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)地克服了一(yi)般充(chong)電(dian)(dian)器(qi)過充(chong)電(dian)(dian)、充(chong)電(dian)(dian)不(bu)足、效(xiao)率低的缺點，實現了對(dui)鋰(li)電(dian)(dian)池(chi)組的智能充(chong)電(dian)(dian)，達到了預期效(xiao)果。該(gai)方案(an)設計靈活，可滿意(yi)多(duo)種型號(hao)的鋰(li)電(dian)(dian)池(chi)充(chong)電(dian)(dian)需求，且(qie)ATtiny261集成化的閃存(cun)使(shi)其(qi)便于軟件調(diao)試(shi)與升級。

鋰電池充電特性
　　鋰(li)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)需要控制它的充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)，限制其充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)。鋰(li)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)通常都采用三段充(chong)(chong)電(dian)(dian)(dian)(dian)法，即預充(chong)(chong)電(dian)(dian)(dian)(dian)、恒流(liu)寬電(dian)(dian)(dian)(dian)和恒壓(ya)充(chong)(chong)電(dian)(dian)(dian)(dian)。鋰(li)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)通常應限制在(zai)1C(C為(wei)鋰(li)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的容量)一下，單體充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)一般為(wei)4．2V，否則可能由于(yu)電(dian)(dian)(dian)(dian)聰過高會造成鍵電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)永久(jiu)性損壞。

　　預(yu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)主要是(shi)完成對過放的(de)(de)(de)鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池進行修復，若電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)低于3V，則必須進行預(yu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，否剛(gang)可(ke)省略該階(jie)段。這(zhe)也是(shi)最普遍(bian)的(de)(de)(de)情況(kuang)。在(zai)恒流階(jie)段，充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)先(xian)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池提供大(da)的(de)(de)(de)恒定電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流，同(tong)時電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)上升，當魄池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)達到(dao)飽和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)對，則轉入(ru)憾(han)壓(ya)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)波(bo)動應控制在(zai)50mV以內(nei)，同(tong)時充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流降低，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流逐(zhu)漸減小到(dao)規定的(de)(de)(de)值時，可(ke)結(jie)束充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過程。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池的(de)(de)(de)大(da)部分電(dian)(dian)(dian)(dian)(dian)(dian)(dian)能(neng)在(zai)慣流及恒壓(ya)階(jie)段從充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)流入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池。曲上可(ke)知，充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)實際(ji)上是(shi)一個精密電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源，其電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)都被限制在(zai)所(suo)要求的(de)(de)(de)范圍之(zhi)內(nei)。

硬件電路設計
　　該系統在電(dian)(dian)路設計上主要由單片開(kai)關電(dian)(dian)源、控制電(dian)(dian)路及保護電(dian)(dian)路三部分組成(cheng)。

　　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(tu)1單片開關電(dian)源

　　該電(dian)源采用配穩(wen)壓(ya)(ya)管的(de)(de)光藕反(fan)饋(kui)電(dian)路實現15V的(de)(de)低壓(ya)(ya)直流(liu)(liu)輸出(chu)，當輸出(chu)電(dian)壓(ya)(ya)發(fa)(fa)生變化時，通過(guo)線(xian)性光藕PC817的(de)(de)發(fa)(fa)光管的(de)(de)電(dian)流(liu)(liu)發(fa)(fa)生相應的(de)(de)變化，使得TNY268P的(de)(de)EN腳流(liu)(liu)出(chu)電(dian)流(liu)(liu)也(ye)發(fa)(fa)生變化，從(cong)而控制其片內功率MOSFET的(de)(de)斷、通、調節(jie)輸出(chu)電(dian)壓(ya)(ya)，使輸壓(ya)(ya)電(dian)壓(ya)(ya)穩(wen)定。詳(xiang)細反(fan)饋(kui)原理分析詳(xiang)見后文(wen)脈寬調制(PWM)的(de)(de)控制。

　　在電(dian)(dian)(dian)(dian)路結(jie)構(gou)上(shang)，線(xian)性光藕PC817，不但可(ke)以(yi)起(qi)(qi)到反饋作(zuo)用(yong)還可(ke)起(qi)(qi)到隔離作(zuo)用(yong)。由PNP管Q2和電(dian)(dian)(dian)(dian)阻R9、R1O及R12組(zu)成的限流電(dian)(dian)(dian)(dian)路，則(ze)從源(yuan)(yuan)(yuan)頭(tou)上(shang)防止(zhi)(zhi)了(le)過電(dian)(dian)(dian)(dian)流的問題。由C6及R11構(gou)成的緩啟(qi)電(dian)(dian)(dian)(dian)路，則(ze)有(you)效(xiao)抑(yi)止(zhi)(zhi)了(le)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)上(shang)電(dian)(dian)(dian)(dian)瞬(shun)間(jian)的產生的電(dian)(dian)(dian)(dian)壓尖峰(feng)。而(er)二極管D9則(ze)防止(zhi)(zhi)了(le)電(dian)(dian)(dian)(dian)池組(zu)的反向(xiang)放(fang)電(dian)(dian)(dian)(dian)。此外(wai)，對(dui)整個充電(dian)(dian)(dian)(dian)系(xi)(xi)統而(er)言，當因意外(wai)情況系(xi)(xi)統失控時，開關電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)所提供的15V直流低壓也在某種程度上(shang)起(qi)(qi)到了(le)限制其最高(gao)電(dian)(dian)(dian)(dian)壓的作(zuo)用(yong)。

　　2.控制電路
　　單(dan)(dan)片機負責控(kong)制(zhi)整個系(xi)統(tong)的(de)運(yun)行(xing)，包(bao)括充電(dian)電(dian)流電(dian)壓值的(de)設定，電(dian)流電(dian)壓的(de)檢測(ce)與(yu)調(diao)整，充放電(dian)狀態的(de)顯示(shi)等。與(yu)專用充電(dian)控(kong)制(zhi)芯片相比，單(dan)(dan)片機控(kong)制(zhi)系(xi)統(tong)不(bu)僅不(bu)受電(dian)池(chi)組容(rong)量(liang)大小(xiao)的(de)阻將電(dian)流轉換為電(dian)壓進行(xing)的(de)，因此其PWM控(kong)制(zhi)調(diao)整過程與(yu)恒(heng)限(xian)制(zhi)，還可(ke)通過軟硬件(jian)配合實現(xian)更靈活的(de)綜合控(kong)制(zhi)，也便于進一步的(de)后續開發。

　　系統控(kong)制(zhi)選(xuan)用Atmel公司(si)的AVRATtiny261來實現，控(kong)制(zhi)框圖見圖2。ATtiny261采(cai)用AVR RISC結構，其大部分指令執(zhi)行(xing)時間僅為1個(ge)時鐘周(zhou)期．可達到接(jie)近1MIPS/MHZ的性能；11路(lu)lObitADC。且15對具有可編程增益的ADC差分通道，精(jing)度高達2.5mV的內(nei)置2．56V基準源(yuan)，3個(ge)獨立PWM發生器，片上溫度傳感器，足(zu)以滿足(zu)設計需求。

圖(tu)2系統控制結構框圖(tu)

　　　系統電(dian)(dian)(dian)壓(ya)(ya)(ya)采樣采用精密電(dian)(dian)(dian)阻分壓(ya)(ya)(ya)方法，將測量(liang)電(dian)(dian)(dian)壓(ya)(ya)(ya)范圍轉換成0-2．56V，然(ran)后通過1倍的差分ADC通道轉換成數字信號，在充(chong)電(dian)(dian)(dian)過程(cheng)中將測得的電(dian)(dian)(dian)壓(ya)(ya)(ya)值與預先(xian)設定的值進行比較，再控制(zhi)調(diao)整PWM占(zhan)空比完(wan)成對充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)(ya)(ya)的控制(zhi)與調(diao)節(jie)。

　  電流檢測
　　在(zai)系統電(dian)(dian)(dian)流(liu)(liu)(liu)的榆(yu)測(ce)上，由于(yu)選(xuan)用ATtiny261的ADC差(cha)分(fen)(fen)通(tong)道，這就要求其正端輸(shu)入電(dian)(dian)(dian)壓(ya)(ya)必須大予負端輸(shu)入電(dian)(dian)(dian)壓(ya)(ya)。困此，在(zai)電(dian)(dian)(dian)路(lu)(lu)設計上，通(tong)過串(chuan)聯(lian)在(zai)電(dian)(dian)(dian)流(liu)(liu)(liu)主回路(lu)(lu)中的高精度采(cai)樣電(dian)(dian)(dian)阻RsenseB和(he)RsenseA，經ADC2-ADCl和(he)ADCl-ADC0兩對32倍的ADC差(cha)分(fen)(fen)通(tong)道(參見圖3)，分(fen)(fen)別(bie)完(wan)成對充、放電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)(liu)的檢測(ce)。可見，差(cha)分(fen)(fen)ADC的選(xuan)用，既保證了電(dian)(dian)(dian)流(liu)(liu)(liu)采(cai)樣的精準，又避(bi)免了因電(dian)(dian)(dian)路(lu)(lu)中引入差(cha)分(fen)(fen)遠(yuan)放所帶來的功率損耗(hao)問題，很好的滿足了系統性能與(yu)功耗(hao)兩方面的要求，充分(fen)(fen)體現了ATtiny261的優勢。

  
圖3電池保(bao)護電路