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，有效(xiao)(xiao)地(di)克服了(le)一(yi)般充(chong)電(dian)(dian)(dian)器(qi)過充(chong)電(dian)(dian)(dian)、充(chong)電(dian)(dian)(dian)不足、效(xiao)(xiao)率(lv)低的(de)(de)缺(que)點(dian)，實現了(le)對鋰電(dian)(dian)(dian)池(chi)組(zu)的(de)(de)智能充(chong)電(dian)(dian)(dian)，達(da)到了(le)預(yu)期效(xiao)(xiao)果。該(gai)方案設計靈活，可(ke)滿意多種型號(hao)的(de)(de)鋰電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)需求，且ATtiny261集成化的(de)(de)閃存使其便于軟件調(diao)試與升級(ji)。

鋰電池充電特性
　　鋰(li)電(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)需(xu)要(yao)控制(zhi)它的(de)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)，限制(zhi)其充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)。鋰(li)電(dian)(dian)(dian)池(chi)(chi)通(tong)常都(dou)采(cai)用(yong)三段(duan)充(chong)(chong)電(dian)(dian)(dian)法，即預(yu)充(chong)(chong)電(dian)(dian)(dian)、恒流(liu)寬電(dian)(dian)(dian)和恒壓(ya)充(chong)(chong)電(dian)(dian)(dian)。鋰(li)電(dian)(dian)(dian)池(chi)(chi)的(de)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)通(tong)常應限制(zhi)在(zai)1C(C為鋰(li)電(dian)(dian)(dian)池(chi)(chi)的(de)容量)一(yi)下(xia)，單體(ti)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)一(yi)般為4．2V，否則可能由于(yu)電(dian)(dian)(dian)聰過高會造成鍵電(dian)(dian)(dian)池(chi)(chi)永久性損壞(huai)。

　　預充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)主要(yao)是完(wan)成對過(guo)放(fang)的(de)(de)(de)鋰電(dian)(dian)(dian)(dian)(dian)池進行修復(fu)，若電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓低于3V，則必須(xu)進行預充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，否剛可(ke)省(sheng)略該階(jie)(jie)段(duan)。這也是最普遍的(de)(de)(de)情況。在恒(heng)(heng)流(liu)階(jie)(jie)段(duan)，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)先給(gei)電(dian)(dian)(dian)(dian)(dian)池提供(gong)大的(de)(de)(de)恒(heng)(heng)定電(dian)(dian)(dian)(dian)(dian)流(liu)，同時(shi)電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓上升，當(dang)魄池電(dian)(dian)(dian)(dian)(dian)壓達到(dao)飽和電(dian)(dian)(dian)(dian)(dian)壓對，則轉入憾壓充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓波動(dong)應控制(zhi)(zhi)在50mV以內，同時(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)降低，當(dang)電(dian)(dian)(dian)(dian)(dian)流(liu)逐漸減(jian)小到(dao)規定的(de)(de)(de)值時(shi)，可(ke)結束充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)過(guo)程(cheng)。電(dian)(dian)(dian)(dian)(dian)池的(de)(de)(de)大部分電(dian)(dian)(dian)(dian)(dian)能(neng)在慣流(liu)及恒(heng)(heng)壓階(jie)(jie)段(duan)從充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)流(liu)入電(dian)(dian)(dian)(dian)(dian)池。曲(qu)上可(ke)知，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)實(shi)際(ji)上是一(yi)個精密電(dian)(dian)(dian)(dian)(dian)源，其電(dian)(dian)(dian)(dian)(dian)流(liu)電(dian)(dian)(dian)(dian)(dian)壓都(dou)被限制(zhi)(zhi)在所(suo)要(yao)求的(de)(de)(de)范圍之內。

硬件電路設計
　　該系(xi)統(tong)在電路設計(ji)上主要由單片開關電源、控制(zhi)電路及保護(hu)電路三(san)部分(fen)組成。

　　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(pei)穩壓(ya)(ya)管的(de)(de)光藕(ou)反饋電(dian)路實(shi)現15V的(de)(de)低壓(ya)(ya)直流(liu)(liu)輸(shu)出(chu)，當輸(shu)出(chu)電(dian)壓(ya)(ya)發(fa)生(sheng)變(bian)化(hua)(hua)時，通過線性光藕(ou)PC817的(de)(de)發(fa)光管的(de)(de)電(dian)流(liu)(liu)發(fa)生(sheng)相應的(de)(de)變(bian)化(hua)(hua)，使得TNY268P的(de)(de)EN腳流(liu)(liu)出(chu)電(dian)流(liu)(liu)也(ye)發(fa)生(sheng)變(bian)化(hua)(hua)，從(cong)而(er)控制(zhi)其(qi)片內功率MOSFET的(de)(de)斷、通、調節輸(shu)出(chu)電(dian)壓(ya)(ya)，使輸(shu)壓(ya)(ya)電(dian)壓(ya)(ya)穩定(ding)。詳(xiang)細反饋原理分析詳(xiang)見(jian)后文脈(mo)寬調制(zhi)(PWM)的(de)(de)控制(zhi)。

　　在電(dian)路(lu)(lu)結構上，線性光藕(ou)PC817，不但可(ke)以起(qi)(qi)(qi)到(dao)反(fan)饋作(zuo)(zuo)用還可(ke)起(qi)(qi)(qi)到(dao)隔(ge)離作(zuo)(zuo)用。由(you)PNP管Q2和(he)電(dian)阻R9、R1O及(ji)R12組成的(de)(de)(de)限流電(dian)路(lu)(lu)，則(ze)(ze)從源頭上防(fang)止(zhi)了(le)(le)過電(dian)流的(de)(de)(de)問題。由(you)C6及(ji)R11構成的(de)(de)(de)緩啟電(dian)路(lu)(lu)，則(ze)(ze)有(you)效抑(yi)止(zhi)了(le)(le)電(dian)源上電(dian)瞬間的(de)(de)(de)產生的(de)(de)(de)電(dian)壓(ya)尖峰。而(er)二極管D9則(ze)(ze)防(fang)止(zhi)了(le)(le)電(dian)池組的(de)(de)(de)反(fan)向放電(dian)。此(ci)外，對整個充電(dian)系(xi)(xi)統而(er)言，當(dang)因意外情況系(xi)(xi)統失控時，開(kai)關電(dian)源所(suo)提供的(de)(de)(de)15V直流低壓(ya)也在某種程(cheng)度上起(qi)(qi)(qi)到(dao)了(le)(le)限制其(qi)最高(gao)電(dian)壓(ya)的(de)(de)(de)作(zuo)(zuo)用。

　　2.控制電路
　　單片(pian)(pian)機負責控制整個系統的(de)(de)運行，包括充電(dian)(dian)電(dian)(dian)流(liu)電(dian)(dian)壓值的(de)(de)設定，電(dian)(dian)流(liu)電(dian)(dian)壓的(de)(de)檢測(ce)與調整，充放電(dian)(dian)狀態的(de)(de)顯示等(deng)。與專(zhuan)用充電(dian)(dian)控制芯(xin)片(pian)(pian)相(xiang)比，單片(pian)(pian)機控制系統不僅不受(shou)電(dian)(dian)池組容(rong)量大小的(de)(de)阻將電(dian)(dian)流(liu)轉換為電(dian)(dian)壓進(jin)(jin)行的(de)(de)，因(yin)此其PWM控制調整過(guo)程與恒限制，還可通(tong)過(guo)軟(ruan)硬件(jian)配合實現更靈活的(de)(de)綜合控制，也便于(yu)進(jin)(jin)一(yi)步的(de)(de)后續開發。

　　系統(tong)控制(zhi)選用Atmel公司(si)的AVRATtiny261來實現，控制(zhi)框(kuang)圖(tu)見(jian)圖(tu)2。ATtiny261采用AVR RISC結構，其(qi)大部(bu)分指(zhi)令執行時(shi)間僅為1個(ge)時(shi)鐘周期(qi)．可達(da)到接(jie)近1MIPS/MHZ的性能；11路(lu)lObitADC。且(qie)15對具有(you)可編程增益(yi)的ADC差分通(tong)道，精(jing)度(du)高達(da)2.5mV的內置(zhi)2．56V基(ji)準源，3個(ge)獨立PWM發生器，片上溫(wen)度(du)傳感器，足以滿足設計需求。

圖2系統控(kong)制結構框(kuang)圖

　　　系統(tong)電(dian)壓(ya)采(cai)樣采(cai)用(yong)精(jing)密電(dian)阻(zu)分壓(ya)方法，將(jiang)測(ce)量(liang)電(dian)壓(ya)范圍(wei)轉換成(cheng)0-2．56V，然(ran)后通(tong)(tong)過(guo)(guo)1倍的(de)(de)(de)差分ADC通(tong)(tong)道轉換成(cheng)數字信號，在充電(dian)過(guo)(guo)程中將(jiang)測(ce)得的(de)(de)(de)電(dian)壓(ya)值與預先設定的(de)(de)(de)值進行比較，再(zai)控制調整PWM占空比完(wan)成(cheng)對充電(dian)電(dian)壓(ya)的(de)(de)(de)控制與調節。

　  電流檢測
　　在系統(tong)電流的(de)(de)榆測上，由于選(xuan)用(yong)ATtiny261的(de)(de)ADC差分(fen)通(tong)(tong)道，這(zhe)就要求(qiu)其正端(duan)輸(shu)入(ru)電壓(ya)必須(xu)大予負端(duan)輸(shu)入(ru)電壓(ya)。困此，在電路設計上，通(tong)(tong)過串聯在電流主回路中的(de)(de)高精(jing)度采樣(yang)電阻RsenseB和RsenseA，經(jing)ADC2-ADCl和ADCl-ADC0兩對32倍的(de)(de)ADC差分(fen)通(tong)(tong)道(參(can)見圖3)，分(fen)別完成對充、放電電流的(de)(de)檢測。可見，差分(fen)ADC的(de)(de)選(xuan)用(yong)，既保證了(le)(le)電流采樣(yang)的(de)(de)精(jing)準，又避(bi)免了(le)(le)因電路中引入(ru)差分(fen)遠放所帶來的(de)(de)功率損耗問題，很好的(de)(de)滿(man)足了(le)(le)系統(tong)性能與功耗兩方面的(de)(de)要求(qiu)，充分(fen)體(ti)現了(le)(le)ATtiny261的(de)(de)優(you)勢。

  
圖3電池(chi)保(bao)護電路