充(chong)電(dian)器為人們的(de)外(wai)出(chu)和出(chu)差辦(ban)公提(ti)供了極大的(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(shou)機在世界范圍內的普及使(shi)用(yong)，手(shou)機電池充電器(qi)的使(shi)用(yong)也越來越廣泛。

本次設(she)計將通過一個(ge)典型的勢力介紹51單(dan)片機(ji)在實(shi)現手機(ji)電池充(chong)(chong)電器方面(mian)的應(ying)用。設(she)計所實(shi)現的充(chong)(chong)電器是一種智(zhi)能充(chong)(chong)電器，它在單(dan)片機(ji)的控制下，具(ju)有預充(chong)(chong)、充(chong)(chong)電保護、自動(dong)斷電和(he)充(chong)(chong)電完成報(bao)警提示功(gong)能。

1.3  本設計功能模塊
本設(she)計的功能模塊主要(yao)如下：

1）單片機(ji)模塊(kuai)：實現充(chong)電器的智能化(hua)控制。比如自動斷電、充(chong)電完成報(bao)警提示等。

2）充電(dian)過(guo)程(cheng)控制模塊：采用專用的電(dian)池充電(dian)芯片實(shi)現充電(dian)過(guo)程(cheng)的控制。

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

4）C51程(cheng)序：單片(pian)機控制電(dian)池(chi)充(chong)(chong)電(dian)芯片(pian)實現充(chong)(chong)電(dian)過程(cheng)的自(zi)動化，并根據充(chong)(chong)電(dian)的狀態給(gei)出有關(guan)的輸出指示(shi)。

第2節  系統設計思路分析
充電(dian)的實現，它(ta)包(bao)括(kuo)兩部分(fen)：一是充電(dian)過程的控制(zhi)；二是需要提(ti)供基本的充電(dian)電(dian)壓。

2.1 智能化的實現
在(zai)充電(dian)(dian)器電(dian)(dian)路(lu)中引入單片機的(de)控制。它為什么需要實現(xian)充電(dian)(dian)器的(de)智能(neng)化呢？

充(chong)電(dian)器實(shi)現的方(fang)式不同會導致充(chong)電(dian)效果的不同。由于充(chong)電(dian)器多采(cai)(cai)用(yong)大電(dian)流的快速(su)充(chong)電(dian)法(fa)，在電(dian)池充(chong)滿(man)后如果不及時停止(zhi)會使電(dian)池發(fa)燙(tang)，過度的充(chong)電(dian)會嚴(yan)重損害電(dian)池的壽(shou)命。一些低成本的充(chong)電(dian)器采(cai)(cai)用(yong)電(dian)壓比較(jiao)法(fa)，為了(le)防(fang)止(zhi)過充(chong)，一般(ban)充(chong)電(dian)到90％就停止(zhi)大電(dian)流快充(chong)，而采(cai)(cai)用(yong)小電(dian)流涓流補充(chong)充(chong)電(dian)。

手機(ji)電(dian)(dian)池(chi)(chi)的使(shi)用(yong)壽命(ming)和單次使(shi)用(yong)時間(jian)與充(chong)電(dian)(dian)過(guo)程密切相關。鋰電(dian)(dian)池(chi)(chi)是手機(ji)最(zui)為(wei)常用(yong)的一種電(dian)(dian)池(chi)(chi)，它(ta)具有(you)較(jiao)(jiao)高(gao)的能(neng)(neng)量重量比、能(neng)(neng)量體積(ji)比，具有(you)記憶效(xiao)應(ying)，可重復充(chong)電(dian)(dian)多(duo)次，使(shi)用(yong)壽命(ming)較(jiao)(jiao)長，價(jia)格也越來越低。鋰電(dian)(dian)池(chi)(chi)對于(yu)(yu)充(chong)電(dian)(dian)器的要(yao)求比較(jiao)(jiao)苛(ke)刻(ke)，需要(yao)保(bao)護(hu)電(dian)(dian)路。為(wei)了有(you)效(xiao)利用(yong)電(dian)(dian)池(chi)(chi)容量，需將(jiang)鋰電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)至最(zui)大電(dian)(dian)壓(ya)，但是過(guo)壓(ya)充(chong)電(dian)(dian)會(hui)造成電(dian)(dian)池(chi)(chi)損壞，這就要(yao)求較(jiao)(jiao)高(gao)的控制精度(du)。另外，對于(yu)(yu)電(dian)(dian)壓(ya)過(guo)低的電(dian)(dian)池(chi)(chi)需要(yao)進行預(yu)充(chong)，充(chong)電(dian)(dian)器最(zui)好帶有(you)熱保(bao)護(hu)和時間(jian)保(bao)護(hu)，為(wei)電(dian)(dian)池(chi)(chi)提供附(fu)加(jia)保(bao)護(hu)。

一部好(hao)的(de)(de)(de)充(chong)電(dian)(dian)(dian)器不但(dan)能(neng)在短時(shi)間(jian)內將電(dian)(dian)(dian)量充(chong)足，而且還可(ke)以對電(dian)(dian)(dian)池起到一定的(de)(de)(de)維(wei)護作用(yong)，修復由(you)于使用(yong)不當造成的(de)(de)(de)記憶(yi)效應，即容量下(xia)降(電(dian)(dian)(dian)池活性衰退)現象。設計比(bi)較科學的(de)(de)(de)充(chong)電(dian)(dian)(dian)器往(wang)往(wang)采用(yong)專(zhuan)用(yong)充(chong)電(dian)(dian)(dian)控制芯(xin)(xin)片(pian)配合單(dan)片(pian)機控制的(de)(de)(de)方法。專(zhuan)用(yong)的(de)(de)(de)充(chong)電(dian)(dian)(dian)芯(xin)(xin)片(pian)具備業界公認較好(hao)的(de)(de)(de)-△v 檢(jian)測，可(ke)以檢(jian)測出電(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)飽和時(shi)發(fa)出的(de)(de)(de)電(dian)(dian)(dian)壓(ya)變化(hua)信號，比(bi)較精(jing)確地結束(shu)充(chong)電(dian)(dian)(dian)工作，通過(guo)單(dan)片(pian)機對這(zhe)些芯(xin)(xin)片(pian)的(de)(de)(de)控制，可(ke)以實現充(chong)電(dian)(dian)(dian)過(guo)程的(de)(de)(de)智能(neng)化(hua)，例如，在充(chong)電(dian)(dian)(dian)后(hou)增加及時(shi)關斷電(dian)(dian)(dian)源、蜂鳴報警和液晶(jing)顯示等功能(neng)。充(chong)電(dian)(dian)(dian)器的(de)(de)(de)智能(neng)化(hua)可(ke)以縮短充(chong)電(dian)(dian)(dian)的(de)(de)(de)時(shi)間(jian)，同時(shi)能(neng)夠維(wei)護電(dian)(dian)(dian)池，延長電(dian)(dian)(dian)池使用(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(chi)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。在選擇具體的電池充電芯片(pian)時，需要參考以下標準(zhun)。

1)電(dian)(dian)池(chi)(chi)類型(xing)：不同(tong)的(de)電(dian)(dian)池(chi)(chi)(鋰電(dian)(dian)池(chi)(chi)、鎳氫電(dian)(dian)池(chi)(chi)、鎳鎘(ge)電(dian)(dian)池(chi)(chi)等)需選擇(ze)不同(tong)的(de)充(chong)電(dian)(dian)芯片。

2)電池數目：可充電池的數目。

3)電(dian)流值：充電(dian)電(dian)流的大小決定了充電(dian)時間。

4)充電方式：是快(kuai)充、慢(man)充還是可(ke)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(qiu)充電快速且(qie)具有優(you)良的(de)電池保(bao)護能力，據此(ci)選擇Maxim 公(gong)司的(de)MAXl898 作為電池充電芯片。

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(jing)確(que)的恒(heng)(heng)流(liu)(liu)/恒(heng)(heng)壓充(chong)電(dian)(dian)，電(dian)(dian)池電(dian)(dian)壓調節精(jing)度(du)為±0.75％，提高了電(dian)(dian)池性能(neng)并延(yan)長了電(dian)(dian)池使用(yong)壽命。充(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)可(ke)由用(yong)戶(hu)設定(ding)，采用(yong)內部(bu)檢流(liu)(liu)，無須(xu)(xu)外(wai)部(bu)檢流(liu)(liu)電(dian)(dian)阻。 MAXl898 提供了充(chong)電(dian)(dian)狀態的輸出指示、輸入電(dian)(dian)源(yuan)是否與充(chong)電(dian)(dian)器連接的輸出指示和充(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)指示。MAXl898 還具(ju)有其他一些(xie)功能(neng)，包括輸入關(guan)斷控制、可(ke)選的充(chong)電(dian)(dian)周期重啟(qi)(無須(xu)(xu)重新上電(dian)(dian))、可(ke)選的充(chong)電(dian)(dian)終(zhong)止安全定(ding)時器和過(guo)放電(dian)(dian)電(dian)(dian)池的低電(dian)(dian)流(liu)(liu)預(yu)充(chong)。

MAXl898 的(de)關鍵(jian)特性如(ru)下(xia)：

1)    簡單、安全的線性充電方式(shi)。

2)    使(shi)用低成本的PNP 或PMOS 調整元件(jian)。

3)    輸入(ru)電壓：4.5～12V。

4)    內置(zhi)檢流電(dian)阻。

5)    ±0.75％電壓(ya)精度。

6)    可(ke)編(bian)程充(chong)電(dian)電(dian)流。

7)    輸入電(dian)源自動檢測。

8)    LED 充電狀態(tai)指示。

9)    可編程(cheng)安全定時(shi)器(qi)。

10)  檢流監視輸出。

11)  可選/可調節(jie)自動(dong)重啟。

12)  小尺(chi)寸uMAX 封裝。

2.2.3 MAX1898 的充(chong)電工作原理

充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯片MAXl898 的(de)(de)(de)(de)內部(bu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)包(bao)括輸(shu)(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)調(diao)節器(qi)(qi)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓檢(jian)測(ce)(ce)器(qi)(qi)、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)檢(jian)測(ce)(ce)器(qi)(qi)、定(ding)時(shi)器(qi)(qi)、溫度檢(jian)測(ce)(ce)器(qi)(qi)和主控(kong)制(zhi)器(qi)(qi)。輸(shu)(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)調(diao)節器(qi)(qi)用于(yu)限制(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)總輸(shu)(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，包(bao)括系(xi)(xi)統負(fu)載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)與(yu)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)。當檢(jian)測(ce)(ce)到(dao)輸(shu)(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)大于(yu)設定(ding)的(de)(de)(de)(de)門限電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)時(shi)，通過(guo)降低充(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)從而控(kong)制(zhi)輸(shu)(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)。因(yin)為系(xi)(xi)統工作時(shi)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)的(de)(de)(de)(de)變化范(fan)圍(wei)較(jiao)大，如果充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)沒有(you)輸(shu)(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)檢(jian)測(ce)(ce)功(gong)能(neng)，則輸(shu)(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)必須能(neng)夠提(ti)供(gong)(gong)最大負(fu)載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)與(yu)最大充(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)之(zhi)和，這將使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)成(cheng)本增(zeng)高、體積增(zeng)大，而利用輸(shu)(shu)(shu)入(ru)限流(liu)功(gong)能(neng)則能(neng)夠降低充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)對直流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)要求，同時(shi)也簡化了輸(shu)(shu)(shu)入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)設計(ji)。 MAXl898 外接限流(liu)型(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)源(yuan)和P 溝道(dao)場(chang)效應管，可(ke)以(yi)(yi)對單節鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池進(jin)行安全有(you)效的(de)(de)(de)(de)快充(chong)(chong)，其最大特點是：在不使(shi)用電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感的(de)(de)(de)(de)情況下，仍能(neng)做到(dao)很(hen)低的(de)(de)(de)(de)功(gong)率(lv)耗散(san)，可(ke)以(yi)(yi)實(shi)現(xian)預充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，具有(you)過(guo)壓保護和溫度保護功(gong)能(neng)，最長充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)問的(de)(de)(de)(de)限制(zhi)可(ke)為鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池提(ti)供(gong)(gong)二次保護。MAX1898 的(de)(de)(de)(de)浮(fu)動方(fang)式(shi)能(neng)夠使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池容量充(chong)(chong)至(zhi)最大。

當充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源和(he)電(dian)(dian)(dian)(dian)池(chi)(chi)在正常的(de)(de)工(gong)作溫(wen)度(du)范圍內時，插入電(dian)(dian)(dian)(dian)池(chi)(chi)將啟動(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)條件是平均的(de)(de)脈(mo)沖充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流達到快充(chong)(chong)電(dian)(dian)(dian)(dian)流的(de)(de) 1％，或時間超出片上預置的(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)時間。MAXl898 能(neng)夠(gou)自動(dong)檢測(ce)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源，沒有電(dian)(dian)(dian)(dian)源時自動(dong)關(guan)斷(duan)以(yi)減(jian)少電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)漏(lou)電(dian)(dian)(dian)(dian)。啟動(dong)快充(chong)(chong)后打(da)開外接的(de)(de)P 型(xing)(xing)場效應管，當檢測(ce)到電(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)壓達到設定的(de)(de)門(men)限時進入脈(mo)沖充(chong)(chong)電(dian)(dian)(dian)(dian)方(fang)式(shi)，P 型(xing)(xing)場效應管打(da)開的(de)(de)時問會(hui)越來越短。充(chong)(chong)電(dian)(dian)(dian)(dian)結束時，指(zhi)示燈將會(hui)按12%的(de)(de)周期(qi)閃爍，MAX1898 的(de)(de)典型(xing)(xing)充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)路如下圖圖2-1所示電(dian)(dian)(dian)(dian)路具體說(shuo)明如下。

圖2-1  MAX1898的典(dian)型充電電路

1）輸(shu)入電壓(ya)范圍為 4.5～12v。鋰電池要求(qiu)的充電方式(shi)是恒流(liu)恒壓(ya)方式(shi)，電源的輸(shu)入需要采(cai)用恒流(liu)恒壓(ya)源，一般可(ke)采(cai)用直流(liu)電源外加變壓(ya)器。

2)通過(guo)外接的場效應管提(ti)供鋰電(dian)池的充電(dian)接口。

3)通過外(wai)接的電(dian)容(rong) CcT 來設(she)置充(chong)電(dian)時(shi)間(jian) tCHG。這(zhe)里的充(chong)電(dian)時(shi)間(jian)指的是快充(chong)時(shi)的最大充(chong)電(dian)時(shi)間(jian)，它和(he)定時(shi)電(dian)容(rong)CcT 的關(guan)系如(ru)下(xia)式所示：

CcT=34.33×tCHG                                                  (2-1)

式中，tCHG 的單(dan)位為小時(shi)，CcT 的單(dan)位為Nf。大(da)多數情況下(xia)，快充(chong)時(shi)最(zui)大(da)充(chong)電時(shi)問(wen)不超(chao)過3 小時(shi)，因此常取CcT 為100nF。

4)在(zai)限(xian)制電(dian)流的(de)(de)模式(shi)下，通(tong)過外(wai)接(jie)的(de)(de)電(dian)阻 RSET 來設(she)置最(zui)大充電(dian)電(dian)IFSTCHG，關系如下式(shi)所(suo)示：IFSTCHG=1400/Rset 式(shi)中(zhong)，RSEI-的(de)(de)單(dan)位為Q，IFSTCHG 的(de)(de)單(dan)位為A。

當充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源(yuan)(yuan)和(he)電(dian)(dian)(dian)(dian)池(chi)在(zai)正常的(de)(de)工作溫度范(fan)圍內時(shi)，插入(ru)電(dian)(dian)(dian)(dian)池(chi)將啟(qi)動一次(ci)充(chong)電(dian)(dian)(dian)(dian)過程。平均(jun)的(de)(de)脈(mo)(mo)沖(chong)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流低于設置(zhi)的(de)(de)快充(chong)電(dian)(dian)(dian)(dian)流的(de)(de)20％，或者(zhe)充(chong)電(dian)(dian)(dian)(dian)時(shi)間超(chao)出(chu)片(pian)上預(yu)置(zhi)的(de)(de)最大充(chong)電(dian)(dian)(dian)(dian)時(shi)問時(shi)，充(chong)電(dian)(dian)(dian)(dian)周期(qi)結束(shu)。MAXl898 能(neng)夠自動檢(jian)測充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源(yuan)(yuan)，沒有(you)電(dian)(dian)(dian)(dian)源(yuan)(yuan)時(shi)自動關斷以減少電(dian)(dian)(dian)(dian)池(chi)的(de)(de)漏電(dian)(dian)(dian)(dian)。啟(qi)動快充(chong)后，打(da)開外接的(de)(de)P 型場(chang)效應管(guan)，當檢(jian)測到電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓達到設定的(de)(de)門限時(shi)進入(ru)脈(mo)(mo)沖(chong)充(chong)電(dian)(dian)(dian)(dian)方(fang)式，P 型場(chang)效應管(guan)打(da)開的(de)(de)時(shi)JI 間會(hui)(hui)越(yue)來越(yue)短。充(chong)電(dian)(dian)(dian)(dian)結束(shu)時(shi)，LED 指示燈將會(hui)(hui)呈現周期(qi)性的(de)(de)閃(shan)爍(shuo)，具體的(de)(de)閃(shan)爍(shuo)含(han)義如表1所示。

表2-

1  MAX1898 典(dian)型充電電路的(de)LED 指示燈狀態說明

充電狀態
LED指示燈電池或充電器沒(mei)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)  系統主要(yao)硬件電(dian)路設計

   硬件電路設計主要圍繞充電芯片MAXl898 展開，而單片機控制部分的電路簡單。

3.1  主(zhu)要器件

本設計的核心器件(jian)是MAXl898。MAXl898 可(ke)對(dui)所有化學類型的Li+電池(chi)進行(xing)安全(quan)充電，它具有高集成(cheng)度，在(zai)小尺寸(cun)內集成(cheng)了更多(duo)功能，盡可(ke)能多(duo)地覆蓋了基本應用電路，只需(xu)要(yao)少數外部(bu)元件(jian)。MAXl898 為10 引腳(jiao)、超(chao)薄型的MAX 封(feng)裝，其引腳(jiao)分布如圖3-1 所示：

圖3-1 MAXl898引腳分布(bu)

其引腳功能如下：

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

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

EN/OK(3 腳)：使能輸(shu)(shu)(shu)入(ru)腳/輸(shu)(shu)(shu)入(ru)電(dian)源“好”輸(shu)(shu)(shu)出指示(shi)(shi)腳。EN 為(wei)輸(shu)(shu)(shu)入(ru)腳，可以(yi)通過輸(shu)(shu)(shu)入(ru)禁止芯片工作(zuo)；OK 為(wei)輸(shu)(shu)(shu)出腳，用于指示(shi)(shi)輸(shu)(shu)(shu)入(ru)電(dian)源是否與(yu)充電(dian)器連(lian)接；

ISET(4 腳(jiao))：充電電流調節(jie)引腳(jiao)。通過串(chuan)接一個電阻到地(di)來設置(zhi)最大(da)充電電流；

CT(5 腳)：安(an)全充電時間設(she)置(zhi)引(yin)腳。接(jie)一個時間電容來設(she)置(zhi)充電時間，電容為(wei) 100nF 時，幾乎為(wei)3 個小時，此(ci)(ci)引(yin)腳直(zhi)接(jie)接(jie)地將(jiang)禁用(yong)此(ci)(ci)功能；

RSTRT(6 腳(jiao))：自(zi)動(dong)(dong)(dong)重(zhong)新啟(qi)動(dong)(dong)(dong)控制引(yin)腳(jiao)。當此引(yin)腳(jiao)直接(jie)接(jie)地時，如果電池電壓(ya)掉至基準電壓(ya)閾值以(yi)下 200mV，將(jiang)會重(zhong)新開始一(yi)輪充電周期。此引(yin)腳(jiao)通過電阻接(jie)地時，可以(yi)降低(di)它的電壓(ya)閾值。此引(yin)腳(jiao)懸(xuan)空或(huo)者 CT 引(yin)腳(jiao)接(jie)地(充電時間設置功能禁用(yong))時，自(zi)動(dong)(dong)(dong)重(zhong)新啟(qi)動(dong)(dong)(dong)功能被(bei)禁用(yong)；

BATT(7 腳)：電池傳感(gan)輸入腳，接單個(ge) Li+電池的正極。此引(yin)腳需(xu)旁接一個(ge)大電解電容到地；

GND(8 腳)：接地端(duan)；

DRV(9 腳)：外部晶體(ti)管(guan)驅(qu)動器，接晶體(ti)管(guan)的基極(ji)；

CS(10 腳(jiao))：電流傳感(gan)輸(shu)入，接(jie)晶體管的發射(she)極。

本(ben)設計的單(dan)片機芯片選用Atmel 公司(si)的AT89C52，它完全可以滿足要(yao)求。

另(ling)外，由于充(chong)電(dian)器外部(bu)為+12V 供電(dian)，因此需(xu)要通過電(dian)壓轉換(huan)芯片(pian)將+12V 電(dian)壓轉換(huan)為 +5V 電(dian)壓，這(zhe)里選用三端(duan)電(dian)壓轉換(huan)芯片(pian)LM7805 來完成(cheng)此功能。

為了降(jiang)低電源干(gan)擾(rao)，保持電路的(de)(de)穩定，在LM7805 完(wan)成(cheng)電壓(ya)轉換，將(jiang)+5v 充電電源送給 MAXl898 之前，先經(jing)過一(yi)次光耦模(mo)(mo)塊 6N137 的(de)(de)處(chu)理(li)，通過單(dan)片機對光耦模(mo)(mo)塊的(de)(de)控制，可以及時關斷充電電源。6N137 的(de)(de)引腳分布如圖3-2 所示：

圖(tu)3-2  6N137 的引(yin)腳分(fen)布

其引腳功能如下：

NC(1 腳(jiao)(jiao)、4 腳(jiao)(jiao))：懸空；

+(2 腳)、-(3 腳)：發(fa)光二極管的正(zheng)、負極；

GND(5 腳)：接地端；

OUTPUT(6 腳(jiao))：輸出腳(jiao)；

EN(7 腳)：使能腳。為低時，無(wu)論有(you)無(wu)輸入，輸出都為高。

不使(shi)用(yong)時，懸(xuan)空即可(ke)；

VCC(8 腳(jiao))：電(dian)源輸入(ru)腳(jiao)。

3.2  電路原理圖(tu)及說明

硬件(jian)電(dian)(dian)路由(you)單(dan)片(pian)機(ji)電(dian)(dian)路、電(dian)(dian)壓(ya)轉換及光耦隔離電(dian)(dian)路、充電(dian)(dian)控制電(dian)(dian)路3 部(bu)分組成。單(dan)片(pian)機(ji)部(bu)分的電(dian)(dian)路原理圖(tu)如下圖(tu)3-3 所(suo)示。

圖3-3  單(dan)片(pian)機部分的電路原(yuan)理圖

圖3-3中，ul 為單(dan)片機AT89C52，工作在11．0592MHz 時鐘；u2 為蜂鳴器，蜂鳴器由(you)(you)單(dan)片機的(de)P2．1 腳控制(zhi)發(fa)出報警聲提示；單(dan)片機的(de)P2．O 腳輸出控制(zhi)光耦器件(jian)，在需要的(de)時候可以及時關斷充(chong)電(dian)電(dian)源；單(dan)片機的(de)外(wai)部中斷O 由(you)(you)充(chong)電(dian)芯片MAXl898 的(de)充(chong)電(dian)狀(zhuang)態輸出信號/ CHG 經過(guo)反相(xiang)后觸發(fa)。

下圖3-4 所示的(de)為電壓轉換(huan)及(ji)光耦(ou)隔離(li)部分電路(lu)的(de)原理圖。