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)地克服(fu)了(le)(le)(le)一(yi)般充(chong)(chong)電(dian)(dian)(dian)器過充(chong)(chong)電(dian)(dian)(dian)、充(chong)(chong)電(dian)(dian)(dian)不足、效(xiao)率低(di)的缺點，實現了(le)(le)(le)對(dui)鋰(li)電(dian)(dian)(dian)池組的智能充(chong)(chong)電(dian)(dian)(dian)，達到(dao)了(le)(le)(le)預期效(xiao)果。該方案設計(ji)靈活(huo)，可滿意多種型號的鋰(li)電(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)需求，且(qie)ATtiny261集(ji)成化(hua)的閃存使其便于軟(ruan)件調試與升(sheng)級。

鋰電池充電特性
　　鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)需要控制(zhi)它的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，限(xian)制(zhi)其充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流。鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)通常都采(cai)用三段充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)法，即(ji)預充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)、恒(heng)流寬電(dian)(dian)(dian)(dian)(dian)(dian)和恒(heng)壓(ya)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流通常應限(xian)制(zhi)在1C(C為(wei)鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)容量)一下，單體充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)一般為(wei)4．2V，否則可(ke)能由(you)于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)聰過高(gao)會造成(cheng)鍵電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)永久性損(sun)壞。

　　預充(chong)(chong)電(dian)(dian)(dian)(dian)主要是完成對(dui)過(guo)放的鋰(li)電(dian)(dian)(dian)(dian)池進行修復，若(ruo)電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)低(di)于3V，則必(bi)須(xu)進行預充(chong)(chong)電(dian)(dian)(dian)(dian)，否剛可(ke)省略該(gai)階(jie)段。這也是最(zui)普遍的情況。在(zai)恒流(liu)階(jie)段，充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)先(xian)給電(dian)(dian)(dian)(dian)池提供大(da)的恒定(ding)電(dian)(dian)(dian)(dian)流(liu)，同(tong)時(shi)電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)上升，當(dang)魄池電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)達到(dao)(dao)飽和(he)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)對(dui)，則轉入憾壓(ya)(ya)(ya)(ya)充(chong)(chong)電(dian)(dian)(dian)(dian)，充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)波動應(ying)控制(zhi)在(zai)50mV以內，同(tong)時(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)降低(di)，當(dang)電(dian)(dian)(dian)(dian)流(liu)逐漸(jian)減小到(dao)(dao)規定(ding)的值時(shi)，可(ke)結束充(chong)(chong)電(dian)(dian)(dian)(dian)過(guo)程。電(dian)(dian)(dian)(dian)池的大(da)部分(fen)電(dian)(dian)(dian)(dian)能在(zai)慣流(liu)及(ji)恒壓(ya)(ya)(ya)(ya)階(jie)段從充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)流(liu)入電(dian)(dian)(dian)(dian)池。曲上可(ke)知，充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)實際上是一個精密(mi)電(dian)(dian)(dian)(dian)源，其電(dian)(dian)(dian)(dian)流(liu)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)都被(bei)限制(zhi)在(zai)所要求的范圍之(zhi)內。

硬件電路設計
　　該系統在電(dian)路(lu)設計上主要由單片開關(guan)電(dian)源、控(kong)制電(dian)路(lu)及保護(hu)電(dian)路(lu)三部(bu)分組成。

　　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(dan)片開關電源

　　該電(dian)(dian)(dian)源采用配穩壓管(guan)的(de)(de)(de)光藕反饋電(dian)(dian)(dian)路實現15V的(de)(de)(de)低壓直流(liu)輸出(chu)，當輸出(chu)電(dian)(dian)(dian)壓發(fa)生(sheng)變化(hua)時，通過線性光藕PC817的(de)(de)(de)發(fa)光管(guan)的(de)(de)(de)電(dian)(dian)(dian)流(liu)發(fa)生(sheng)相應(ying)的(de)(de)(de)變化(hua)，使得TNY268P的(de)(de)(de)EN腳流(liu)出(chu)電(dian)(dian)(dian)流(liu)也發(fa)生(sheng)變化(hua)，從而控制其片內功率MOSFET的(de)(de)(de)斷、通、調節輸出(chu)電(dian)(dian)(dian)壓，使輸壓電(dian)(dian)(dian)壓穩定。詳細(xi)反饋原理分析詳見后文脈寬調制(PWM)的(de)(de)(de)控制。

　　在(zai)電(dian)(dian)路(lu)結(jie)構上(shang)(shang)，線性光藕PC817，不但可(ke)以起(qi)到(dao)反饋(kui)作用(yong)還可(ke)起(qi)到(dao)隔離作用(yong)。由(you)PNP管Q2和電(dian)(dian)阻R9、R1O及R12組(zu)成(cheng)(cheng)的(de)限(xian)流(liu)電(dian)(dian)路(lu)，則從源頭(tou)上(shang)(shang)防止(zhi)(zhi)了(le)過電(dian)(dian)流(liu)的(de)問題。由(you)C6及R11構成(cheng)(cheng)的(de)緩(huan)啟(qi)電(dian)(dian)路(lu)，則有(you)效抑止(zhi)(zhi)了(le)電(dian)(dian)源上(shang)(shang)電(dian)(dian)瞬間的(de)產生的(de)電(dian)(dian)壓(ya)尖(jian)峰(feng)。而(er)二極管D9則防止(zhi)(zhi)了(le)電(dian)(dian)池組(zu)的(de)反向放電(dian)(dian)。此(ci)外(wai)，對整個充電(dian)(dian)系(xi)統而(er)言，當因(yin)意外(wai)情況系(xi)統失控時，開(kai)關電(dian)(dian)源所提供的(de)15V直流(liu)低壓(ya)也在(zai)某種程度上(shang)(shang)起(qi)到(dao)了(le)限(xian)制其最高電(dian)(dian)壓(ya)的(de)作用(yong)。

　　2.控制電路
　　單片機負(fu)責控(kong)制(zhi)(zhi)整個系統的(de)(de)運行，包括充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)壓值的(de)(de)設定，電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)壓的(de)(de)檢測與調(diao)整，充放電(dian)(dian)(dian)(dian)狀態的(de)(de)顯示等(deng)。與專用充電(dian)(dian)(dian)(dian)控(kong)制(zhi)(zhi)芯片相(xiang)比(bi)，單片機控(kong)制(zhi)(zhi)系統不(bu)僅不(bu)受電(dian)(dian)(dian)(dian)池組(zu)容量大小(xiao)的(de)(de)阻(zu)將電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)轉換為電(dian)(dian)(dian)(dian)壓進行的(de)(de)，因(yin)此(ci)其PWM控(kong)制(zhi)(zhi)調(diao)整過程與恒限制(zhi)(zhi)，還可通過軟硬件配(pei)合實(shi)現更(geng)靈活的(de)(de)綜合控(kong)制(zhi)(zhi)，也(ye)便于進一步(bu)的(de)(de)后續開發。

　　系統(tong)控(kong)(kong)制(zhi)選(xuan)用(yong)Atmel公(gong)司的(de)AVRATtiny261來實現，控(kong)(kong)制(zhi)框圖見圖2。ATtiny261采用(yong)AVR RISC結構，其大部分(fen)指(zhi)令執行時(shi)(shi)間僅(jin)為1個時(shi)(shi)鐘(zhong)周(zhou)期．可達到接近1MIPS/MHZ的(de)性能(neng)；11路lObitADC。且15對具(ju)有(you)可編(bian)程(cheng)增益的(de)ADC差分(fen)通(tong)道，精度(du)高達2.5mV的(de)內置2．56V基準源，3個獨(du)立PWM發生(sheng)器，片(pian)上(shang)溫(wen)度(du)傳感器，足以滿(man)足設(she)計需求。

圖(tu)2系統(tong)控制(zhi)結構框圖(tu)

　　　系統電(dian)(dian)(dian)壓(ya)(ya)采樣采用精密電(dian)(dian)(dian)阻分壓(ya)(ya)方法(fa)，將測量電(dian)(dian)(dian)壓(ya)(ya)范圍(wei)轉(zhuan)換成0-2．56V，然后通(tong)過1倍(bei)的差分ADC通(tong)道轉(zhuan)換成數字信號，在充電(dian)(dian)(dian)過程中將測得的電(dian)(dian)(dian)壓(ya)(ya)值與預先(xian)設定(ding)的值進行比較，再控制調(diao)整PWM占(zhan)空比完成對充電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)(ya)的控制與調(diao)節。

　  電流檢測
　　在系統電(dian)(dian)流的(de)(de)榆測(ce)上，由于(yu)選用(yong)ATtiny261的(de)(de)ADC差(cha)(cha)分(fen)(fen)通道，這就要求其正端(duan)輸入(ru)(ru)電(dian)(dian)壓(ya)必(bi)須大予負端(duan)輸入(ru)(ru)電(dian)(dian)壓(ya)。困(kun)此，在電(dian)(dian)路(lu)(lu)設計上，通過串聯在電(dian)(dian)流主回路(lu)(lu)中的(de)(de)高精度采樣電(dian)(dian)阻RsenseB和(he)RsenseA，經ADC2-ADCl和(he)ADCl-ADC0兩對32倍(bei)的(de)(de)ADC差(cha)(cha)分(fen)(fen)通道(參見(jian)圖(tu)3)，分(fen)(fen)別完成對充、放電(dian)(dian)電(dian)(dian)流的(de)(de)檢測(ce)。可見(jian)，差(cha)(cha)分(fen)(fen)ADC的(de)(de)選用(yong)，既(ji)保證了(le)(le)電(dian)(dian)流采樣的(de)(de)精準，又避(bi)免了(le)(le)因(yin)電(dian)(dian)路(lu)(lu)中引入(ru)(ru)差(cha)(cha)分(fen)(fen)遠放所帶來的(de)(de)功(gong)率損耗問題，很好的(de)(de)滿足(zu)了(le)(le)系統性能與功(gong)耗兩方面(mian)的(de)(de)要求，充分(fen)(fen)體現了(le)(le)ATtiny261的(de)(de)優(you)勢。

  
圖3電池保護電路