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組成的充電(dian)(dian)(dian)電(dian)(dian)(dian)壓檢測和控制線路，這些線路無論從控制精度還是功能(neng)方面(mian)都不能(neng)滿足鋰電(dian)(dian)(dian)池充電(dian)(dian)(dian)特性的要求(qiu)，直接導(dao)致電(dian)(dian)(dian)池充不滿，電(dian)(dian)(dian)池壽命減短以及越來(lai)越多的電(dian)(dian)(dian)池損壞、爆炸等案例(li)發生。而(er)如果采(cai)用(yong)國外專(zhuan)用(yong)IC來(lai)設(she)計，則其極其高昂的成本實在令人無法(fa)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(zai)大致相當的(de)總體成(cheng)本下提供了遠(yuan)遠(yuan)超過LM324方(fang)案的(de)性能，具有(you)極高的(de)新(xin)穎性和市場(chang)前(qian)景。

　　PT7M7433T是上海百(bai)利通公司最新設(she)計的(de)(de)(de)極高(gao)精(jing)度的(de)(de)(de)一系列電壓檢測器的(de)(de)(de)其(qi)(qi)中(zhong)一款，其(qi)(qi)檢測精(jing)度在0-Vcc （5.5V）范(fan)圍內小(xiao)于1mV,而且其(qi)(qi)批(pi)量(liang)IC的(de)(de)(de)檢測值偏差<±2.5%,這樣完全保證(zheng)了批(pi)量(liang)產品的(de)(de)(de)性能(neng)一致(zhi)性和(he)極高(gao)的(de)(de)(de)總體性能(neng)，我們利用其(qi)(qi)配合(he)少(shao)量(liang)外部電路即可組成相當簡單(dan)的(de)(de)(de)鋰(li)電池充電線路。

　　該(gai)IC的內部(bu)框(kuang)圖(tu)和簡單(dan)介紹如下(xia)：（圖(tu)一）

　　IC內(nei)含一個(ge)高精(jing)度的615mV基準電(dian)(dian)(dian)壓源、兩個(ge)比較器、一個(ge)RS觸發器和其它一些邏(luo)輯電(dian)(dian)(dian)路，其大致(zhi)功能是(shi)：VCC電(dian)(dian)(dian)壓或其它待檢測電(dian)(dian)(dian)壓通(tong)過R1-R3組成的分壓網(wang)絡接(jie)在IC的LTHIN /HTHIN檢測引(yin)腳(jiao)(jiao)(jiao)，當待測電(dian)(dian)(dian)壓下(xia)降導致(zhi)LTHIN引(yin)腳(jiao)(jiao)(jiao)低于615mV時(shi)，輸出(chu)腳(jiao)(jiao)(jiao)LBO輸出(chu)低電(dian)(dian)(dian)平(ping)，而如果待測電(dian)(dian)(dian)壓上升導致(zhi)HTHIN引(yin)腳(jiao)(jiao)(jiao)高于615 mV時(shi)，經過內(nei)部邏(luo)輯判斷和簡單(dan)延時(shi)后，輸出(chu)腳(jiao)(jiao)(jiao)LBO輸出(chu)高電(dian)(dian)(dian)平(ping)。

　　利用(yong)這個IC裝制的充(chong)電器電路如(ru)下（圖二(er)）

　　其(qi)工(gong)作流(liu)程大致(zhi)是(shi)：當接上Li+電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)和(he)供電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源時，IC通(tong)過R1/R2/R3組成的(de)(de)(de)(de)網絡(luo)檢(jian)測電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，如(ru)果電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低(di)于(yu)3.3V（由R1-R3的(de)(de)(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)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)低(di)于(yu)615mV,則IC4腳輸出(chu)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)平，通(tong)過R5/D2拉低(di)Q1的(de)(de)(de)(de)柵極(ji)(ji)使之導(dao)通(tong)，從而(er)通(tong)過Q1/R9/D1給(gei)(gei)(gei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行大電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)一路(lu)上升直至超過4.20V,此時IC的(de)(de)(de)(de)1腳電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)高(gao)(gao)(gao)過615mV,IC內部(bu)經簡(jian)單判斷(duan)和(he)延時，令4腳輸出(chu)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)平，從而(er)關閉大電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)通(tong)道，但是(shi)4腳的(de)(de)(de)(de)高(gao)(gao)(gao)電(dian)(dian)(dian)(dian)(dian)(dian)平同時給(gei)(gei)(gei)R7/C2的(de)(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)回路(lu)供電(dian)(dian)(dian)(dian)(dian)(dian)，令到Q3的(de)(de)(de)(de)柵極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)慢慢升高(gao)(gao)(gao)，并給(gei)(gei)(gei)R8提供通(tong)路(lu)導(dao)致(zhi)Q2導(dao)通(tong)，通(tong)過R10給(gei)(gei)(gei)Q1提供一個較弱的(de)(de)(de)(de)導(dao)通(tong)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，使之微(wei)微(wei)導(dao)通(tong)，從而(er)為(wei)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)提供一個較少的(de)(de)(de)(de)補充(chong)(chong)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)。按照圖中所示元件參數(shu)將于(yu)大約十(shi)分鐘后，由于(yu)C2的(de)(de)(de)(de)不斷(duan)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，其(qi)端電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)即Q3的(de)(de)(de)(de)柵極(ji)(ji)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)不斷(duan)上升直至使Q3導(dao)通(tong)，從而(er)關閉Q2,令到整(zheng)個充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過程結束(shu)。

　　上面的(de)方案(an)還存在一(yi)(yi)些不(bu)足之(zhi)處(chu)(chu)，例如檢測精(jing)度(du)由(you)外接電(dian)(dian)阻R1/R2/R3的(de)精(jing)度(du)決定，對于過放電(dian)(dian)的(de)電(dian)(dian)池(chi)(chi)(chi)（電(dian)(dian)池(chi)(chi)(chi)端電(dian)(dian)壓低于2.8V）沒有一(yi)(yi)個(ge)(ge)小電(dian)(dian)流(liu)預(yu)充(chong)的(de)過程(cheng)，另外該方案(an)的(de)10分(fen)鐘補充(chong)充(chong)電(dian)(dian)時間對于較(jiao)大容量(liang)的(de)電(dian)(dian)池(chi)(chi)(chi)來說不(bu)是太足夠(gou)，因此針對上述不(bu)足之(zhi)處(chu)(chu)，我們還提供一(yi)(yi)個(ge)(ge)成本稍高一(yi)(yi)點，性能更加完善(shan)的(de)方案(an)：（圖三）

　　乍看之下，這(zhe)個(ge)(ge)方案采(cai)(cai)用(yong)了三(san)個(ge)(ge)IC,可是(shi)U1和U2是(shi)采(cai)(cai)用(yong)的(de)SOT-23或(huo)者TO-92封裝(zhuang)，就好像普(pu)通三(san)極(ji)管(guan)一(yi)(yi)樣(yang)，其價格(ge)也就是(shi)2-3個(ge)(ge)三(san)極(ji)管(guan)的(de)價格(ge)，而U3（PT8A2513NE）也是(shi)采(cai)(cai)用(yong)的(de)TO-94封裝(zhuang)，外形和三(san)極(ji)管(guan)很相似，價錢也相當便宜，不過，這(zhe)個(ge)(ge)電(dian)路可以實現智能判斷電(dian)池(chi)是(shi)否過放電(dian)，決定(ding)是(shi)否在開始充(chong)電(dian)時采(cai)(cai)用(yong)小電(dian)流預充(chong)，另(ling)外，采(cai)(cai)用(yong)U3后(hou)也將充(chong)電(dian)后(hou)期(qi)的(de)補充(chong)充(chong)電(dian)過程延長到大約一(yi)(yi)個(ge)(ge)小時！

　　首先讓我(wo)們介紹(shao)一下(xia)該(gai)電(dian)路中幾個IC的功能：

　　（圖四）是U1/U2的內部框圖，這兩(liang)個IC只是內部電(dian)阻R1/R2的數值不(bu)同而已，它(ta)們的功能也很簡單：當Vcc低于IC的設定(ding)值時（根據IC編號(hao)不(bu)同，內部R3/R4阻值也不(bu)同從而導(dao)致檢測電(dian)壓(ya)值不(bu)同，對(dui)(dui)于PT7M6128指的是2.80V），RST引腳輸出(chu)低電(dian)平(ping)，反之當Vcc 高于1.05倍(bei)標稱值時（例如對(dui)(dui)于PT7M6140,此數值為1.05x4.0 =4.20V）則RST引腳輸出(chu)高電(dian)平(ping)。

　　上(shang)面電(dian)路(lu)的(de)另外一(yi)個(ge)IC（PT8A25 13）則(ze)是一(yi)個(ge)極簡(jian)單卻極穩定(ding)的(de)延時IC,其延時時間(jian)(jian)僅(jin)僅(jin)取決(jue)于 OSC腳的(de)頻(pin)(pin)率。事實上(shang)該(gai)IC就是將OSC震蕩頻(pin)(pin)率進行32768次分(fen)頻(pin)(pin)后用(yong)來控(kong)制輸(shu)出的(de)。之所以采用(yong)這個(ge)電(dian)路(lu)而(er)不采用(yong)LM555或(huo)者CD4060等通用(yong)IC的(de)原因就是因為它相(xiang)對而(er)言定(ding)時精度更高（其它IC不分(fen)頻(pin)(pin)），定(ding)時時間(jian)(jian)更長（可達數小時）。并且電(dian)路(lu)更加簡(jian)單，采用(yong)TO-94或(huo)SOT-23-4封裝(zhuang)，就像一(yi)個(ge)三極管(guan)一(yi)樣。而(er)價錢(qian)也跟CD4060差不多，使用(yong)效果(guo)可就好(hao)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。