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(cheng)的充電電壓檢測和(he)控(kong)制線路(lu)，這些線路(lu)無論從控(kong)制精度(du)還是功能方面都不能滿(man)足鋰電池充電特(te)性的要(yao)求，直接(jie)導致電池充不滿(man)，電池壽命減短以及越來越多的電池損壞、爆炸等案例發生。而如果采(cai)(cai)用國外專用IC來設(she)計，則(ze)其極其高昂(ang)的成(cheng)本實在令人(ren)無法接(jie)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(zai)大致(zhi)相當(dang)的總(zong)體(ti)成本下提供了遠遠超過LM324方案(an)的性(xing)能，具有極高的新穎性(xing)和市場前景。

　　PT7M7433T是上海(hai)百利(li)(li)通公司最(zui)新設(she)計的極高精度的一系列電(dian)(dian)壓檢(jian)測(ce)器的其(qi)中一款，其(qi)檢(jian)測(ce)精度在0-Vcc （5.5V）范圍內(nei)小于1mV,而且其(qi)批量IC的檢(jian)測(ce)值偏差<±2.5%,這樣完全保證(zheng)了批量產品的性(xing)能一致性(xing)和(he)極高的總體(ti)性(xing)能，我們(men)利(li)(li)用其(qi)配(pei)合少量外(wai)部電(dian)(dian)路即可組成相當簡單的鋰電(dian)(dian)池充(chong)電(dian)(dian)線路。

　　該IC的(de)內(nei)部框圖和(he)簡單介紹如下：（圖一）

　　IC內含一(yi)個高精度的615mV基準電(dian)壓(ya)源、兩個比較(jiao)器(qi)、一(yi)個RS觸發器(qi)和其(qi)它一(yi)些邏輯(ji)電(dian)路，其(qi)大致(zhi)功(gong)能(neng)是：VCC電(dian)壓(ya)或(huo)其(qi)它待(dai)(dai)檢測(ce)(ce)電(dian)壓(ya)通(tong)過R1-R3組成的分(fen)壓(ya)網絡接(jie)在IC的LTHIN /HTHIN檢測(ce)(ce)引(yin)腳(jiao)(jiao)，當(dang)待(dai)(dai)測(ce)(ce)電(dian)壓(ya)下降導致(zhi)LTHIN引(yin)腳(jiao)(jiao)低于(yu)615mV時，輸出腳(jiao)(jiao)LBO輸出低電(dian)平，而如果待(dai)(dai)測(ce)(ce)電(dian)壓(ya)上升導致(zhi)HTHIN引(yin)腳(jiao)(jiao)高于(yu)615 mV時，經過內部邏輯(ji)判斷和簡單(dan)延時后，輸出腳(jiao)(jiao)LBO輸出高電(dian)平。

　　利用這(zhe)個IC裝制的充電器(qi)電路如下(xia)（圖(tu)二(er)）

　　其工作流程大(da)致是：當(dang)接上(shang)Li+電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)和(he)供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源時(shi)(shi)(shi)，IC通(tong)(tong)(tong)過(guo)(guo)R1/R2/R3組成(cheng)的網絡檢測(ce)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓，如果電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓低(di)(di)于(yu)3.3V（由R1-R3的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻值決定），或者按(an)(an)下(xia)按(an)(an)制SW1,此時(shi)(shi)(shi)IC3腳(jiao)(jiao)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓低(di)(di)于(yu)615mV,則IC4腳(jiao)(jiao)輸出低(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)，通(tong)(tong)(tong)過(guo)(guo)R5/D2拉低(di)(di)Q1的柵(zha)極使(shi)之(zhi)(zhi)導(dao)通(tong)(tong)(tong)，從(cong)而(er)通(tong)(tong)(tong)過(guo)(guo)Q1/R9/D1給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行大(da)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓一路上(shang)升(sheng)直至超過(guo)(guo)4.20V,此時(shi)(shi)(shi)IC的1腳(jiao)(jiao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓高(gao)(gao)過(guo)(guo)615mV,IC內部經簡單判(pan)斷和(he)延時(shi)(shi)(shi)，令4腳(jiao)(jiao)輸出高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)，從(cong)而(er)關閉大(da)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)通(tong)(tong)(tong)道，但是4腳(jiao)(jiao)的高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)同時(shi)(shi)(shi)給R7/C2的充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)回路供(gong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，令到(dao)Q3的柵(zha)極電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓慢慢升(sheng)高(gao)(gao)，并給R8提供(gong)通(tong)(tong)(tong)路導(dao)致Q2導(dao)通(tong)(tong)(tong)，通(tong)(tong)(tong)過(guo)(guo)R10給Q1提供(gong)一個較弱的導(dao)通(tong)(tong)(tong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流，使(shi)之(zhi)(zhi)微微導(dao)通(tong)(tong)(tong)，從(cong)而(er)為電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)提供(gong)一個較少的補充(chong)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流。按(an)(an)照圖中所示元件參數將于(yu)大(da)約十(shi)分鐘(zhong)后(hou)，由于(yu)C2的不斷充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，其端電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓即Q3的柵(zha)極電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓不斷上(shang)升(sheng)直至使(shi)Q3導(dao)通(tong)(tong)(tong)，從(cong)而(er)關閉Q2,令到(dao)整個充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)(guo)程結(jie)束(shu)。

　　上面的(de)方案還存在一些不足之處，例(li)如檢測精度由外接電(dian)(dian)(dian)阻R1/R2/R3的(de)精度決定，對(dui)(dui)(dui)于(yu)過(guo)放(fang)電(dian)(dian)(dian)的(de)電(dian)(dian)(dian)池（電(dian)(dian)(dian)池端電(dian)(dian)(dian)壓低于(yu)2.8V）沒有一個(ge)小電(dian)(dian)(dian)流預充的(de)過(guo)程(cheng)，另外該方案的(de)10分鐘補充充電(dian)(dian)(dian)時間對(dui)(dui)(dui)于(yu)較(jiao)大容量的(de)電(dian)(dian)(dian)池來(lai)說不是太足夠，因此針對(dui)(dui)(dui)上述(shu)不足之處，我(wo)們還提供(gong)一個(ge)成(cheng)本稍高(gao)一點，性能更加完善(shan)的(de)方案：（圖(tu)三）

　　乍看之下，這個(ge)方案采(cai)用(yong)了三個(ge)IC,可是(shi)U1和(he)U2是(shi)采(cai)用(yong)的SOT-23或者(zhe)TO-92封裝，就好像普通三極(ji)管(guan)一樣，其價格也(ye)就是(shi)2-3個(ge)三極(ji)管(guan)的價格，而U3（PT8A2513NE）也(ye)是(shi)采(cai)用(yong)的TO-94封裝，外形和(he)三極(ji)管(guan)很相似，價錢也(ye)相當便宜，不(bu)過(guo)，這個(ge)電(dian)(dian)路可以實現智能判斷電(dian)(dian)池是(shi)否過(guo)放電(dian)(dian)，決定(ding)是(shi)否在開始(shi)充(chong)電(dian)(dian)時采(cai)用(yong)小(xiao)電(dian)(dian)流(liu)預充(chong)，另外，采(cai)用(yong)U3后(hou)也(ye)將(jiang)充(chong)電(dian)(dian)后(hou)期的補充(chong)充(chong)電(dian)(dian)過(guo)程延長(chang)到(dao)大約一個(ge)小(xiao)時！

　　首先讓我(wo)們介紹一下該電路中幾個IC的功能(neng)：

　　（圖四）是(shi)U1/U2的(de)(de)內部(bu)(bu)框圖，這兩個IC只(zhi)是(shi)內部(bu)(bu)電阻R1/R2的(de)(de)數值(zhi)(zhi)不同而已，它們(men)的(de)(de)功能也很簡單：當(dang)Vcc低于(yu)(yu)IC的(de)(de)設定值(zhi)(zhi)時(shi)（根據IC編號(hao)不同，內部(bu)(bu)R3/R4阻值(zhi)(zhi)也不同從而導(dao)致(zhi)檢測電壓值(zhi)(zhi)不同，對于(yu)(yu)PT7M6128指的(de)(de)是(shi)2.80V），RST引(yin)腳輸(shu)出低電平(ping)，反(fan)之當(dang)Vcc 高于(yu)(yu)1.05倍標稱(cheng)值(zhi)(zhi)時(shi)（例如對于(yu)(yu)PT7M6140,此數值(zhi)(zhi)為1.05x4.0 =4.20V）則RST引(yin)腳輸(shu)出高電平(ping)。

　　上面(mian)電路(lu)(lu)的(de)另外一(yi)(yi)個(ge)IC（PT8A25 13）則是一(yi)(yi)個(ge)極簡單卻極穩定的(de)延時IC,其延時時間僅僅取決于 OSC腳的(de)頻(pin)(pin)率(lv)。事實上該IC就(jiu)是將(jiang)OSC震蕩頻(pin)(pin)率(lv)進(jin)行32768次分頻(pin)(pin)后用來控制輸出的(de)。之所以采(cai)(cai)用這個(ge)電路(lu)(lu)而(er)不采(cai)(cai)用LM555或者CD4060等通用IC的(de)原因(yin)就(jiu)是因(yin)為它相對(dui)而(er)言(yan)定時精(jing)度(du)更高（其它IC不分頻(pin)(pin)），定時時間更長（可達數小時）。并且電路(lu)(lu)更加簡單，采(cai)(cai)用TO-94或SOT-23-4封(feng)裝，就(jiu)像(xiang)一(yi)(yi)個(ge)三極管一(yi)(yi)樣。而(er)價(jia)錢也跟CD4060差不多，使用效果(guo)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。