隨著手機、MP3、PMP、DC/DV等手持電子產品越來越大眾化，鋰金屬（Li）和鋰電池使用越來越普遍，而配用的充電器無論是市售的15元手機充電器還是較高檔的DC/DV兼容充電器，絕大部分是采(cai)(cai)用LM324組成的(de)(de)充(chong)電(dian)電(dian)壓檢(jian)測(ce)和控制線路，這些線路無(wu)論從控制精(jing)度還是功能方面都不能滿(man)足鋰電(dian)池(chi)充(chong)電(dian)特性的(de)(de)要求，直接(jie)導致電(dian)池(chi)充(chong)不滿(man)，電(dian)池(chi)壽命減短以及越來越多的(de)(de)電(dian)池(chi)損壞、爆炸等案例發生。而如果采(cai)(cai)用國外專用IC來設計，則其極其高(gao)昂的(de)(de)成本實(shi)在令人無(wu)法接(jie)受(shou)。

　　有鑒于此，筆者在此介紹兩款由國產新型IC組成的鋰電池充電器，在大致相當的總體成本下提供了遠遠超(chao)過LM324方案的性(xing)能，具有極高的新穎性(xing)和市(shi)場(chang)前景。

　　PT7M7433T是上海百利通(tong)公司最新(xin)設(she)計(ji)的(de)極(ji)高精度的(de)一系(xi)列(lie)電(dian)壓(ya)檢測器的(de)其中一款，其檢測精度在0-Vcc （5.5V）范(fan)圍內小于1mV,而且其批量IC的(de)檢測值偏(pian)差<±2.5%,這樣(yang)完全保證了批量產品的(de)性(xing)能一致(zhi)性(xing)和極(ji)高的(de)總體性(xing)能，我們利用(yong)其配合少(shao)量外部電(dian)路(lu)即(ji)可組成相當簡(jian)單的(de)鋰電(dian)池(chi)充電(dian)線(xian)路(lu)。

　　該IC的內部框圖和簡單(dan)介紹如下：（圖一）

　　IC內(nei)含一個(ge)高精度的(de)615mV基(ji)準(zhun)電(dian)壓(ya)源、兩個(ge)比較(jiao)器、一個(ge)RS觸(chu)發器和其(qi)它(ta)一些邏(luo)輯電(dian)路(lu)，其(qi)大致功能是：VCC電(dian)壓(ya)或(huo)其(qi)它(ta)待(dai)檢測(ce)電(dian)壓(ya)通過(guo)R1-R3組成(cheng)的(de)分壓(ya)網絡接在(zai)IC的(de)LTHIN /HTHIN檢測(ce)引腳(jiao)，當待(dai)測(ce)電(dian)壓(ya)下降導致LTHIN引腳(jiao)低(di)(di)于615mV時(shi)，輸(shu)(shu)出(chu)腳(jiao)LBO輸(shu)(shu)出(chu)低(di)(di)電(dian)平，而如(ru)果待(dai)測(ce)電(dian)壓(ya)上(shang)升導致HTHIN引腳(jiao)高于615 mV時(shi)，經過(guo)內(nei)部邏(luo)輯判斷和簡(jian)單延時(shi)后，輸(shu)(shu)出(chu)腳(jiao)LBO輸(shu)(shu)出(chu)高電(dian)平。

　　利用這個(ge)IC裝制的充(chong)電器電路如下(xia)（圖(tu)二）

　　其工作流程大(da)(da)致是：當接上(shang)Li+電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池和供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源時，IC通(tong)(tong)(tong)過R1/R2/R3組成(cheng)的(de)(de)(de)(de)網(wang)絡檢測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，如果(guo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低(di)于(yu)(yu)3.3V（由R1-R3的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻值決定），或者(zhe)按(an)下按(an)制SW1,此時IC3腳(jiao)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低(di)于(yu)(yu)615mV,則IC4腳(jiao)輸出低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)，通(tong)(tong)(tong)過R5/D2拉低(di)Q1的(de)(de)(de)(de)柵(zha)極使(shi)之導通(tong)(tong)(tong)，從(cong)而通(tong)(tong)(tong)過Q1/R9/D1給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池進行(xing)大(da)(da)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，當電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)一路上(shang)升(sheng)直(zhi)至(zhi)超過4.20V,此時IC的(de)(de)(de)(de)1腳(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)高(gao)過615mV,IC內部經簡單判(pan)斷和延時，令(ling)4腳(jiao)輸出高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)，從(cong)而關(guan)閉大(da)(da)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)通(tong)(tong)(tong)道，但是4腳(jiao)的(de)(de)(de)(de)高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)同時給(gei)R7/C2的(de)(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)回路供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，令(ling)到Q3的(de)(de)(de)(de)柵(zha)極電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)慢(man)慢(man)升(sheng)高(gao)，并給(gei)R8提供(gong)通(tong)(tong)(tong)路導致Q2導通(tong)(tong)(tong)，通(tong)(tong)(tong)過R10給(gei)Q1提供(gong)一個較(jiao)弱的(de)(de)(de)(de)導通(tong)(tong)(tong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流，使(shi)之微微導通(tong)(tong)(tong)，從(cong)而為電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池提供(gong)一個較(jiao)少(shao)的(de)(de)(de)(de)補(bu)充(chong)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流。按(an)照圖中所示元件參數將(jiang)于(yu)(yu)大(da)(da)約十分鐘(zhong)后，由于(yu)(yu)C2的(de)(de)(de)(de)不斷充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)，其端電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)即Q3的(de)(de)(de)(de)柵(zha)極電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)不斷上(shang)升(sheng)直(zhi)至(zhi)使(shi)Q3導通(tong)(tong)(tong)，從(cong)而關(guan)閉Q2,令(ling)到整個充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過程結束。

　　上面的(de)方(fang)案(an)(an)還(huan)存在一(yi)些(xie)不(bu)足之(zhi)(zhi)處，例(li)如(ru)檢測(ce)精(jing)度由(you)外(wai)接(jie)電(dian)(dian)阻R1/R2/R3的(de)精(jing)度決(jue)定，對于過放(fang)電(dian)(dian)的(de)電(dian)(dian)池（電(dian)(dian)池端電(dian)(dian)壓低(di)于2.8V）沒有(you)一(yi)個(ge)小電(dian)(dian)流(liu)預(yu)充(chong)的(de)過程，另外(wai)該方(fang)案(an)(an)的(de)10分鐘補(bu)充(chong)充(chong)電(dian)(dian)時(shi)間對于較大容量的(de)電(dian)(dian)池來(lai)說不(bu)是太足夠，因此(ci)針對上述不(bu)足之(zhi)(zhi)處，我們還(huan)提供一(yi)個(ge)成本(ben)稍高(gao)一(yi)點，性(xing)能更加完善(shan)的(de)方(fang)案(an)(an)：（圖三）

　　乍(zha)看(kan)之下(xia)，這(zhe)個(ge)方案采用了三(san)(san)個(ge)IC,可是(shi)(shi)U1和U2是(shi)(shi)采用的(de)(de)SOT-23或者TO-92封(feng)裝，就(jiu)好像普通三(san)(san)極管(guan)(guan)一樣(yang)，其價(jia)格也(ye)(ye)就(jiu)是(shi)(shi)2-3個(ge)三(san)(san)極管(guan)(guan)的(de)(de)價(jia)格，而(er)U3（PT8A2513NE）也(ye)(ye)是(shi)(shi)采用的(de)(de)TO-94封(feng)裝，外形和三(san)(san)極管(guan)(guan)很相似，價(jia)錢也(ye)(ye)相當便宜(yi)，不過(guo)(guo)，這(zhe)個(ge)電(dian)路可以實現智能判斷電(dian)池是(shi)(shi)否過(guo)(guo)放電(dian)，決定是(shi)(shi)否在開始充電(dian)時采用小(xiao)電(dian)流預(yu)充，另外，采用U3后(hou)(hou)也(ye)(ye)將充電(dian)后(hou)(hou)期的(de)(de)補充充電(dian)過(guo)(guo)程(cheng)延長到大約一個(ge)小(xiao)時！

　　首先(xian)讓我們介紹一(yi)下該電路中幾個IC的功能：

　　（圖四）是(shi)U1/U2的內(nei)部框圖，這(zhe)兩(liang)個IC只是(shi)內(nei)部電(dian)阻(zu)R1/R2的數值(zhi)(zhi)不(bu)同(tong)而(er)已(yi)，它(ta)們(men)的功(gong)能也很簡(jian)單：當(dang)Vcc低于IC的設定值(zhi)(zhi)時(shi)（根據IC編號不(bu)同(tong)，內(nei)部R3/R4阻(zu)值(zhi)(zhi)也不(bu)同(tong)從而(er)導致檢測電(dian)壓(ya)值(zhi)(zhi)不(bu)同(tong)，對(dui)(dui)于PT7M6128指(zhi)的是(shi)2.80V），RST引(yin)腳(jiao)輸出低電(dian)平，反之當(dang)Vcc 高(gao)(gao)于1.05倍標稱值(zhi)(zhi)時(shi)（例如對(dui)(dui)于PT7M6140,此數值(zhi)(zhi)為1.05x4.0 =4.20V）則RST引(yin)腳(jiao)輸出高(gao)(gao)電(dian)平。

　　上面(mian)電路的(de)另外一個(ge)IC（PT8A25 13）則是(shi)一個(ge)極(ji)簡單(dan)(dan)卻極(ji)穩定的(de)延時IC,其(qi)延時時間僅僅取(qu)決于(yu) OSC腳的(de)頻率。事實上該(gai)IC就(jiu)是(shi)將(jiang)OSC震蕩頻率進行(xing)32768次分(fen)頻后(hou)用來控制輸(shu)出的(de)。之(zhi)所以采(cai)(cai)用這個(ge)電路而不(bu)采(cai)(cai)用LM555或(huo)者CD4060等(deng)通用IC的(de)原因(yin)就(jiu)是(shi)因(yin)為它(ta)相(xiang)對而言定時精度更(geng)高（其(qi)它(ta)IC不(bu)分(fen)頻），定時時間更(geng)長(chang)（可達數小(xiao)時）。并(bing)且電路更(geng)加簡單(dan)(dan)，采(cai)(cai)用TO-94或(huo)SOT-23-4封裝，就(jiu)像一個(ge)三極(ji)管一樣。而價(jia)錢(qian)也跟(gen)CD4060差不(bu)多，使用效果可就(jiu)好的(de)太多了。

　　至此大家想必也大致了解了圖三的工作流程了：接上電池和充電器，如果電池電壓低于2.8V,則U1輸出為低（U2輸出也是低），這樣R3和R4的回路都不通，只有R2回路導通，給Q1提供微弱的導通，使之輸出約數毫安的電流給電池進行預充電，當電池電壓上升到超過2.94V（1.05X2.8）時或者剛接上電池電壓就超過2.94V時，U1輸出高電平而U2繼續輸出低電平（電池電壓還沒達到4.2V J），這時R2通路截止而R3通路導通（因為Q4導通且其源極電平為低-因U1輸出拉低），從而由較小阻值的R3令Q1完全導通，提供一個數百毫安的大電流恒流充電，而當這個恒流充電過程慢慢令到被充電的Li+電池端電壓上升到4.2V時，U2也輸出高電平從而關閉Q4,但是它同時也給U3提供了電源導致U3開始工作，這樣U3觸發Q3使R4導通提供一個很小的補充充電電流，直至U3達到定時時間從而關閉Q3,這時整個充電過程才完全結束。

　　相比而言，第二個方案增加了前期智能判斷電池狀態和自動預充電過程，以及延長了末尾的補充充電過程的時間，各個階段的充電電流可調并且補充充電時間可調（數分鐘至數小時），因此該方案對鋰電池充電具有更好的精確性和安全性，加上價錢便宜，功能也比較完善，相信很快會取代市面中低檔的充電器特別是那些廉價的手機電池充電器。