充電器為人們的(de)外出和出差辦公提供(gong)了極(ji)大的(de)方便。

單片機在電池充電器領域也有著廣泛的應用，利用它的處理控制能力可以實現充電器的智能化。充電器的種類繁多，但從嚴格意義上講，只有單片機參與處理和控制的充電器才能稱為智能充電器。

隨著手機(ji)(ji)在(zai)世界范圍內的普及使用(yong)，手機(ji)(ji)電池充電器的使用(yong)也越(yue)(yue)來越(yue)(yue)廣泛。

本次設(she)計(ji)將通(tong)過一個典型的(de)(de)勢力介紹51單(dan)片機在(zai)實現(xian)手(shou)機電(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)器(qi)方面的(de)(de)應用(yong)。設(she)計(ji)所實現(xian)的(de)(de)充(chong)(chong)電(dian)(dian)(dian)器(qi)是一種智能充(chong)(chong)電(dian)(dian)(dian)器(qi)，它在(zai)單(dan)片機的(de)(de)控(kong)制下，具有(you)預充(chong)(chong)、充(chong)(chong)電(dian)(dian)(dian)保護、自動斷電(dian)(dian)(dian)和充(chong)(chong)電(dian)(dian)(dian)完成報警提示(shi)功能。

1.3  本設計功能模塊
本設計的功(gong)能模塊主要如下：

1）單片機模塊：實現充(chong)電器(qi)的智能化控制。比如(ru)自動斷電、充(chong)電完(wan)成報(bao)警提示等。

2）充電過程控制模塊：采用專用的電池充電芯(xin)片實現充電過程的控制。

3）充電(dian)電(dian)壓(ya)(ya)(ya)提供模(mo)塊：采用電(dian)壓(ya)(ya)(ya)轉換芯片(pian)將外部+12V電(dian)壓(ya)(ya)(ya)轉換為需要的+5V電(dian)壓(ya)(ya)(ya)。

4）C51程序：單片機控制(zhi)電池充電芯片實(shi)現(xian)充電過(guo)程的自動化，并根據充電的狀態給(gei)出(chu)有關的輸出(chu)指示。

第2節  系統設計思路分析
充電的(de)實現(xian)，它包括兩部分(fen)：一是(shi)充電過程的(de)控(kong)制；二是(shi)需要提供基本的(de)充電電壓。

2.1 智能化的實現
在充電器電路中(zhong)引入單片機(ji)的控制。它為什么需要實現充電器的智能化呢？

充(chong)(chong)電(dian)器(qi)實現的(de)方式不同會(hui)導(dao)致充(chong)(chong)電(dian)效果(guo)的(de)不同。由于充(chong)(chong)電(dian)器(qi)多采(cai)用(yong)大電(dian)流(liu)(liu)的(de)快速(su)充(chong)(chong)電(dian)法(fa)，在電(dian)池充(chong)(chong)滿后(hou)如果(guo)不及時(shi)停止會(hui)使電(dian)池發(fa)燙，過度(du)的(de)充(chong)(chong)電(dian)會(hui)嚴重損害電(dian)池的(de)壽命(ming)。一些低成本的(de)充(chong)(chong)電(dian)器(qi)采(cai)用(yong)電(dian)壓比(bi)較法(fa)，為了防止過充(chong)(chong)，一般(ban)充(chong)(chong)電(dian)到90％就停止大電(dian)流(liu)(liu)快充(chong)(chong)，而采(cai)用(yong)小電(dian)流(liu)(liu)涓流(liu)(liu)補充(chong)(chong)充(chong)(chong)電(dian)。

手機(ji)電池的(de)使用(yong)壽命和單次(ci)使用(yong)時間與充(chong)電過(guo)程密切相關。鋰(li)電池是手機(ji)最為(wei)(wei)常用(yong)的(de)一種電池，它具有(you)較(jiao)(jiao)高(gao)的(de)能量重量比(bi)(bi)、能量體(ti)積比(bi)(bi)，具有(you)記憶效(xiao)應，可重復充(chong)電多次(ci)，使用(yong)壽命較(jiao)(jiao)長，價(jia)格(ge)也越來越低(di)(di)。鋰(li)電池對于充(chong)電器(qi)的(de)要(yao)(yao)求(qiu)比(bi)(bi)較(jiao)(jiao)苛刻，需要(yao)(yao)保護(hu)電路。為(wei)(wei)了有(you)效(xiao)利用(yong)電池容量，需將鋰(li)電池充(chong)電至最大電壓(ya)，但是過(guo)壓(ya)充(chong)電會造成電池損壞，這就(jiu)要(yao)(yao)求(qiu)較(jiao)(jiao)高(gao)的(de)控制精度。另外，對于電壓(ya)過(guo)低(di)(di)的(de)電池需要(yao)(yao)進行預充(chong)，充(chong)電器(qi)最好帶(dai)有(you)熱保護(hu)和時間保護(hu)，為(wei)(wei)電池提供附加保護(hu)。

一部好的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器不(bu)(bu)但能在(zai)短時間(jian)內將電(dian)(dian)(dian)(dian)(dian)(dian)量(liang)(liang)充(chong)(chong)(chong)足，而且(qie)還可(ke)(ke)以(yi)對電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)起到(dao)一定(ding)的(de)(de)(de)維(wei)護作用(yong)(yong)，修復由于使(shi)用(yong)(yong)不(bu)(bu)當造成的(de)(de)(de)記憶效應(ying)，即容量(liang)(liang)下降(電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)活性衰退(tui))現象(xiang)。設計比較科(ke)學的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器往(wang)(wang)往(wang)(wang)采用(yong)(yong)專用(yong)(yong)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)控制(zhi)芯(xin)片(pian)(pian)(pian)配合(he)單(dan)片(pian)(pian)(pian)機控制(zhi)的(de)(de)(de)方法。專用(yong)(yong)的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)芯(xin)片(pian)(pian)(pian)具備(bei)業(ye)界公認較好的(de)(de)(de)-△v 檢(jian)測，可(ke)(ke)以(yi)檢(jian)測出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)飽(bao)和時發出(chu)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓變化(hua)信號，比較精確地(di)結束(shu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)工作，通過單(dan)片(pian)(pian)(pian)機對這(zhe)些芯(xin)片(pian)(pian)(pian)的(de)(de)(de)控制(zhi)，可(ke)(ke)以(yi)實現充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過程的(de)(de)(de)智能化(hua)，例如(ru)，在(zai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)后增加及時關斷電(dian)(dian)(dian)(dian)(dian)(dian)源、蜂鳴報警和液晶顯(xian)示等功能。充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器的(de)(de)(de)智能化(hua)可(ke)(ke)以(yi)縮短充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)時間(jian)，同時能夠(gou)維(wei)護電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)，延長電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)使(shi)用(yong)(yong)壽命(ming)。

2.2 電池充電芯片的選擇
2.2.1 如何選擇電(dian)池充電(dian)芯片

目前市場上存在大量的電池充電芯片，它們可直接用于進行充電器設計。在(zai)選(xuan)擇(ze)具體的電(dian)池充(chong)電(dian)芯片時，需要(yao)參考(kao)以下標(biao)準。

1)電(dian)池(chi)類型(xing)：不同(tong)的電(dian)池(chi)(鋰電(dian)池(chi)、鎳(nie)(nie)氫電(dian)池(chi)、鎳(nie)(nie)鎘電(dian)池(chi)等)需選擇不同(tong)的充電(dian)芯片。

2)電池數目：可充電池的數目。

3)電流(liu)值：充(chong)電電流(liu)的(de)大小(xiao)決定(ding)了充(chong)電時間。

4)充(chong)(chong)電(dian)方式：是(shi)快充(chong)(chong)、慢充(chong)(chong)還是(shi)可控充(chong)(chong)電(dian)過程。

本設計要實現的是手機的單節鋰離子電池充電器，要求充(chong)電快(kuai)速且具有優良的電池保護能(neng)力，據此選擇Maxim 公司的MAXl898 作(zuo)為電池充(chong)電芯片。

2.2.2 芯片MAX1898 的(de)特點

MAXl898 配合外部PNP 或PMOS 晶體管可以組成完整的單節鋰電池充電器。

MAX1898提(ti)供精確的恒(heng)流(liu)(liu)/恒(heng)壓充(chong)電(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓調節精度為±0.75％，提(ti)高了電(dian)(dian)(dian)(dian)(dian)池性能并延長了電(dian)(dian)(dian)(dian)(dian)池使用(yong)(yong)壽命。充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)可由用(yong)(yong)戶設定，采用(yong)(yong)內部檢流(liu)(liu)，無須(xu)外部檢流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)阻。 MAXl898 提(ti)供了充(chong)電(dian)(dian)(dian)(dian)(dian)狀態的輸(shu)出指示(shi)、輸(shu)入電(dian)(dian)(dian)(dian)(dian)源是否與充(chong)電(dian)(dian)(dian)(dian)(dian)器連接(jie)的輸(shu)出指示(shi)和充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)指示(shi)。MAXl898 還具有其他(ta)一些功能，包(bao)括輸(shu)入關斷控制、可選的充(chong)電(dian)(dian)(dian)(dian)(dian)周期重(zhong)啟(無須(xu)重(zhong)新(xin)上電(dian)(dian)(dian)(dian)(dian))、可選的充(chong)電(dian)(dian)(dian)(dian)(dian)終止安全定時器和過放電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)池的低電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)預充(chong)。

MAXl898 的(de)關鍵(jian)特性如下：

1)    簡單、安全的線性充電方式。

2)    使(shi)用(yong)低(di)成本的PNP 或PMOS 調整元件。

3)    輸入電壓(ya)：4.5～12V。

4)    內置(zhi)檢流(liu)電阻。

5)    ±0.75％電(dian)壓精度。

6)    可(ke)編程充電(dian)電(dian)流。

7)    輸入(ru)電源自動(dong)檢測。

8)    LED 充電狀態指示。

9)    可(ke)編程安全定時器。

10)  檢流監視輸出(chu)。

11)  可選(xuan)/可調節自動重啟。

12)  小(xiao)尺(chi)寸uMAX 封(feng)裝(zhuang)。

2.2.3 MAX1898 的充電工(gong)作原理(li)

充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯片MAXl898 的(de)內部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)包括輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)調(diao)節器、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓檢(jian)(jian)測(ce)(ce)器、充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)檢(jian)(jian)測(ce)(ce)器、定時器、溫度檢(jian)(jian)測(ce)(ce)器和(he)主控制(zhi)(zhi)器。輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)調(diao)節器用于限制(zhi)(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源的(de)總(zong)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)，包括系(xi)統(tong)負載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)與充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)。當檢(jian)(jian)測(ce)(ce)到(dao)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)大(da)于設定的(de)門限電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)時，通(tong)過降(jiang)低充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)從(cong)而(er)控制(zhi)(zhi)輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)。因為系(xi)統(tong)工作時電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的(de)變(bian)化(hua)范圍較大(da)，如果(guo)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器沒有輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)檢(jian)(jian)測(ce)(ce)功能(neng)(neng)(neng)，則輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源必須能(neng)(neng)(neng)夠提供(gong)最(zui)大(da)負載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)與最(zui)大(da)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)之(zhi)和(he)，這將使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源的(de)成本增高(gao)、體積增大(da)，而(er)利用輸(shu)入(ru)限流(liu)(liu)(liu)(liu)功能(neng)(neng)(neng)則能(neng)(neng)(neng)夠降(jiang)低充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器對直(zhi)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源的(de)要(yao)求(qiu)，同時也(ye)簡化(hua)了輸(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源的(de)設計。 MAXl898 外接(jie)限流(liu)(liu)(liu)(liu)型充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源和(he)P 溝道場效應管，可以(yi)對單節鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池進行(xing)安(an)全有效的(de)快充，其最(zui)大(da)特點是：在(zai)不使(shi)用電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感的(de)情況下，仍(reng)能(neng)(neng)(neng)做到(dao)很(hen)低的(de)功率耗散，可以(yi)實現(xian)預充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，具(ju)有過壓保護和(he)溫度保護功能(neng)(neng)(neng)，最(zui)長充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時問(wen)的(de)限制(zhi)(zhi)可為鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池提供(gong)二次保護。MAX1898 的(de)浮動方式(shi)能(neng)(neng)(neng)夠使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池容量充至最(zui)大(da)。

當充電(dian)(dian)(dian)電(dian)(dian)(dian)源和電(dian)(dian)(dian)池(chi)在正常的工作溫度范圍(wei)內(nei)時，插入電(dian)(dian)(dian)池(chi)將啟動一次充電(dian)(dian)(dian)過程；充電(dian)(dian)(dian)結束(shu)的條(tiao)件是平均的脈沖充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)達(da)到(dao)(dao)快充電(dian)(dian)(dian)流(liu)的 1％，或時間超出片上預置的充電(dian)(dian)(dian)時間。MAXl898 能夠自動檢(jian)測充電(dian)(dian)(dian)電(dian)(dian)(dian)源，沒有(you)電(dian)(dian)(dian)源時自動關斷(duan)以減少電(dian)(dian)(dian)池(chi)的漏(lou)電(dian)(dian)(dian)。啟動快充后(hou)打開(kai)外(wai)接的P 型(xing)場效(xiao)應(ying)管(guan)，當檢(jian)測到(dao)(dao)電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓達(da)到(dao)(dao)設定的門(men)限時進入脈沖充電(dian)(dian)(dian)方式(shi)，P 型(xing)場效(xiao)應(ying)管(guan)打開(kai)的時問會(hui)越(yue)(yue)來越(yue)(yue)短。充電(dian)(dian)(dian)結束(shu)時，指示(shi)燈將會(hui)按12%的周期閃爍(shuo)，MAX1898 的典型(xing)充電(dian)(dian)(dian)電(dian)(dian)(dian)路如下(xia)圖圖2-1所示(shi)電(dian)(dian)(dian)路具(ju)體說明如下(xia)。

圖2-1  MAX1898的典型充(chong)電電路

1）輸入(ru)電壓(ya)范圍(wei)為 4.5～12v。鋰電池(chi)要(yao)求的充電方式是恒流(liu)恒壓(ya)方式，電源(yuan)(yuan)的輸入(ru)需要(yao)采用恒流(liu)恒壓(ya)源(yuan)(yuan)，一般可采用直流(liu)電源(yuan)(yuan)外加(jia)變壓(ya)器。

2)通過外接的場(chang)效應(ying)管提(ti)供鋰電(dian)池的充電(dian)接口(kou)。

3)通過外接的(de)電(dian)(dian)容(rong) CcT 來設置(zhi)充(chong)(chong)電(dian)(dian)時(shi)間 tCHG。這里的(de)充(chong)(chong)電(dian)(dian)時(shi)間指的(de)是快充(chong)(chong)時(shi)的(de)最(zui)大充(chong)(chong)電(dian)(dian)時(shi)間，它和定時(shi)電(dian)(dian)容(rong)CcT 的(de)關系(xi)如下式(shi)所示：

CcT=34.33×tCHG                                         ;         (2-1)

式中，tCHG 的(de)單位為小(xiao)時(shi)，CcT 的(de)單位為Nf。大多數情況下，快充(chong)時(shi)最大充(chong)電(dian)時(shi)問不(bu)超過3 小(xiao)時(shi)，因此(ci)常取(qu)CcT 為100nF。

4)在限制電流的模式下(xia)(xia)，通過外接(jie)的電阻(zu) RSET 來設置最大充電電IFSTCHG，關系如(ru)下(xia)(xia)式所示(shi)：IFSTCHG=1400/Rset 式中，RSEI-的單位為Q，IFSTCHG 的單位為A。

當(dang)(dang)充(chong)(chong)(chong)電電源和電池在正常的(de)工作溫度范圍內時(shi)(shi)(shi)(shi)，插(cha)入(ru)電池將(jiang)(jiang)啟動(dong)(dong)一(yi)次(ci)充(chong)(chong)(chong)電過程。平(ping)均的(de)脈沖充(chong)(chong)(chong)電電流(liu)低(di)于設置(zhi)的(de)快(kuai)充(chong)(chong)(chong)電流(liu)的(de)20％，或者充(chong)(chong)(chong)電時(shi)(shi)(shi)(shi)間超出(chu)片上預置(zhi)的(de)最大充(chong)(chong)(chong)電時(shi)(shi)(shi)(shi)問時(shi)(shi)(shi)(shi)，充(chong)(chong)(chong)電周期(qi)(qi)結束。MAXl898 能夠自(zi)動(dong)(dong)檢(jian)測充(chong)(chong)(chong)電電源，沒(mei)有電源時(shi)(shi)(shi)(shi)自(zi)動(dong)(dong)關斷(duan)以減少電池的(de)漏電。啟動(dong)(dong)快(kuai)充(chong)(chong)(chong)后，打開外接(jie)的(de)P 型場效(xiao)應管，當(dang)(dang)檢(jian)測到電池電壓達到設定的(de)門(men)限時(shi)(shi)(shi)(shi)進入(ru)脈沖充(chong)(chong)(chong)電方式，P 型場效(xiao)應管打開的(de)時(shi)(shi)(shi)(shi)JI 間會越(yue)來越(yue)短。充(chong)(chong)(chong)電結束時(shi)(shi)(shi)(shi)，LED 指(zhi)示燈將(jiang)(jiang)會呈(cheng)現周期(qi)(qi)性(xing)的(de)閃爍，具(ju)體的(de)閃爍含(han)義(yi)如表1所示。

表2-

1  MAX1898 典型充(chong)電電路的LED 指示燈狀態說明

充電狀態
LED指示燈電池(chi)或(huo)充電器(qi)沒有安裝(zhuang)

預充或快充

亮

充電結束

滅

充電出錯

頻率閃爍

第(di)3節  系統(tong)主要硬件電(dian)路設計

   硬件電路(lu)設計(ji)主要(yao)圍繞充(chong)電芯(xin)片MAXl898 展開，而單(dan)片機(ji)控制部分的電路(lu)簡單(dan)。

3.1  主(zhu)要器(qi)件

本(ben)設計的核心(xin)器件是MAXl898。MAXl898 可對所有(you)化學類(lei)型的Li+電(dian)池進行安(an)全充電(dian)，它具有(you)高集成度，在小(xiao)尺寸內集成了更多功能，盡可能多地覆蓋了基(ji)本(ben)應用電(dian)路(lu)，只需要少(shao)數外部元件。MAXl898 為10 引(yin)腳、超(chao)薄型的MAX 封裝，其(qi)引(yin)腳分(fen)布如(ru)圖3-1 所示：

圖3-1 MAXl898引(yin)腳分布

其引腳功能如下：

IN(1 腳)：傳感輸入，檢測輸入的(de)電壓或電流；

CHG(2 腳)：充(chong)電狀態指(zhi)示腳，同(tong)時驅動LED；

EN/OK(3 腳(jiao))：使能輸(shu)入(ru)(ru)腳(jiao)/輸(shu)入(ru)(ru)電(dian)源(yuan)“好”輸(shu)出指示腳(jiao)。EN 為(wei)輸(shu)入(ru)(ru)腳(jiao)，可以(yi)通過輸(shu)入(ru)(ru)禁止芯片工(gong)作；OK 為(wei)輸(shu)出腳(jiao)，用(yong)于指示輸(shu)入(ru)(ru)電(dian)源(yuan)是否與充電(dian)器連(lian)接；

ISET(4 腳)：充(chong)電(dian)電(dian)流調節引腳。通(tong)過串(chuan)接(jie)一(yi)個電(dian)阻到地來設(she)置(zhi)最(zui)大充(chong)電(dian)電(dian)流；

CT(5 腳)：安全(quan)充電時(shi)間(jian)(jian)(jian)設置(zhi)引腳。接一個(ge)時(shi)間(jian)(jian)(jian)電容來設置(zhi)充電時(shi)間(jian)(jian)(jian)，電容為 100nF 時(shi)，幾乎為3 個(ge)小(xiao)時(shi)，此引腳直接接地將(jiang)禁用此功(gong)能；

RSTRT(6 腳(jiao))：自動(dong)重新啟(qi)動(dong)控制(zhi)引(yin)腳(jiao)。當此引(yin)腳(jiao)直接接地(di)時(shi)，如果(guo)電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)掉至(zhi)基準(zhun)電(dian)(dian)(dian)壓(ya)閾值以(yi)下 200mV，將會重新開始一(yi)輪充電(dian)(dian)(dian)周期。此引(yin)腳(jiao)通(tong)過電(dian)(dian)(dian)阻接地(di)時(shi)，可以(yi)降低它的電(dian)(dian)(dian)壓(ya)閾值。此引(yin)腳(jiao)懸空或者 CT 引(yin)腳(jiao)接地(di)(充電(dian)(dian)(dian)時(shi)間設置功能禁(jin)用)時(shi)，自動(dong)重新啟(qi)動(dong)功能被禁(jin)用；

BATT(7 腳)：電(dian)池(chi)傳(chuan)感輸入(ru)腳，接單個 Li+電(dian)池(chi)的(de)正(zheng)極。此(ci)引(yin)腳需旁接一個大電(dian)解(jie)電(dian)容到地；

GND(8 腳)：接地端；

DRV(9 腳)：外部晶(jing)體管驅動(dong)器，接(jie)晶(jing)體管的基極；

CS(10 腳)：電流傳感輸入，接(jie)晶(jing)體管(guan)的發射極。

本設計的單片機芯片選(xuan)用Atmel 公司的AT89C52，它完全(quan)可以滿足要求。

另外，由于充電器外部為+12V 供電，因此需要(yao)通過(guo)電壓轉(zhuan)(zhuan)換芯片將+12V 電壓轉(zhuan)(zhuan)換為 +5V 電壓，這里(li)選(xuan)用三端(duan)電壓轉(zhuan)(zhuan)換芯片LM7805 來(lai)完(wan)成此功能。

為了降(jiang)低電源干擾，保持(chi)電路的(de)穩定，在LM7805 完成電壓轉換，將+5v 充(chong)電電源送給 MAXl898 之(zhi)前，先經過(guo)一次光耦模塊 6N137 的(de)處理(li)，通(tong)過(guo)單(dan)片機(ji)對光耦模塊的(de)控(kong)制，可以及時關斷充(chong)電電源。6N137 的(de)引腳(jiao)分布如圖3-2 所示(shi)：

圖3-2  6N137 的引腳分布

其引腳功能如下：

NC(1 腳、4 腳)：懸空(kong)；

+(2 腳(jiao))、-(3 腳(jiao))：發光(guang)二(er)極(ji)管的(de)正(zheng)、負極(ji)；

GND(5 腳)：接地(di)端；

OUTPUT(6 腳)：輸出腳；

EN(7 腳)：使能腳。為(wei)低時，無論有(you)無輸入，輸出都(dou)為(wei)高。

不使用(yong)時，懸空即可；

VCC(8 腳(jiao))：電(dian)源輸入(ru)腳(jiao)。

3.2  電路原理圖及說明

硬件電(dian)(dian)(dian)路(lu)(lu)由單片機電(dian)(dian)(dian)路(lu)(lu)、電(dian)(dian)(dian)壓(ya)轉(zhuan)換及(ji)光耦隔離電(dian)(dian)(dian)路(lu)(lu)、充電(dian)(dian)(dian)控(kong)制電(dian)(dian)(dian)路(lu)(lu)3 部(bu)分組成(cheng)。單片機部(bu)分的電(dian)(dian)(dian)路(lu)(lu)原理圖如下圖3-3 所示。

圖3-3  單片機部分的電路原理(li)圖

圖3-3中，ul 為單(dan)片機(ji)AT89C52，工作在11．0592MHz 時鐘；u2 為蜂(feng)鳴器，蜂(feng)鳴器由單(dan)片機(ji)的P2．1 腳控制(zhi)發出(chu)報警聲提(ti)示；單(dan)片機(ji)的P2．O 腳輸出(chu)控制(zhi)光(guang)耦器件，在需(xu)要的時候可以及時關斷(duan)充(chong)電(dian)電(dian)源；單(dan)片機(ji)的外部中斷(duan)O 由充(chong)電(dian)芯片MAXl898 的充(chong)電(dian)狀態輸出(chu)信號/ CHG 經過反相后觸(chu)發。

下圖3-4 所示(shi)的為電壓轉換及光耦(ou)隔離部分電路的原理(li)圖。