充電(dian)器為(wei)人們(men)的外出和出差辦公提供(gong)了極大的方便。

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。

隨著手機在(zai)世界范(fan)圍內(nei)的(de)普及使(shi)用(yong)(yong)，手機電(dian)池充(chong)電(dian)器的(de)使(shi)用(yong)(yong)也越來(lai)越廣泛。

本次設(she)計(ji)將通(tong)過(guo)一(yi)個典型的(de)勢力介紹51單(dan)片(pian)(pian)機(ji)(ji)在實現手機(ji)(ji)電池充(chong)(chong)電器方面(mian)的(de)應用。設(she)計(ji)所實現的(de)充(chong)(chong)電器是一(yi)種智(zhi)能充(chong)(chong)電器，它(ta)在單(dan)片(pian)(pian)機(ji)(ji)的(de)控制下，具有預充(chong)(chong)、充(chong)(chong)電保護、自動斷(duan)電和充(chong)(chong)電完成(cheng)報(bao)警提示功能。

1.3  本設計功能模塊
本(ben)設計(ji)的功能模塊(kuai)主要如下(xia)：

1）單(dan)片機模塊：實現(xian)充電器的(de)智能化控制(zhi)。比如自動(dong)斷電、充電完(wan)成報警提示等。

2）充電過程控(kong)制模塊：采用專用的電池充電芯片實現充電過程的控(kong)制。

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

4）C51程序：單片機(ji)控制電(dian)池充電(dian)芯片實現充電(dian)過程的自(zi)動(dong)化，并根(gen)據充電(dian)的狀態給出有關的輸(shu)出指(zhi)示。

第2節  系統設計思路分析
充(chong)電的(de)實現，它包括(kuo)兩部分：一是充(chong)電過程的(de)控制；二是需(xu)要提供(gong)基本(ben)的(de)充(chong)電電壓。

2.1 智能化的實現
在(zai)充電器電路(lu)中引入(ru)單片機的控制。它為什(shen)么(me)需要實現充電器的智能化(hua)呢？

充(chong)電(dian)(dian)(dian)器實(shi)現(xian)的(de)方式(shi)不同(tong)會導致充(chong)電(dian)(dian)(dian)效(xiao)果的(de)不同(tong)。由于充(chong)電(dian)(dian)(dian)器多采(cai)用大電(dian)(dian)(dian)流(liu)的(de)快(kuai)速充(chong)電(dian)(dian)(dian)法(fa)，在電(dian)(dian)(dian)池(chi)充(chong)滿(man)后如果不及(ji)時停止會使電(dian)(dian)(dian)池(chi)發燙，過度(du)的(de)充(chong)電(dian)(dian)(dian)會嚴重損害電(dian)(dian)(dian)池(chi)的(de)壽命(ming)。一(yi)些低成本的(de)充(chong)電(dian)(dian)(dian)器采(cai)用電(dian)(dian)(dian)壓比較(jiao)法(fa)，為了防止過充(chong)，一(yi)般充(chong)電(dian)(dian)(dian)到90％就停止大電(dian)(dian)(dian)流(liu)快(kuai)充(chong)，而采(cai)用小電(dian)(dian)(dian)流(liu)涓流(liu)補充(chong)充(chong)電(dian)(dian)(dian)。

手機(ji)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)的(de)(de)使(shi)(shi)用(yong)壽命和(he)(he)單次使(shi)(shi)用(yong)時間(jian)與充(chong)電(dian)(dian)(dian)(dian)過程(cheng)密切(qie)相關。鋰(li)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)是(shi)手機(ji)最(zui)為常用(yong)的(de)(de)一種電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)，它具有(you)(you)較(jiao)高的(de)(de)能量重量比、能量體(ti)積比，具有(you)(you)記(ji)憶效應，可重復(fu)充(chong)電(dian)(dian)(dian)(dian)多次，使(shi)(shi)用(yong)壽命較(jiao)長，價格也越來越低。鋰(li)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)對于充(chong)電(dian)(dian)(dian)(dian)器(qi)的(de)(de)要(yao)求比較(jiao)苛(ke)刻(ke)，需(xu)(xu)要(yao)保(bao)護(hu)(hu)電(dian)(dian)(dian)(dian)路(lu)。為了(le)有(you)(you)效利用(yong)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)容量，需(xu)(xu)將鋰(li)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)充(chong)電(dian)(dian)(dian)(dian)至最(zui)大電(dian)(dian)(dian)(dian)壓，但是(shi)過壓充(chong)電(dian)(dian)(dian)(dian)會造成電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)損壞，這就要(yao)求較(jiao)高的(de)(de)控制精度。另外，對于電(dian)(dian)(dian)(dian)壓過低的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)需(xu)(xu)要(yao)進行預(yu)充(chong)，充(chong)電(dian)(dian)(dian)(dian)器(qi)最(zui)好帶有(you)(you)熱保(bao)護(hu)(hu)和(he)(he)時間(jian)保(bao)護(hu)(hu)，為電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)提供附加保(bao)護(hu)(hu)。

一(yi)部好的(de)(de)充(chong)(chong)電(dian)(dian)(dian)器不(bu)但(dan)能(neng)在(zai)短時(shi)間內將電(dian)(dian)(dian)量充(chong)(chong)足(zu)，而且(qie)還可以(yi)對電(dian)(dian)(dian)池起到一(yi)定的(de)(de)維(wei)護作用(yong)(yong)，修復(fu)由于使用(yong)(yong)不(bu)當造成的(de)(de)記憶效應，即容量下降(電(dian)(dian)(dian)池活性衰退)現象。設計比(bi)較(jiao)科學的(de)(de)充(chong)(chong)電(dian)(dian)(dian)器往往采用(yong)(yong)專用(yong)(yong)充(chong)(chong)電(dian)(dian)(dian)控(kong)(kong)制(zhi)芯片配(pei)合單(dan)片機控(kong)(kong)制(zhi)的(de)(de)方法。專用(yong)(yong)的(de)(de)充(chong)(chong)電(dian)(dian)(dian)芯片具備(bei)業(ye)界公認較(jiao)好的(de)(de)-△v 檢測(ce)，可以(yi)檢測(ce)出(chu)電(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)飽和時(shi)發(fa)出(chu)的(de)(de)電(dian)(dian)(dian)壓變化(hua)信號，比(bi)較(jiao)精確地(di)結(jie)束充(chong)(chong)電(dian)(dian)(dian)工(gong)作，通過單(dan)片機對這些(xie)芯片的(de)(de)控(kong)(kong)制(zhi)，可以(yi)實(shi)現充(chong)(chong)電(dian)(dian)(dian)過程的(de)(de)智能(neng)化(hua)，例如，在(zai)充(chong)(chong)電(dian)(dian)(dian)后增加及(ji)時(shi)關斷電(dian)(dian)(dian)源、蜂鳴報(bao)警和液(ye)晶顯示等功能(neng)。充(chong)(chong)電(dian)(dian)(dian)器的(de)(de)智能(neng)化(hua)可以(yi)縮短充(chong)(chong)電(dian)(dian)(dian)的(de)(de)時(shi)間，同時(shi)能(neng)夠維(wei)護電(dian)(dian)(dian)池，延長電(dian)(dian)(dian)池使用(yong)(yong)壽命。

2.2 電池充電芯片的選擇
2.2.1 如何(he)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)選擇具體(ti)的電池(chi)充(chong)電芯(xin)片時，需要參考以下標準。

1)電池(chi)類型(xing)：不(bu)同的電池(chi)(鋰(li)電池(chi)、鎳(nie)氫電池(chi)、鎳(nie)鎘電池(chi)等)需選(xuan)擇不(bu)同的充(chong)電芯(xin)片(pian)。

2)電池數目：可充(chong)電池的數目。

3)電(dian)流(liu)值：充(chong)電(dian)電(dian)流(liu)的大小(xiao)決定了充(chong)電(dian)時(shi)間(jian)。

4)充電方式(shi)：是(shi)快(kuai)充、慢(man)充還是(shi)可控充電過程。

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(dian)快(kuai)速且(qie)具(ju)有優良的電(dian)池(chi)保護(hu)能力，據此選擇Maxim 公司的MAXl898 作為電(dian)池(chi)充電(dian)芯片。

2.2.2 芯片MAX1898 的特點

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提供精確的(de)(de)(de)恒(heng)流(liu)/恒(heng)壓充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓調(diao)節(jie)精度為±0.75％，提高了(le)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)性(xing)能并(bing)延長(chang)了(le)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)使用壽(shou)命。充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)可(ke)由用戶設定，采(cai)用內部檢(jian)流(liu)，無(wu)須外(wai)部檢(jian)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻。 MAXl898 提供了(le)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)狀態的(de)(de)(de)輸(shu)出(chu)指示、輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源是否(fou)與充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器連接的(de)(de)(de)輸(shu)出(chu)指示和充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)指示。MAXl898 還(huan)具有(you)其他一些功(gong)能，包(bao)括輸(shu)入關(guan)斷控制、可(ke)選的(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)周期重(zhong)啟(無(wu)須重(zhong)新(xin)上電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian))、可(ke)選的(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)終止安全(quan)定時器和過放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)預充(chong)。

MAXl898 的(de)關鍵(jian)特(te)性如下：

1)    簡單、安全的線性充電方(fang)式。

2)    使(shi)用低成(cheng)本(ben)的PNP 或PMOS 調整元件(jian)。

3)    輸入(ru)電壓(ya)：4.5～12V。

4)    內置檢流電阻(zu)。

5)    ±0.75％電壓精(jing)度(du)。

6)    可編(bian)程充(chong)電(dian)電(dian)流。

7)    輸(shu)入電(dian)源自動(dong)檢測。

8)    LED 充電狀態指示。

9)    可編程安(an)全定時器。

10)  檢流監視輸出。

11)  可選/可調節自動重啟(qi)。

12)  小尺寸uMAX 封(feng)裝。

2.2.3 MAX1898 的充電工作原理

充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯(xin)片MAXl898 的內(nei)部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路包括輸(shu)(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)調(diao)節器(qi)(qi)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓檢(jian)測(ce)器(qi)(qi)、充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)檢(jian)測(ce)器(qi)(qi)、定(ding)時器(qi)(qi)、溫度檢(jian)測(ce)器(qi)(qi)和主控制(zhi)器(qi)(qi)。輸(shu)(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)調(diao)節器(qi)(qi)用(yong)(yong)于限制(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的總輸(shu)(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)，包括系(xi)統負載(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)與(yu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)。當(dang)檢(jian)測(ce)到輸(shu)(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)大(da)(da)于設定(ding)的門限電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)時，通(tong)過降低(di)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)從而控制(zhi)輸(shu)(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)。因為系(xi)統工作時電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)的變化(hua)范圍較大(da)(da)，如果充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)沒有輸(shu)(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)檢(jian)測(ce)功(gong)(gong)能(neng)，則輸(shu)(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)必須能(neng)夠提供(gong)最(zui)大(da)(da)負載(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)與(yu)最(zui)大(da)(da)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)之和，這將使電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的成本增(zeng)高、體積增(zeng)大(da)(da)，而利(li)用(yong)(yong)輸(shu)(shu)(shu)入(ru)(ru)限流(liu)(liu)(liu)功(gong)(gong)能(neng)則能(neng)夠降低(di)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)對(dui)直流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的要(yao)求，同時也簡化(hua)了輸(shu)(shu)(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的設計。 MAXl898 外接限流(liu)(liu)(liu)型充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)和P 溝道場(chang)效應管，可以對(dui)單節鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池進行安全有效的快充(chong)(chong)(chong)，其最(zui)大(da)(da)特(te)點是：在不使用(yong)(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感的情(qing)況下，仍能(neng)做(zuo)到很低(di)的功(gong)(gong)率耗散，可以實現(xian)預充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，具有過壓保(bao)護(hu)和溫度保(bao)護(hu)功(gong)(gong)能(neng)，最(zui)長充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時問(wen)的限制(zhi)可為鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池提供(gong)二次保(bao)護(hu)。MAX1898 的浮動方式能(neng)夠使電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池容量充(chong)(chong)(chong)至最(zui)大(da)(da)。

當充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源和電(dian)(dian)(dian)(dian)池在(zai)正常的(de)(de)工作溫度范圍(wei)內時(shi)(shi)(shi)(shi)，插入(ru)電(dian)(dian)(dian)(dian)池將啟(qi)(qi)動(dong)(dong)一次充(chong)(chong)電(dian)(dian)(dian)(dian)過程；充(chong)(chong)電(dian)(dian)(dian)(dian)結束的(de)(de)條件(jian)是平均的(de)(de)脈(mo)沖(chong)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流達(da)(da)到快充(chong)(chong)電(dian)(dian)(dian)(dian)流的(de)(de) 1％，或時(shi)(shi)(shi)(shi)間(jian)超出片上預置的(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)(shi)(shi)(shi)間(jian)。MAXl898 能夠(gou)自(zi)動(dong)(dong)檢(jian)測充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源，沒(mei)有電(dian)(dian)(dian)(dian)源時(shi)(shi)(shi)(shi)自(zi)動(dong)(dong)關斷(duan)以(yi)減(jian)少電(dian)(dian)(dian)(dian)池的(de)(de)漏電(dian)(dian)(dian)(dian)。啟(qi)(qi)動(dong)(dong)快充(chong)(chong)后打(da)開(kai)外接的(de)(de)P 型場(chang)效(xiao)應(ying)管，當檢(jian)測到電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓達(da)(da)到設定(ding)的(de)(de)門限時(shi)(shi)(shi)(shi)進入(ru)脈(mo)沖(chong)充(chong)(chong)電(dian)(dian)(dian)(dian)方式，P 型場(chang)效(xiao)應(ying)管打(da)開(kai)的(de)(de)時(shi)(shi)(shi)(shi)問會(hui)越(yue)來越(yue)短。充(chong)(chong)電(dian)(dian)(dian)(dian)結束時(shi)(shi)(shi)(shi)，指示(shi)燈將會(hui)按12%的(de)(de)周期(qi)閃爍，MAX1898 的(de)(de)典型充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)路如(ru)下圖圖2-1所(suo)示(shi)電(dian)(dian)(dian)(dian)路具體說明(ming)如(ru)下。

圖2-1  MAX1898的典(dian)型(xing)充電電路

1）輸(shu)入電(dian)壓范圍為 4.5～12v。鋰(li)電(dian)池要(yao)求的充電(dian)方式是恒(heng)流(liu)恒(heng)壓方式，電(dian)源的輸(shu)入需(xu)要(yao)采用恒(heng)流(liu)恒(heng)壓源，一般可采用直流(liu)電(dian)源外加變壓器。

2)通過(guo)外接的(de)場(chang)效(xiao)應管(guan)提供鋰電池(chi)的(de)充電接口(kou)。

3)通(tong)過外接的(de)(de)電(dian)(dian)容(rong) CcT 來設置充(chong)(chong)電(dian)(dian)時(shi)間(jian) tCHG。這里的(de)(de)充(chong)(chong)電(dian)(dian)時(shi)間(jian)指的(de)(de)是快(kuai)充(chong)(chong)時(shi)的(de)(de)最大充(chong)(chong)電(dian)(dian)時(shi)間(jian)，它(ta)和定時(shi)電(dian)(dian)容(rong)CcT 的(de)(de)關系如下(xia)式所示：

CcT=34.33×tCHG                                                  (2-1)

式中，tCHG 的單(dan)位為小時，CcT 的單(dan)位為Nf。大(da)(da)多數情(qing)況下(xia)，快(kuai)充時最大(da)(da)充電時問不(bu)超過3 小時，因(yin)此(ci)常(chang)取CcT 為100nF。

4)在(zai)限制(zhi)電流的模式下，通(tong)過外接(jie)的電阻 RSET 來設置最大充電電IFSTCHG，關系如下式所示：IFSTCHG=1400/Rset 式中，RSEI-的單(dan)位為Q，IFSTCHG 的單(dan)位為A。

當充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)和電(dian)(dian)(dian)池(chi)在正常的(de)工作溫度范(fan)圍內時(shi)(shi)(shi)，插入電(dian)(dian)(dian)池(chi)將啟(qi)動一次充(chong)(chong)(chong)電(dian)(dian)(dian)過(guo)程。平均(jun)的(de)脈沖充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流低于設置(zhi)的(de)快充(chong)(chong)(chong)電(dian)(dian)(dian)流的(de)20％，或者充(chong)(chong)(chong)電(dian)(dian)(dian)時(shi)(shi)(shi)間超(chao)出片上預置(zhi)的(de)最大充(chong)(chong)(chong)電(dian)(dian)(dian)時(shi)(shi)(shi)問時(shi)(shi)(shi)，充(chong)(chong)(chong)電(dian)(dian)(dian)周期結(jie)束。MAXl898 能夠自(zi)動檢測充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)，沒有電(dian)(dian)(dian)源(yuan)時(shi)(shi)(shi)自(zi)動關(guan)斷(duan)以減少電(dian)(dian)(dian)池(chi)的(de)漏電(dian)(dian)(dian)。啟(qi)動快充(chong)(chong)(chong)后，打開外接的(de)P 型(xing)場效應管(guan)，當檢測到電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓達到設定的(de)門限時(shi)(shi)(shi)進入脈沖充(chong)(chong)(chong)電(dian)(dian)(dian)方式(shi)，P 型(xing)場效應管(guan)打開的(de)時(shi)(shi)(shi)JI 間會(hui)越來越短。充(chong)(chong)(chong)電(dian)(dian)(dian)結(jie)束時(shi)(shi)(shi)，LED 指示燈將會(hui)呈現周期性的(de)閃爍(shuo)，具體的(de)閃爍(shuo)含義如表1所(suo)示。

表2-

1  MAX1898 典型充(chong)電電路的LED 指(zhi)示燈狀態(tai)說(shuo)明

充電狀態
LED指示燈電池(chi)或充電器沒有安裝

預充或快充

亮

充電結束

滅

充電出錯

頻率閃爍

第3節(jie)  系統主(zhu)要硬(ying)件電路設計(ji)

   硬(ying)件電(dian)路(lu)設計(ji)主要圍繞充電(dian)芯片MAXl898 展(zhan)開(kai)，而單(dan)片機(ji)控制部分(fen)的電(dian)路(lu)簡單(dan)。

3.1  主要器件(jian)

本設計的核心(xin)器(qi)件是MAXl898。MAXl898 可對(dui)所有化(hua)學類型的Li+電(dian)池進行安全充電(dian)，它具(ju)有高集(ji)成(cheng)度，在小(xiao)尺寸內(nei)集(ji)成(cheng)了更多(duo)功能，盡可能多(duo)地覆蓋(gai)了基本應用電(dian)路，只需要(yao)少數外部元件。MAXl898 為10 引腳(jiao)(jiao)、超薄型的MAX 封裝，其引腳(jiao)(jiao)分(fen)布如圖3-1 所示：

圖3-1 MAXl898引(yin)腳分布

其引腳功能如下：

IN(1 腳(jiao))：傳感輸入，檢測輸入的(de)電壓(ya)或電流；

CHG(2 腳)：充電狀態指示腳，同時驅動LED；

EN/OK(3 腳(jiao))：使能輸(shu)(shu)入腳(jiao)/輸(shu)(shu)入電(dian)源(yuan)“好”輸(shu)(shu)出指(zhi)(zhi)示(shi)腳(jiao)。EN 為輸(shu)(shu)入腳(jiao)，可(ke)以通過輸(shu)(shu)入禁止芯片工作(zuo)；OK 為輸(shu)(shu)出腳(jiao)，用于(yu)指(zhi)(zhi)示(shi)輸(shu)(shu)入電(dian)源(yuan)是否與充電(dian)器連接；

ISET(4 腳)：充電電流(liu)調節引腳。通過串接一個電阻到地來設置最大充電電流(liu)；

CT(5 腳(jiao))：安全(quan)充(chong)電(dian)時(shi)(shi)(shi)(shi)間(jian)設置(zhi)(zhi)引(yin)腳(jiao)。接(jie)一個(ge)時(shi)(shi)(shi)(shi)間(jian)電(dian)容來設置(zhi)(zhi)充(chong)電(dian)時(shi)(shi)(shi)(shi)間(jian)，電(dian)容為(wei)(wei) 100nF 時(shi)(shi)(shi)(shi)，幾乎為(wei)(wei)3 個(ge)小時(shi)(shi)(shi)(shi)，此(ci)引(yin)腳(jiao)直接(jie)接(jie)地將禁用此(ci)功能；

RSTRT(6 腳)：自動(dong)重(zhong)新(xin)啟動(dong)控制引(yin)(yin)(yin)腳。當此(ci)(ci)引(yin)(yin)(yin)腳直接(jie)接(jie)地時(shi)，如(ru)果電(dian)(dian)池(chi)電(dian)(dian)壓(ya)掉至基準電(dian)(dian)壓(ya)閾值以(yi)下(xia) 200mV，將(jiang)會重(zhong)新(xin)開始(shi)一輪充電(dian)(dian)周期。此(ci)(ci)引(yin)(yin)(yin)腳通過電(dian)(dian)阻接(jie)地時(shi)，可以(yi)降低它的電(dian)(dian)壓(ya)閾值。此(ci)(ci)引(yin)(yin)(yin)腳懸空或者 CT 引(yin)(yin)(yin)腳接(jie)地(充電(dian)(dian)時(shi)間設(she)置功能禁用)時(shi)，自動(dong)重(zhong)新(xin)啟動(dong)功能被禁用；

BATT(7 腳(jiao))：電(dian)池傳感輸入腳(jiao)，接單個 Li+電(dian)池的正極。此(ci)引腳(jiao)需(xu)旁接一個大(da)電(dian)解電(dian)容到(dao)地；

GND(8 腳)：接地端；

DRV(9 腳)：外部晶(jing)(jing)體管驅(qu)動器，接晶(jing)(jing)體管的(de)基極；

CS(10 腳)：電流傳感輸入(ru)，接晶體管的發射極(ji)。

本(ben)設計的(de)單片機(ji)芯片選用Atmel 公司(si)的(de)AT89C52，它完全(quan)可以滿足要求。

另(ling)外(wai)，由于充(chong)電(dian)器外(wai)部為(wei)+12V 供電(dian)，因此(ci)需要通(tong)過電(dian)壓(ya)(ya)轉換芯(xin)(xin)片(pian)將+12V 電(dian)壓(ya)(ya)轉換為(wei) +5V 電(dian)壓(ya)(ya)，這里選用三端電(dian)壓(ya)(ya)轉換芯(xin)(xin)片(pian)LM7805 來完成此(ci)功能。

為了降低電(dian)源(yuan)干(gan)擾，保持電(dian)路的穩定，在LM7805 完成電(dian)壓轉換，將+5v 充電(dian)電(dian)源(yuan)送給 MAXl898 之前，先經(jing)過(guo)一次光(guang)(guang)耦(ou)(ou)模塊 6N137 的處理，通(tong)過(guo)單(dan)片機對光(guang)(guang)耦(ou)(ou)模塊的控制(zhi)，可以及時關(guan)斷充電(dian)電(dian)源(yuan)。6N137 的引腳分布如圖3-2 所(suo)示：

圖3-2  6N137 的引腳(jiao)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))：發光二極管的正、負極；

GND(5 腳)：接地(di)端；

OUTPUT(6 腳)：輸(shu)出腳；

EN(7 腳)：使能腳。為低(di)時，無論(lun)有無輸入，輸出都為高。

不(bu)使用時，懸(xuan)空即可；

VCC(8 腳(jiao))：電源輸入腳(jiao)。

3.2  電路原理圖及說明

硬件電(dian)(dian)(dian)路由(you)單片(pian)機電(dian)(dian)(dian)路、電(dian)(dian)(dian)壓轉(zhuan)換(huan)及光(guang)耦隔離電(dian)(dian)(dian)路、充電(dian)(dian)(dian)控制電(dian)(dian)(dian)路3 部分(fen)組成。單片(pian)機部分(fen)的(de)電(dian)(dian)(dian)路原理圖如下圖3-3 所示。

圖(tu)3-3  單片機部(bu)分的電路(lu)原理圖(tu)

圖3-3中，ul 為(wei)單(dan)片機(ji)AT89C52，工(gong)作(zuo)在11．0592MHz 時鐘；u2 為(wei)蜂鳴器(qi)，蜂鳴器(qi)由單(dan)片機(ji)的P2．1 腳(jiao)控制發出(chu)報警聲提示；單(dan)片機(ji)的P2．O 腳(jiao)輸(shu)出(chu)控制光耦器(qi)件，在需要的時候可以及時關斷充電(dian)電(dian)源；單(dan)片機(ji)的外(wai)部中斷O 由充電(dian)芯(xin)片MAXl898 的充電(dian)狀(zhuang)態輸(shu)出(chu)信號/ CHG 經過(guo)反相后觸發。

下圖(tu)3-4 所示的(de)為電壓轉換及光(guang)耦隔離部分電路的(de)原理圖(tu)。