5V電壓;
b.4個通(tong)用16位計數(shu)器(qi)/定時器(qi);
c.16位可編程計數器(qi)/定時器(qi)陣列(lie)(PCA),有5個捕捉/比較模塊;
d.使用PCA或定時(shi)器(qi)和(he)外(wai)部時(shi)鐘(zhong)源的實(shi)時(shi)時(shi)鐘(zhong)方式。
控制電路中如圖(tu)2所(suo)示,P0.3口提供充(chong)電電源,P0.6口檢(jian)測充(chong)電電壓的(de)大小,P0.5口檢(jian)測充(chong)電電流的(de)大小,P0.4口檢(jian)測電池的(de)溫度(du)。
充電電流(liu)由單片機脈(mo)寬調(diao)制PWM產(chan)生,充電電流(liu)由AD轉(zhuan)換再(zai)經(jing)過計算(suan)得出(chu)。
4 充電部分及檢測部分電路設計(ji)
圖2 控制電路接線圖
圖3 充電電路(lu)與檢測電路(lu)圖
圖3為充電(dian)電(dian)路(lu)與(yu)檢測電(dian)路(lu)圖。
①充電過程曲線
圖4 鋰電(dian)池充電(dian)曲(qu)線
如圖4所示,充(chong)電過程由預充(chong)狀(zhuang)態(tai),恒流充(chong)電狀(zhuang)態(tai)和(he)恒壓(ya)充(chong)電狀(zhuang)態(tai)組成。
②快速轉換器
實現漸弱終止充電器的(de)(de)最經濟的(de)(de)方法就(jiu)是(shi)用(yong)(yong)一(yi)個(ge)(ge)快速轉(zhuan)換(huan)器。快速轉(zhuan)換(huan)器是(shi)用(yong)(yong)一(yi)個(ge)(ge)電(dian)(dian)感和(he)/或一(yi)個(ge)(ge)變(bian)壓(ya)(ya)器(需要(yao)隔離的(de)(de)時候用(yong)(yong)變(bian)壓(ya)(ya)器)作為能量存儲單(dan)元以離散的(de)(de)能量包(bao)的(de)(de)形(xing)式將(jiang)能量從輸(shu)(shu)入傳輸(shu)(shu)至(zhi)輸(shu)(shu)出(chu)的(de)(de)開關調(diao)節器反饋電(dian)(dian)路,通過晶體管來調(diao)節能量的(de)(de)傳輸(shu)(shu),同(tong)時也作為過濾(lv)開關,以確保(bao)電(dian)(dian)壓(ya)(ya)或電(dian)(dian)流(liu)在負載時保(bao)持(chi)恒定。
如圖a開(kai)關閉合
如圖b開(kai)關(guan)打開(kai)
快(kuai)速調節器(qi)的(de)操作(zuo)是通過控制一個晶(jing)體管開關的(de)占空(kong)比來實現(xian)的(de)。占空(kong)比會自動增加以使電(dian)池(chi)流入更多的(de)電(dian)流。當VBATT
③電感的確定
電感(gan)對(dui)交(jiao)(jiao)流(liu)電是有阻(zu)(zu)(zu)(zu)礙作用的(de)(de)(de)(de)。在交(jiao)(jiao)流(liu)電頻率一(yi)定的(de)(de)(de)(de)情況下,電感(gan)量(liang)(liang)越(yue)大,對(dui)交(jiao)(jiao)流(liu)電的(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)礙能(neng)力越(yue)強,電感(gan)量(liang)(liang)越(yue)小(xiao),其阻(zu)(zu)(zu)(zu)礙能(neng)力越(yue)小(xiao)。另外,在電感(gan)量(liang)(liang)一(yi)定的(de)(de)(de)(de)情況下,交(jiao)(jiao)流(liu)電的(de)(de)(de)(de)頻率越(yue)高,電感(gan)對(dui)交(jiao)(jiao)流(liu)電的(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)礙能(neng)力越(yue)大,頻率越(yue)低,電感(gan)對(dui)交(jiao)(jiao)流(liu)電的(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)礙能(neng)力越(yue)小(xiao)。也就(jiu)是說(shuo),電感(gan)有阻(zu)(zu)(zu)(zu)止交(jiao)(jiao)流(liu)電通過的(de)(de)(de)(de)特(te)性。
其工作(zuo)(zuo)原理是(shi)這樣(yang)的(de)(de)(de):當負(fu)(fu)載(zai)(zai)兩(liang)端(duan)的(de)(de)(de)電(dian)(dian)壓(ya)要降低時,通(tong)(tong)(tong)過(guo)(guo)MOSFET場(chang)效應管(guan)(guan)的(de)(de)(de)開(kai)(kai)(kai)關(guan)作(zuo)(zuo)用,外部電(dian)(dian)源(yuan)對電(dian)(dian)感(gan)進行充電(dian)(dian)并達到所需的(de)(de)(de)額定(ding)電(dian)(dian)壓(ya)。當負(fu)(fu)載(zai)(zai)兩(liang)端(duan)地(di)電(dian)(dian)壓(ya)升高(gao)時,通(tong)(tong)(tong)過(guo)(guo)MOSFET場(chang)效應管(guan)(guan)的(de)(de)(de)開(kai)(kai)(kai)關(guan)作(zuo)(zuo)用,外部電(dian)(dian)源(yuan)供電(dian)(dian)斷開(kai)(kai)(kai),電(dian)(dian)感(gan)釋(shi)放出(chu)剛(gang)才充入的(de)(de)(de)能量(liang)(liang),這時電(dian)(dian)感(gan)就變成了(le)電(dian)(dian)源(yuan)繼續(xu)對負(fu)(fu)載(zai)(zai)供電(dian)(dian)。隨(sui)著電(dian)(dian)感(gan)上存儲(chu)的(de)(de)(de)能量(liang)(liang)地(di)消耗。負(fu)(fu)載(zai)(zai)兩(liang)端(duan)的(de)(de)(de)電(dian)(dian)壓(ya)開(kai)(kai)(kai)始逐漸降低,外部電(dian)(dian)源(yuan)通(tong)(tong)(tong)過(guo)(guo)MOSFET場(chang)效應管(guan)(guan)的(de)(de)(de)開(kai)(kai)(kai)關(guan)作(zuo)(zuo)用又要充電(dian)(dian)。依次類(lei)推在(zai)不斷的(de)(de)(de)充電(dian)(dian)和(he)放電(dian)(dian)的(de)(de)(de)過(guo)(guo)程中形成了(le)一種(zhong)穩定(ding)的(de)(de)(de)電(dian)(dian)壓(ya),永(yong)遠使負(fu)(fu)載(zai)(zai)兩(liang)端(duan)地(di)電(dian)(dian)壓(ya)不會(hui)升高(gao)也不會(hui)降低,這就是(shi)開(kai)(kai)(kai)關(guan)電(dian)(dian)源(yuan)的(de)(de)(de)最大優(you)勢。
要確定快速轉(zhuan)換器中(zhong)電感的(de)大小首先應假(jia)定晶(jing)體管的(de)占空比為50%,因為此時的(de)轉(zhuan)換器操(cao)作操(cao)作效率最高。占空比由(you)方程式1給(gei)出:
(其中T是PWM的周期在程(cheng)序示例中T=10.5s)
占(zhan)空比=ton/T (1)
至(zhi)此(ci)就可(ke)以選(xuan)擇(ze)一個(ge)PWM的(de)轉(zhuan)換頻率(lv)(如方程式2所(suo)示)PWM的(de)轉(zhuan)換頻率(lv)越大,則電感(gan)的(de)值越小(xiao),也(ye)越節約成本。
我的(de)示例(li)代(dai)碼配置F310的(de)8位硬件PWM是使用內部24.5MHz主時(shi)鐘(zhong)的(de)256分頻來產(chan)生一個95.7kHz的(de)轉(zhuan)換速(su)率(lv)。
L=(Vi-Vsat-Voton)/2Iomax (2)
現在我們可(ke)以計算電(dian)感的(de)大(da)小了,假定充電(dian)電(dian)壓(ya)Vi的(de)值(zhi)為15V,飽和電(dian)壓(ya)Vsat的(de)值(zhi)為0.5V,需要(yao)獲得的(de)輸(shu)出電(dian)壓(ya)值(zhi)為4.2V,并且最大(da)輸(shu)出電(dian)流IOMAX為1500mA,那么,電(dian)感的(de)值(zhi)至(zhi)少應選為18H。
需(xu)要注(zhu)意的(de)是:在本電(dian)(dian)路中的(de)電(dian)(dian)容僅(jin)(jin)僅(jin)(jin)是一個紋(wen)波衰減器,因為(wei)紋(wen)波與電(dian)(dian)容的(de)大小成反比例關系,所以電(dian)(dian)容的(de)值越(yue)大,衰減效果(guo)越(yue)好。