開關型鉛酸蓄電池智能充電器
設計了一種基于UC3906與UC3823的免維護鉛酸蓄電池開關型雙電平智能充電器， 這種充電器可保證蓄電池在(zai)很寬的溫度(du)范圍內精確充電(dian)， 延長蓄電(dian)池的使用壽命; 可以消除充電(dian)過程中的極化現象， 提高充電(dian)效率。
1 UC3906的結構及工作原理。
UC3906內部框圖如圖1所示，該芯片內含有獨立的電壓控制電路和限流放大器， 它可以控制芯片內的驅動器， 驅動器提供的輸出電流達25 mA, 可直接驅動外部串聯的調整管， 從而調整充電器的輸(shu)出電(dian)(dian)(dian)壓與電(dian)(dian)(dian)流。電(dian)(dian)(dian)壓和電(dian)(dian)(dian)流檢(jian)測比較器(qi)檢(jian)測蓄電(dian)(dian)(dian)池的充電(dian)(dian)(dian)狀(zhuang)(zhuang)態(tai)， 并控(kong)制(zhi)狀(zhuang)(zhuang)態(tai)邏輯電(dian)(dian)(dian)路的輸(shu)入(ru)信號。
圖1 UC3906內(nei)部結構框圖
當蓄電池電壓或電流過低時， 充電起動比較器控制充電器進入涓流充電狀態， 當驅動器截止時，該比較器還能輸出25 mA涓流充電電流。這樣， 當蓄電池短路或反接時， 充電器只能以小電流充電，避免(mian)了因充電(dian)電(dian)流過大而(er)損壞蓄電(dian)池(chi)。
蓄電(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)電(dian)(dian)壓與(yu)環境(jing)溫(wen)(wen)度(du)(du)有(you)關， 溫(wen)(wen)度(du)(du)每升高(gao)1 ℃， 蓄電(dian)(dian)池(chi)(chi)單格電(dian)(dian)壓下(xia)降4 mV, 也就(jiu)是說(shuo)蓄電(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)浮充(chong)電(dian)(dian)壓有(you)負的(de)(de)(de)(de)溫(wen)(wen)度(du)(du)系數- 4 mV/℃。普通(tong)充(chong)電(dian)(dian)器(qi)如果在(zai)(zai)25 ℃處于(yu)最佳工作(zuo)(zuo)狀態， 在(zai)(zai)環境(jing)溫(wen)(wen)度(du)(du)為0 ℃就(jiu)會充(chong)電(dian)(dian)不足(zu)， 而(er)在(zai)(zai)溫(wen)(wen)度(du)(du)為45 ℃時可(ke)能(neng)因嚴重過(guo)充(chong)電(dian)(dian)而(er)縮短(duan)蓄電(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)使(shi)用壽(shou)命(ming)。而(er)UC3906的(de)(de)(de)(de)最重要的(de)(de)(de)(de)特(te)性是具有(you)精確(que)的(de)(de)(de)(de)基準電(dian)(dian)壓， 其基準電(dian)(dian)壓的(de)(de)(de)(de)大(da)小(xiao)隨(sui)環境(jing)溫(wen)(wen)度(du)(du)而(er)變化(hua)， 且變化(hua)規律(lv)與(yu)鉛(qian)酸(suan)蓄電(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)溫(wen)(wen)度(du)(du)特(te)性一致。同時芯片只需1.7 mA的(de)(de)(de)(de)輸入電(dian)(dian)流就(jiu)可(ke)工作(zuo)(zuo)， 這樣可(ke)以盡量減小(xiao)芯片的(de)(de)(de)(de)功耗， 實現(xian)(xian)對環境(jing)溫(wen)(wen)度(du)(du)的(de)(de)(de)(de)準確(que)檢測。在(zai)(zai)0~70 ℃溫(wen)(wen)度(du)(du)范圍內可(ke)以保證蓄電(dian)(dian)池(chi)(chi)既充(chong)足(zu)電(dian)(dian)又(you)不會出現(xian)(xian)過(guo)充(chong)電(dian)(dian)現(xian)(xian)象， 完全(quan)滿足(zu)蓄電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)需要。
UC3906可構成雙電平浮充充電器， 充電(dian)過(guo)程(cheng)分為3個充電(dian)狀(zhuang)態(tai)(tai)， 如圖2所示(shi)： 大(da)電(dian)流(liu)恒(heng)流(liu)充電(dian)狀(zhuang)態(tai)(tai)， 高電(dian)壓過(guo)充電(dian)狀(zhuang)態(tai)(tai)和低電(dian)壓恒(heng)壓浮充狀(zhuang)態(tai)(tai)。
圖2 雙電平(ping)浮充充電狀態(tai)曲(qu)線
充電過程從大電流恒流充電狀態開始， 在這種狀態下充電器輸出恒定的充電電流Imax, 同時充電器連續監控蓄電池組的兩端電壓， 當蓄電池的電壓達到轉換電壓U12時， 其電量已恢復到放電容量的70%~90%, 充電器轉入過充電狀態。在此狀態下， 充電器輸出電壓升高到Uoc; 由于充電器輸出電壓保持恒定不變， 所以充電電流連續下降， 當電流下降到Ioct時， 蓄電池的容量已達到額定容量的100% ,充電器輸(shu)出電(dian)壓下降到(dao)較低的(de)浮充電(dian)壓UF.
2 電路設計。
對于較大容量的鉛酸蓄電池， 為了提高充電效率， 通常選用開關型充電器。設計的24V20Ah鉛酸蓄電池開關型充電器實際電路見圖3, 在該電路中，用兩只專用集成電路UC3906與UC3823和一只通用運放即可完成全部控制功能。充電器主電路(lu)由功率MOSFET ( IRF9503) 、續流二極(ji)管( UES2402) 和濾(lv)波電感( 130 μH) 等元件組成。
圖3 24 V 20 Ah鉛酸蓄電池開關型雙電平浮充智能充電器電路圖
2.1 電(dian)(dian)(dian)壓電(dian)(dian)(dian)流(liu)控制回(hui)路與(yu)電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)邏輯狀(zhuang)態電(dian)(dian)(dian)路
對小容量蓄(xu)(xu)電(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)器(qi)可采用線(xian)性(xing)串聯調(diao)整管來(lai)控(kong)制充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流， 而對于開關型充(chong)(chong)(chong)電(dian)(dian)(dian)器(qi)， UC3906鉛(qian)酸蓄(xu)(xu)電(dian)(dian)(dian)池(chi)充(chong)(chong)(chong)電(dian)(dian)(dian)控(kong)制集(ji)成電(dian)(dian)(dian)路(lu)具(ju)有充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓控(kong)制和充(chong)(chong)(chong)電(dian)(dian)(dian)邏(luo)輯(ji)狀態控(kong)制的功能(neng)， 并能(neng)提供充(chong)(chong)(chong)電(dian)(dian)(dian)的溫(wen)度補償控(kong)制功能(neng)。
蓄電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池兩(liang)端的分壓電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻監控蓄電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓， 分壓電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻的阻值確定浮充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓、過充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓和涓流充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)門限電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓。差動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流取樣比較器(qi)產生(sheng)過充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)狀態的轉換信(xin)號， 電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓放大(da)器(qi)放大(da)補償(chang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓回路的信(xin)號。
在(zai)溫度為(wei)25 ℃， Uref值為(wei)2.3 V時：
過充電壓：
浮充電壓：
過(guo)充(chong)轉換電壓：U12=0.95Uoc=28.03 V
浮充轉換電壓(ya)：U13=0.9UF=24.8 V
最大充電電流：
過充終止電流：
2.2 開關型電流(liu)源控制回路(lu)
輸入電(dian)壓(ya)( 35 /50 V) 經(jing)(jing)10 kΩ電(dian)阻與(yu)1N4744穩壓(ya)管組成的(de)穩壓(ya)電(dian)路(lu)穩壓(ya)后， 又經(jing)(jing)TIP31晶體管射隨器輸出+14 V電(dian)壓(ya)， 作(zuo)為控(kong)制電(dian)路(lu)的(de)電(dian)源(yuan)電(dian)壓(ya)。
PWM頻率設定為(wei)100 kHz, 以減小輸出濾波(bo)器的體積(ji)， 蓄電(dian)池充電(dian)電(dian)流(liu)從0.1 Ω/5 W電(dian)阻上取(qu)樣， 差動(dong)放大增益為(wei)5。
開關(guan)型電(dian)(dian)(dian)(dian)流(liu)源控(kong)(kong)制(zhi)(zhi)回(hui)路的(de)(de)(de)性能(neng)(neng)(neng)對(dui)充(chong)電(dian)(dian)(dian)(dian)狀(zhuang)態控(kong)(kong)制(zhi)(zhi)轉換有很大(da)的(de)(de)(de)影響， 在(zai)大(da)電(dian)(dian)(dian)(dian)流(liu)快速充(chong)電(dian)(dian)(dian)(dian)狀(zhuang)態下(xia)(xia)(xia)， 充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)要能(neng)(neng)(neng)提(ti)供(gong)最(zui)大(da)的(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu); 在(zai)浮充(chong)狀(zhuang)態下(xia)(xia)(xia)， 充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)輸出電(dian)(dian)(dian)(dian)流(liu)很小(xiao)。因此， 充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)電(dian)(dian)(dian)(dian)流(liu)控(kong)(kong)制(zhi)(zhi)回(hui)路的(de)(de)(de)增(zeng)益變化(hua)范(fan)圍(wei)應大(da)于60 db, 采用(yong)普通的(de)(de)(de)峰(feng)值電(dian)(dian)(dian)(dian)流(liu)反饋很難滿(man)足要求， 24 V20 Ah鉛酸(suan)蓄電(dian)(dian)(dian)(dian)池開關(guan)型充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)采用(yong)平(ping)(ping)均(jun)電(dian)(dian)(dian)(dian)流(liu)反饋回(hui)路見圖4.它比(bi)峰(feng)值電(dian)(dian)(dian)(dian)流(liu)反饋控(kong)(kong)制(zhi)(zhi)相對(dui)復雜， 利用(yong)平(ping)(ping)均(jun)電(dian)(dian)(dian)(dian)流(liu)反饋控(kong)(kong)制(zhi)(zhi)回(hui)路可(ke)以使(shi)充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)電(dian)(dian)(dian)(dian)路在(zai)以下(xia)(xia)(xia)幾(ji)方面有所改進： ①由(you)于誤差放大(da)在(zai)較低(di)工(gong)作頻率范(fan)圍(wei)內的(de)(de)(de)高增(zeng)益， 從而使(shi)閉環電(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)控(kong)(kong)制(zhi)(zhi)精度得到(dao)了提(ti)高; ②在(zai)大(da)電(dian)(dian)(dian)(dian)流(liu)充(chong)電(dian)(dian)(dian)(dian)的(de)(de)(de)工(gong)作狀(zhuang)態下(xia)(xia)(xia)， 當電(dian)(dian)(dian)(dian)感(gan)電(dian)(dian)(dian)(dian)流(liu)不連續時， 可(ke)以改善大(da)電(dian)(dian)(dian)(dian)流(liu)輸出級的(de)(de)(de)非線性; ③可(ke)以提(ti)高充(chong)電(dian)(dian)(dian)(dian)器(qi)(qi)電(dian)(dian)(dian)(dian)路在(zai)很小(xiao)的(de)(de)(de)脈沖(chong)占空(kong)比(bi)工(gong)作條件下(xia)(xia)(xia)的(de)(de)(de)抗(kang)開關(guan)峰(feng)值噪聲(sheng)的(de)(de)(de)能(neng)(neng)(neng)力。
圖4 平均電(dian)流反饋電(dian)路圖
電(dian)流控制(zhi)回路選用(yong)UC3823PWM控制(zhi)器(qi)(qi)， 因為它在非(fei)常(chang)小的(de)脈沖(chong)占(zhan)空(kong)(kong)比(bi)(bi)到100%的(de)脈沖(chong)占(zhan)空(kong)(kong)比(bi)(bi)的(de)變化范圍內能(neng)夠線(xian)性工作(zuo); UC3823PWM控制(zhi)器(qi)(qi)的(de)帶寬(kuan)和電(dian)路結構完全滿足平均電(dian)流控制(zhi)回路的(de)要求; UC3823PWM控制(zhi)器(qi)(qi)輸(shu)出驅動級與開(kai)關電(dian)流源輸(shu)出功率級連接簡單(dan)。運放(fang)(fang)當(dang)作(zuo)差動放(fang)(fang)大器(qi)(qi)使用(yong)，用(yong)以檢測開(kai)關電(dian)流源的(de)輸(shu)出電(dian)流， 并(bing)把該電(dian)流信號(hao)變換為適當(dang)的(de)電(dian)壓信號(hao)。
2.3 功率(lv)輸出級
功率輸出級(ji)采用降壓(ya)式開關(guan)電(dian)(dian)(dian)流(liu)源。為了簡(jian)化UC3823的(de)高(gao)端驅動電(dian)(dian)(dian)路(lu)， 輸出開關(guan)管采用直接耦(ou)合P溝(gou)道MOSFET.流(liu)入(ru)MOSFET的(de)開關(guan)電(dian)(dian)(dian)流(liu)提供柵(zha)極電(dian)(dian)(dian)荷(he)， 使MOSFET導通， 接在(zai)柵(zha)極與源極的(de)穩壓(ya)管將柵(zha)極電(dian)(dian)(dian)壓(ya)限制在(zai)12 V.PNP管的(de)作用是釋放柵(zha)極電(dian)(dian)(dian)荷(he)， 從而(er)使MOSFET加速關(guan)斷。在(zai)續流(liu)二極管兩端加入(ru)RC緩沖器(qi)， 可以抑制電(dian)(dian)(dian)路(lu)寄生參數引(yin)起的(de)高(gao)頻自激(ji)振蕩(dang)。在(zai)輸出電(dian)(dian)(dian)路(lu)中加入(ru)整流(liu)管， 可以避(bi)免(mian)在(zai)電(dian)(dian)(dian)源中斷后蓄(xu)電(dian)(dian)(dian)池(chi)組對充電(dian)(dian)(dian)器(qi)放電(dian)(dian)(dian)。
1) UC3906內部基準電壓的(de)溫(wen)度系數與(yu)鉛酸蓄電池(chi)(chi)的(de)溫(wen)度系數相(xiang)同， 從而保證了蓄電池(chi)(chi)在較寬(kuan)的(de)溫(wen)度范圍內實現蓄電池(chi)(chi)的(de)精(jing)確快速充(chong)電， 且不(bu)會過充(chong)影響蓄電池(chi)(chi)壽命(ming)。
2) UC3823PWM控(kong)制器在非常小的(de)脈(mo)沖占空(kong)比到100%的(de)脈(mo)沖占空(kong)比的(de)變化(hua)范(fan)圍內能夠(gou)線性工作;UC3823PWM控(kong)制器的(de)帶(dai)寬和電路結構完全滿足平均電流(liu)控(kong)制回路的(de)要求。