充電器(qi)為人們的(de)外出(chu)和出(chu)差辦公提供了極大的(de)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。

隨著手機在世(shi)界范圍內的普(pu)及使(shi)用，手機電(dian)池充電(dian)器的使(shi)用也越來越廣泛。

本次設計(ji)將(jiang)通(tong)過一(yi)個典型的勢力(li)介紹51單(dan)片(pian)機(ji)在實現手機(ji)電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)器方面的應用。設計(ji)所實現的充(chong)(chong)電(dian)(dian)器是一(yi)種(zhong)智能(neng)充(chong)(chong)電(dian)(dian)器，它在單(dan)片(pian)機(ji)的控(kong)制下(xia)，具有預充(chong)(chong)、充(chong)(chong)電(dian)(dian)保護、自(zi)動(dong)斷電(dian)(dian)和充(chong)(chong)電(dian)(dian)完成(cheng)報警提示功能(neng)。

1.3  本設計功能模塊
本設計的功能模塊主要(yao)如下：

1）單片機模塊：實現充電(dian)(dian)器的(de)智能化控制。比如自動(dong)斷電(dian)(dian)、充電(dian)(dian)完(wan)成報警提示等(deng)。

2）充電(dian)過(guo)程控(kong)制模塊：采(cai)用(yong)專用(yong)的電(dian)池充電(dian)芯片(pian)實現充電(dian)過(guo)程的控(kong)制。

3）充電(dian)電(dian)壓(ya)提供模塊：采用電(dian)壓(ya)轉換(huan)芯片(pian)將外部+12V電(dian)壓(ya)轉換(huan)為需要(yao)的+5V電(dian)壓(ya)。

4）C51程序：單(dan)片機控制電(dian)池充(chong)電(dian)芯片實(shi)現(xian)充(chong)電(dian)過程的(de)自動化(hua)，并根據充(chong)電(dian)的(de)狀態給出(chu)有(you)關(guan)的(de)輸(shu)出(chu)指示。

第2節  系統設計思路分析
充(chong)電(dian)(dian)的(de)(de)實(shi)現，它(ta)包(bao)括兩部(bu)分：一(yi)是(shi)充(chong)電(dian)(dian)過程的(de)(de)控制(zhi)；二是(shi)需要提供(gong)基本的(de)(de)充(chong)電(dian)(dian)電(dian)(dian)壓(ya)。

2.1 智能化的實現
在充(chong)電器(qi)電路(lu)中引入單片機(ji)的控制。它(ta)為什么需(xu)要實現充(chong)電器(qi)的智能化呢？

充(chong)(chong)電(dian)(dian)(dian)器實現的方式不同會(hui)導致充(chong)(chong)電(dian)(dian)(dian)效果的不同。由于充(chong)(chong)電(dian)(dian)(dian)器多采用(yong)大電(dian)(dian)(dian)流(liu)的快速充(chong)(chong)電(dian)(dian)(dian)法，在(zai)電(dian)(dian)(dian)池充(chong)(chong)滿(man)后如果不及時停止(zhi)會(hui)使電(dian)(dian)(dian)池發燙，過(guo)度的充(chong)(chong)電(dian)(dian)(dian)會(hui)嚴(yan)重損害電(dian)(dian)(dian)池的壽命。一(yi)些低成(cheng)本(ben)的充(chong)(chong)電(dian)(dian)(dian)器采用(yong)電(dian)(dian)(dian)壓比較法，為了防(fang)止(zhi)過(guo)充(chong)(chong)，一(yi)般(ban)充(chong)(chong)電(dian)(dian)(dian)到90％就(jiu)停止(zhi)大電(dian)(dian)(dian)流(liu)快充(chong)(chong)，而采用(yong)小電(dian)(dian)(dian)流(liu)涓流(liu)補充(chong)(chong)充(chong)(chong)電(dian)(dian)(dian)。

手機電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)使(shi)用壽(shou)命(ming)和(he)單次(ci)使(shi)用時間與充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)過(guo)程密切相關。鋰電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)是(shi)手機最為(wei)常用的(de)一(yi)種電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)，它具(ju)有較(jiao)高(gao)的(de)能量重量比、能量體(ti)積(ji)比，具(ju)有記憶效應，可重復充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)多次(ci)，使(shi)用壽(shou)命(ming)較(jiao)長，價格(ge)也越來越低。鋰電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)對(dui)于充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)的(de)要(yao)求(qiu)比較(jiao)苛刻，需要(yao)保(bao)護電(dian)(dian)(dian)(dian)(dian)路。為(wei)了(le)有效利用電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)容量，需將(jiang)鋰電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)至最大電(dian)(dian)(dian)(dian)(dian)壓(ya)，但是(shi)過(guo)壓(ya)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)會造成(cheng)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)損(sun)壞，這就要(yao)求(qiu)較(jiao)高(gao)的(de)控制精度。另外，對(dui)于電(dian)(dian)(dian)(dian)(dian)壓(ya)過(guo)低的(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)需要(yao)進行預充(chong)(chong)，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)(qi)最好帶有熱保(bao)護和(he)時間保(bao)護，為(wei)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)提供附(fu)加(jia)保(bao)護。

一部好的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器不但能在短時(shi)(shi)間(jian)(jian)內(nei)將電(dian)(dian)(dian)(dian)(dian)量充(chong)(chong)(chong)(chong)足，而(er)且還可以(yi)對電(dian)(dian)(dian)(dian)(dian)池(chi)起到一定的(de)維護作(zuo)用(yong)，修復(fu)由于使用(yong)不當(dang)造成的(de)記憶(yi)效應，即(ji)容量下降(電(dian)(dian)(dian)(dian)(dian)池(chi)活性(xing)衰(shuai)退)現(xian)象(xiang)。設計比較(jiao)科學的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器往往采用(yong)專用(yong)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)控(kong)制(zhi)芯(xin)片配合單片機控(kong)制(zhi)的(de)方(fang)法。專用(yong)的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)芯(xin)片具備(bei)業界公認較(jiao)好的(de)-△v 檢測(ce)，可以(yi)檢測(ce)出(chu)電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)飽和(he)時(shi)(shi)發出(chu)的(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)變化信號，比較(jiao)精確地結束充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)工(gong)作(zuo)，通過單片機對這(zhe)些芯(xin)片的(de)控(kong)制(zhi)，可以(yi)實現(xian)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)過程的(de)智能化，例如，在充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)后增加及(ji)時(shi)(shi)關斷電(dian)(dian)(dian)(dian)(dian)源、蜂鳴報警(jing)和(he)液晶顯示(shi)等功能。充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器的(de)智能化可以(yi)縮短充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)的(de)時(shi)(shi)間(jian)(jian)，同時(shi)(shi)能夠維護電(dian)(dian)(dian)(dian)(dian)池(chi)，延長電(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。在選擇具體的電池充電芯片時，需要參(can)考(kao)以下(xia)標準。

1)電池(chi)類型：不(bu)同的電池(chi)(鋰電池(chi)、鎳氫電池(chi)、鎳鎘電池(chi)等)需選擇不(bu)同的充(chong)電芯片。

2)電池(chi)數(shu)目：可充電池(chi)的數(shu)目。

3)電流(liu)值：充電電流(liu)的(de)大小(xiao)決定了充電時(shi)間。

4)充電(dian)方式：是(shi)快充、慢充還是(shi)可控充電(dian)過程(cheng)。

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(chong)電(dian)快速且具有優良的電(dian)池(chi)保護能(neng)力，據此(ci)選擇Maxim 公司的MAXl898 作為電(dian)池(chi)充(chong)電(dian)芯片。

2.2.2 芯片MAX1898 的特點(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(ti)供(gong)精(jing)確的(de)恒(heng)流(liu)(liu)(liu)(liu)/恒(heng)壓(ya)充(chong)(chong)(chong)電(dian)(dian)，電(dian)(dian)池(chi)電(dian)(dian)壓(ya)調節(jie)精(jing)度為±0.75％，提(ti)高了電(dian)(dian)池(chi)性(xing)能并延長(chang)了電(dian)(dian)池(chi)使用壽命。充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)(liu)(liu)可由用戶設(she)定，采用內部檢流(liu)(liu)(liu)(liu)，無須(xu)外(wai)部檢流(liu)(liu)(liu)(liu)電(dian)(dian)阻。 MAXl898 提(ti)供(gong)了充(chong)(chong)(chong)電(dian)(dian)狀態的(de)輸出指示(shi)、輸入(ru)電(dian)(dian)源是(shi)否與充(chong)(chong)(chong)電(dian)(dian)器(qi)連接的(de)輸出指示(shi)和充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)(liu)(liu)(liu)指示(shi)。MAXl898 還具(ju)有其他一些功能，包(bao)括輸入(ru)關斷控制(zhi)、可選(xuan)的(de)充(chong)(chong)(chong)電(dian)(dian)周(zhou)期重啟(無須(xu)重新上電(dian)(dian))、可選(xuan)的(de)充(chong)(chong)(chong)電(dian)(dian)終止安全定時器(qi)和過放電(dian)(dian)電(dian)(dian)池(chi)的(de)低電(dian)(dian)流(liu)(liu)(liu)(liu)預充(chong)(chong)(chong)。

MAXl898 的(de)關鍵特性如(ru)下(xia)：

1)    簡單、安全的線性充電方式。

2)    使用低(di)成本的(de)PNP 或PMOS 調整元件。

3)    輸入電壓(ya)：4.5～12V。

4)    內(nei)置檢流電阻。

5)    ±0.75％電壓精度。

6)    可(ke)編程充(chong)電電流(liu)。

7)    輸入(ru)電源(yuan)自動檢(jian)測。

8)    LED 充電狀態指示(shi)。

9)    可(ke)編程(cheng)安全定時器。

10)  檢(jian)流(liu)監視(shi)輸(shu)出(chu)。

11)  可選/可調節自動重啟。

12)  小尺寸uMAX 封裝。

2.2.3 MAX1898 的充電工(gong)作原理(li)

充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯片(pian)MAXl898 的(de)(de)內部電(dian)(dian)(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)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)調(diao)節(jie)(jie)器(qi)(qi)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓檢(jian)測器(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)(liu)(liu)檢(jian)測器(qi)(qi)、定(ding)時(shi)器(qi)(qi)、溫度(du)檢(jian)測器(qi)(qi)和(he)(he)(he)主控(kong)制(zhi)(zhi)器(qi)(qi)。輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)調(diao)節(jie)(jie)器(qi)(qi)用(yong)于限(xian)制(zhi)(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)的(de)(de)總(zong)輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)，包括(kuo)系統負載(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)與充(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)(liu)(liu)。當檢(jian)測到輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)大(da)于設定(ding)的(de)(de)門限(xian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)時(shi)，通(tong)過(guo)降低充(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)(liu)(liu)從而控(kong)制(zhi)(zhi)輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)。因為(wei)系統工作時(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)的(de)(de)變化范圍較大(da)，如果充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)沒有(you)輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)檢(jian)測功(gong)(gong)能(neng)，則(ze)輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)必須能(neng)夠(gou)(gou)提(ti)供最(zui)大(da)負載(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)與最(zui)大(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)(liu)(liu)之和(he)(he)(he)，這(zhe)將使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)的(de)(de)成本(ben)增高、體積增大(da)，而利(li)用(yong)輸(shu)入(ru)(ru)限(xian)流(liu)(liu)(liu)(liu)(liu)功(gong)(gong)能(neng)則(ze)能(neng)夠(gou)(gou)降低充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)對直流(liu)(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)的(de)(de)要(yao)求，同時(shi)也簡(jian)化了輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)的(de)(de)設計。 MAXl898 外接限(xian)流(liu)(liu)(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)(yuan)(yuan)和(he)(he)(he)P 溝(gou)道場效(xiao)應管，可(ke)以對單節(jie)(jie)鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行安(an)全有(you)效(xiao)的(de)(de)快充(chong)(chong)(chong)，其最(zui)大(da)特(te)點(dian)是：在不使(shi)用(yong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感的(de)(de)情況(kuang)下(xia)，仍能(neng)做到很低的(de)(de)功(gong)(gong)率(lv)耗散，可(ke)以實現(xian)預充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，具有(you)過(guo)壓保(bao)護和(he)(he)(he)溫度(du)保(bao)護功(gong)(gong)能(neng)，最(zui)長(chang)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)問的(de)(de)限(xian)制(zhi)(zhi)可(ke)為(wei)鋰(li)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)提(ti)供二次(ci)保(bao)護。MAX1898 的(de)(de)浮動(dong)方(fang)式(shi)能(neng)夠(gou)(gou)使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)容量充(chong)(chong)(chong)至最(zui)大(da)。

當充(chong)(chong)(chong)電電源和電池(chi)(chi)在正常的(de)(de)工作溫度(du)范圍內(nei)時(shi)，插入電池(chi)(chi)將(jiang)啟動(dong)(dong)(dong)一次(ci)充(chong)(chong)(chong)電過(guo)程；充(chong)(chong)(chong)電結束的(de)(de)條件是平(ping)均(jun)的(de)(de)脈沖充(chong)(chong)(chong)電電流達(da)到(dao)快充(chong)(chong)(chong)電流的(de)(de) 1％，或時(shi)間超出片上預(yu)置的(de)(de)充(chong)(chong)(chong)電時(shi)間。MAXl898 能夠自(zi)動(dong)(dong)(dong)檢(jian)測充(chong)(chong)(chong)電電源，沒(mei)有電源時(shi)自(zi)動(dong)(dong)(dong)關斷(duan)以減少電池(chi)(chi)的(de)(de)漏電。啟動(dong)(dong)(dong)快充(chong)(chong)(chong)后打開外接的(de)(de)P 型場(chang)(chang)效應(ying)管，當檢(jian)測到(dao)電池(chi)(chi)電壓達(da)到(dao)設定的(de)(de)門限時(shi)進入脈沖充(chong)(chong)(chong)電方式，P 型場(chang)(chang)效應(ying)管打開的(de)(de)時(shi)問會越來越短。充(chong)(chong)(chong)電結束時(shi)，指示燈將(jiang)會按12%的(de)(de)周期閃(shan)爍(shuo)，MAX1898 的(de)(de)典型充(chong)(chong)(chong)電電路(lu)如下(xia)圖圖2-1所示電路(lu)具(ju)體(ti)說明如下(xia)。

圖2-1  MAX1898的典(dian)型充電電路(lu)

1）輸入電(dian)壓范圍為 4.5～12v。鋰電(dian)池要(yao)求的充電(dian)方式(shi)是恒流恒壓方式(shi)，電(dian)源的輸入需(xu)要(yao)采(cai)用恒流恒壓源，一(yi)般可采(cai)用直流電(dian)源外加變壓器。

2)通(tong)過外接(jie)的場效應(ying)管提供鋰(li)電池的充電接(jie)口。

3)通過外接的電(dian)(dian)(dian)容(rong) CcT 來設置充(chong)(chong)電(dian)(dian)(dian)時(shi)間 tCHG。這(zhe)里的充(chong)(chong)電(dian)(dian)(dian)時(shi)間指的是快充(chong)(chong)時(shi)的最(zui)大充(chong)(chong)電(dian)(dian)(dian)時(shi)間，它和定時(shi)電(dian)(dian)(dian)容(rong)CcT 的關(guan)系如下式所示：

CcT=34.33×tCHG                                                  (2-1)

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

4)在限制電(dian)流(liu)的(de)模式(shi)下，通過外接的(de)電(dian)阻 RSET 來設置最(zui)大充電(dian)電(dian)IFSTCHG，關系(xi)如下式(shi)所示：IFSTCHG=1400/Rset 式(shi)中，RSEI-的(de)單位為(wei)Q，IFSTCHG 的(de)單位為(wei)A。

當充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)在(zai)正(zheng)常的(de)(de)(de)(de)(de)工作溫度范圍內時(shi)(shi)，插入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)將(jiang)啟動(dong)一次充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程。平均(jun)的(de)(de)(de)(de)(de)脈沖充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)低(di)于設(she)置(zhi)的(de)(de)(de)(de)(de)快充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)20％，或者充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)間(jian)(jian)超出片上(shang)預(yu)置(zhi)的(de)(de)(de)(de)(de)最大充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)問時(shi)(shi)，充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)周期(qi)結(jie)束(shu)。MAXl898 能夠自動(dong)檢測(ce)(ce)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源，沒(mei)有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源時(shi)(shi)自動(dong)關斷(duan)以減少電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)(de)(de)漏電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。啟動(dong)快充(chong)后，打(da)開外接的(de)(de)(de)(de)(de)P 型場(chang)(chang)效(xiao)應管(guan)，當檢測(ce)(ce)到電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)達到設(she)定的(de)(de)(de)(de)(de)門限(xian)時(shi)(shi)進入脈沖充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)方(fang)式，P 型場(chang)(chang)效(xiao)應管(guan)打(da)開的(de)(de)(de)(de)(de)時(shi)(shi)JI 間(jian)(jian)會(hui)越(yue)來(lai)越(yue)短(duan)。充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)結(jie)束(shu)時(shi)(shi)，LED 指示燈將(jiang)會(hui)呈現周期(qi)性的(de)(de)(de)(de)(de)閃爍，具體的(de)(de)(de)(de)(de)閃爍含義如表(biao)1所示。

表2-

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

充電狀態
LED指示燈(deng)電池或(huo)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  系統主要硬(ying)件電路設(she)計

   硬件(jian)電(dian)路(lu)設計主要圍繞充電(dian)芯(xin)片(pian)MAXl898 展開，而單片(pian)機控制部分(fen)的電(dian)路(lu)簡單。

3.1  主(zhu)要器件(jian)

本設計(ji)的核心器件是MAXl898。MAXl898 可(ke)對所有(you)化學(xue)類型的Li+電池進行(xing)安全充電，它(ta)具有(you)高集成(cheng)度(du)，在小尺寸內集成(cheng)了(le)(le)更多功(gong)能(neng)，盡可(ke)能(neng)多地覆蓋了(le)(le)基本應(ying)用電路，只需要少數外部元件。MAXl898 為10 引(yin)腳、超薄型的MAX 封裝，其(qi)引(yin)腳分布如圖3-1 所示：

圖3-1 MAXl898引腳分布

其引腳功能如下：

IN(1 腳(jiao))：傳感輸入(ru)，檢測輸入(ru)的電(dian)壓或電(dian)流；

CHG(2 腳)：充電(dian)狀態指示腳，同時驅動LED；

EN/OK(3 腳(jiao))：使能輸(shu)(shu)入(ru)腳(jiao)/輸(shu)(shu)入(ru)電(dian)源(yuan)(yuan)“好”輸(shu)(shu)出指(zhi)示腳(jiao)。EN 為輸(shu)(shu)入(ru)腳(jiao)，可以通過輸(shu)(shu)入(ru)禁止(zhi)芯片工作；OK 為輸(shu)(shu)出腳(jiao)，用于指(zhi)示輸(shu)(shu)入(ru)電(dian)源(yuan)(yuan)是否與充電(dian)器連接；

ISET(4 腳(jiao))：充電(dian)電(dian)流調(diao)節引腳(jiao)。通過串接一個電(dian)阻(zu)到地來設置最(zui)大充電(dian)電(dian)流；

CT(5 腳(jiao))：安全充電(dian)(dian)(dian)時間(jian)設置引(yin)腳(jiao)。接一個時間(jian)電(dian)(dian)(dian)容(rong)來設置充電(dian)(dian)(dian)時間(jian)，電(dian)(dian)(dian)容(rong)為(wei) 100nF 時，幾乎(hu)為(wei)3 個小時，此引(yin)腳(jiao)直接接地(di)將禁用此功(gong)能；

RSTRT(6 腳(jiao)(jiao))：自動重(zhong)新啟動控制引腳(jiao)(jiao)。當此引腳(jiao)(jiao)直接接地時(shi)(shi)，如果電池電壓掉至基(ji)準電壓閾值(zhi)以下 200mV，將會重(zhong)新開始一輪充(chong)(chong)電周(zhou)期(qi)。此引腳(jiao)(jiao)通(tong)過電阻(zu)接地時(shi)(shi)，可以降低它(ta)的(de)電壓閾值(zhi)。此引腳(jiao)(jiao)懸空(kong)或者 CT 引腳(jiao)(jiao)接地(充(chong)(chong)電時(shi)(shi)間設置功能禁用)時(shi)(shi)，自動重(zhong)新啟動功能被禁用；

BATT(7 腳(jiao)(jiao)(jiao))：電池傳(chuan)感輸(shu)入腳(jiao)(jiao)(jiao)，接單個(ge) Li+電池的正極(ji)。此引腳(jiao)(jiao)(jiao)需旁接一個(ge)大電解電容到(dao)地；

GND(8 腳)：接(jie)地(di)端；

DRV(9 腳(jiao))：外部晶體(ti)管驅動器，接晶體(ti)管的基極；

CS(10 腳)：電流傳感輸入，接晶體管的(de)發射極。

本設計的單片機芯(xin)片選用Atmel 公司的AT89C52，它完全可(ke)以滿足(zu)要求。

另(ling)外，由于充電器外部為+12V 供(gong)電，因此(ci)需要通(tong)過電壓轉換芯片將+12V 電壓轉換為 +5V 電壓，這里選用(yong)三端(duan)電壓轉換芯片LM7805 來完(wan)成(cheng)此(ci)功(gong)能。

為了降低電(dian)(dian)源(yuan)干(gan)擾，保持(chi)電(dian)(dian)路的(de)穩定，在LM7805 完成電(dian)(dian)壓轉換，將+5v 充(chong)電(dian)(dian)電(dian)(dian)源(yuan)送給 MAXl898 之前(qian)，先(xian)經(jing)過(guo)一次光(guang)耦模(mo)塊 6N137 的(de)處理，通過(guo)單片機對光(guang)耦模(mo)塊的(de)控制，可以及(ji)時關斷(duan)充(chong)電(dian)(dian)電(dian)(dian)源(yuan)。6N137 的(de)引腳(jiao)分布如圖3-2 所示(shi)：

圖3-2  6N137 的引腳分布

其引腳功能如下：

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

+(2 腳(jiao))、-(3 腳(jiao))：發光二極管的正(zheng)、負極；

GND(5 腳(jiao))：接地端；

OUTPUT(6 腳(jiao))：輸出腳(jiao)；

EN(7 腳(jiao))：使(shi)能腳(jiao)。為(wei)低時，無(wu)論有無(wu)輸(shu)入(ru)，輸(shu)出都為(wei)高。

不(bu)使用時，懸空即(ji)可；

VCC(8 腳)：電源輸入腳。

3.2  電路原理圖及說明

硬件電(dian)路(lu)(lu)(lu)由單片(pian)機(ji)電(dian)路(lu)(lu)(lu)、電(dian)壓轉換及光(guang)耦隔(ge)離電(dian)路(lu)(lu)(lu)、充(chong)電(dian)控制電(dian)路(lu)(lu)(lu)3 部分組成。單片(pian)機(ji)部分的電(dian)路(lu)(lu)(lu)原理圖如(ru)下圖3-3 所示。

圖3-3  單片機(ji)部分(fen)的電路原理(li)圖

圖3-3中(zhong)，ul 為單(dan)(dan)片機(ji)AT89C52，工作(zuo)在(zai)11．0592MHz 時鐘(zhong)；u2 為蜂(feng)(feng)鳴(ming)器，蜂(feng)(feng)鳴(ming)器由(you)單(dan)(dan)片機(ji)的(de)P2．1 腳(jiao)控制(zhi)發出(chu)報警(jing)聲提示；單(dan)(dan)片機(ji)的(de)P2．O 腳(jiao)輸出(chu)控制(zhi)光耦器件(jian)，在(zai)需要的(de)時候可以及時關(guan)斷(duan)充(chong)電(dian)電(dian)源；單(dan)(dan)片機(ji)的(de)外部中(zhong)斷(duan)O 由(you)充(chong)電(dian)芯片MAXl898 的(de)充(chong)電(dian)狀態輸出(chu)信號/ CHG 經過(guo)反相后觸(chu)發。

下圖3-4 所示的為電(dian)壓轉(zhuan)換及光耦(ou)隔(ge)離(li)部分電(dian)路的原理(li)圖。