充電(dian)器為人們的外(wai)出和出差辦公提供了極大的方(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(jie)范(fan)圍內的(de)普及使用，手(shou)機電池充電器的(de)使用也越來越廣泛(fan)。

本(ben)次設(she)計將通過(guo)一個典(dian)型的勢力介(jie)紹51單(dan)片機(ji)在實現手(shou)機(ji)電(dian)(dian)(dian)池充電(dian)(dian)(dian)器方面的應用。設(she)計所實現的充電(dian)(dian)(dian)器是一種(zhong)智(zhi)能充電(dian)(dian)(dian)器，它在單(dan)片機(ji)的控制下，具(ju)有(you)預充、充電(dian)(dian)(dian)保護、自動(dong)斷電(dian)(dian)(dian)和充電(dian)(dian)(dian)完成報警提示功能。

1.3  本設計功能模塊
本設(she)計的功能(neng)模塊主要如下：

1）單片(pian)機模塊：實現充(chong)電器(qi)的智能(neng)化控制。比如自動斷電、充(chong)電完成報警提示等。

2）充電(dian)(dian)過程控(kong)制(zhi)模(mo)塊：采用(yong)(yong)專用(yong)(yong)的電(dian)(dian)池充電(dian)(dian)芯片實現充電(dian)(dian)過程的控(kong)制(zhi)。

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

4）C51程(cheng)序：單片機控(kong)制電(dian)池充(chong)(chong)電(dian)芯片實現充(chong)(chong)電(dian)過(guo)程(cheng)的(de)自動化，并根據(ju)充(chong)(chong)電(dian)的(de)狀態給出有關(guan)的(de)輸出指示。

第2節  系統設計思路分析
充(chong)電(dian)(dian)(dian)的(de)實現，它包括兩部(bu)分：一是(shi)充(chong)電(dian)(dian)(dian)過程的(de)控制；二是(shi)需(xu)要提供基(ji)本的(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓。

2.1 智能化的實現
在充(chong)電器(qi)電路中引入單(dan)片機的控制。它為(wei)什么需要實現充(chong)電器(qi)的智能化呢？

充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)器(qi)(qi)實現(xian)的(de)方式不(bu)同會(hui)(hui)導(dao)致充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)效果(guo)的(de)不(bu)同。由于充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)器(qi)(qi)多(duo)采(cai)用大電(dian)(dian)(dian)流的(de)快(kuai)速充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)法(fa)，在電(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)(chong)(chong)滿后如果(guo)不(bu)及(ji)時停止會(hui)(hui)使(shi)電(dian)(dian)(dian)池(chi)(chi)發燙，過(guo)度(du)的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)會(hui)(hui)嚴重損害電(dian)(dian)(dian)池(chi)(chi)的(de)壽(shou)命(ming)。一些低(di)成(cheng)本(ben)的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)器(qi)(qi)采(cai)用電(dian)(dian)(dian)壓(ya)比較法(fa)，為了防止過(guo)充(chong)(chong)(chong)(chong)，一般(ban)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)到(dao)90％就停止大電(dian)(dian)(dian)流快(kuai)充(chong)(chong)(chong)(chong)，而采(cai)用小電(dian)(dian)(dian)流涓(juan)流補充(chong)(chong)(chong)(chong)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)。

手(shou)機(ji)電(dian)(dian)(dian)池(chi)的(de)使用壽命(ming)和單次使用時間(jian)與充(chong)電(dian)(dian)(dian)過(guo)程密切相關。鋰電(dian)(dian)(dian)池(chi)是手(shou)機(ji)最(zui)為(wei)(wei)常用的(de)一種(zhong)電(dian)(dian)(dian)池(chi)，它(ta)具有較(jiao)高的(de)能(neng)量(liang)重量(liang)比(bi)、能(neng)量(liang)體積比(bi)，具有記憶效應，可(ke)重復充(chong)電(dian)(dian)(dian)多次，使用壽命(ming)較(jiao)長，價格也越(yue)來越(yue)低(di)。鋰電(dian)(dian)(dian)池(chi)對于充(chong)電(dian)(dian)(dian)器(qi)的(de)要(yao)求比(bi)較(jiao)苛刻，需要(yao)保(bao)護電(dian)(dian)(dian)路。為(wei)(wei)了有效利用電(dian)(dian)(dian)池(chi)容(rong)量(liang)，需將鋰電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)至最(zui)大電(dian)(dian)(dian)壓(ya)，但是過(guo)壓(ya)充(chong)電(dian)(dian)(dian)會造(zao)成電(dian)(dian)(dian)池(chi)損壞，這就(jiu)要(yao)求較(jiao)高的(de)控制精度。另外，對于電(dian)(dian)(dian)壓(ya)過(guo)低(di)的(de)電(dian)(dian)(dian)池(chi)需要(yao)進行預充(chong)，充(chong)電(dian)(dian)(dian)器(qi)最(zui)好帶有熱保(bao)護和時間(jian)保(bao)護，為(wei)(wei)電(dian)(dian)(dian)池(chi)提供附加保(bao)護。

一部好的(de)(de)(de)充(chong)(chong)(chong)電(dian)器不但能在短時(shi)間內將電(dian)量充(chong)(chong)(chong)足，而且還可(ke)以(yi)對電(dian)池起到一定的(de)(de)(de)維護作(zuo)用(yong)，修復由于(yu)使用(yong)不當造成的(de)(de)(de)記憶效應，即容(rong)量下(xia)降(電(dian)池活(huo)性(xing)衰退)現象。設(she)計比較科(ke)學的(de)(de)(de)充(chong)(chong)(chong)電(dian)器往往采(cai)用(yong)專用(yong)充(chong)(chong)(chong)電(dian)控(kong)(kong)制芯片配(pei)合單片機控(kong)(kong)制的(de)(de)(de)方法。專用(yong)的(de)(de)(de)充(chong)(chong)(chong)電(dian)芯片具備業界公認較好的(de)(de)(de)-△v 檢測，可(ke)以(yi)檢測出電(dian)池充(chong)(chong)(chong)電(dian)飽和(he)時(shi)發出的(de)(de)(de)電(dian)壓(ya)變化信號，比較精(jing)確(que)地結束充(chong)(chong)(chong)電(dian)工作(zuo)，通過單片機對這些芯片的(de)(de)(de)控(kong)(kong)制，可(ke)以(yi)實(shi)現充(chong)(chong)(chong)電(dian)過程的(de)(de)(de)智能化，例如，在充(chong)(chong)(chong)電(dian)后增加及時(shi)關斷電(dian)源、蜂鳴(ming)報警(jing)和(he)液晶顯示等功(gong)能。充(chong)(chong)(chong)電(dian)器的(de)(de)(de)智能化可(ke)以(yi)縮短充(chong)(chong)(chong)電(dian)的(de)(de)(de)時(shi)間，同(tong)時(shi)能夠維護電(dian)池，延長電(dian)池使用(yong)壽命。

2.2 電池充電芯片的選擇
2.2.1 如何選擇電(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(ju)體的電池充電芯片時(shi)，需要參考以下標(biao)準(zhun)。

1)電(dian)池類型(xing)：不同(tong)的電(dian)池(鋰電(dian)池、鎳氫電(dian)池、鎳鎘(ge)電(dian)池等)需選擇不同(tong)的充電(dian)芯片。

2)電(dian)池(chi)數目：可(ke)充電(dian)池(chi)的數目。

3)電流值：充電電流的大小決定了充電時間。

4)充電方式：是(shi)快充、慢充還(huan)是(shi)可控充電過程(cheng)。

本設計要實現的是手機的單節鋰離子電池充電器，要求充電(dian)(dian)快速且具有優(you)良的電(dian)(dian)池保護能力，據此(ci)選擇Maxim 公司的MAXl898 作為電(dian)(dian)池充電(dian)(dian)芯(xin)片。

2.2.2 芯片(pian)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(gong)精(jing)(jing)確的(de)恒(heng)流/恒(heng)壓充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)壓調節精(jing)(jing)度為(wei)±0.75％，提高了電(dian)(dian)(dian)(dian)(dian)(dian)池性(xing)能(neng)并延(yan)長了電(dian)(dian)(dian)(dian)(dian)(dian)池使用壽命(ming)。充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流可(ke)(ke)由用戶設定(ding)，采用內(nei)部(bu)檢(jian)流，無(wu)須(xu)外部(bu)檢(jian)流電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)。 MAXl898 提供(gong)了充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)狀態的(de)輸出(chu)指(zhi)(zhi)示(shi)(shi)、輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)源是(shi)否(fou)與充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器連接的(de)輸出(chu)指(zhi)(zhi)示(shi)(shi)和充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流指(zhi)(zhi)示(shi)(shi)。MAXl898 還具有其他一(yi)些功(gong)能(neng)，包括輸入(ru)關(guan)斷控制(zhi)、可(ke)(ke)選的(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)周期重啟(qi)(無(wu)須(xu)重新上電(dian)(dian)(dian)(dian)(dian)(dian))、可(ke)(ke)選的(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)終止(zhi)安全定(ding)時器和過放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)池的(de)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)流預充(chong)。

MAXl898 的關鍵(jian)特性如下：

1)    簡單、安全的(de)線性充電方(fang)式(shi)。

2)    使用低(di)成本(ben)的PNP 或(huo)PMOS 調整元件。

3)    輸入電壓(ya)：4.5～12V。

4)    內置(zhi)檢(jian)流電阻。

5)    ±0.75％電(dian)壓精度。

6)    可編程(cheng)充電電流(liu)。

7)    輸入電源自動檢測。

8)    LED 充電狀(zhuang)態指示。

9)    可編程安全定時(shi)器。

10)  檢(jian)流監視輸出(chu)。

11)  可選(xuan)/可調節(jie)自動重啟。

12)  小尺寸uMAX 封裝。

2.2.3 MAX1898 的充電工(gong)作原(yuan)理

充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯片MAXl898 的(de)(de)內部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路包括輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)調節(jie)器(qi)(qi)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)檢測器(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)檢測器(qi)(qi)、定時(shi)器(qi)(qi)、溫度(du)檢測器(qi)(qi)和(he)主控制(zhi)器(qi)(qi)。輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)調節(jie)器(qi)(qi)用于限(xian)(xian)制(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)總(zong)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)，包括系(xi)統(tong)負載(zai)(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(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)。當檢測到(dao)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)大(da)于設定的(de)(de)門限(xian)(xian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)時(shi)，通過(guo)降(jiang)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)從(cong)而(er)控制(zhi)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)。因為系(xi)統(tong)工作時(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)變化(hua)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)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)檢測功能，則(ze)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)必須能夠(gou)提(ti)供最(zui)大(da)負載(zai)(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(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)之和(he)，這將使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)成本增(zeng)高、體積增(zeng)大(da)，而(er)利用輸入(ru)限(xian)(xian)流(liu)功能則(ze)能夠(gou)降(jiang)低充(chong)(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)(yuan)的(de)(de)要(yao)求(qiu)，同時(shi)也簡化(hua)了輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)設計(ji)。 MAXl898 外接限(xian)(xian)流(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)和(he)P 溝道場效應管，可(ke)以對單節(jie)鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行安全有(you)效的(de)(de)快(kuai)充(chong)(chong)(chong)，其最(zui)大(da)特點是：在不(bu)使(shi)用電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感的(de)(de)情況下，仍能做到(dao)很低的(de)(de)功率耗散，可(ke)以實現預充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，具有(you)過(guo)壓(ya)保(bao)(bao)護(hu)和(he)溫度(du)保(bao)(bao)護(hu)功能，最(zui)長充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)問的(de)(de)限(xian)(xian)制(zhi)可(ke)為鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)提(ti)供二次保(bao)(bao)護(hu)。MAX1898 的(de)(de)浮動方式能夠(gou)使(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)容量(liang)充(chong)(chong)(chong)至(zhi)最(zui)大(da)。

當充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源和電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)在(zai)正常的(de)(de)(de)工作溫度范圍內時(shi)，插(cha)入電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)將(jiang)啟動(dong)一(yi)次充電(dian)(dian)(dian)(dian)(dian)(dian)過程；充電(dian)(dian)(dian)(dian)(dian)(dian)結束的(de)(de)(de)條(tiao)件是平均的(de)(de)(de)脈沖充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流達到(dao)快充電(dian)(dian)(dian)(dian)(dian)(dian)流的(de)(de)(de) 1％，或(huo)時(shi)間超出片上預置的(de)(de)(de)充電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)間。MAXl898 能夠自動(dong)檢測(ce)充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)源，沒有電(dian)(dian)(dian)(dian)(dian)(dian)源時(shi)自動(dong)關斷以減少電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)漏電(dian)(dian)(dian)(dian)(dian)(dian)。啟動(dong)快充后打(da)開(kai)外(wai)接的(de)(de)(de)P 型場(chang)效應管(guan)，當檢測(ce)到(dao)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓達到(dao)設定(ding)的(de)(de)(de)門限(xian)時(shi)進入脈沖充電(dian)(dian)(dian)(dian)(dian)(dian)方式，P 型場(chang)效應管(guan)打(da)開(kai)的(de)(de)(de)時(shi)問會越(yue)來越(yue)短。充電(dian)(dian)(dian)(dian)(dian)(dian)結束時(shi)，指示燈將(jiang)會按12%的(de)(de)(de)周(zhou)期(qi)閃爍，MAX1898 的(de)(de)(de)典型充電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)如(ru)下圖(tu)(tu)圖(tu)(tu)2-1所示電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)具體說明如(ru)下。

圖2-1  MAX1898的典型充電電路

1）輸(shu)入(ru)電(dian)壓(ya)(ya)范圍為 4.5～12v。鋰電(dian)池要求的充電(dian)方式是恒流(liu)(liu)恒壓(ya)(ya)方式，電(dian)源的輸(shu)入(ru)需要采用恒流(liu)(liu)恒壓(ya)(ya)源，一般可采用直流(liu)(liu)電(dian)源外(wai)加變壓(ya)(ya)器。

2)通過外接的場(chang)效應(ying)管提供鋰電(dian)池(chi)的充電(dian)接口。

3)通過(guo)外(wai)接的(de)電容(rong) CcT 來設置充電時間 tCHG。這(zhe)里的(de)充電時間指(zhi)的(de)是快充時的(de)最(zui)大充電時間，它(ta)和定時電容(rong)CcT 的(de)關系如下式所示：

CcT=34.33×tCHG                                                  (2-1)

式中(zhong)，tCHG 的(de)單位為(wei)(wei)小時(shi)，CcT 的(de)單位為(wei)(wei)Nf。大多數情(qing)況下，快充(chong)時(shi)最大充(chong)電時(shi)問不超過3 小時(shi)，因此常取CcT 為(wei)(wei)100nF。

4)在限制電(dian)流的模式(shi)下，通過外接的電(dian)阻 RSET 來設(she)置最大充(chong)電(dian)電(dian)IFSTCHG，關系如下式(shi)所示：IFSTCHG=1400/Rset 式(shi)中，RSEI-的單位為Q，IFSTCHG 的單位為A。

當(dang)(dang)充(chong)(chong)電(dian)(dian)電(dian)(dian)源(yuan)和電(dian)(dian)池(chi)在正常(chang)的(de)(de)(de)工作溫度范圍(wei)內(nei)時(shi)(shi)，插(cha)入電(dian)(dian)池(chi)將啟(qi)(qi)動(dong)一次(ci)充(chong)(chong)電(dian)(dian)過程。平均的(de)(de)(de)脈沖(chong)(chong)充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)低于設置的(de)(de)(de)快充(chong)(chong)電(dian)(dian)流(liu)的(de)(de)(de)20％，或者(zhe)充(chong)(chong)電(dian)(dian)時(shi)(shi)間(jian)超出片上預置的(de)(de)(de)最大充(chong)(chong)電(dian)(dian)時(shi)(shi)問時(shi)(shi)，充(chong)(chong)電(dian)(dian)周期(qi)(qi)結束。MAXl898 能夠自(zi)動(dong)檢測充(chong)(chong)電(dian)(dian)電(dian)(dian)源(yuan)，沒(mei)有電(dian)(dian)源(yuan)時(shi)(shi)自(zi)動(dong)關斷以減少電(dian)(dian)池(chi)的(de)(de)(de)漏電(dian)(dian)。啟(qi)(qi)動(dong)快充(chong)(chong)后，打(da)開外接的(de)(de)(de)P 型(xing)場效應(ying)管，當(dang)(dang)檢測到電(dian)(dian)池(chi)電(dian)(dian)壓達到設定(ding)的(de)(de)(de)門限時(shi)(shi)進入脈沖(chong)(chong)充(chong)(chong)電(dian)(dian)方式，P 型(xing)場效應(ying)管打(da)開的(de)(de)(de)時(shi)(shi)JI 間(jian)會(hui)越來越短。充(chong)(chong)電(dian)(dian)結束時(shi)(shi)，LED 指(zhi)示燈將會(hui)呈現周期(qi)(qi)性的(de)(de)(de)閃(shan)爍(shuo)，具體的(de)(de)(de)閃(shan)爍(shuo)含義如(ru)表1所示。

表2-

1  MAX1898 典(dian)型充電(dian)電(dian)路(lu)的LED 指示燈(deng)狀態說明(ming)

充電狀態
LED指示(shi)燈(deng)電池或充電器(qi)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  系統主要硬件電路(lu)設計

   硬件電路設計主(zhu)要圍繞充電芯片MAXl898 展(zhan)開，而(er)單片機控(kong)制部分(fen)的電路簡單。

3.1  主要(yao)器件

本(ben)(ben)設計的核心器件是MAXl898。MAXl898 可對所有(you)化(hua)學類(lei)型的Li+電池進行安(an)全(quan)充電，它具有(you)高集成(cheng)度，在小尺寸內集成(cheng)了(le)更多功能，盡可能多地覆(fu)蓋了(le)基本(ben)(ben)應用電路(lu)，只需(xu)要(yao)少數外部(bu)元件。MAXl898 為10 引腳(jiao)、超薄型的MAX 封裝，其引腳(jiao)分布如圖(tu)3-1 所示：

圖3-1 MAXl898引腳(jiao)分布

其引腳功能如下：

IN(1 腳)：傳感輸(shu)入，檢(jian)測輸(shu)入的電(dian)壓或(huo)電(dian)流；

CHG(2 腳)：充電狀態指示腳，同(tong)時(shi)驅動(dong)LED；

EN/OK(3 腳(jiao)(jiao))：使能(neng)輸入(ru)(ru)(ru)腳(jiao)(jiao)/輸入(ru)(ru)(ru)電源“好”輸出(chu)指(zhi)示(shi)腳(jiao)(jiao)。EN 為(wei)輸入(ru)(ru)(ru)腳(jiao)(jiao)，可以(yi)通過輸入(ru)(ru)(ru)禁(jin)止芯片工作；OK 為(wei)輸出(chu)腳(jiao)(jiao)，用于指(zhi)示(shi)輸入(ru)(ru)(ru)電源是否(fou)與充電器連接；

ISET(4 腳(jiao))：充電(dian)電(dian)流調節引(yin)腳(jiao)。通過串接(jie)一個電(dian)阻到地來(lai)設置最大充電(dian)電(dian)流；

CT(5 腳(jiao))：安全充(chong)電時(shi)(shi)間設置引腳(jiao)。接一個時(shi)(shi)間電容來設置充(chong)電時(shi)(shi)間，電容為(wei)(wei) 100nF 時(shi)(shi)，幾乎(hu)為(wei)(wei)3 個小時(shi)(shi)，此(ci)引腳(jiao)直接接地將禁用此(ci)功能；

RSTRT(6 腳(jiao))：自動(dong)(dong)重新啟(qi)動(dong)(dong)控制引(yin)腳(jiao)。當此引(yin)腳(jiao)直接(jie)接(jie)地(di)時(shi)(shi)，如果電(dian)(dian)(dian)池電(dian)(dian)(dian)壓掉至基準電(dian)(dian)(dian)壓閾(yu)值以(yi)下 200mV，將會重新開始(shi)一輪充(chong)電(dian)(dian)(dian)周期。此引(yin)腳(jiao)通過電(dian)(dian)(dian)阻接(jie)地(di)時(shi)(shi)，可以(yi)降低(di)它的電(dian)(dian)(dian)壓閾(yu)值。此引(yin)腳(jiao)懸空或者 CT 引(yin)腳(jiao)接(jie)地(di)(充(chong)電(dian)(dian)(dian)時(shi)(shi)間設置功能禁(jin)用(yong))時(shi)(shi)，自動(dong)(dong)重新啟(qi)動(dong)(dong)功能被(bei)禁(jin)用(yong)；

BATT(7 腳(jiao))：電池傳感輸入(ru)腳(jiao)，接單個 Li+電池的正(zheng)極。此(ci)引腳(jiao)需旁接一個大(da)電解電容到地；

GND(8 腳)：接地端(duan)；

DRV(9 腳)：外部晶(jing)體管驅動器，接晶(jing)體管的基(ji)極；

CS(10 腳)：電流傳感輸入(ru)，接(jie)晶體管的發(fa)射極。

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

另(ling)外，由于充電(dian)(dian)(dian)器外部為(wei)(wei)+12V 供電(dian)(dian)(dian)，因此(ci)需要通過(guo)電(dian)(dian)(dian)壓轉(zhuan)換芯片將(jiang)+12V 電(dian)(dian)(dian)壓轉(zhuan)換為(wei)(wei) +5V 電(dian)(dian)(dian)壓，這里選用三端(duan)電(dian)(dian)(dian)壓轉(zhuan)換芯片LM7805 來(lai)完成此(ci)功能。

為(wei)了降低電(dian)(dian)源干(gan)擾，保持(chi)電(dian)(dian)路的(de)穩定，在LM7805 完成電(dian)(dian)壓轉換，將(jiang)+5v 充電(dian)(dian)電(dian)(dian)源送(song)給 MAXl898 之(zhi)前，先經過一次光耦(ou)模(mo)塊(kuai) 6N137 的(de)處理，通過單片機(ji)對光耦(ou)模(mo)塊(kuai)的(de)控(kong)制，可(ke)以(yi)及時關斷充電(dian)(dian)電(dian)(dian)源。6N137 的(de)引(yin)腳分布如圖(tu)3-2 所示：

圖(tu)3-2  6N137 的引腳分(fen)布

其引腳功能如下：

NC(1 腳、4 腳)：懸(xuan)空；

+(2 腳)、-(3 腳)：發(fa)光二極管(guan)的(de)正、負(fu)極；

GND(5 腳)：接地(di)端；

OUTPUT(6 腳)：輸出腳；

EN(7 腳)：使能腳。為(wei)低時，無論有無輸(shu)入(ru)，輸(shu)出都為(wei)高(gao)。

不使用時，懸空即可(ke)；

VCC(8 腳)：電源(yuan)輸入腳。

3.2  電路(lu)原理(li)圖及說(shuo)明

硬件電(dian)路(lu)由單片(pian)機電(dian)路(lu)、電(dian)壓(ya)轉換(huan)及光耦(ou)隔(ge)離電(dian)路(lu)、充電(dian)控制電(dian)路(lu)3 部分組成。單片(pian)機部分的電(dian)路(lu)原理圖如下圖3-3 所示。

圖3-3  單片機部分的電路原(yuan)理(li)圖

圖3-3中(zhong)，ul 為(wei)單(dan)(dan)片(pian)機(ji)AT89C52，工作在11．0592MHz 時(shi)鐘；u2 為(wei)蜂(feng)鳴(ming)器(qi)(qi)，蜂(feng)鳴(ming)器(qi)(qi)由(you)單(dan)(dan)片(pian)機(ji)的(de)P2．1 腳(jiao)控制發(fa)出報警聲(sheng)提示；單(dan)(dan)片(pian)機(ji)的(de)P2．O 腳(jiao)輸(shu)出控制光(guang)耦器(qi)(qi)件，在需要的(de)時(shi)候可以(yi)及時(shi)關斷充電(dian)電(dian)源(yuan)；單(dan)(dan)片(pian)機(ji)的(de)外部中(zhong)斷O 由(you)充電(dian)芯(xin)片(pian)MAXl898 的(de)充電(dian)狀(zhuang)態輸(shu)出信號(hao)/ CHG 經過(guo)反相后(hou)觸(chu)發(fa)。

下圖3-4 所(suo)示的(de)為電(dian)壓(ya)轉換及光(guang)耦(ou)隔離部(bu)分電(dian)路的(de)原理圖。