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LM324組(zu)成的充電(dian)(dian)(dian)電(dian)(dian)(dian)壓檢(jian)測和(he)控制線路，這些線路無(wu)論從控制精度還是功能(neng)方(fang)面都不(bu)(bu)能(neng)滿足鋰電(dian)(dian)(dian)池(chi)(chi)充電(dian)(dian)(dian)特性的要求(qiu)，直接導致(zhi)電(dian)(dian)(dian)池(chi)(chi)充不(bu)(bu)滿，電(dian)(dian)(dian)池(chi)(chi)壽命減短以(yi)及(ji)越來越多的電(dian)(dian)(dian)池(chi)(chi)損(sun)壞、爆炸等案例(li)發生。而(er)如果采(cai)用國外(wai)專(zhuan)用IC來設計，則其極其高昂的成本實(shi)在令人無(wu)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(da)致相當的(de)總體成本下提供了遠遠超過LM324方案的(de)性能(neng)，具有極高的(de)新穎性和市場前景(jing)。

　　PT7M7433T是上海(hai)百利通公(gong)司最新設計的(de)(de)極(ji)(ji)高(gao)精(jing)度(du)的(de)(de)一系列(lie)電(dian)(dian)壓檢(jian)測器的(de)(de)其中一款，其檢(jian)測精(jing)度(du)在(zai)0-Vcc （5.5V）范圍內(nei)小于1mV,而且其批(pi)量IC的(de)(de)檢(jian)測值偏差<±2.5%,這樣完(wan)全(quan)保(bao)證了批(pi)量產品的(de)(de)性能一致(zhi)性和極(ji)(ji)高(gao)的(de)(de)總體性能，我們利用其配合少量外(wai)部電(dian)(dian)路即可組成(cheng)相(xiang)當簡單的(de)(de)鋰電(dian)(dian)池充電(dian)(dian)線路。

　　該IC的(de)內部框圖(tu)和簡單(dan)介紹(shao)如下：（圖(tu)一）

　　IC內含(han)一個高(gao)(gao)精度的(de)(de)615mV基準(zhun)電(dian)壓(ya)(ya)源、兩(liang)個比較器、一個RS觸(chu)發器和其(qi)它(ta)一些(xie)邏輯電(dian)路，其(qi)大致(zhi)(zhi)功(gong)能是：VCC電(dian)壓(ya)(ya)或其(qi)它(ta)待檢測電(dian)壓(ya)(ya)通過(guo)R1-R3組成的(de)(de)分壓(ya)(ya)網絡接(jie)在IC的(de)(de)LTHIN /HTHIN檢測引腳，當待測電(dian)壓(ya)(ya)下降導(dao)致(zhi)(zhi)LTHIN引腳低(di)于(yu)615mV時(shi)，輸(shu)出腳LBO輸(shu)出低(di)電(dian)平，而如果待測電(dian)壓(ya)(ya)上升導(dao)致(zhi)(zhi)HTHIN引腳高(gao)(gao)于(yu)615 mV時(shi)，經(jing)過(guo)內部邏輯判斷和簡單(dan)延(yan)時(shi)后，輸(shu)出腳LBO輸(shu)出高(gao)(gao)電(dian)平。

　　利用(yong)這個IC裝(zhuang)制的(de)充電(dian)器電(dian)路如下(xia)（圖二）

　　其工作流(liu)程大(da)(da)致是：當(dang)接(jie)上(shang)Li+電(dian)(dian)(dian)(dian)(dian)池和(he)供電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)源時，IC通(tong)(tong)過(guo)R1/R2/R3組成的(de)(de)(de)網絡檢測(ce)電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)，如果電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)低(di)于(yu)(yu)3.3V（由R1-R3的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)阻值決定），或者按下按制SW1,此時IC3腳(jiao)(jiao)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)低(di)于(yu)(yu)615mV,則IC4腳(jiao)(jiao)輸(shu)出(chu)低(di)電(dian)(dian)(dian)(dian)(dian)平(ping)，通(tong)(tong)過(guo)R5/D2拉低(di)Q1的(de)(de)(de)柵極使(shi)之導(dao)通(tong)(tong)，從而(er)通(tong)(tong)過(guo)Q1/R9/D1給電(dian)(dian)(dian)(dian)(dian)池進行大(da)(da)電(dian)(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，當(dang)電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)一(yi)路(lu)上(shang)升直(zhi)至超過(guo)4.20V,此時IC的(de)(de)(de)1腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)壓(ya)高(gao)(gao)過(guo)615mV,IC內部經簡單判斷和(he)延時，令(ling)4腳(jiao)(jiao)輸(shu)出(chu)高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)平(ping)，從而(er)關(guan)閉大(da)(da)電(dian)(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)通(tong)(tong)道，但(dan)是4腳(jiao)(jiao)的(de)(de)(de)高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)平(ping)同時給R7/C2的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)回路(lu)供電(dian)(dian)(dian)(dian)(dian)，令(ling)到Q3的(de)(de)(de)柵極電(dian)(dian)(dian)(dian)(dian)壓(ya)慢(man)慢(man)升高(gao)(gao)，并給R8提(ti)供通(tong)(tong)路(lu)導(dao)致Q2導(dao)通(tong)(tong)，通(tong)(tong)過(guo)R10給Q1提(ti)供一(yi)個(ge)(ge)較弱的(de)(de)(de)導(dao)通(tong)(tong)電(dian)(dian)(dian)(dian)(dian)流(liu)，使(shi)之微(wei)微(wei)導(dao)通(tong)(tong)，從而(er)為電(dian)(dian)(dian)(dian)(dian)池提(ti)供一(yi)個(ge)(ge)較少的(de)(de)(de)補充(chong)(chong)(chong)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)。按照圖中所示(shi)元(yuan)件參數(shu)將于(yu)(yu)大(da)(da)約十分鐘后，由于(yu)(yu)C2的(de)(de)(de)不(bu)斷充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，其端電(dian)(dian)(dian)(dian)(dian)壓(ya)即Q3的(de)(de)(de)柵極電(dian)(dian)(dian)(dian)(dian)壓(ya)不(bu)斷上(shang)升直(zhi)至使(shi)Q3導(dao)通(tong)(tong)，從而(er)關(guan)閉Q2,令(ling)到整個(ge)(ge)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)過(guo)程結束。

　　上面的(de)方(fang)案還存在(zai)一(yi)些不足之處(chu)，例(li)如檢測精度(du)由(you)外接電(dian)阻(zu)R1/R2/R3的(de)精度(du)決定，對(dui)于過放電(dian)的(de)電(dian)池（電(dian)池端電(dian)壓低于2.8V）沒有(you)一(yi)個(ge)小(xiao)電(dian)流預充(chong)的(de)過程，另外該方(fang)案的(de)10分鐘補充(chong)充(chong)電(dian)時間對(dui)于較大容量的(de)電(dian)池來說不是太足夠(gou)，因此針對(dui)上述不足之處(chu)，我們還提供一(yi)個(ge)成本稍高一(yi)點，性能更加完善的(de)方(fang)案：（圖(tu)三）

　　乍(zha)看之下，這個(ge)方案采(cai)(cai)用(yong)(yong)了三(san)個(ge)IC,可是(shi)(shi)U1和(he)U2是(shi)(shi)采(cai)(cai)用(yong)(yong)的SOT-23或者TO-92封裝，就好像(xiang)普通三(san)極管(guan)(guan)一樣(yang)，其價格也就是(shi)(shi)2-3個(ge)三(san)極管(guan)(guan)的價格，而U3（PT8A2513NE）也是(shi)(shi)采(cai)(cai)用(yong)(yong)的TO-94封裝，外(wai)形和(he)三(san)極管(guan)(guan)很相(xiang)似，價錢也相(xiang)當便宜，不過，這個(ge)電(dian)路可以實現智能(neng)判斷電(dian)池是(shi)(shi)否過放電(dian)，決定是(shi)(shi)否在(zai)開始充(chong)電(dian)時采(cai)(cai)用(yong)(yong)小電(dian)流預充(chong)，另外(wai)，采(cai)(cai)用(yong)(yong)U3后也將充(chong)電(dian)后期的補充(chong)充(chong)電(dian)過程延長到(dao)大約一個(ge)小時！

　　首先讓我(wo)們(men)介(jie)紹一下該電路中幾個IC的功能：

　　（圖四）是(shi)U1/U2的(de)內(nei)部框(kuang)圖，這兩個(ge)IC只是(shi)內(nei)部電(dian)阻R1/R2的(de)數(shu)值不同而已，它們的(de)功能也很簡單：當Vcc低于IC的(de)設定值時（根據IC編號不同，內(nei)部R3/R4阻值也不同從而導致檢(jian)測(ce)電(dian)壓值不同，對(dui)于PT7M6128指(zhi)的(de)是(shi)2.80V），RST引腳輸出低電(dian)平，反之當Vcc 高于1.05倍標稱值時（例如對(dui)于PT7M6140,此數(shu)值為1.05x4.0 =4.20V）則RST引腳輸出高電(dian)平。

　　上(shang)面電(dian)路(lu)的(de)(de)(de)另外(wai)一(yi)個IC（PT8A25 13）則是一(yi)個極簡單卻極穩定的(de)(de)(de)延時(shi)IC,其延時(shi)時(shi)間僅僅取決于(yu) OSC腳的(de)(de)(de)頻(pin)率。事實上(shang)該IC就是將OSC震蕩頻(pin)率進行(xing)32768次分(fen)(fen)頻(pin)后(hou)用(yong)來控制輸出的(de)(de)(de)。之所以采(cai)用(yong)這個電(dian)路(lu)而(er)不(bu)采(cai)用(yong)LM555或者(zhe)CD4060等通(tong)用(yong)IC的(de)(de)(de)原因就是因為它(ta)相(xiang)對而(er)言定時(shi)精度更高（其它(ta)IC不(bu)分(fen)(fen)頻(pin)），定時(shi)時(shi)間更長（可達數小時(shi)）。并(bing)且電(dian)路(lu)更加簡單，采(cai)用(yong)TO-94或SOT-23-4封裝，就像一(yi)個三極管一(yi)樣。而(er)價錢也跟CD4060差不(bu)多(duo)，使用(yong)效果可就好的(de)(de)(de)太(tai)多(duo)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。