充電器(qi)為人們的(de)外出(chu)和出(chu)差(cha)辦公提供(gong)了極大的(de)方便(bian)。

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(shi)界范圍內的普及使用，手機(ji)(ji)電(dian)(dian)池(chi)充電(dian)(dian)器的使用也越來越廣泛。

本次(ci)設(she)計將通(tong)過一個(ge)典(dian)型的(de)(de)勢力(li)介紹51單(dan)片機(ji)(ji)在實(shi)現(xian)手機(ji)(ji)電池充電器(qi)方面的(de)(de)應用。設(she)計所(suo)實(shi)現(xian)的(de)(de)充電器(qi)是(shi)一種(zhong)智能(neng)充電器(qi)，它在單(dan)片機(ji)(ji)的(de)(de)控(kong)制下，具有預充、充電保護、自動(dong)斷(duan)電和(he)充電完成(cheng)報警提示(shi)功能(neng)。

1.3  本設計功能模塊
本設(she)計(ji)的功能(neng)模(mo)塊(kuai)主(zhu)要如下：

1）單片機模塊：實現充電(dian)器的智(zhi)能化(hua)控制。比如自(zi)動斷電(dian)、充電(dian)完成報警提(ti)示等。

2）充(chong)電(dian)過程(cheng)控(kong)制模塊：采用(yong)專用(yong)的(de)電(dian)池充(chong)電(dian)芯片實現充(chong)電(dian)過程(cheng)的(de)控(kong)制。

3）充(chong)電電壓(ya)(ya)提供模塊：采用電壓(ya)(ya)轉換芯片將外部+12V電壓(ya)(ya)轉換為需要的(de)+5V電壓(ya)(ya)。

4）C51程序：單片(pian)機控制電池充(chong)電芯片(pian)實現(xian)充(chong)電過(guo)程的(de)自動化(hua)，并(bing)根據充(chong)電的(de)狀態給出有關的(de)輸出指(zhi)示。

第2節  系統設計思路分析
充(chong)電(dian)的實(shi)現，它包括兩部分：一(yi)是充(chong)電(dian)過程的控制；二是需要提供基本的充(chong)電(dian)電(dian)壓(ya)。

2.1 智能化的實現
在(zai)充電(dian)(dian)器(qi)(qi)電(dian)(dian)路中引入單片機(ji)的(de)控制。它(ta)為什么需要(yao)實現充電(dian)(dian)器(qi)(qi)的(de)智能(neng)化呢(ni)？

充(chong)(chong)電(dian)器(qi)實現的(de)(de)方式不同(tong)會導致(zhi)充(chong)(chong)電(dian)效果的(de)(de)不同(tong)。由于充(chong)(chong)電(dian)器(qi)多采(cai)(cai)用(yong)(yong)大(da)電(dian)流的(de)(de)快(kuai)(kuai)速充(chong)(chong)電(dian)法，在電(dian)池(chi)充(chong)(chong)滿(man)后如果不及時停止(zhi)會使電(dian)池(chi)發燙，過(guo)度的(de)(de)充(chong)(chong)電(dian)會嚴重(zhong)損(sun)害電(dian)池(chi)的(de)(de)壽命。一些低成本的(de)(de)充(chong)(chong)電(dian)器(qi)采(cai)(cai)用(yong)(yong)電(dian)壓(ya)比較(jiao)法，為(wei)了防止(zhi)過(guo)充(chong)(chong)，一般(ban)充(chong)(chong)電(dian)到90％就停止(zhi)大(da)電(dian)流快(kuai)(kuai)充(chong)(chong)，而(er)采(cai)(cai)用(yong)(yong)小(xiao)電(dian)流涓流補充(chong)(chong)充(chong)(chong)電(dian)。

手機(ji)電(dian)(dian)池(chi)的(de)使(shi)用(yong)(yong)(yong)壽命和單次使(shi)用(yong)(yong)(yong)時間與充(chong)電(dian)(dian)過(guo)程密切(qie)相關。鋰電(dian)(dian)池(chi)是(shi)手機(ji)最(zui)為(wei)常用(yong)(yong)(yong)的(de)一種電(dian)(dian)池(chi)，它(ta)具有較(jiao)高的(de)能量重量比、能量體積比，具有記憶效(xiao)應，可重復充(chong)電(dian)(dian)多(duo)次，使(shi)用(yong)(yong)(yong)壽命較(jiao)長，價(jia)格(ge)也越(yue)來越(yue)低(di)。鋰電(dian)(dian)池(chi)對于(yu)充(chong)電(dian)(dian)器(qi)的(de)要求比較(jiao)苛刻，需(xu)要保護電(dian)(dian)路。為(wei)了有效(xiao)利(li)用(yong)(yong)(yong)電(dian)(dian)池(chi)容(rong)量，需(xu)將鋰電(dian)(dian)池(chi)充(chong)電(dian)(dian)至(zhi)最(zui)大電(dian)(dian)壓，但是(shi)過(guo)壓充(chong)電(dian)(dian)會造(zao)成電(dian)(dian)池(chi)損壞，這就(jiu)要求較(jiao)高的(de)控制(zhi)精度。另外，對于(yu)電(dian)(dian)壓過(guo)低(di)的(de)電(dian)(dian)池(chi)需(xu)要進行預充(chong)，充(chong)電(dian)(dian)器(qi)最(zui)好帶有熱保護和時間保護，為(wei)電(dian)(dian)池(chi)提供附(fu)加保護。

一部好的(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器不但能(neng)在(zai)短時(shi)間內將電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)量充(chong)足，而且還可(ke)以(yi)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)起到一定的(de)(de)(de)維(wei)護作用(yong)，修復由(you)于(yu)使用(yong)不當造(zao)成的(de)(de)(de)記憶效應，即(ji)容(rong)量下(xia)降(電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)活性(xing)衰退)現象(xiang)。設計(ji)比較(jiao)科(ke)學的(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器往(wang)(wang)往(wang)(wang)采用(yong)專(zhuan)用(yong)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)控制(zhi)芯(xin)片配(pei)合單(dan)片機(ji)控制(zhi)的(de)(de)(de)方法。專(zhuan)用(yong)的(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯(xin)片具備(bei)業界(jie)公認較(jiao)好的(de)(de)(de)-△v 檢測，可(ke)以(yi)檢測出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)飽和時(shi)發出(chu)(chu)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓變化(hua)信號，比較(jiao)精確地(di)結束充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)工作，通過單(dan)片機(ji)對這些芯(xin)片的(de)(de)(de)控制(zhi)，可(ke)以(yi)實現充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過程的(de)(de)(de)智(zhi)能(neng)化(hua)，例如，在(zai)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)后(hou)增(zeng)加及時(shi)關斷電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)、蜂(feng)鳴(ming)報警(jing)和液晶顯示(shi)等功能(neng)。充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器的(de)(de)(de)智(zhi)能(neng)化(hua)可(ke)以(yi)縮短充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)時(shi)間，同時(shi)能(neng)夠維(wei)護電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)，延長電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)使用(yong)壽命。

2.2 電池充電芯片的選擇
2.2.1 如何選擇(ze)電(dian)池(chi)充電(dian)芯片(pian)

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)選擇具體的電(dian)池充電(dian)芯片時，需要參考以下標(biao)準。

1)電(dian)(dian)池類(lei)型(xing)：不同的電(dian)(dian)池(鋰電(dian)(dian)池、鎳(nie)氫電(dian)(dian)池、鎳(nie)鎘電(dian)(dian)池等)需(xu)選擇不同的充(chong)電(dian)(dian)芯片(pian)。

2)電池(chi)數目：可充電池(chi)的數目。

3)電(dian)流(liu)值(zhi)：充電(dian)電(dian)流(liu)的大(da)小決定了充電(dian)時間。

4)充(chong)電方式：是快充(chong)、慢(man)充(chong)還是可控充(chong)電過程。

本設計要實現的是手機的單節鋰離子電池充電器，要求充電快(kuai)速且具有(you)優(you)良的電池保護能力，據此(ci)選擇Maxim 公司的MAXl898 作為電池充電芯片。

2.2.2 芯片MAX1898 的特(te)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(gong)精(jing)確(que)的(de)恒(heng)流(liu)/恒(heng)壓充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓調節精(jing)度為(wei)±0.75％，提(ti)高了(le)電(dian)(dian)(dian)(dian)(dian)池(chi)性能并延(yan)長(chang)了(le)電(dian)(dian)(dian)(dian)(dian)池(chi)使(shi)用壽命。充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)可(ke)由用戶設(she)定，采用內部檢流(liu)，無(wu)須外部檢流(liu)電(dian)(dian)(dian)(dian)(dian)阻。 MAXl898 提(ti)供(gong)了(le)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)狀態的(de)輸出(chu)指(zhi)示(shi)、輸入(ru)電(dian)(dian)(dian)(dian)(dian)源是否與(yu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器連接的(de)輸出(chu)指(zhi)示(shi)和(he)(he)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)指(zhi)示(shi)。MAXl898 還(huan)具有(you)其(qi)他一些功能，包(bao)括輸入(ru)關斷控(kong)制、可(ke)選(xuan)的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)周(zhou)期重啟(qi)(無(wu)須重新上(shang)電(dian)(dian)(dian)(dian)(dian))、可(ke)選(xuan)的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)終(zhong)止(zhi)安(an)全(quan)定時器和(he)(he)過放電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)池(chi)的(de)低電(dian)(dian)(dian)(dian)(dian)流(liu)預充(chong)(chong)。

MAXl898 的關鍵特性如下：

1)    簡單、安全的線性(xing)充電方式。

2)    使用低成本的PNP 或PMOS 調整元件(jian)。

3)    輸入電壓：4.5～12V。

4)    內置(zhi)檢流電(dian)阻。

5)    ±0.75％電(dian)壓精度。

6)    可編程充電電流。

7)    輸入電源自(zi)動(dong)檢測。

8)    LED 充電狀態指示。

9)    可編(bian)程安全(quan)定時(shi)器。

10)  檢流監視輸出。

11)  可(ke)選/可(ke)調(diao)節自動重(zhong)啟(qi)。

12)  小尺(chi)寸uMAX 封(feng)裝(zhuang)。

2.2.3 MAX1898 的充電工作原理

充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯片MAXl898 的(de)(de)(de)內部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路包括(kuo)輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)調節(jie)(jie)(jie)器(qi)(qi)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓檢測(ce)(ce)器(qi)(qi)、充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)檢測(ce)(ce)器(qi)(qi)、定時(shi)器(qi)(qi)、溫度(du)檢測(ce)(ce)器(qi)(qi)和主控制(zhi)器(qi)(qi)。輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)調節(jie)(jie)(jie)器(qi)(qi)用于限(xian)制(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)總輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)，包括(kuo)系統負(fu)載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)與(yu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)。當檢測(ce)(ce)到(dao)輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)大(da)(da)(da)于設定的(de)(de)(de)門限(xian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)時(shi)，通過降(jiang)低(di)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)從而控制(zhi)輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)。因為系統工作時(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的(de)(de)(de)變化范圍較(jiao)大(da)(da)(da)，如果充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)沒有輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)檢測(ce)(ce)功(gong)(gong)能(neng)(neng)(neng)(neng)，則(ze)輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)必須能(neng)(neng)(neng)(neng)夠(gou)提供最(zui)大(da)(da)(da)負(fu)載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)與(yu)最(zui)大(da)(da)(da)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)之和，這將使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)成本(ben)增(zeng)高、體(ti)積增(zeng)大(da)(da)(da)，而利(li)用輸(shu)入(ru)(ru)限(xian)流(liu)(liu)(liu)(liu)功(gong)(gong)能(neng)(neng)(neng)(neng)則(ze)能(neng)(neng)(neng)(neng)夠(gou)降(jiang)低(di)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)對直流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)要求(qiu)，同時(shi)也(ye)簡(jian)化了輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)設計。 MAXl898 外接限(xian)流(liu)(liu)(liu)(liu)型充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)和P 溝道場效(xiao)應(ying)管，可以對單節(jie)(jie)(jie)鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行安全有效(xiao)的(de)(de)(de)快(kuai)充(chong)，其最(zui)大(da)(da)(da)特點是：在不使(shi)用電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感的(de)(de)(de)情況下，仍能(neng)(neng)(neng)(neng)做到(dao)很低(di)的(de)(de)(de)功(gong)(gong)率耗散(san)，可以實現預充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，具有過壓保護和溫度(du)保護功(gong)(gong)能(neng)(neng)(neng)(neng)，最(zui)長充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)問的(de)(de)(de)限(xian)制(zhi)可為鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)提供二次保護。MAX1898 的(de)(de)(de)浮(fu)動方式能(neng)(neng)(neng)(neng)夠(gou)使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)容量充(chong)至最(zui)大(da)(da)(da)。

當充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)和(he)電(dian)(dian)(dian)(dian)(dian)(dian)池在(zai)正常的(de)(de)工(gong)作溫度范圍內時，插入電(dian)(dian)(dian)(dian)(dian)(dian)池將啟(qi)動一次充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程；充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)結(jie)束的(de)(de)條件是(shi)平(ping)均的(de)(de)脈沖(chong)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)達到(dao)(dao)快(kuai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de) 1％，或時間超出片上預置的(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時間。MAXl898 能夠自動檢測充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)，沒(mei)有電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)時自動關(guan)斷以(yi)減少(shao)電(dian)(dian)(dian)(dian)(dian)(dian)池的(de)(de)漏電(dian)(dian)(dian)(dian)(dian)(dian)。啟(qi)動快(kuai)充(chong)(chong)(chong)后打(da)(da)開外(wai)接的(de)(de)P 型(xing)場(chang)效(xiao)應管(guan)，當檢測到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)壓達到(dao)(dao)設定的(de)(de)門限(xian)時進入脈沖(chong)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)方(fang)式，P 型(xing)場(chang)效(xiao)應管(guan)打(da)(da)開的(de)(de)時問會越來越短。充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)結(jie)束時，指示燈將會按12%的(de)(de)周期閃(shan)爍，MAX1898 的(de)(de)典型(xing)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)路如(ru)下(xia)圖圖2-1所示電(dian)(dian)(dian)(dian)(dian)(dian)路具體說明如(ru)下(xia)。

圖2-1  MAX1898的典(dian)型充電電路

1）輸入(ru)電(dian)壓(ya)范圍為 4.5～12v。鋰電(dian)池(chi)要求的(de)(de)充電(dian)方式(shi)是(shi)恒(heng)流恒(heng)壓(ya)方式(shi)，電(dian)源(yuan)(yuan)的(de)(de)輸入(ru)需要采(cai)用(yong)恒(heng)流恒(heng)壓(ya)源(yuan)(yuan)，一般可采(cai)用(yong)直流電(dian)源(yuan)(yuan)外加變壓(ya)器。

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

3)通過外接的電(dian)(dian)(dian)容(rong) CcT 來設置充電(dian)(dian)(dian)時(shi)間(jian) tCHG。這里的充電(dian)(dian)(dian)時(shi)間(jian)指的是快充時(shi)的最大充電(dian)(dian)(dian)時(shi)間(jian)，它和(he)定時(shi)電(dian)(dian)(dian)容(rong)CcT 的關系(xi)如(ru)下式所示(shi)：

CcT=34.33×tCHG                                                  (2-1)

式(shi)中，tCHG 的單位(wei)(wei)為小(xiao)(xiao)時，CcT 的單位(wei)(wei)為Nf。大多數(shu)情況下，快充時最大充電時問不超過3 小(xiao)(xiao)時，因(yin)此常取CcT 為100nF。

4)在限(xian)制(zhi)電(dian)流的模式下，通過(guo)外接的電(dian)阻 RSET 來設置最大充電(dian)電(dian)IFSTCHG，關系如下式所示(shi)：IFSTCHG=1400/Rset 式中，RSEI-的單(dan)位為Q，IFSTCHG 的單(dan)位為A。

當(dang)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源和電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)在(zai)正常的(de)工(gong)作溫度范圍內時(shi)，插入電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)將(jiang)啟(qi)動一次充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過程。平均的(de)脈沖充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流低于(yu)設置(zhi)的(de)快(kuai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)20％，或者充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)間超出片上預置(zhi)的(de)最大(da)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)問時(shi)，充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)周期結束。MAXl898 能夠自(zi)動檢測充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源，沒有(you)電(dian)(dian)(dian)(dian)(dian)(dian)源時(shi)自(zi)動關斷(duan)以減少電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)漏電(dian)(dian)(dian)(dian)(dian)(dian)。啟(qi)動快(kuai)充(chong)(chong)(chong)后，打(da)開外接的(de)P 型場效應管，當(dang)檢測到電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓達(da)到設定的(de)門(men)限(xian)時(shi)進入脈沖充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)方式，P 型場效應管打(da)開的(de)時(shi)JI 間會越來越短。充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)結束時(shi)，LED 指示燈將(jiang)會呈現周期性的(de)閃爍，具(ju)體的(de)閃爍含義如(ru)表(biao)1所示。

表2-

1  MAX1898 典型充電(dian)電(dian)路的LED 指示燈(deng)狀態(tai)說明

充電狀態
LED指(zhi)示燈電(dian)池或充電(dian)器沒有安(an)裝

預充或快充

亮

充電結束

滅

充電出錯

頻率閃爍

第(di)3節  系統主要硬件電(dian)路(lu)設計(ji)

   硬件電(dian)路設計主要圍繞充電(dian)芯片(pian)MAXl898 展開，而單片(pian)機(ji)控(kong)制部分(fen)的電(dian)路簡單。

3.1  主要(yao)器件(jian)

本設計的核心器件(jian)(jian)是MAXl898。MAXl898 可(ke)對所有化學類(lei)型的Li+電(dian)池(chi)進行(xing)安全充電(dian)，它具(ju)有高集(ji)成(cheng)度，在(zai)小尺寸內集(ji)成(cheng)了更(geng)多(duo)功能(neng)，盡(jin)可(ke)能(neng)多(duo)地覆蓋(gai)了基本應用電(dian)路，只需要少數外(wai)部元件(jian)(jian)。MAXl898 為10 引腳、超薄型的MAX 封裝，其(qi)引腳分(fen)布如圖3-1 所示：

圖3-1 MAXl898引腳分(fen)布(bu)

其引腳功能如下：

IN(1 腳)：傳(chuan)感輸入，檢測輸入的電壓或電流；

CHG(2 腳)：充電(dian)狀態指(zhi)示腳，同時驅動(dong)LED；

EN/OK(3 腳(jiao)(jiao))：使能輸(shu)(shu)(shu)入腳(jiao)(jiao)/輸(shu)(shu)(shu)入電源“好”輸(shu)(shu)(shu)出指(zhi)示腳(jiao)(jiao)。EN 為輸(shu)(shu)(shu)入腳(jiao)(jiao)，可以通過輸(shu)(shu)(shu)入禁止芯片工作(zuo)；OK 為輸(shu)(shu)(shu)出腳(jiao)(jiao)，用于指(zhi)示輸(shu)(shu)(shu)入電源是否(fou)與充電器(qi)連接；

ISET(4 腳(jiao))：充電(dian)(dian)電(dian)(dian)流(liu)調節引腳(jiao)。通過串(chuan)接一(yi)個電(dian)(dian)阻到地(di)來設置最大(da)充電(dian)(dian)電(dian)(dian)流(liu)；

CT(5 腳(jiao))：安全充電(dian)時(shi)間(jian)(jian)設置引(yin)腳(jiao)。接一個時(shi)間(jian)(jian)電(dian)容來設置充電(dian)時(shi)間(jian)(jian)，電(dian)容為 100nF 時(shi)，幾乎(hu)為3 個小(xiao)時(shi)，此(ci)引(yin)腳(jiao)直接接地(di)將禁(jin)用(yong)此(ci)功能；

RSTRT(6 腳(jiao)(jiao)(jiao))：自動(dong)(dong)(dong)重(zhong)(zhong)新(xin)啟動(dong)(dong)(dong)控制引腳(jiao)(jiao)(jiao)。當此(ci)引腳(jiao)(jiao)(jiao)直(zhi)接(jie)接(jie)地(di)時，如果電(dian)(dian)池(chi)電(dian)(dian)壓掉至(zhi)基準電(dian)(dian)壓閾(yu)值以下(xia) 200mV，將會重(zhong)(zhong)新(xin)開(kai)始一輪充(chong)電(dian)(dian)周期。此(ci)引腳(jiao)(jiao)(jiao)通過電(dian)(dian)阻接(jie)地(di)時，可(ke)以降低它(ta)的電(dian)(dian)壓閾(yu)值。此(ci)引腳(jiao)(jiao)(jiao)懸(xuan)空或者 CT 引腳(jiao)(jiao)(jiao)接(jie)地(di)(充(chong)電(dian)(dian)時間(jian)設置功能禁用)時，自動(dong)(dong)(dong)重(zhong)(zhong)新(xin)啟動(dong)(dong)(dong)功能被禁用；

BATT(7 腳(jiao))：電池傳感輸入腳(jiao)，接單個 Li+電池的正(zheng)極。此(ci)引腳(jiao)需旁接一(yi)個大電解電容到地；

GND(8 腳(jiao))：接地端；

DRV(9 腳)：外部晶體(ti)管驅動器，接晶體(ti)管的(de)基(ji)極；

CS(10 腳(jiao))：電流傳(chuan)感輸入，接晶體(ti)管的(de)發射(she)極。

本(ben)設計(ji)的單(dan)片機芯片選(xuan)用(yong)Atmel 公(gong)司的AT89C52，它完(wan)全可以滿足要求。

另(ling)外(wai)，由于充(chong)電(dian)器外(wai)部為+12V 供電(dian)，因此需要(yao)通(tong)過電(dian)壓(ya)轉換(huan)芯片(pian)將+12V 電(dian)壓(ya)轉換(huan)為 +5V 電(dian)壓(ya)，這里選(xuan)用(yong)三端電(dian)壓(ya)轉換(huan)芯片(pian)LM7805 來(lai)完成(cheng)此功能(neng)。

為了降低電(dian)源干擾，保持電(dian)路的(de)穩定，在LM7805 完成電(dian)壓轉換，將+5v 充(chong)電(dian)電(dian)源送給 MAXl898 之前(qian)，先(xian)經過一次光耦(ou)模(mo)塊 6N137 的(de)處理，通過單片機對光耦(ou)模(mo)塊的(de)控制，可(ke)以及時(shi)關斷充(chong)電(dian)電(dian)源。6N137 的(de)引腳分(fen)布(bu)如圖(tu)3-2 所示(shi)：

圖3-2  6N137 的引腳分布(bu)

其引腳功能如下：

NC(1 腳(jiao)、4 腳(jiao))：懸空；

+(2 腳(jiao))、-(3 腳(jiao))：發光(guang)二極管的正(zheng)、負極；

GND(5 腳(jiao))：接地端(duan)；

OUTPUT(6 腳)：輸(shu)出腳；

EN(7 腳)：使能腳。為(wei)低(di)時，無論有無輸(shu)入，輸(shu)出都為(wei)高。

不使用時，懸空(kong)即可；

VCC(8 腳(jiao))：電源(yuan)輸入腳(jiao)。

3.2  電路原理圖及說(shuo)明

硬件電(dian)路由單(dan)片機電(dian)路、電(dian)壓轉換及光耦隔離電(dian)路、充電(dian)控制電(dian)路3 部分(fen)組(zu)成。單(dan)片機部分(fen)的(de)電(dian)路原理圖如下圖3-3 所(suo)示。

圖3-3  單片機部分的電路原(yuan)理圖

圖3-3中，ul 為單片機(ji)(ji)AT89C52，工作(zuo)在(zai)11．0592MHz 時鐘；u2 為蜂鳴(ming)器(qi)，蜂鳴(ming)器(qi)由單片機(ji)(ji)的(de)(de)P2．1 腳控制(zhi)發(fa)出(chu)報警聲提(ti)示；單片機(ji)(ji)的(de)(de)P2．O 腳輸出(chu)控制(zhi)光耦器(qi)件，在(zai)需要的(de)(de)時候(hou)可(ke)以(yi)及時關斷充電(dian)電(dian)源；單片機(ji)(ji)的(de)(de)外部中斷O 由充電(dian)芯片MAXl898 的(de)(de)充電(dian)狀態輸出(chu)信號/ CHG 經過反(fan)相后觸發(fa)。

下圖3-4 所示的(de)為電壓轉換及光耦(ou)隔(ge)離(li)部分電路的(de)原理圖。