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)地克服了(le)一般(ban)充(chong)電(dian)(dian)器(qi)過充(chong)電(dian)(dian)、充(chong)電(dian)(dian)不足、效(xiao)(xiao)率低的(de)缺點，實(shi)現了(le)對鋰電(dian)(dian)池組(zu)的(de)智能充(chong)電(dian)(dian)，達到(dao)了(le)預期效(xiao)(xiao)果。該方案(an)設計(ji)靈(ling)活，可滿意多(duo)種型(xing)號的(de)鋰電(dian)(dian)池充(chong)電(dian)(dian)需求(qiu)，且ATtiny261集(ji)成(cheng)化的(de)閃存使其便于軟件調試與升(sheng)級。

鋰電池充電特性
　　鋰(li)電(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)需(xu)要控(kong)制它的(de)(de)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓，限(xian)制其充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)。鋰(li)電(dian)(dian)(dian)池通常都采(cai)用三段(duan)充(chong)(chong)電(dian)(dian)(dian)法，即(ji)預充(chong)(chong)電(dian)(dian)(dian)、恒流(liu)寬電(dian)(dian)(dian)和(he)恒壓充(chong)(chong)電(dian)(dian)(dian)。鋰(li)電(dian)(dian)(dian)池的(de)(de)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)通常應限(xian)制在1C(C為鋰(li)電(dian)(dian)(dian)池的(de)(de)容量)一(yi)下，單體充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓一(yi)般為4．2V，否(fou)則可能(neng)由于電(dian)(dian)(dian)聰過高會造成(cheng)鍵電(dian)(dian)(dian)池永久性(xing)損壞。

　　預(yu)充(chong)電(dian)(dian)(dian)主要是完(wan)成對過(guo)放的(de)鋰電(dian)(dian)(dian)池(chi)進行修復，若電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(ya)(ya)低(di)于3V，則(ze)必須進行預(yu)充(chong)電(dian)(dian)(dian)，否剛可省略該階(jie)(jie)段。這也是最普遍的(de)情況。在恒流(liu)階(jie)(jie)段，充(chong)電(dian)(dian)(dian)器(qi)先給電(dian)(dian)(dian)池(chi)提供大的(de)恒定(ding)電(dian)(dian)(dian)流(liu)，同時(shi)電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(ya)(ya)上(shang)(shang)升(sheng)，當魄池(chi)電(dian)(dian)(dian)壓(ya)(ya)達到(dao)(dao)飽和電(dian)(dian)(dian)壓(ya)(ya)對，則(ze)轉入憾壓(ya)(ya)充(chong)電(dian)(dian)(dian)，充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)(ya)波動應(ying)控制在50mV以內，同時(shi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)降低(di)，當電(dian)(dian)(dian)流(liu)逐漸減小到(dao)(dao)規定(ding)的(de)值時(shi)，可結束充(chong)電(dian)(dian)(dian)過(guo)程(cheng)。電(dian)(dian)(dian)池(chi)的(de)大部分電(dian)(dian)(dian)能在慣流(liu)及(ji)恒壓(ya)(ya)階(jie)(jie)段從充(chong)電(dian)(dian)(dian)器(qi)流(liu)入電(dian)(dian)(dian)池(chi)。曲(qu)上(shang)(shang)可知，充(chong)電(dian)(dian)(dian)器(qi)實際上(shang)(shang)是一個精密電(dian)(dian)(dian)源，其(qi)電(dian)(dian)(dian)流(liu)電(dian)(dian)(dian)壓(ya)(ya)都(dou)被限(xian)制在所要求的(de)范圍之內。

硬件電路設計
　　該系統在電路(lu)設(she)計上主要由(you)單(dan)片(pian)開關電源、控制電路(lu)及保護電路(lu)三(san)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單片(pian)開(kai)關電源

　　該電源采(cai)用配穩壓(ya)管(guan)的(de)(de)(de)(de)光(guang)(guang)藕(ou)反饋電路(lu)實現15V的(de)(de)(de)(de)低壓(ya)直(zhi)流(liu)輸出，當輸出電壓(ya)發(fa)生變化時，通過線性光(guang)(guang)藕(ou)PC817的(de)(de)(de)(de)發(fa)光(guang)(guang)管(guan)的(de)(de)(de)(de)電流(liu)發(fa)生相應的(de)(de)(de)(de)變化，使得(de)TNY268P的(de)(de)(de)(de)EN腳流(liu)出電流(liu)也發(fa)生變化，從(cong)而控(kong)制其片內功率MOSFET的(de)(de)(de)(de)斷、通、調(diao)節(jie)輸出電壓(ya)，使輸壓(ya)電壓(ya)穩定(ding)。詳細反饋原理分析(xi)詳見(jian)后文脈寬調(diao)制(PWM)的(de)(de)(de)(de)控(kong)制。

　　在電(dian)路(lu)結構(gou)上(shang)，線性光藕PC817，不但可(ke)以起到反(fan)饋作用(yong)還(huan)可(ke)起到隔(ge)離作用(yong)。由PNP管Q2和電(dian)阻R9、R1O及(ji)R12組(zu)成的(de)(de)限(xian)流電(dian)路(lu)，則(ze)從源(yuan)(yuan)頭上(shang)防止(zhi)了(le)過電(dian)流的(de)(de)問題。由C6及(ji)R11構(gou)成的(de)(de)緩啟電(dian)路(lu)，則(ze)有效抑止(zhi)了(le)電(dian)源(yuan)(yuan)上(shang)電(dian)瞬間的(de)(de)產生的(de)(de)電(dian)壓(ya)尖峰。而(er)二極管D9則(ze)防止(zhi)了(le)電(dian)池組(zu)的(de)(de)反(fan)向放電(dian)。此(ci)外，對整(zheng)個充電(dian)系(xi)統而(er)言，當(dang)因意外情況系(xi)統失控時(shi)，開(kai)關電(dian)源(yuan)(yuan)所提供的(de)(de)15V直流低壓(ya)也(ye)在某種程(cheng)度上(shang)起到了(le)限(xian)制其最高電(dian)壓(ya)的(de)(de)作用(yong)。

　　2.控制電路
　　單片機負責控(kong)制(zhi)整(zheng)個(ge)系(xi)統的(de)(de)(de)(de)運行，包括(kuo)充電(dian)電(dian)流(liu)(liu)電(dian)壓值的(de)(de)(de)(de)設(she)定，電(dian)流(liu)(liu)電(dian)壓的(de)(de)(de)(de)檢測(ce)與調(diao)整(zheng)，充放電(dian)狀態(tai)的(de)(de)(de)(de)顯示等(deng)。與專用充電(dian)控(kong)制(zhi)芯片相比，單片機控(kong)制(zhi)系(xi)統不僅(jin)不受電(dian)池(chi)組容量(liang)大小(xiao)的(de)(de)(de)(de)阻將電(dian)流(liu)(liu)轉換(huan)為電(dian)壓進行的(de)(de)(de)(de)，因此其PWM控(kong)制(zhi)調(diao)整(zheng)過程與恒限制(zhi)，還可(ke)通過軟硬件配合實現更(geng)靈活的(de)(de)(de)(de)綜合控(kong)制(zhi)，也便于進一步的(de)(de)(de)(de)后續開發(fa)。

　　系(xi)統控(kong)制選(xuan)用(yong)Atmel公(gong)司的(de)AVRATtiny261來實現(xian)，控(kong)制框圖(tu)見圖(tu)2。ATtiny261采用(yong)AVR RISC結(jie)構，其(qi)大部分指令(ling)執行(xing)時間僅為1個(ge)時鐘(zhong)周期．可(ke)達(da)到接(jie)近(jin)1MIPS/MHZ的(de)性能；11路lObitADC。且15對具有可(ke)編程(cheng)增(zeng)益的(de)ADC差分通道，精度(du)高達(da)2.5mV的(de)內置2．56V基準(zhun)源，3個(ge)獨立PWM發生器(qi)，片上溫(wen)度(du)傳感器(qi)，足以滿(man)足設(she)計需求。

圖2系統(tong)控制結構框(kuang)圖

　　　系(xi)統電(dian)(dian)壓(ya)采(cai)樣采(cai)用精密電(dian)(dian)阻分壓(ya)方法，將測量電(dian)(dian)壓(ya)范(fan)圍轉換成0-2．56V，然后(hou)通(tong)過1倍的(de)差分ADC通(tong)道(dao)轉換成數(shu)字信(xin)號，在充(chong)電(dian)(dian)過程中將測得(de)的(de)電(dian)(dian)壓(ya)值(zhi)(zhi)與預(yu)先設定(ding)的(de)值(zhi)(zhi)進行(xing)比較，再控制(zhi)(zhi)調(diao)整PWM占空比完成對充(chong)電(dian)(dian)電(dian)(dian)壓(ya)的(de)控制(zhi)(zhi)與調(diao)節。

　  電流檢測
　　在(zai)系(xi)統(tong)電(dian)(dian)流(liu)(liu)(liu)的(de)(de)(de)榆(yu)測(ce)上(shang)，由(you)于選用ATtiny261的(de)(de)(de)ADC差分通道(dao)，這就(jiu)要(yao)求其正端輸入電(dian)(dian)壓(ya)必須大予負端輸入電(dian)(dian)壓(ya)。困此，在(zai)電(dian)(dian)路(lu)設(she)計(ji)上(shang)，通過串聯(lian)在(zai)電(dian)(dian)流(liu)(liu)(liu)主回路(lu)中的(de)(de)(de)高精度采(cai)樣電(dian)(dian)阻RsenseB和RsenseA，經ADC2-ADCl和ADCl-ADC0兩(liang)對32倍的(de)(de)(de)ADC差分通道(dao)(參(can)見(jian)圖3)，分別完成對充、放電(dian)(dian)電(dian)(dian)流(liu)(liu)(liu)的(de)(de)(de)檢測(ce)。可見(jian)，差分ADC的(de)(de)(de)選用，既(ji)保證了(le)電(dian)(dian)流(liu)(liu)(liu)采(cai)樣的(de)(de)(de)精準，又避免了(le)因電(dian)(dian)路(lu)中引入差分遠(yuan)放所帶來的(de)(de)(de)功(gong)率損耗問題，很好的(de)(de)(de)滿(man)足了(le)系(xi)統(tong)性能與功(gong)耗兩(liang)方面的(de)(de)(de)要(yao)求，充分體(ti)現了(le)ATtiny261的(de)(de)(de)優(you)勢。

  
圖3電池保護電路(lu)