充電(dian)器為人們的(de)(de)外出和(he)出差辦公提供了極大的(de)(de)方(fang)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(shou)機在世界范圍內的普及使用，手(shou)機電池充電器的使用也越來(lai)越廣泛。

本次設計將(jiang)通過一(yi)個典型的勢力介紹(shao)51單(dan)片(pian)機在實現手機電(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)器方面的應用(yong)。設計所實現的充(chong)(chong)電(dian)(dian)(dian)(dian)器是一(yi)種智能充(chong)(chong)電(dian)(dian)(dian)(dian)器，它在單(dan)片(pian)機的控制下，具有預充(chong)(chong)、充(chong)(chong)電(dian)(dian)(dian)(dian)保護、自(zi)動斷電(dian)(dian)(dian)(dian)和(he)充(chong)(chong)電(dian)(dian)(dian)(dian)完成報警提示(shi)功能。

1.3  本設計功能模塊
本(ben)設計的功能模塊(kuai)主(zhu)要(yao)如下：

1）單片機模塊：實現充電(dian)(dian)器的智能化控制(zhi)。比如自動(dong)斷電(dian)(dian)、充電(dian)(dian)完(wan)成報警(jing)提示(shi)等(deng)。

2）充(chong)電(dian)過程控(kong)制模塊：采(cai)用專(zhuan)用的電(dian)池充(chong)電(dian)芯(xin)片實現充(chong)電(dian)過程的控(kong)制。

3）充(chong)電(dian)電(dian)壓(ya)提供模(mo)塊：采用電(dian)壓(ya)轉換(huan)芯片將外部+12V電(dian)壓(ya)轉換(huan)為(wei)需要的+5V電(dian)壓(ya)。

4）C51程(cheng)序：單片(pian)(pian)機(ji)控制電池(chi)充電芯片(pian)(pian)實現充電過程(cheng)的(de)自動化，并根據充電的(de)狀態給出有關的(de)輸出指示。

第2節  系統設計思路分析
充電的實現，它包括兩部分(fen)：一是充電過程的控制；二是需要提(ti)供基本的充電電壓。

2.1 智能化的實現
在充電(dian)器電(dian)路(lu)中(zhong)引(yin)入單(dan)片機(ji)的控制。它為什么需要實現充電(dian)器的智能化呢？

充電(dian)(dian)(dian)器(qi)(qi)實現的(de)方(fang)式不同會導致充電(dian)(dian)(dian)效果(guo)的(de)不同。由于充電(dian)(dian)(dian)器(qi)(qi)多采用(yong)大電(dian)(dian)(dian)流(liu)的(de)快(kuai)速(su)充電(dian)(dian)(dian)法(fa)(fa)，在電(dian)(dian)(dian)池充滿后如果(guo)不及時停止(zhi)會使電(dian)(dian)(dian)池發燙，過(guo)(guo)度(du)的(de)充電(dian)(dian)(dian)會嚴(yan)重損害電(dian)(dian)(dian)池的(de)壽(shou)命。一(yi)些低成本的(de)充電(dian)(dian)(dian)器(qi)(qi)采用(yong)電(dian)(dian)(dian)壓(ya)比較法(fa)(fa)，為了防(fang)止(zhi)過(guo)(guo)充，一(yi)般充電(dian)(dian)(dian)到90％就停止(zhi)大電(dian)(dian)(dian)流(liu)快(kuai)充，而采用(yong)小電(dian)(dian)(dian)流(liu)涓流(liu)補充充電(dian)(dian)(dian)。

手機(ji)電(dian)(dian)(dian)(dian)池(chi)的(de)(de)使用(yong)(yong)(yong)壽命和(he)單次(ci)使用(yong)(yong)(yong)時(shi)間與充電(dian)(dian)(dian)(dian)過程密切相關。鋰電(dian)(dian)(dian)(dian)池(chi)是手機(ji)最為常用(yong)(yong)(yong)的(de)(de)一(yi)種(zhong)電(dian)(dian)(dian)(dian)池(chi)，它(ta)具(ju)有較高(gao)的(de)(de)能量(liang)(liang)重量(liang)(liang)比、能量(liang)(liang)體積比，具(ju)有記憶效(xiao)應，可(ke)重復(fu)充電(dian)(dian)(dian)(dian)多(duo)次(ci)，使用(yong)(yong)(yong)壽命較長，價(jia)格也越來(lai)越低(di)。鋰電(dian)(dian)(dian)(dian)池(chi)對于充電(dian)(dian)(dian)(dian)器(qi)的(de)(de)要(yao)求(qiu)比較苛(ke)刻(ke)，需要(yao)保(bao)護(hu)電(dian)(dian)(dian)(dian)路。為了(le)有效(xiao)利用(yong)(yong)(yong)電(dian)(dian)(dian)(dian)池(chi)容(rong)量(liang)(liang)，需將鋰電(dian)(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)(dian)至最大電(dian)(dian)(dian)(dian)壓(ya)，但是過壓(ya)充電(dian)(dian)(dian)(dian)會造成(cheng)電(dian)(dian)(dian)(dian)池(chi)損壞，這(zhe)就(jiu)要(yao)求(qiu)較高(gao)的(de)(de)控制精度。另外，對于電(dian)(dian)(dian)(dian)壓(ya)過低(di)的(de)(de)電(dian)(dian)(dian)(dian)池(chi)需要(yao)進行預充，充電(dian)(dian)(dian)(dian)器(qi)最好帶(dai)有熱保(bao)護(hu)和(he)時(shi)間保(bao)護(hu)，為電(dian)(dian)(dian)(dian)池(chi)提(ti)供附(fu)加保(bao)護(hu)。

一部好的(de)(de)(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)不但(dan)能(neng)在(zai)短時間內(nei)將電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)量(liang)充(chong)(chong)足，而且還可(ke)以對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池起到一定的(de)(de)(de)(de)(de)維(wei)護作用(yong)(yong)(yong)(yong)，修復由于使用(yong)(yong)(yong)(yong)不當造成的(de)(de)(de)(de)(de)記(ji)憶效應，即容(rong)量(liang)下降(電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池活性衰退)現象。設(she)計比(bi)較科學(xue)的(de)(de)(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)往往采用(yong)(yong)(yong)(yong)專用(yong)(yong)(yong)(yong)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)控制(zhi)芯(xin)(xin)片(pian)配合單片(pian)機控制(zhi)的(de)(de)(de)(de)(de)方法。專用(yong)(yong)(yong)(yong)的(de)(de)(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯(xin)(xin)片(pian)具備業(ye)界公認較好的(de)(de)(de)(de)(de)-△v 檢測(ce)，可(ke)以檢測(ce)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)飽和時發出的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓變化信號，比(bi)較精確(que)地(di)結束充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)工作，通過(guo)單片(pian)機對這些芯(xin)(xin)片(pian)的(de)(de)(de)(de)(de)控制(zhi)，可(ke)以實現充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程的(de)(de)(de)(de)(de)智(zhi)(zhi)能(neng)化，例(li)如(ru)，在(zai)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)后增(zeng)加及時關斷電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源、蜂鳴報警和液晶顯示(shi)等功能(neng)。充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)的(de)(de)(de)(de)(de)智(zhi)(zhi)能(neng)化可(ke)以縮短充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)(de)時間，同時能(neng)夠(gou)維(wei)護電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池，延(yan)長電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池使用(yong)(yong)(yong)(yong)壽命。

2.2 電池充電芯片的選擇
2.2.1 如(ru)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)具體的電池充電芯片時(shi)，需要參考以下標準(zhun)。

1)電池(chi)類型(xing)：不同(tong)的電池(chi)(鋰電池(chi)、鎳氫(qing)電池(chi)、鎳鎘電池(chi)等)需選(xuan)擇不同(tong)的充(chong)電芯(xin)片。

2)電池數目：可充電池的數目。

3)電流值：充電電流的大小決定了充電時間。

4)充電方(fang)式：是快(kuai)充、慢充還(huan)是可控充電過程。

本設計要實現的是手機的單節鋰離子電池充電器，要(yao)求充電(dian)快(kuai)速且具(ju)有優良的(de)電(dian)池保護能力，據此選(xuan)擇Maxim 公(gong)司的(de)MAXl898 作(zuo)為電(dian)池充電(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(ti)供(gong)精確的(de)恒(heng)流(liu)/恒(heng)壓充電(dian)(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓調節(jie)精度為±0.75％，提(ti)高(gao)了電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)性能并延長了電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)使(shi)用(yong)壽命。充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)可(ke)由用(yong)戶設定，采用(yong)內部(bu)檢(jian)流(liu)，無須(xu)外部(bu)檢(jian)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)阻。 MAXl898 提(ti)供(gong)了充電(dian)(dian)(dian)(dian)(dian)(dian)狀態的(de)輸(shu)出(chu)指示(shi)、輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)源是否與(yu)充電(dian)(dian)(dian)(dian)(dian)(dian)器連接的(de)輸(shu)出(chu)指示(shi)和充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)指示(shi)。MAXl898 還具有其他一(yi)些功能，包括輸(shu)入關(guan)斷控(kong)制、可(ke)選(xuan)的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)周期重啟(qi)(無須(xu)重新(xin)上電(dian)(dian)(dian)(dian)(dian)(dian))、可(ke)選(xuan)的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)終止安全定時器和過放電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)低電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)預(yu)充。

MAXl898 的關鍵特性如(ru)下：

1)    簡單、安全的線性充電(dian)方式。

2)    使用低成本的PNP 或PMOS 調整元(yuan)件。

3)    輸入電壓：4.5～12V。

4)    內置檢流電阻。

5)    ±0.75％電壓(ya)精度。

6)    可編程充電(dian)電(dian)流。

7)    輸入電源自動檢測。

8)    LED 充電狀態指示。

9)    可編程(cheng)安全(quan)定時器。

10)  檢流監視輸出。

11)  可選/可調節自動(dong)重啟(qi)。

12)  小(xiao)尺寸uMAX 封(feng)裝。

2.2.3 MAX1898 的充電工作原理

充(chong)電(dian)(dian)(dian)芯片MAXl898 的(de)(de)(de)內部電(dian)(dian)(dian)路(lu)包括(kuo)輸(shu)(shu)入(ru)電(dian)(dian)(dian)流(liu)調(diao)節器(qi)(qi)、電(dian)(dian)(dian)壓檢測器(qi)(qi)、充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)檢測器(qi)(qi)、定(ding)時(shi)(shi)器(qi)(qi)、溫度(du)檢測器(qi)(qi)和主控(kong)制器(qi)(qi)。輸(shu)(shu)入(ru)電(dian)(dian)(dian)流(liu)調(diao)節器(qi)(qi)用(yong)于限制電(dian)(dian)(dian)源(yuan)的(de)(de)(de)總輸(shu)(shu)入(ru)電(dian)(dian)(dian)流(liu)，包括(kuo)系(xi)統負載(zai)電(dian)(dian)(dian)流(liu)與充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)。當檢測到輸(shu)(shu)入(ru)電(dian)(dian)(dian)流(liu)大(da)(da)(da)于設定(ding)的(de)(de)(de)門限電(dian)(dian)(dian)流(liu)時(shi)(shi)，通過降低充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)從而控(kong)制輸(shu)(shu)入(ru)電(dian)(dian)(dian)流(liu)。因為系(xi)統工作時(shi)(shi)電(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)流(liu)的(de)(de)(de)變化范(fan)圍(wei)較(jiao)大(da)(da)(da)，如(ru)果充(chong)電(dian)(dian)(dian)器(qi)(qi)沒有(you)輸(shu)(shu)入(ru)電(dian)(dian)(dian)流(liu)檢測功(gong)能(neng)，則輸(shu)(shu)入(ru)電(dian)(dian)(dian)源(yuan)必須能(neng)夠(gou)(gou)提供(gong)最(zui)(zui)大(da)(da)(da)負載(zai)電(dian)(dian)(dian)流(liu)與最(zui)(zui)大(da)(da)(da)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)之和，這將使(shi)電(dian)(dian)(dian)源(yuan)的(de)(de)(de)成本增高、體積增大(da)(da)(da)，而利用(yong)輸(shu)(shu)入(ru)限流(liu)功(gong)能(neng)則能(neng)夠(gou)(gou)降低充(chong)電(dian)(dian)(dian)器(qi)(qi)對(dui)直流(liu)電(dian)(dian)(dian)源(yuan)的(de)(de)(de)要求，同(tong)時(shi)(shi)也簡化了輸(shu)(shu)入(ru)電(dian)(dian)(dian)源(yuan)的(de)(de)(de)設計(ji)。 MAXl898 外接限流(liu)型(xing)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)和P 溝(gou)道(dao)場(chang)效應管，可(ke)以對(dui)單節鋰(li)電(dian)(dian)(dian)池(chi)進行安全有(you)效的(de)(de)(de)快充(chong)，其(qi)最(zui)(zui)大(da)(da)(da)特點是：在(zai)不使(shi)用(yong)電(dian)(dian)(dian)感的(de)(de)(de)情況下，仍能(neng)做到很低的(de)(de)(de)功(gong)率(lv)耗散，可(ke)以實(shi)現預(yu)充(chong)電(dian)(dian)(dian)，具有(you)過壓保護和溫度(du)保護功(gong)能(neng)，最(zui)(zui)長充(chong)電(dian)(dian)(dian)時(shi)(shi)問的(de)(de)(de)限制可(ke)為鋰(li)電(dian)(dian)(dian)池(chi)提供(gong)二次保護。MAX1898 的(de)(de)(de)浮動方(fang)式能(neng)夠(gou)(gou)使(shi)電(dian)(dian)(dian)池(chi)容量充(chong)至最(zui)(zui)大(da)(da)(da)。

當充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源和電(dian)(dian)(dian)(dian)池(chi)在正常的(de)工(gong)作溫(wen)度范圍內時(shi)(shi)(shi)，插(cha)入(ru)電(dian)(dian)(dian)(dian)池(chi)將啟動(dong)一次(ci)充電(dian)(dian)(dian)(dian)過程；充電(dian)(dian)(dian)(dian)結(jie)(jie)束的(de)條件是平均的(de)脈(mo)沖(chong)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流達(da)(da)到(dao)快充電(dian)(dian)(dian)(dian)流的(de) 1％，或時(shi)(shi)(shi)間(jian)(jian)超出片(pian)上預置的(de)充電(dian)(dian)(dian)(dian)時(shi)(shi)(shi)間(jian)(jian)。MAXl898 能(neng)夠自(zi)動(dong)檢測充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源，沒有電(dian)(dian)(dian)(dian)源時(shi)(shi)(shi)自(zi)動(dong)關(guan)斷(duan)以減少(shao)電(dian)(dian)(dian)(dian)池(chi)的(de)漏電(dian)(dian)(dian)(dian)。啟動(dong)快充后打開外接(jie)的(de)P 型場效應(ying)管，當檢測到(dao)電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓達(da)(da)到(dao)設定的(de)門(men)限時(shi)(shi)(shi)進入(ru)脈(mo)沖(chong)充電(dian)(dian)(dian)(dian)方式，P 型場效應(ying)管打開的(de)時(shi)(shi)(shi)問會越(yue)來越(yue)短。充電(dian)(dian)(dian)(dian)結(jie)(jie)束時(shi)(shi)(shi)，指示(shi)燈將會按(an)12%的(de)周期閃爍(shuo)，MAX1898 的(de)典型充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)路(lu)如下圖圖2-1所(suo)示(shi)電(dian)(dian)(dian)(dian)路(lu)具體(ti)說明如下。

圖(tu)2-1  MAX1898的典型充電(dian)電(dian)路

1）輸(shu)入(ru)電(dian)(dian)壓范圍為(wei) 4.5～12v。鋰電(dian)(dian)池要求的充電(dian)(dian)方式(shi)是恒流恒壓方式(shi)，電(dian)(dian)源的輸(shu)入(ru)需要采用恒流恒壓源，一般可(ke)采用直流電(dian)(dian)源外加變壓器。

2)通過外接的(de)(de)場(chang)效應管(guan)提(ti)供鋰電(dian)池的(de)(de)充電(dian)接口。

3)通過(guo)外接的(de)電容 CcT 來設置充(chong)電時間(jian) tCHG。這(zhe)里(li)的(de)充(chong)電時間(jian)指(zhi)的(de)是快充(chong)時的(de)最大充(chong)電時間(jian)，它和定時電容CcT 的(de)關系如下式所(suo)示(shi)：

CcT=34.33×tCHG                                                  (2-1)

式中，tCHG 的單位(wei)為小時，CcT 的單位(wei)為Nf。大多(duo)數情(qing)況下，快充時最大充電時問不(bu)超過3 小時，因(yin)此常取(qu)CcT 為100nF。

4)在(zai)限制(zhi)電(dian)流的模式下，通過外接的電(dian)阻 RSET 來(lai)設置最大充電(dian)電(dian)IFSTCHG，關(guan)系如(ru)下式所示：IFSTCHG=1400/Rset 式中，RSEI-的單位(wei)為Q，IFSTCHG 的單位(wei)為A。

當(dang)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)源和電(dian)(dian)(dian)(dian)(dian)池在正常的(de)(de)(de)(de)工作溫(wen)度范圍內(nei)時(shi)(shi)，插入電(dian)(dian)(dian)(dian)(dian)池將啟動(dong)一次充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)過程。平均(jun)的(de)(de)(de)(de)脈沖充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)低于設(she)置(zhi)的(de)(de)(de)(de)快充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)20％，或者充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)(shi)間超出片上預置(zhi)的(de)(de)(de)(de)最大充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)(shi)問時(shi)(shi)，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)周(zhou)(zhou)期結束。MAXl898 能夠自(zi)動(dong)檢測(ce)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)源，沒有(you)電(dian)(dian)(dian)(dian)(dian)源時(shi)(shi)自(zi)動(dong)關(guan)斷以減少電(dian)(dian)(dian)(dian)(dian)池的(de)(de)(de)(de)漏電(dian)(dian)(dian)(dian)(dian)。啟動(dong)快充(chong)(chong)后，打開(kai)外(wai)接的(de)(de)(de)(de)P 型場效應管，當(dang)檢測(ce)到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓達到(dao)(dao)設(she)定(ding)的(de)(de)(de)(de)門限(xian)時(shi)(shi)進入脈沖充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)方式，P 型場效應管打開(kai)的(de)(de)(de)(de)時(shi)(shi)JI 間會越(yue)來越(yue)短。充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)結束時(shi)(shi)，LED 指示(shi)燈將會呈現周(zhou)(zhou)期性的(de)(de)(de)(de)閃(shan)爍，具體(ti)的(de)(de)(de)(de)閃(shan)爍含義如表(biao)1所示(shi)。

表2-

1  MAX1898 典型充電電路的(de)LED 指示燈(deng)狀態說明

充電狀態
LED指(zhi)示燈電(dian)池(chi)或充電(dian)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(di)3節(jie)  系統主要硬(ying)件電路設計

   硬件(jian)電路(lu)設計主要圍繞充電芯片(pian)MAXl898 展開(kai)，而(er)單片(pian)機控制部分的電路(lu)簡單。

3.1  主要器件

本(ben)設計的(de)核心器件是MAXl898。MAXl898 可(ke)對所有化(hua)學類型的(de)Li+電(dian)池進行安全(quan)充電(dian)，它(ta)具有高集(ji)成度，在小尺寸內(nei)集(ji)成了(le)更多功能，盡可(ke)能多地(di)覆蓋了(le)基本(ben)應(ying)用電(dian)路，只需(xu)要少數外部(bu)元件。MAXl898 為10 引(yin)腳、超薄型的(de)MAX 封裝(zhuang)，其引(yin)腳分(fen)布如(ru)圖3-1 所示：

圖3-1 MAXl898引腳分布(bu)

其引腳功能如下：

IN(1 腳)：傳感輸入(ru)(ru)，檢測輸入(ru)(ru)的電壓(ya)或電流；

CHG(2 腳(jiao))：充電狀態(tai)指示(shi)腳(jiao)，同時驅動LED；

EN/OK(3 腳(jiao))：使能輸(shu)(shu)(shu)入腳(jiao)/輸(shu)(shu)(shu)入電(dian)源“好(hao)”輸(shu)(shu)(shu)出指示腳(jiao)。EN 為(wei)輸(shu)(shu)(shu)入腳(jiao)，可以通(tong)過輸(shu)(shu)(shu)入禁止芯片工(gong)作；OK 為(wei)輸(shu)(shu)(shu)出腳(jiao)，用于(yu)指示輸(shu)(shu)(shu)入電(dian)源是否與充電(dian)器連接；

ISET(4 腳(jiao))：充電電流調節引腳(jiao)。通過串(chuan)接一個電阻(zu)到地來設置最大充電電流；

CT(5 腳)：安全充電(dian)時(shi)(shi)間(jian)設置引腳。接一個(ge)時(shi)(shi)間(jian)電(dian)容(rong)來設置充電(dian)時(shi)(shi)間(jian)，電(dian)容(rong)為 100nF 時(shi)(shi)，幾乎為3 個(ge)小(xiao)時(shi)(shi)，此引腳直接接地將禁用此功能；

RSTRT(6 腳)：自動重新啟動控制引(yin)腳。當此引(yin)腳直接(jie)接(jie)地時，如(ru)果電(dian)(dian)池電(dian)(dian)壓(ya)掉至(zhi)基準電(dian)(dian)壓(ya)閾(yu)值以下 200mV，將(jiang)會重新開始一輪充(chong)電(dian)(dian)周期。此引(yin)腳通過(guo)電(dian)(dian)阻(zu)接(jie)地時，可以降低它(ta)的電(dian)(dian)壓(ya)閾(yu)值。此引(yin)腳懸空或者(zhe) CT 引(yin)腳接(jie)地(充(chong)電(dian)(dian)時間設置(zhi)功能禁用)時，自動重新啟動功能被禁用；

BATT(7 腳(jiao))：電(dian)池(chi)傳感輸入腳(jiao)，接單個(ge) Li+電(dian)池(chi)的正極(ji)。此引腳(jiao)需旁接一個(ge)大電(dian)解電(dian)容到地；

GND(8 腳)：接地端；

DRV(9 腳(jiao))：外部(bu)晶體管(guan)驅動器，接晶體管(guan)的基極；

CS(10 腳)：電(dian)流傳感(gan)輸(shu)入，接晶(jing)體管的發射極。

本設計的(de)單片機芯片選(xuan)用Atmel 公司的(de)AT89C52，它完(wan)全可以滿足要(yao)求。

另(ling)外(wai)，由于充(chong)電(dian)(dian)器外(wai)部為+12V 供電(dian)(dian)，因此(ci)(ci)需要通過(guo)電(dian)(dian)壓(ya)轉換(huan)(huan)芯(xin)片(pian)將(jiang)+12V 電(dian)(dian)壓(ya)轉換(huan)(huan)為 +5V 電(dian)(dian)壓(ya)，這里選(xuan)用三(san)端電(dian)(dian)壓(ya)轉換(huan)(huan)芯(xin)片(pian)LM7805 來完成(cheng)此(ci)(ci)功能。

為了降(jiang)低電(dian)(dian)(dian)源(yuan)(yuan)干擾(rao)，保(bao)持電(dian)(dian)(dian)路的(de)穩(wen)定，在LM7805 完成(cheng)電(dian)(dian)(dian)壓(ya)轉換，將+5v 充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)(yuan)送(song)給 MAXl898 之前，先(xian)經過一(yi)次(ci)光耦模塊(kuai) 6N137 的(de)處理(li)，通過單片機(ji)對光耦模塊(kuai)的(de)控制，可以及時關(guan)斷充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)(yuan)。6N137 的(de)引腳(jiao)分布如(ru)圖3-2 所示：

圖3-2  6N137 的引腳分(fen)布

其引腳功能如下：

NC(1 腳、4 腳)：懸空；

+(2 腳)、-(3 腳)：發(fa)光二(er)極管(guan)的正、負極；

GND(5 腳)：接地端(duan)；

OUTPUT(6 腳)：輸出腳；

EN(7 腳)：使(shi)能腳。為(wei)低(di)時(shi)，無(wu)論(lun)有(you)無(wu)輸(shu)入(ru)，輸(shu)出都為(wei)高。

不使用時，懸空即可；

VCC(8 腳)：電源輸入腳。

3.2  電(dian)路原理圖及說明

硬(ying)件電(dian)(dian)(dian)(dian)路(lu)(lu)由單片(pian)(pian)機電(dian)(dian)(dian)(dian)路(lu)(lu)、電(dian)(dian)(dian)(dian)壓(ya)轉換(huan)及光耦隔離電(dian)(dian)(dian)(dian)路(lu)(lu)、充電(dian)(dian)(dian)(dian)控制電(dian)(dian)(dian)(dian)路(lu)(lu)3 部(bu)分(fen)組(zu)成。單片(pian)(pian)機部(bu)分(fen)的電(dian)(dian)(dian)(dian)路(lu)(lu)原理(li)圖如(ru)下圖3-3 所(suo)示(shi)。

圖3-3  單片機部(bu)分的電(dian)路(lu)原理圖

圖3-3中，ul 為(wei)單(dan)片(pian)機(ji)(ji)AT89C52，工作(zuo)在(zai)11．0592MHz 時(shi)鐘；u2 為(wei)蜂(feng)鳴(ming)器，蜂(feng)鳴(ming)器由(you)單(dan)片(pian)機(ji)(ji)的(de)P2．1 腳(jiao)控(kong)制(zhi)發(fa)出(chu)報警聲提示；單(dan)片(pian)機(ji)(ji)的(de)P2．O 腳(jiao)輸出(chu)控(kong)制(zhi)光(guang)耦器件，在(zai)需(xu)要的(de)時(shi)候可以(yi)及(ji)時(shi)關斷充電電源；單(dan)片(pian)機(ji)(ji)的(de)外部中斷O 由(you)充電芯片(pian)MAXl898 的(de)充電狀態(tai)輸出(chu)信號(hao)/ CHG 經過反相(xiang)后觸發(fa)。

下圖3-4 所示的為電(dian)(dian)壓轉換及光耦隔離部分電(dian)(dian)路的原理圖。