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)用(yong)LM324組成的(de)充(chong)(chong)電電壓檢測和控制線路，這些線路無論(lun)從控制精度(du)還是功能方面(mian)都不能滿(man)足(zu)鋰電池充(chong)(chong)電特性(xing)的(de)要求，直(zhi)接導致電池充(chong)(chong)不滿(man)，電池壽命減(jian)短以及(ji)越來(lai)越多的(de)電池損(sun)壞(huai)、爆(bao)炸等案(an)例(li)發生。而如果(guo)采(cai)用(yong)國(guo)外專用(yong)IC來(lai)設計，則其極其高昂的(de)成本實在令(ling)人無法接受。

　　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(xiang)當的總體成本下提供了遠(yuan)遠(yuan)超過LM324方案的性能，具有極(ji)高(gao)的新穎性和市場前景。

　　PT7M7433T是上海百利通公(gong)司最新(xin)設(she)計的極(ji)高精度的一(yi)系列電(dian)壓檢測器(qi)的其(qi)中(zhong)一(yi)款，其(qi)檢測精度在(zai)0-Vcc （5.5V）范(fan)圍內小于(yu)1mV,而且其(qi)批量(liang)IC的檢測值偏差<±2.5%,這樣完全(quan)保(bao)證(zheng)了批量(liang)產品的性(xing)(xing)能一(yi)致性(xing)(xing)和極(ji)高的總體性(xing)(xing)能，我們利用其(qi)配合少量(liang)外(wai)部電(dian)路即(ji)可(ke)組成相當簡單的鋰(li)電(dian)池充電(dian)線路。

　　該(gai)IC的(de)內部(bu)框圖和簡(jian)單介紹如下：（圖一(yi)）

　　IC內含一個(ge)高(gao)精度的(de)615mV基準電(dian)(dian)(dian)壓(ya)源(yuan)、兩個(ge)比較器、一個(ge)RS觸發(fa)器和其(qi)(qi)它(ta)一些(xie)邏輯電(dian)(dian)(dian)路，其(qi)(qi)大(da)致(zhi)功能是：VCC電(dian)(dian)(dian)壓(ya)或其(qi)(qi)它(ta)待檢測電(dian)(dian)(dian)壓(ya)通過(guo)(guo)R1-R3組(zu)成的(de)分壓(ya)網絡接在IC的(de)LTHIN /HTHIN檢測引(yin)腳，當待測電(dian)(dian)(dian)壓(ya)下降導致(zhi)LTHIN引(yin)腳低(di)于(yu)615mV時(shi)(shi)，輸出腳LBO輸出低(di)電(dian)(dian)(dian)平，而如果待測電(dian)(dian)(dian)壓(ya)上升導致(zhi)HTHIN引(yin)腳高(gao)于(yu)615 mV時(shi)(shi)，經(jing)過(guo)(guo)內部邏輯判斷和簡單(dan)延時(shi)(shi)后，輸出腳LBO輸出高(gao)電(dian)(dian)(dian)平。

　　利(li)用這個IC裝制的充電器電路如下（圖二）

　　其工作流(liu)(liu)程(cheng)大(da)致是：當接(jie)上Li+電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)和供電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源時，IC通(tong)過(guo)R1/R2/R3組成(cheng)的(de)(de)網絡檢(jian)測電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)，如(ru)果電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)低(di)于(yu)3.3V（由R1-R3的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)阻值決定(ding)），或者按下按制SW1,此時IC3腳的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)低(di)于(yu)615mV,則IC4腳輸(shu)出低(di)電(dian)(dian)(dian)(dian)(dian)(dian)平，通(tong)過(guo)R5/D2拉低(di)Q1的(de)(de)柵極使(shi)之(zhi)導通(tong)，從(cong)而通(tong)過(guo)Q1/R9/D1給(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)進行大(da)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)一路上升直至超(chao)過(guo)4.20V,此時IC的(de)(de)1腳電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)高(gao)過(guo)615mV,IC內部經簡單判斷(duan)和延時，令4腳輸(shu)出高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)平，從(cong)而關(guan)閉(bi)大(da)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)通(tong)道，但(dan)是4腳的(de)(de)高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)平同時給(gei)R7/C2的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)回路供電(dian)(dian)(dian)(dian)(dian)(dian)，令到Q3的(de)(de)柵極電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)慢(man)慢(man)升高(gao)，并給(gei)R8提供通(tong)路導致Q2導通(tong)，通(tong)過(guo)R10給(gei)Q1提供一個(ge)(ge)較(jiao)弱的(de)(de)導通(tong)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，使(shi)之(zhi)微微導通(tong)，從(cong)而為(wei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)提供一個(ge)(ge)較(jiao)少(shao)的(de)(de)補充(chong)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。按照圖中所示元件參(can)數將于(yu)大(da)約(yue)十(shi)分(fen)鐘后，由于(yu)C2的(de)(de)不斷(duan)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，其端電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)即Q3的(de)(de)柵極電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)不斷(duan)上升直至使(shi)Q3導通(tong)，從(cong)而關(guan)閉(bi)Q2,令到整個(ge)(ge)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程(cheng)結束。

　　上面的(de)(de)方(fang)案還存在一些不(bu)足(zu)之(zhi)處(chu)，例如(ru)檢測精度由外接電(dian)阻R1/R2/R3的(de)(de)精度決定(ding)，對(dui)于(yu)過(guo)放電(dian)的(de)(de)電(dian)池(chi)（電(dian)池(chi)端(duan)電(dian)壓低于(yu)2.8V）沒有(you)一個小(xiao)電(dian)流預充的(de)(de)過(guo)程，另外該(gai)方(fang)案的(de)(de)10分鐘補充充電(dian)時間對(dui)于(yu)較大容量的(de)(de)電(dian)池(chi)來說不(bu)是太足(zu)夠(gou)，因(yin)此針(zhen)對(dui)上述不(bu)足(zu)之(zhi)處(chu)，我們還提供一個成(cheng)本稍高一點，性能更(geng)加(jia)完善的(de)(de)方(fang)案：（圖三）

　　乍看之下，這個(ge)方案采用(yong)了(le)三個(ge)IC,可(ke)是(shi)U1和(he)U2是(shi)采用(yong)的SOT-23或者TO-92封(feng)裝(zhuang)，就好像(xiang)普通三極(ji)管(guan)一樣，其價(jia)格(ge)(ge)也(ye)就是(shi)2-3個(ge)三極(ji)管(guan)的價(jia)格(ge)(ge)，而(er)U3（PT8A2513NE）也(ye)是(shi)采用(yong)的TO-94封(feng)裝(zhuang)，外形和(he)三極(ji)管(guan)很相似，價(jia)錢也(ye)相當便(bian)宜，不過，這個(ge)電(dian)路(lu)可(ke)以實現智能判(pan)斷電(dian)池是(shi)否(fou)過放(fang)電(dian)，決定是(shi)否(fou)在開始(shi)充(chong)(chong)(chong)電(dian)時采用(yong)小(xiao)電(dian)流預充(chong)(chong)(chong)，另外，采用(yong)U3后(hou)也(ye)將充(chong)(chong)(chong)電(dian)后(hou)期的補充(chong)(chong)(chong)充(chong)(chong)(chong)電(dian)過程延(yan)長到大(da)約(yue)一個(ge)小(xiao)時！

　　首先讓我們(men)介紹一(yi)下(xia)該電路中幾(ji)個IC的(de)功能：

　　（圖四(si)）是U1/U2的內部(bu)框圖，這(zhe)兩個IC只是內部(bu)電(dian)阻R1/R2的數值(zhi)不(bu)同而(er)已，它們(men)的功能(neng)也很(hen)簡單：當Vcc低于(yu)IC的設定值(zhi)時（根據IC編號不(bu)同，內部(bu)R3/R4阻值(zhi)也不(bu)同從(cong)而(er)導(dao)致(zhi)檢測電(dian)壓值(zhi)不(bu)同，對于(yu)PT7M6128指(zhi)的是2.80V），RST引腳輸(shu)出低電(dian)平，反之當Vcc 高于(yu)1.05倍標稱值(zhi)時（例如(ru)對于(yu)PT7M6140,此數值(zhi)為1.05x4.0 =4.20V）則RST引腳輸(shu)出高電(dian)平。

　　上面(mian)電路的(de)另外一個IC（PT8A25 13）則是(shi)(shi)一個極簡單卻極穩定的(de)延時(shi)IC,其(qi)(qi)延時(shi)時(shi)間僅(jin)僅(jin)取決于 OSC腳(jiao)的(de)頻(pin)率。事實上該IC就是(shi)(shi)將OSC震蕩頻(pin)率進行32768次分(fen)頻(pin)后用(yong)來控制輸出的(de)。之所以采用(yong)這個電路而(er)不(bu)采用(yong)LM555或(huo)者CD4060等(deng)通用(yong)IC的(de)原因就是(shi)(shi)因為它相對而(er)言(yan)定時(shi)精度(du)更(geng)高（其(qi)(qi)它IC不(bu)分(fen)頻(pin)），定時(shi)時(shi)間更(geng)長（可達數小(xiao)時(shi)）。并(bing)且電路更(geng)加簡單，采用(yong)TO-94或(huo)SOT-23-4封裝，就像一個三(san)極管一樣。而(er)價錢也跟CD4060差不(bu)多，使(shi)用(yong)效(xiao)果(guo)可就好的(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。