充電器(qi)為人們的(de)外出(chu)(chu)和出(chu)(chu)差辦公提(ti)供(gong)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(shou)機(ji)(ji)在世(shi)界范圍內的(de)普及(ji)使用，手(shou)機(ji)(ji)電池充電器的(de)使用也越來(lai)越廣泛(fan)。

本次設計將通過一(yi)個典型的(de)勢力介紹51單(dan)(dan)片(pian)機(ji)在實(shi)(shi)現手(shou)機(ji)電(dian)池(chi)充(chong)電(dian)器方面(mian)的(de)應用。設計所實(shi)(shi)現的(de)充(chong)電(dian)器是一(yi)種智能(neng)充(chong)電(dian)器，它在單(dan)(dan)片(pian)機(ji)的(de)控制下，具有預充(chong)、充(chong)電(dian)保護、自動斷(duan)電(dian)和充(chong)電(dian)完(wan)成報警提示(shi)功能(neng)。

1.3  本設計功能模塊
本設計的(de)功能模(mo)塊主要如下：

1）單片機模塊：實現充電器的智能化控制。比如自動斷電、充電完成(cheng)報警(jing)提示等。

2）充電(dian)過程控制(zhi)模塊(kuai)：采(cai)用專用的(de)電(dian)池充電(dian)芯片實現充電(dian)過程的(de)控制(zhi)。

3）充電電壓(ya)提(ti)供模塊：采用電壓(ya)轉換芯片將外(wai)部+12V電壓(ya)轉換為需要的+5V電壓(ya)。

4）C51程序：單片機(ji)控制電池充(chong)電芯片實(shi)現充(chong)電過程的自動化(hua)，并根據充(chong)電的狀態給出有(you)關的輸出指示。

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

2.1 智能化的實現
在充電(dian)器(qi)電(dian)路中引(yin)入單片(pian)機的控制。它為(wei)什(shen)么需要實現(xian)充電(dian)器(qi)的智能化(hua)呢？

充(chong)電(dian)(dian)(dian)器實現的(de)方式不同(tong)會導致充(chong)電(dian)(dian)(dian)效果的(de)不同(tong)。由于充(chong)電(dian)(dian)(dian)器多(duo)采用(yong)大(da)電(dian)(dian)(dian)流的(de)快速充(chong)電(dian)(dian)(dian)法，在電(dian)(dian)(dian)池(chi)充(chong)滿后如果不及時停(ting)止會使電(dian)(dian)(dian)池(chi)發燙，過(guo)度的(de)充(chong)電(dian)(dian)(dian)會嚴重損害電(dian)(dian)(dian)池(chi)的(de)壽命。一些低(di)成本(ben)的(de)充(chong)電(dian)(dian)(dian)器采用(yong)電(dian)(dian)(dian)壓比較法，為了(le)防止過(guo)充(chong)，一般充(chong)電(dian)(dian)(dian)到90％就(jiu)停(ting)止大(da)電(dian)(dian)(dian)流快充(chong)，而采用(yong)小(xiao)電(dian)(dian)(dian)流涓流補充(chong)充(chong)電(dian)(dian)(dian)。

手機電(dian)池(chi)(chi)(chi)(chi)(chi)的使(shi)用壽命和(he)單次使(shi)用時間與(yu)充(chong)電(dian)過(guo)程密(mi)切相(xiang)關。鋰(li)(li)電(dian)池(chi)(chi)(chi)(chi)(chi)是手機最為常用的一種電(dian)池(chi)(chi)(chi)(chi)(chi)，它具(ju)有(you)較高的能(neng)量重量比、能(neng)量體積比，具(ju)有(you)記(ji)憶效應，可(ke)重復充(chong)電(dian)多次，使(shi)用壽命較長，價格也越來越低(di)。鋰(li)(li)電(dian)池(chi)(chi)(chi)(chi)(chi)對于(yu)充(chong)電(dian)器的要求比較苛刻，需要保(bao)護(hu)(hu)電(dian)路。為了(le)有(you)效利用電(dian)池(chi)(chi)(chi)(chi)(chi)容量，需將鋰(li)(li)電(dian)池(chi)(chi)(chi)(chi)(chi)充(chong)電(dian)至最大電(dian)壓，但(dan)是過(guo)壓充(chong)電(dian)會(hui)造成電(dian)池(chi)(chi)(chi)(chi)(chi)損(sun)壞(huai)，這就要求較高的控制(zhi)精度。另外，對于(yu)電(dian)壓過(guo)低(di)的電(dian)池(chi)(chi)(chi)(chi)(chi)需要進行預充(chong)，充(chong)電(dian)器最好(hao)帶有(you)熱保(bao)護(hu)(hu)和(he)時間保(bao)護(hu)(hu)，為電(dian)池(chi)(chi)(chi)(chi)(chi)提供附(fu)加保(bao)護(hu)(hu)。

一部好的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器不但能(neng)(neng)在短時(shi)間(jian)內將電(dian)(dian)(dian)(dian)(dian)量充(chong)(chong)(chong)足，而且還可(ke)(ke)以(yi)(yi)對電(dian)(dian)(dian)(dian)(dian)池起到一定(ding)的(de)(de)(de)維護作(zuo)用，修復由于使用不當造成的(de)(de)(de)記(ji)憶效應，即(ji)容量下降(電(dian)(dian)(dian)(dian)(dian)池活性衰退)現象。設計比較(jiao)科學的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器往往采用專用充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)控制芯片配合(he)單(dan)片機控制的(de)(de)(de)方法(fa)。專用的(de)(de)(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)芯片具備業界(jie)公認(ren)較(jiao)好的(de)(de)(de)-△v 檢(jian)測，可(ke)(ke)以(yi)(yi)檢(jian)測出(chu)電(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)飽和時(shi)發出(chu)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)變化(hua)信號，比較(jiao)精確地結束充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)工作(zuo)，通過單(dan)片機對這(zhe)些(xie)芯片的(de)(de)(de)控制，可(ke)(ke)以(yi)(yi)實(shi)現充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)過程的(de)(de)(de)智能(neng)(neng)化(hua)，例如，在充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)后增加及時(shi)關斷電(dian)(dian)(dian)(dian)(dian)源、蜂鳴報(bao)警和液晶顯(xian)示等功能(neng)(neng)。充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器的(de)(de)(de)智能(neng)(neng)化(hua)可(ke)(ke)以(yi)(yi)縮(suo)短充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)時(shi)間(jian)，同時(shi)能(neng)(neng)夠(gou)維護電(dian)(dian)(dian)(dian)(dian)池，延長電(dian)(dian)(dian)(dian)(dian)池使用壽命。

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)考以下標(biao)準。

1)電(dian)池(chi)類(lei)型：不同的電(dian)池(chi)(鋰電(dian)池(chi)、鎳氫電(dian)池(chi)、鎳鎘(ge)電(dian)池(chi)等)需(xu)選擇不同的充電(dian)芯片。

2)電(dian)池(chi)數(shu)(shu)目：可(ke)充電(dian)池(chi)的數(shu)(shu)目。

3)電流(liu)值：充電電流(liu)的(de)大小決(jue)定(ding)了充電時間。

4)充(chong)(chong)電方式：是快充(chong)(chong)、慢充(chong)(chong)還是可控充(chong)(chong)電過程。

本設計要實現的是手機的單節鋰離子電池充電器，要求充電快速且具有優良的電池保護能力(li)，據此選擇(ze)Maxim 公司的MAXl898 作(zuo)為電池充電芯片(pian)。

2.2.2 芯(xin)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提供精(jing)確的恒流(liu)/恒壓充(chong)(chong)(chong)電(dian)(dian)，電(dian)(dian)池(chi)電(dian)(dian)壓調節精(jing)度為±0.75％，提高了電(dian)(dian)池(chi)性能并延長了電(dian)(dian)池(chi)使用(yong)壽命(ming)。充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)可(ke)由用(yong)戶設定，采用(yong)內部檢(jian)流(liu)，無須外部檢(jian)流(liu)電(dian)(dian)阻。 MAXl898 提供了充(chong)(chong)(chong)電(dian)(dian)狀態(tai)的輸(shu)出(chu)指(zhi)示(shi)、輸(shu)入電(dian)(dian)源(yuan)是否與(yu)充(chong)(chong)(chong)電(dian)(dian)器(qi)連接(jie)的輸(shu)出(chu)指(zhi)示(shi)和充(chong)(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)指(zhi)示(shi)。MAXl898 還具有其他一些功能，包括(kuo)輸(shu)入關斷控制(zhi)、可(ke)選(xuan)的充(chong)(chong)(chong)電(dian)(dian)周期重啟(無須重新上(shang)電(dian)(dian))、可(ke)選(xuan)的充(chong)(chong)(chong)電(dian)(dian)終止(zhi)安全定時器(qi)和過(guo)放電(dian)(dian)電(dian)(dian)池(chi)的低電(dian)(dian)流(liu)預充(chong)(chong)(chong)。

MAXl898 的關鍵特性如(ru)下：

1)    簡單(dan)、安全的線(xian)性充(chong)電方式(shi)。

2)    使用低成本的PNP 或PMOS 調整元件。

3)    輸入電壓(ya)：4.5～12V。

4)    內置檢流電阻。

5)    ±0.75％電壓精度(du)。

6)    可編程充電電流。

7)    輸(shu)入電源自動(dong)檢測。

8)    LED 充電(dian)狀態指(zhi)示。

9)    可編程安全定時(shi)器。

10)  檢流監視輸出。

11)  可(ke)選/可(ke)調節自動(dong)重啟。

12)  小尺(chi)寸uMAX 封裝。

2.2.3 MAX1898 的充電工作原理

充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯片MAXl898 的內部電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路包(bao)括輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)調節(jie)器(qi)(qi)(qi)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓檢(jian)測器(qi)(qi)(qi)、充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)檢(jian)測器(qi)(qi)(qi)、定時(shi)(shi)器(qi)(qi)(qi)、溫(wen)度(du)檢(jian)測器(qi)(qi)(qi)和(he)(he)主控制(zhi)器(qi)(qi)(qi)。輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)調節(jie)器(qi)(qi)(qi)用于限(xian)(xian)制(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的總輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)，包(bao)括系(xi)統負載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)與充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)。當檢(jian)測到(dao)輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)大(da)(da)(da)(da)于設(she)定的門限(xian)(xian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)時(shi)(shi)，通過(guo)(guo)降低(di)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)從而控制(zhi)輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)。因為系(xi)統工(gong)作時(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)的變化(hua)范(fan)圍較大(da)(da)(da)(da)，如果充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)沒有(you)輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)檢(jian)測功能(neng)(neng)(neng)，則輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)必須能(neng)(neng)(neng)夠提供最(zui)大(da)(da)(da)(da)負載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)與最(zui)大(da)(da)(da)(da)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)之和(he)(he)，這將(jiang)使電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的成本增(zeng)高、體積增(zeng)大(da)(da)(da)(da)，而利用輸(shu)(shu)入限(xian)(xian)流(liu)(liu)(liu)(liu)功能(neng)(neng)(neng)則能(neng)(neng)(neng)夠降低(di)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器(qi)(qi)(qi)對(dui)直流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的要求，同時(shi)(shi)也簡化(hua)了輸(shu)(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)的設(she)計。 MAXl898 外(wai)接(jie)限(xian)(xian)流(liu)(liu)(liu)(liu)型充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)和(he)(he)P 溝道場效應管(guan)，可以對(dui)單節(jie)鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池進行安全有(you)效的快充(chong)(chong)(chong)(chong)，其最(zui)大(da)(da)(da)(da)特點(dian)是：在不使用電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)感的情況(kuang)下，仍(reng)能(neng)(neng)(neng)做到(dao)很(hen)低(di)的功率(lv)耗散，可以實現預充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，具有(you)過(guo)(guo)壓保(bao)護(hu)(hu)和(he)(he)溫(wen)度(du)保(bao)護(hu)(hu)功能(neng)(neng)(neng)，最(zui)長充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)時(shi)(shi)問(wen)的限(xian)(xian)制(zhi)可為鋰電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池提供二次(ci)保(bao)護(hu)(hu)。MAX1898 的浮動方式能(neng)(neng)(neng)夠使電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池容量充(chong)(chong)(chong)(chong)至最(zui)大(da)(da)(da)(da)。

當充(chong)電(dian)(dian)電(dian)(dian)源和電(dian)(dian)池(chi)(chi)在正(zheng)常(chang)的(de)(de)工作溫(wen)度范圍內時(shi)(shi)(shi)，插入(ru)電(dian)(dian)池(chi)(chi)將啟動(dong)一次(ci)充(chong)電(dian)(dian)過(guo)程(cheng)；充(chong)電(dian)(dian)結束的(de)(de)條件是平(ping)均的(de)(de)脈(mo)沖充(chong)電(dian)(dian)電(dian)(dian)流達(da)到(dao)快(kuai)充(chong)電(dian)(dian)流的(de)(de) 1％，或時(shi)(shi)(shi)間超出片上預置(zhi)的(de)(de)充(chong)電(dian)(dian)時(shi)(shi)(shi)間。MAXl898 能夠自動(dong)檢(jian)測充(chong)電(dian)(dian)電(dian)(dian)源，沒(mei)有(you)電(dian)(dian)源時(shi)(shi)(shi)自動(dong)關斷以減少電(dian)(dian)池(chi)(chi)的(de)(de)漏電(dian)(dian)。啟動(dong)快(kuai)充(chong)后打開(kai)外接的(de)(de)P 型(xing)場效應管(guan)，當檢(jian)測到(dao)電(dian)(dian)池(chi)(chi)電(dian)(dian)壓達(da)到(dao)設定的(de)(de)門限時(shi)(shi)(shi)進入(ru)脈(mo)沖充(chong)電(dian)(dian)方(fang)式，P 型(xing)場效應管(guan)打開(kai)的(de)(de)時(shi)(shi)(shi)問會越來越短。充(chong)電(dian)(dian)結束時(shi)(shi)(shi)，指示燈將會按12%的(de)(de)周期閃(shan)爍，MAX1898 的(de)(de)典型(xing)充(chong)電(dian)(dian)電(dian)(dian)路(lu)如(ru)下圖圖2-1所示電(dian)(dian)路(lu)具(ju)體說明如(ru)下。

圖2-1  MAX1898的(de)典型充電電路

1）輸入(ru)電壓范(fan)圍為 4.5～12v。鋰電池要求的充電方式(shi)是(shi)恒流(liu)恒壓方式(shi)，電源(yuan)的輸入(ru)需要采(cai)用恒流(liu)恒壓源(yuan)，一(yi)般可采(cai)用直(zhi)流(liu)電源(yuan)外加變壓器。

2)通(tong)過外(wai)接(jie)的場效應管提(ti)供鋰(li)電(dian)池的充電(dian)接(jie)口。

3)通(tong)過(guo)外接(jie)的(de)電(dian)容(rong) CcT 來設置充電(dian)時(shi)間 tCHG。這里(li)的(de)充電(dian)時(shi)間指(zhi)的(de)是快充時(shi)的(de)最大充電(dian)時(shi)間，它和定(ding)時(shi)電(dian)容(rong)CcT 的(de)關系如(ru)下式所示(shi)：

CcT=34.33×tCHG                                                  (2-1)

式中，tCHG 的單位為小(xiao)時(shi)(shi)(shi)，CcT 的單位為Nf。大多數情況下，快充時(shi)(shi)(shi)最大充電時(shi)(shi)(shi)問不超(chao)過3 小(xiao)時(shi)(shi)(shi)，因此常取CcT 為100nF。

4)在限制電(dian)(dian)(dian)流的模式下(xia)，通過外接的電(dian)(dian)(dian)阻 RSET 來設置最大充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)IFSTCHG，關(guan)系如下(xia)式所示(shi)：IFSTCHG=1400/Rset 式中(zhong)，RSEI-的單(dan)位為Q，IFSTCHG 的單(dan)位為A。

當充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源(yuan)(yuan)和電(dian)(dian)(dian)(dian)池(chi)在正常的(de)(de)(de)工(gong)作溫度范圍內時(shi)(shi)(shi)，插入電(dian)(dian)(dian)(dian)池(chi)將啟(qi)動一次充(chong)(chong)電(dian)(dian)(dian)(dian)過程。平均的(de)(de)(de)脈沖充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)低于設置的(de)(de)(de)快(kuai)充(chong)(chong)電(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)20％，或者充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)(shi)(shi)間超出片上(shang)預置的(de)(de)(de)最(zui)大(da)充(chong)(chong)電(dian)(dian)(dian)(dian)時(shi)(shi)(shi)問時(shi)(shi)(shi)，充(chong)(chong)電(dian)(dian)(dian)(dian)周期結束。MAXl898 能(neng)夠(gou)自動檢測充(chong)(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)源(yuan)(yuan)，沒有電(dian)(dian)(dian)(dian)源(yuan)(yuan)時(shi)(shi)(shi)自動關斷以減少電(dian)(dian)(dian)(dian)池(chi)的(de)(de)(de)漏電(dian)(dian)(dian)(dian)。啟(qi)動快(kuai)充(chong)(chong)后，打開外接的(de)(de)(de)P 型(xing)場效應管(guan)，當檢測到(dao)電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓達到(dao)設定的(de)(de)(de)門限時(shi)(shi)(shi)進入脈沖充(chong)(chong)電(dian)(dian)(dian)(dian)方式，P 型(xing)場效應管(guan)打開的(de)(de)(de)時(shi)(shi)(shi)JI 間會越來越短。充(chong)(chong)電(dian)(dian)(dian)(dian)結束時(shi)(shi)(shi)，LED 指示(shi)燈將會呈(cheng)現周期性的(de)(de)(de)閃(shan)爍，具(ju)體的(de)(de)(de)閃(shan)爍含(han)義如表1所示(shi)。

表2-

1  MAX1898 典型(xing)充電電路的LED 指示燈(deng)狀(zhuang)態說明

充電狀態
LED指示燈電池(chi)或充電器沒有(you)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  系統主要硬件電路設計

   硬(ying)件電(dian)路設計主要圍繞充電(dian)芯片MAXl898 展開，而(er)單(dan)片機(ji)控(kong)制部分的(de)電(dian)路簡單(dan)。

3.1  主(zhu)要器件

本設(she)計(ji)的核心器件是MAXl898。MAXl898 可(ke)對所有(you)化學類型的Li+電池進行安(an)全充電，它具有(you)高集成(cheng)度，在小尺寸內集成(cheng)了(le)更多功能(neng)，盡可(ke)能(neng)多地(di)覆蓋了(le)基(ji)本應用電路，只需要(yao)少數(shu)外部元件。MAXl898 為10 引(yin)腳(jiao)、超薄型的MAX 封(feng)裝，其引(yin)腳(jiao)分布如圖3-1 所示：

圖(tu)3-1 MAXl898引腳(jiao)分布

其引腳功能如下：

IN(1 腳)：傳感(gan)輸入，檢測輸入的電壓或電流(liu)；

CHG(2 腳)：充電狀態指示腳，同時驅動LED；

EN/OK(3 腳)：使能輸(shu)入(ru)腳/輸(shu)入(ru)電源“好”輸(shu)出(chu)指(zhi)示腳。EN 為輸(shu)入(ru)腳，可以通過輸(shu)入(ru)禁(jin)止(zhi)芯片工作；OK 為輸(shu)出(chu)腳，用于指(zhi)示輸(shu)入(ru)電源是否與充電器連接；

ISET(4 腳)：充電(dian)電(dian)流調節(jie)引腳。通過串接一(yi)個電(dian)阻到地來設置最大充電(dian)電(dian)流；

CT(5 腳)：安全充(chong)電(dian)(dian)時(shi)間設置引(yin)腳。接一(yi)個(ge)時(shi)間電(dian)(dian)容來設置充(chong)電(dian)(dian)時(shi)間，電(dian)(dian)容為 100nF 時(shi)，幾乎為3 個(ge)小時(shi)，此(ci)引(yin)腳直接接地將禁(jin)用此(ci)功能；

RSTRT(6 腳)：自動重新(xin)啟動控制(zhi)引腳。當此引腳直接(jie)接(jie)地(di)時(shi)，如果電池電壓掉至基準電壓閾(yu)值以下 200mV，將(jiang)會重新(xin)開始一(yi)輪充電周期(qi)。此引腳通過電阻接(jie)地(di)時(shi)，可(ke)以降低它的電壓閾(yu)值。此引腳懸空或者 CT 引腳接(jie)地(di)(充電時(shi)間設置功能禁(jin)用(yong))時(shi)，自動重新(xin)啟動功能被禁(jin)用(yong)；

BATT(7 腳(jiao)(jiao))：電池傳(chuan)感(gan)輸入腳(jiao)(jiao)，接(jie)單(dan)個(ge) Li+電池的正極(ji)。此(ci)引腳(jiao)(jiao)需旁接(jie)一個(ge)大電解電容到地(di)；

GND(8 腳)：接地端；

DRV(9 腳)：外部晶體管驅動器，接晶體管的基極；

CS(10 腳)：電流傳感輸入，接晶體管(guan)的發射(she)極。

本設計的(de)單片機芯片選用Atmel 公司(si)的(de)AT89C52，它完全可以滿足要(yao)求。

另外，由于充電器外部為+12V 供(gong)電，因此(ci)需要通過電壓(ya)(ya)轉(zhuan)(zhuan)換芯片將+12V 電壓(ya)(ya)轉(zhuan)(zhuan)換為 +5V 電壓(ya)(ya)，這里(li)選用(yong)三端電壓(ya)(ya)轉(zhuan)(zhuan)換芯片LM7805 來(lai)完成此(ci)功能。

為了降(jiang)低(di)電(dian)(dian)源干擾，保持電(dian)(dian)路(lu)的穩(wen)定，在LM7805 完成電(dian)(dian)壓轉換，將+5v 充(chong)電(dian)(dian)電(dian)(dian)源送給 MAXl898 之前，先經過一次光(guang)耦模(mo)塊 6N137 的處理，通過單(dan)片機對(dui)光(guang)耦模(mo)塊的控制，可以及(ji)時關斷充(chong)電(dian)(dian)電(dian)(dian)源。6N137 的引腳(jiao)分布如圖3-2 所示：

圖3-2  6N137 的引腳分布

其引腳功能如下：

NC(1 腳(jiao)、4 腳(jiao))：懸空；

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

GND(5 腳)：接地端(duan)；

OUTPUT(6 腳)：輸出腳；

EN(7 腳(jiao))：使能腳(jiao)。為低時，無論有(you)無輸入，輸出都(dou)為高。

不使用時(shi)，懸空即(ji)可；

VCC(8 腳)：電(dian)源輸入腳。

3.2  電路(lu)原理(li)圖及說明(ming)

硬件(jian)電(dian)(dian)路(lu)由單(dan)片機電(dian)(dian)路(lu)、電(dian)(dian)壓轉換及光耦隔離電(dian)(dian)路(lu)、充電(dian)(dian)控制電(dian)(dian)路(lu)3 部分組成。單(dan)片機部分的電(dian)(dian)路(lu)原理圖如下(xia)圖3-3 所示。

圖(tu)3-3  單片機部分的電路(lu)原(yuan)理圖(tu)

圖3-3中，ul 為單片(pian)機AT89C52，工作在(zai)11．0592MHz 時(shi)鐘(zhong)；u2 為蜂鳴器(qi)，蜂鳴器(qi)由(you)單片(pian)機的(de)P2．1 腳(jiao)控制(zhi)發(fa)出報警聲提(ti)示；單片(pian)機的(de)P2．O 腳(jiao)輸(shu)出控制(zhi)光耦器(qi)件，在(zai)需要的(de)時(shi)候可以及時(shi)關斷(duan)充(chong)電(dian)電(dian)源(yuan)；單片(pian)機的(de)外部中斷(duan)O 由(you)充(chong)電(dian)芯片(pian)MAXl898 的(de)充(chong)電(dian)狀態輸(shu)出信號/ CHG 經過反相后觸發(fa)。

下圖(tu)3-4 所示(shi)的為電(dian)(dian)壓轉換(huan)及(ji)光耦隔離部分電(dian)(dian)路的原理圖(tu)。