鋰電池閑其比能量高、自放電小等長處，成為便攜式電子設備的理想電源。近年來，隨著筆記本電腦、PDA，無繩電話等大功耗大容量便攜式電子產品的普及，其對電源系統的要求也日益提高。為此，研發性能穩定、安全可靠、高效經濟的鋰電池充電器顯得尤為重要。

　　本文在綜合考慮電池安全充電的成本、設計散率及重要性的基礎上，設計了一種基于ATtiny261單片機PWM控制的單片開關電源式鋰電池充電器，有(you)效地克服(fu)了一般充(chong)(chong)電(dian)器過充(chong)(chong)電(dian)、充(chong)(chong)電(dian)不(bu)足(zu)、效率低的(de)(de)缺點，實現了對鋰電(dian)池組(zu)的(de)(de)智能充(chong)(chong)電(dian)，達到(dao)了預期效果。該方案設計靈活，可滿意多種(zhong)型(xing)號的(de)(de)鋰電(dian)池充(chong)(chong)電(dian)需求，且ATtiny261集成化(hua)的(de)(de)閃(shan)存(cun)使其便于軟件調(diao)試與(yu)升級。

鋰電池充電特性
　　鋰(li)電(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)需要(yao)控制(zhi)它的充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓，限(xian)制(zhi)其充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流。鋰(li)電(dian)(dian)(dian)池(chi)(chi)通(tong)(tong)常都采(cai)用(yong)三段充(chong)(chong)電(dian)(dian)(dian)法，即預(yu)充(chong)(chong)電(dian)(dian)(dian)、恒(heng)流寬電(dian)(dian)(dian)和(he)恒(heng)壓充(chong)(chong)電(dian)(dian)(dian)。鋰(li)電(dian)(dian)(dian)池(chi)(chi)的充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流通(tong)(tong)常應限(xian)制(zhi)在1C(C為(wei)鋰(li)電(dian)(dian)(dian)池(chi)(chi)的容量(liang))一(yi)下，單體充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓一(yi)般(ban)為(wei)4．2V，否則可能由(you)于電(dian)(dian)(dian)聰(cong)過高(gao)會(hui)造成鍵(jian)電(dian)(dian)(dian)池(chi)(chi)永久性損壞(huai)。

　　預(yu)(yu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)主要(yao)是(shi)完成(cheng)對過(guo)放(fang)的(de)(de)鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進(jin)行(xing)修復，若電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)低于(yu)3V，則(ze)必須進(jin)行(xing)預(yu)(yu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，否剛可省略(lve)該階段(duan)。這也(ye)是(shi)最普遍的(de)(de)情況(kuang)。在(zai)恒流階段(duan)，充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器先給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)提供大(da)的(de)(de)恒定電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流，同時(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)上升，當魄池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)達到飽和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)對，則(ze)轉入(ru)(ru)憾(han)壓(ya)(ya)(ya)(ya)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)波動應控制(zhi)(zhi)在(zai)50mV以內，同時(shi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流降低，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流逐漸減小到規(gui)定的(de)(de)值時(shi)，可結束充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)大(da)部分電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)能在(zai)慣流及恒壓(ya)(ya)(ya)(ya)階段(duan)從充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器流入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)。曲上可知(zhi)，充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器實際上是(shi)一個精密電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源，其電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)都被限(xian)制(zhi)(zhi)在(zai)所要(yao)求的(de)(de)范圍之內。

硬件電路設計
　　該系統在(zai)電路設計上主要由單片開關電源(yuan)、控制電路及(ji)保護電路三部分組(zu)成。

　　1.單片開關電源
　　單片開關電源負責將電能轉化為電池充電所需要的形式，構成了充電器的主要功率轉換方式。與傳統線性充電器大損耗、低效率的缺點相比，由美國Power Integrations公司的TNY268P構成的單片開關電源，其輸入電壓范圍寬(85265VAC)、體積小、重量輕、效率高，其有調壓、限流、過熱保護等功能，特殊適合于構成充電電源。其原理圖如圖1所示。
 

圖1單片開關電源

　　該電(dian)源采用配穩壓(ya)(ya)管的(de)(de)光藕(ou)反饋電(dian)路(lu)實(shi)現(xian)15V的(de)(de)低壓(ya)(ya)直流(liu)輸(shu)出，當輸(shu)出電(dian)壓(ya)(ya)發生(sheng)變(bian)(bian)(bian)化(hua)時(shi)，通(tong)過線性光藕(ou)PC817的(de)(de)發光管的(de)(de)電(dian)流(liu)發生(sheng)相應的(de)(de)變(bian)(bian)(bian)化(hua)，使得(de)TNY268P的(de)(de)EN腳流(liu)出電(dian)流(liu)也發生(sheng)變(bian)(bian)(bian)化(hua)，從而控制(zhi)其片(pian)內功率MOSFET的(de)(de)斷、通(tong)、調(diao)節輸(shu)出電(dian)壓(ya)(ya)，使輸(shu)壓(ya)(ya)電(dian)壓(ya)(ya)穩定。詳細反饋原理(li)分析詳見后文脈(mo)寬調(diao)制(zhi)(PWM)的(de)(de)控制(zhi)。

　　在電(dian)(dian)(dian)(dian)路(lu)結構上，線性光藕PC817，不但(dan)可以起到(dao)反饋作用(yong)還(huan)可起到(dao)隔離作用(yong)。由(you)(you)PNP管Q2和(he)電(dian)(dian)(dian)(dian)阻(zu)R9、R1O及R12組成(cheng)的(de)(de)(de)限流電(dian)(dian)(dian)(dian)路(lu)，則從源(yuan)頭上防(fang)止了(le)(le)過電(dian)(dian)(dian)(dian)流的(de)(de)(de)問題。由(you)(you)C6及R11構成(cheng)的(de)(de)(de)緩啟(qi)電(dian)(dian)(dian)(dian)路(lu)，則有效(xiao)抑止了(le)(le)電(dian)(dian)(dian)(dian)源(yuan)上電(dian)(dian)(dian)(dian)瞬間的(de)(de)(de)產生(sheng)的(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya)尖(jian)峰。而(er)二極(ji)管D9則防(fang)止了(le)(le)電(dian)(dian)(dian)(dian)池組的(de)(de)(de)反向放電(dian)(dian)(dian)(dian)。此外(wai)，對整個充電(dian)(dian)(dian)(dian)系(xi)統而(er)言，當因(yin)意外(wai)情況(kuang)系(xi)統失(shi)控時，開關(guan)電(dian)(dian)(dian)(dian)源(yuan)所提供(gong)的(de)(de)(de)15V直流低(di)壓(ya)也(ye)在某種程(cheng)度上起到(dao)了(le)(le)限制(zhi)其最高(gao)電(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)作用(yong)。

　　2.控制電路
　　單片(pian)機負責(ze)控(kong)制(zhi)(zhi)整個(ge)系統的(de)(de)運行，包括充電(dian)電(dian)流(liu)(liu)電(dian)壓(ya)值的(de)(de)設定，電(dian)流(liu)(liu)電(dian)壓(ya)的(de)(de)檢測與調整，充放電(dian)狀態(tai)的(de)(de)顯示等。與專用充電(dian)控(kong)制(zhi)(zhi)芯片(pian)相比，單片(pian)機控(kong)制(zhi)(zhi)系統不僅(jin)不受電(dian)池組(zu)容(rong)量大小的(de)(de)阻將電(dian)流(liu)(liu)轉換為(wei)電(dian)壓(ya)進行的(de)(de)，因此其PWM控(kong)制(zhi)(zhi)調整過(guo)程與恒限制(zhi)(zhi)，還可通過(guo)軟硬件配合實(shi)現更(geng)靈活的(de)(de)綜合控(kong)制(zhi)(zhi)，也便于進一步(bu)的(de)(de)后(hou)續開發。

　　系(xi)統控(kong)制選用Atmel公司的AVRATtiny261來(lai)實(shi)現，控(kong)制框圖見(jian)圖2。ATtiny261采用AVR RISC結(jie)構(gou)，其大部分(fen)指令執行時間僅為1個時鐘周期．可達(da)到接近(jin)1MIPS/MHZ的性能；11路lObitADC。且15對具有可編程增(zeng)益(yi)的ADC差分(fen)通道(dao)，精度(du)高達(da)2.5mV的內置2．56V基(ji)準源，3個獨立PWM發生器(qi)，片(pian)上溫度(du)傳感(gan)器(qi)，足以滿足設計需求。

圖2系統(tong)控制結構(gou)框圖

　　　系(xi)統(tong)電壓采樣(yang)采用(yong)精密電阻分壓方(fang)法，將測(ce)量電壓范圍轉換成0-2．56V，然(ran)后通(tong)過1倍(bei)的(de)(de)差分ADC通(tong)道轉換成數字信號，在充(chong)電過程中(zhong)將測(ce)得的(de)(de)電壓值與預先設定的(de)(de)值進行比較，再控制(zhi)調(diao)整(zheng)PWM占空比完(wan)成對充(chong)電電壓的(de)(de)控制(zhi)與調(diao)節。

　  電流檢測
　　在(zai)系統(tong)電(dian)流的榆測上(shang)，由(you)于選用(yong)ATtiny261的ADC差(cha)分(fen)(fen)通道，這就要求其正端輸入(ru)(ru)電(dian)壓必須大予負端輸入(ru)(ru)電(dian)壓。困此，在(zai)電(dian)路設計上(shang)，通過串聯在(zai)電(dian)流主(zhu)回路中的高精度采樣電(dian)阻RsenseB和(he)RsenseA，經ADC2-ADCl和(he)ADCl-ADC0兩(liang)對32倍的ADC差(cha)分(fen)(fen)通道(參(can)見圖3)，分(fen)(fen)別(bie)完成對充、放電(dian)電(dian)流的檢(jian)測。可見，差(cha)分(fen)(fen)ADC的選用(yong)，既(ji)保證了(le)電(dian)流采樣的精準，又避(bi)免(mian)了(le)因電(dian)路中引入(ru)(ru)差(cha)分(fen)(fen)遠放所帶來的功(gong)率損耗問題，很好的滿足(zu)了(le)系統(tong)性(xing)能與(yu)功(gong)耗兩(liang)方(fang)面的要求，充分(fen)(fen)體現了(le)ATtiny261的優勢(shi)。

  
圖(tu)3電池保(bao)護(hu)電路