充(chong)電器為人們的(de)外出和出差辦(ban)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。

隨著手機在世界范圍內的(de)普(pu)及(ji)使用(yong)(yong)，手機電池充電器的(de)使用(yong)(yong)也越(yue)來越(yue)廣泛。

本(ben)次設(she)計(ji)將通過(guo)一(yi)個典型(xing)的(de)勢力介(jie)紹51單片(pian)機(ji)(ji)在實(shi)現(xian)手機(ji)(ji)電池充(chong)(chong)(chong)電器方面的(de)應用。設(she)計(ji)所實(shi)現(xian)的(de)充(chong)(chong)(chong)電器是一(yi)種智能充(chong)(chong)(chong)電器，它(ta)在單片(pian)機(ji)(ji)的(de)控(kong)制下，具有預充(chong)(chong)(chong)、充(chong)(chong)(chong)電保護(hu)、自動斷電和充(chong)(chong)(chong)電完(wan)成報警(jing)提示功能。

1.3  本設計功能模塊
本設計的功(gong)能(neng)模塊主要如下：

1）單(dan)片機模塊(kuai)：實現充(chong)電(dian)器的智能化控(kong)制。比如自動斷電(dian)、充(chong)電(dian)完成(cheng)報(bao)警(jing)提示等。

2）充(chong)電(dian)(dian)過程控制(zhi)(zhi)模塊：采(cai)用專用的(de)電(dian)(dian)池(chi)充(chong)電(dian)(dian)芯片實現充(chong)電(dian)(dian)過程的(de)控制(zhi)(zhi)。

3）充(chong)電(dian)電(dian)壓提供(gong)模塊：采用電(dian)壓轉換芯片將外部(bu)+12V電(dian)壓轉換為需要的+5V電(dian)壓。

4）C51程(cheng)序(xu)：單片機控制電(dian)(dian)池(chi)充電(dian)(dian)芯片實現充電(dian)(dian)過(guo)程(cheng)的(de)(de)自(zi)動化，并根(gen)據充電(dian)(dian)的(de)(de)狀(zhuang)態給出有關的(de)(de)輸出指示(shi)。

第2節  系統設計思路分析
充電的實現，它包(bao)括(kuo)兩(liang)部分：一是充電過程的控制；二是需要提供基(ji)本的充電電壓。

2.1 智能化的實現
在充電器電路中引入單片機的(de)控制。它為什么需要實現充電器的(de)智(zhi)能化呢？

充(chong)電(dian)(dian)(dian)器實現(xian)的方(fang)式不(bu)同會導致充(chong)電(dian)(dian)(dian)效果的不(bu)同。由于充(chong)電(dian)(dian)(dian)器多采(cai)用(yong)大(da)電(dian)(dian)(dian)流(liu)的快(kuai)速(su)充(chong)電(dian)(dian)(dian)法，在(zai)電(dian)(dian)(dian)池充(chong)滿后(hou)如果不(bu)及時停(ting)止(zhi)會使電(dian)(dian)(dian)池發燙，過度的充(chong)電(dian)(dian)(dian)會嚴重損害電(dian)(dian)(dian)池的壽命(ming)。一(yi)些低成(cheng)本的充(chong)電(dian)(dian)(dian)器采(cai)用(yong)電(dian)(dian)(dian)壓比較法，為了防(fang)止(zhi)過充(chong)，一(yi)般充(chong)電(dian)(dian)(dian)到90％就停(ting)止(zhi)大(da)電(dian)(dian)(dian)流(liu)快(kuai)充(chong)，而采(cai)用(yong)小電(dian)(dian)(dian)流(liu)涓流(liu)補充(chong)充(chong)電(dian)(dian)(dian)。

手(shou)機(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的使用(yong)壽命(ming)和單次使用(yong)時(shi)間與充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程密切相關。鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)是手(shou)機(ji)最為(wei)常用(yong)的一種電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)，它具有(you)較高(gao)的能量重量比、能量體積比，具有(you)記(ji)憶效應，可重復充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)多次，使用(yong)壽命(ming)較長，價格也越來(lai)越低。鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)對于(yu)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器的要(yao)求(qiu)比較苛(ke)刻，需(xu)(xu)要(yao)保(bao)護(hu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路。為(wei)了有(you)效利用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)容量，需(xu)(xu)將鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)至最大電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓，但是過(guo)壓充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)會造成電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)損壞，這就(jiu)要(yao)求(qiu)較高(gao)的控制(zhi)精度(du)。另外(wai)，對于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓過(guo)低的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)需(xu)(xu)要(yao)進(jin)行預(yu)充(chong)(chong)，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)器最好帶有(you)熱保(bao)護(hu)和時(shi)間保(bao)護(hu)，為(wei)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)提供(gong)附加保(bao)護(hu)。

一部好的(de)(de)(de)(de)充(chong)(chong)電(dian)器(qi)不但能(neng)(neng)(neng)在短時(shi)間(jian)(jian)內將電(dian)量(liang)充(chong)(chong)足，而且還可以對電(dian)池(chi)(chi)起到(dao)一定(ding)的(de)(de)(de)(de)維護作(zuo)用，修復由于使(shi)用不當造(zao)成的(de)(de)(de)(de)記憶效應，即容量(liang)下降(電(dian)池(chi)(chi)活性衰退)現象。設計比(bi)較科學的(de)(de)(de)(de)充(chong)(chong)電(dian)器(qi)往(wang)往(wang)采用專(zhuan)用充(chong)(chong)電(dian)控制芯片配合單片機(ji)控制的(de)(de)(de)(de)方法(fa)。專(zhuan)用的(de)(de)(de)(de)充(chong)(chong)電(dian)芯片具備業界公認(ren)較好的(de)(de)(de)(de)-△v 檢測(ce)(ce)，可以檢測(ce)(ce)出電(dian)池(chi)(chi)充(chong)(chong)電(dian)飽和時(shi)發出的(de)(de)(de)(de)電(dian)壓(ya)變化(hua)信號(hao)，比(bi)較精確地結束充(chong)(chong)電(dian)工(gong)作(zuo)，通過單片機(ji)對這些(xie)芯片的(de)(de)(de)(de)控制，可以實現充(chong)(chong)電(dian)過程(cheng)的(de)(de)(de)(de)智(zhi)能(neng)(neng)(neng)化(hua)，例如，在充(chong)(chong)電(dian)后(hou)增加及時(shi)關(guan)斷電(dian)源、蜂(feng)鳴報警和液晶顯(xian)示等功能(neng)(neng)(neng)。充(chong)(chong)電(dian)器(qi)的(de)(de)(de)(de)智(zhi)能(neng)(neng)(neng)化(hua)可以縮(suo)短充(chong)(chong)電(dian)的(de)(de)(de)(de)時(shi)間(jian)(jian)，同(tong)時(shi)能(neng)(neng)(neng)夠維護電(dian)池(chi)(chi)，延長電(dian)池(chi)(chi)使(shi)用壽命(ming)。

2.2 電池充電芯片的選擇
2.2.1 如何選擇電池充電芯片

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。在選擇(ze)具體的電池充(chong)電芯(xin)片(pian)時，需要參考以下標準。

1)電池(chi)類型：不(bu)同(tong)的電池(chi)(鋰(li)電池(chi)、鎳氫電池(chi)、鎳鎘電池(chi)等)需選擇不(bu)同(tong)的充電芯片(pian)。

2)電池(chi)數(shu)目：可(ke)充電池(chi)的數(shu)目。

3)電(dian)流值：充(chong)電(dian)電(dian)流的大小決定(ding)了(le)充(chong)電(dian)時間。

4)充(chong)(chong)電方式(shi)：是快(kuai)充(chong)(chong)、慢(man)充(chong)(chong)還(huan)是可控(kong)充(chong)(chong)電過(guo)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)(dian)(dian)快速且具有優良的電(dian)(dian)(dian)池保(bao)護能力(li)，據(ju)此選擇Maxim 公司(si)的MAXl898 作為電(dian)(dian)(dian)池充電(dian)(dian)(dian)芯片。

2.2.2 芯(xin)片MAX1898 的特(te)點(dian)

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(gong)精確的(de)(de)恒(heng)流(liu)/恒(heng)壓(ya)充(chong)電(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(ya)調節精度為±0.75％，提高(gao)了(le)(le)電(dian)(dian)(dian)(dian)池(chi)性能并延長了(le)(le)電(dian)(dian)(dian)(dian)池(chi)使用壽(shou)命。充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)可由(you)用戶設定(ding)(ding)，采用內部檢流(liu)，無須外部檢流(liu)電(dian)(dian)(dian)(dian)阻。 MAXl898 提供(gong)了(le)(le)充(chong)電(dian)(dian)(dian)(dian)狀態的(de)(de)輸(shu)出(chu)指(zhi)示、輸(shu)入電(dian)(dian)(dian)(dian)源是否與充(chong)電(dian)(dian)(dian)(dian)器連接(jie)的(de)(de)輸(shu)出(chu)指(zhi)示和充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)指(zhi)示。MAXl898 還(huan)具(ju)有其他一些(xie)功能，包括(kuo)輸(shu)入關斷控制(zhi)、可選(xuan)的(de)(de)充(chong)電(dian)(dian)(dian)(dian)周期重啟(無須重新上電(dian)(dian)(dian)(dian))、可選(xuan)的(de)(de)充(chong)電(dian)(dian)(dian)(dian)終(zhong)止(zhi)安全定(ding)(ding)時器和過放電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)池(chi)的(de)(de)低電(dian)(dian)(dian)(dian)流(liu)預(yu)充(chong)。

MAXl898 的關鍵特性如下：

1)    簡單、安(an)全的線性(xing)充電(dian)方式。

2)    使(shi)用低成本的PNP 或PMOS 調整元件。

3)    輸入(ru)電壓：4.5～12V。

4)    內置檢流電阻(zu)。

5)    ±0.75％電(dian)壓精度。

6)    可(ke)編程(cheng)充(chong)電電流。

7)    輸入(ru)電(dian)源自動檢(jian)測。

8)    LED 充電狀態指示。

9)    可(ke)編程安全定時器(qi)。

10)  檢流監視輸(shu)出。

11)  可(ke)選/可(ke)調節自動重啟。

12)  小尺寸(cun)uMAX 封裝。

2.2.3 MAX1898 的充電(dian)工作原理(li)

充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯片(pian)MAXl898 的(de)(de)(de)內部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)包括輸(shu)(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)調(diao)節(jie)(jie)器(qi)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓檢(jian)(jian)(jian)測(ce)器(qi)、充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)檢(jian)(jian)(jian)測(ce)器(qi)、定時器(qi)、溫度檢(jian)(jian)(jian)測(ce)器(qi)和主控制器(qi)。輸(shu)(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)調(diao)節(jie)(jie)器(qi)用(yong)于限制電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)總輸(shu)(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)，包括系統負(fu)載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)與充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)。當檢(jian)(jian)(jian)測(ce)到輸(shu)(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)大(da)于設定的(de)(de)(de)門限電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)時，通(tong)過降低(di)(di)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)從而控制輸(shu)(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)。因為系統工作時電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)的(de)(de)(de)變(bian)化范圍較大(da)，如(ru)果充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)沒有輸(shu)(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)檢(jian)(jian)(jian)測(ce)功(gong)能，則輸(shu)(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)必須能夠(gou)提供(gong)(gong)最(zui)大(da)負(fu)載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)與最(zui)大(da)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)之(zhi)和，這將使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)成本增(zeng)高、體積增(zeng)大(da)，而利用(yong)輸(shu)(shu)入(ru)(ru)(ru)限流(liu)(liu)(liu)功(gong)能則能夠(gou)降低(di)(di)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)對直流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)要求(qiu)，同(tong)時也(ye)簡化了輸(shu)(shu)入(ru)(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)設計(ji)。 MAXl898 外接限流(liu)(liu)(liu)型充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)和P 溝道場(chang)效應管，可以對單(dan)節(jie)(jie)鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行(xing)安全有效的(de)(de)(de)快(kuai)充(chong)，其最(zui)大(da)特點是：在不使(shi)用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感的(de)(de)(de)情況(kuang)下(xia)，仍能做到很低(di)(di)的(de)(de)(de)功(gong)率耗散(san)，可以實(shi)現預(yu)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，具有過壓保護(hu)和溫度保護(hu)功(gong)能，最(zui)長充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時問(wen)的(de)(de)(de)限制可為鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)提供(gong)(gong)二次(ci)保護(hu)。MAX1898 的(de)(de)(de)浮(fu)動方式能夠(gou)使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)容量充(chong)至最(zui)大(da)。

當充(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)(yuan)和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)在正常的工作溫度(du)范圍內時，插入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)將啟(qi)動(dong)一(yi)次充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過程；充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)結束的條件(jian)是平均(jun)的脈(mo)沖充(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)達到(dao)快充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的 1％，或(huo)時間超出片上預置的充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時間。MAXl898 能夠自動(dong)檢(jian)測(ce)(ce)充(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)(yuan)，沒有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)時自動(dong)關斷以減少(shao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的漏電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。啟(qi)動(dong)快充(chong)(chong)后打開外接的P 型(xing)(xing)場效應(ying)管，當檢(jian)測(ce)(ce)到(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓達到(dao)設(she)定的門限時進入脈(mo)沖充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)方式(shi)，P 型(xing)(xing)場效應(ying)管打開的時問會越來(lai)越短(duan)。充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)結束時，指示燈將會按12%的周期(qi)閃爍，MAX1898 的典型(xing)(xing)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路如(ru)下圖圖2-1所示電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路具(ju)體(ti)說(shuo)明如(ru)下。

圖(tu)2-1  MAX1898的典型充電(dian)電(dian)路

1）輸入電壓(ya)范圍為 4.5～12v。鋰(li)電池要(yao)求的充電方(fang)式(shi)是(shi)恒(heng)流恒(heng)壓(ya)方(fang)式(shi)，電源(yuan)(yuan)的輸入需要(yao)采(cai)用恒(heng)流恒(heng)壓(ya)源(yuan)(yuan)，一般可(ke)采(cai)用直(zhi)流電源(yuan)(yuan)外加變壓(ya)器。

2)通過(guo)外接(jie)的場效應管提供鋰(li)電池的充電接(jie)口。

3)通(tong)過外接的(de)(de)電容(rong) CcT 來設置充(chong)電時(shi)(shi)間(jian) tCHG。這里的(de)(de)充(chong)電時(shi)(shi)間(jian)指的(de)(de)是快充(chong)時(shi)(shi)的(de)(de)最大充(chong)電時(shi)(shi)間(jian)，它和定時(shi)(shi)電容(rong)CcT 的(de)(de)關系如(ru)下式(shi)所(suo)示：

CcT=34.33×tCHG                                                  (2-1)

式中，tCHG 的(de)單(dan)位(wei)為(wei)小時，CcT 的(de)單(dan)位(wei)為(wei)Nf。大多數情況下(xia)，快充(chong)(chong)時最(zui)大充(chong)(chong)電時問不(bu)超過3 小時，因(yin)此(ci)常取CcT 為(wei)100nF。

4)在限制電(dian)流的(de)模式下(xia)，通過外接的(de)電(dian)阻 RSET 來設(she)置最大充電(dian)電(dian)IFSTCHG，關系如下(xia)式所示：IFSTCHG=1400/Rset 式中(zhong)，RSEI-的(de)單位為Q，IFSTCHG 的(de)單位為A。

當充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)源和電(dian)(dian)(dian)池(chi)在正常(chang)的(de)工作溫度范圍內時(shi)(shi)，插入電(dian)(dian)(dian)池(chi)將啟動(dong)一次充(chong)電(dian)(dian)(dian)過程(cheng)。平(ping)均的(de)脈沖充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流低于設置(zhi)的(de)快充(chong)電(dian)(dian)(dian)流的(de)20％，或者充(chong)電(dian)(dian)(dian)時(shi)(shi)間超(chao)出(chu)片上預(yu)置(zhi)的(de)最大充(chong)電(dian)(dian)(dian)時(shi)(shi)問(wen)時(shi)(shi)，充(chong)電(dian)(dian)(dian)周期結束。MAXl898 能夠自(zi)動(dong)檢測充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)源，沒有電(dian)(dian)(dian)源時(shi)(shi)自(zi)動(dong)關(guan)斷以減少電(dian)(dian)(dian)池(chi)的(de)漏電(dian)(dian)(dian)。啟動(dong)快充(chong)后，打開外接的(de)P 型場效應管(guan)，當檢測到電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓達到設定(ding)的(de)門限(xian)時(shi)(shi)進入脈沖充(chong)電(dian)(dian)(dian)方式(shi)，P 型場效應管(guan)打開的(de)時(shi)(shi)JI 間會(hui)越(yue)來越(yue)短。充(chong)電(dian)(dian)(dian)結束時(shi)(shi)，LED 指示燈將會(hui)呈現(xian)周期性的(de)閃(shan)爍，具體的(de)閃(shan)爍含義如表1所示。

表2-

1  MAX1898 典型充電電路的LED 指示(shi)燈狀態說明

充電狀態
LED指示燈電(dian)池(chi)或充電(dian)器沒有(you)安(an)裝

預充或快充

亮

充電結束

滅

充電出錯

頻率閃爍

第3節  系(xi)統主要(yao)硬件電路(lu)設計

   硬件(jian)電路設計(ji)主要圍繞(rao)充電芯片MAXl898 展開(kai)，而單(dan)片機控制部分(fen)的電路簡單(dan)。

3.1  主要器件

本設計的核心器(qi)件是MAXl898。MAXl898 可對所(suo)有化學類(lei)型(xing)的Li+電(dian)池進行安(an)全充電(dian)，它具有高集成(cheng)度，在小(xiao)尺(chi)寸內集成(cheng)了更多功能，盡(jin)可能多地(di)覆蓋了基本應用電(dian)路，只需(xu)要少數外(wai)部(bu)元件。MAXl898 為(wei)10 引腳、超薄型(xing)的MAX 封裝，其(qi)引腳分(fen)布如圖3-1 所(suo)示(shi)：

圖(tu)3-1 MAXl898引腳分布

其引腳功能如下：

IN(1 腳)：傳感輸(shu)入，檢測輸(shu)入的電壓或電流(liu)；

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

EN/OK(3 腳(jiao))：使能輸入(ru)(ru)腳(jiao)/輸入(ru)(ru)電源(yuan)“好”輸出(chu)指示(shi)腳(jiao)。EN 為(wei)輸入(ru)(ru)腳(jiao)，可以通過輸入(ru)(ru)禁止芯片工作；OK 為(wei)輸出(chu)腳(jiao)，用于指示(shi)輸入(ru)(ru)電源(yuan)是否與(yu)充電器連(lian)接；

ISET(4 腳)：充(chong)電電流調節引腳。通(tong)過串接一個(ge)電阻到地來設置最大充(chong)電電流；

CT(5 腳)：安全充電時(shi)間設置(zhi)引腳。接一個時(shi)間電容來設置(zhi)充電時(shi)間，電容為 100nF 時(shi)，幾乎為3 個小時(shi)，此(ci)引腳直(zhi)接接地將(jiang)禁用此(ci)功能；

RSTRT(6 腳(jiao))：自動(dong)(dong)(dong)重(zhong)新啟(qi)動(dong)(dong)(dong)控制(zhi)引(yin)(yin)(yin)腳(jiao)。當此(ci)引(yin)(yin)(yin)腳(jiao)直接(jie)接(jie)地時(shi)，如果(guo)電(dian)(dian)池電(dian)(dian)壓(ya)(ya)掉(diao)至基準電(dian)(dian)壓(ya)(ya)閾(yu)值(zhi)以(yi)下 200mV，將會(hui)重(zhong)新開(kai)始一(yi)輪充(chong)電(dian)(dian)周期。此(ci)引(yin)(yin)(yin)腳(jiao)通(tong)過電(dian)(dian)阻(zu)接(jie)地時(shi)，可(ke)以(yi)降(jiang)低它的電(dian)(dian)壓(ya)(ya)閾(yu)值(zhi)。此(ci)引(yin)(yin)(yin)腳(jiao)懸空或(huo)者(zhe) CT 引(yin)(yin)(yin)腳(jiao)接(jie)地(充(chong)電(dian)(dian)時(shi)間(jian)設置功能禁用(yong)(yong))時(shi)，自動(dong)(dong)(dong)重(zhong)新啟(qi)動(dong)(dong)(dong)功能被禁用(yong)(yong)；

BATT(7 腳(jiao))：電池(chi)傳(chuan)感輸入腳(jiao)，接(jie)(jie)單個 Li+電池(chi)的正極。此引腳(jiao)需(xu)旁接(jie)(jie)一個大電解電容到地(di)；

GND(8 腳)：接地(di)端；

DRV(9 腳(jiao))：外(wai)部(bu)晶體(ti)管驅(qu)動器，接晶體(ti)管的基極；

CS(10 腳)：電流傳感(gan)輸入，接晶體(ti)管的發射極。

本設計的單片機(ji)芯(xin)片選用(yong)Atmel 公司(si)的AT89C52，它完(wan)全可以滿(man)足要求。

另外(wai)，由于充電器外(wai)部為+12V 供電，因此需要通過電壓(ya)轉換(huan)芯片將+12V 電壓(ya)轉換(huan)為 +5V 電壓(ya)，這里選(xuan)用三端電壓(ya)轉換(huan)芯片LM7805 來完成此功能。

為了降低電源干擾，保持電路的穩定(ding)，在(zai)LM7805 完成電壓(ya)轉換，將+5v 充(chong)電電源送給 MAXl898 之前，先經過一(yi)次(ci)光耦(ou)模(mo)塊 6N137 的處理，通過單(dan)片機對光耦(ou)模(mo)塊的控制，可以及時(shi)關(guan)斷(duan)充(chong)電電源。6N137 的引腳分(fen)布如圖(tu)3-2 所示：

圖3-2  6N137 的(de)引腳分布

其引腳功能如下：

NC(1 腳、4 腳)：懸空；

+(2 腳)、-(3 腳)：發光二極(ji)管的正、負極(ji)；

GND(5 腳)：接地端；

OUTPUT(6 腳)：輸出(chu)腳；

EN(7 腳)：使能腳。為低時，無論(lun)有無輸入，輸出(chu)都為高。

不使用時(shi)，懸空即可；

VCC(8 腳)：電源(yuan)輸入腳。

3.2  電路原理圖及說明

硬件電路(lu)(lu)由(you)單(dan)片(pian)機電路(lu)(lu)、電壓轉換及光耦隔離電路(lu)(lu)、充電控(kong)制電路(lu)(lu)3 部分(fen)組成。單(dan)片(pian)機部分(fen)的電路(lu)(lu)原理圖如下圖3-3 所示。

圖3-3  單片機部分(fen)的電路原理圖

圖3-3中，ul 為單(dan)片機AT89C52，工作在11．0592MHz 時(shi)(shi)鐘；u2 為蜂(feng)鳴(ming)器，蜂(feng)鳴(ming)器由單(dan)片機的P2．1 腳(jiao)控(kong)制(zhi)(zhi)發出(chu)報(bao)警(jing)聲提示(shi)；單(dan)片機的P2．O 腳(jiao)輸出(chu)控(kong)制(zhi)(zhi)光耦器件，在需要的時(shi)(shi)候可以及時(shi)(shi)關斷(duan)充電電源；單(dan)片機的外(wai)部中斷(duan)O 由充電芯片MAXl898 的充電狀態輸出(chu)信號/ CHG 經過(guo)反相后觸發。

下圖(tu)3-4 所示的(de)為電壓轉換及光耦隔離部(bu)分電路(lu)的(de)原(yuan)理圖(tu)。