適用于全球交流電源鋰離子電池充電器設計
本文介紹了(le)一(yi)個單節(jie)鋰離子(Li+)電池的充電方案,該方案基于MAX5022芯片,適用于全球(qiu)的交流電源,而且無需軟(ruan)件控制(zhi)或(huo)微處理器干預就能(neng)實現(xian)所(suo)有的充電功能(neng)。
一次性電池不能夠充電,完全放電后的電池即為報廢電池。二次電池可以多次充電,但不同的化學特性對充電的要求也不同,特別是“快充”控制。目前,最常用的可充電電池是Li+、鎳氫(NiMH)、鎳鎘(Nicd)和鉛酸電池,其它類型的電池還很多,但沒有大規模投入使用。因為本文僅討論利用交流適配器供電的充電器設計,沒有考慮汽車電源供電的SLI鉛酸電池或更大容量電池的充電器。
不同化學類型的電池對充電器的要求
通常快速充電比涓流充電更受歡迎,但快速充電對電路的要求也復雜,鎳氫或鎳鎘電池的快速充電技術與其它電池也是不同的。鎳鎘和鎳氫電池通常在恒流狀態下快充,而不是恒壓狀態下。快充終止檢測基于電壓和溫度的變化率,充電器還應具備過壓保護和過熱保護功能。Li+和鉛酸電池充電器必須保(bao)證作用到電(dian)(dian)(dian)(dian)池上(shang)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)和電(dian)(dian)(dian)(dian)流最大值(zhi)在規定的(de)(de)(de)(de)范圍內(nei),當電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)維持在最大單節電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya),充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流下降到一個較低值(zhi)時(shi),充(chong)電(dian)(dian)(dian)(dian)器終止充(chong)電(dian)(dian)(dian)(dian)。Li+和鉛酸(suan)(suan)電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)器的(de)(de)(de)(de)區別在于(yu)所(suo)允(yun)許的(de)(de)(de)(de)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流、最大電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya),另外鉛酸(suan)(suan)電(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)器一般(ban)具(ju)有浮(fu)充(chong)能力(浮(fu)充(chong)是(shi)為了補充(chong)鉛酸(suan)(suan)電(dian)(dian)(dian)(dian)池的(de)(de)(de)(de)自放(fang)電(dian)(dian)(dian)(dian),而對一個已(yi)經完全充(chong)滿的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)池繼續輸入充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流的(de)(de)(de)(de)技(ji)術),Li+電(dian)(dian)(dian)(dian)池的(de)(de)(de)(de)自放(fang)電(dian)(dian)(dian)(dian)非常低,所(suo)以不需要浮(fu)充(chong)。
Li+電(dian)池
為(wei)便(bian)攜式(shi)產(chan)品(pin)選擇電(dian)(dian)池(chi)(chi)時,最重要的(de)是高(gao)能量密度(du)、尺寸(cun)、重量和價格。迄今(jin)為(wei)止,Li+電(dian)(dian)池(chi)(chi)在最為(wei)流行的(de)電(dian)(dian)池(chi)(chi)中(zhong)能夠(gou)提供最高(gao)的(de)體積和能量密度(du),但其每瓦時的(de)成本也較高(gao)。鉛(qian)酸電(dian)(dian)池(chi)(chi)的(de)每瓦時成本最低(di),但比較笨重。本文以Li+電(dian)(dian)池(chi)(chi)為(wei)例討論充電(dian)(dian)器的(de)設計(ji),它在便(bian)攜式(shi)產(chan)品(pin)中(zhong)已經被普遍使用。我們選擇780mA的(de)充電(dian)(dian)電(dian)(dian)流和4.2V的(de)終止電(dian)(dian)壓(ya)。
圖1：通用輸入交流電壓的離線式Li+電池充電器。
圖1所示充電器無需微處理器(qi)干預,輸入電(dian)(dian)(dian)源可(ke)以采用全球(qiu)范圍的(de)任(ren)何交流電(dian)(dian)(dian)源,省去了(le)大(da)體積60Hz變(bian)壓器(qi),而且可(ke)提供單節Li+電(dian)(dian)(dian)池所要求的(de)精確的(de)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓和電(dian)(dian)(dian)流。充(chong)電(dian)(dian)(dian)器(qi)IC(U4)集成了(le)全面(mian)的(de)保(bao)護功能(電(dian)(dian)(dian)壓、電(dian)(dian)(dian)流和自保(bao)護),確保(bao)Li+電(dian)(dian)(dian)池的(de)安全充(chong)電(dian)(dian)(dian)。
假設Li+電(dian)池帶有過流、過壓和過熱保(bao)護,這些保(bao)護特性(xing)在電(dian)池包里是(shi)必需的,因(yin)為充電(dian)期(qi)間(jian)一(yi)旦(dan)電(dian)路(lu)出現故障(zhang),Li+電(dian)池將存在很大的危險(xian)性(xing),過流、過壓或溫度過高都有可(ke)能(neng)造成Li+電(dian)池爆炸。
電路描述
圖1包括兩顆主器件(U1和U4)、精密基準(U3)和光耦(U2)。U1是離線式開關控制器,配合隔離變壓器、光耦和基準產生隔離的穩壓直流輸出。直流電壓供給電池充電器(U4),U4提供電流限制、電壓調節、電池充電和充電指示等功能。本方案中,U4是一款簡單的線性充電器,內置(zhi)調整管,結合其熱控制環路提供快速充電。
MAX5022的特性
U1(MAX5022)在寬輸入范圍的應用中很容易設計,本文所提供的方案要求能夠滿足全球各地的交流電源規格,這里假設通用的輸入電源電壓范圍為85VAC至265VAC。MAX5022的輸入范圍指標以及評估板電路的輸入范圍恰好滿足這一需求。對于圖1所示充電器的電源端MAX5022評估板不需要作(zuo)任何(he)修改,隔離(li)端只需對評估板的電阻值稍作(zuo)修改。
對(dui)于更(geng)大(da)(da)(da)(da)功率(lv)的(de)(de)應用,只(zhi)需(xu)選(xuan)(xuan)取功率(lv)較大(da)(da)(da)(da)的(de)(de)開關管和能(neng)夠(gou)處理更(geng)大(da)(da)(da)(da)功率(lv)的(de)(de)變(bian)(bian)(bian)壓器(qi)(qi)即可。圖1所示電(dian)(dian)(dian)路要求充電(dian)(dian)(dian)電(dian)(dian)(dian)流為(wei)(wei)780mA,最(zui)大(da)(da)(da)(da)電(dian)(dian)(dian)池電(dian)(dian)(dian)壓為(wei)(wei)4.2V。對(dui)充電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)的(de)(de)要求與MAX5022評(ping)估(gu)板所提供(gong)的(de)(de)輸出(chu)相(xiang)吻合(he)：5V@1A,因此,不需(xu)要更(geng)換評(ping)估(gu)板的(de)(de)晶(jing)體(ti)管和變(bian)(bian)(bian)壓器(qi)(qi)。U4采(cai)用SOT23封裝,所以,充電(dian)(dian)(dian)器(qi)(qi)的(de)(de)尺(chi)寸在很(hen)大(da)(da)(da)(da)程(cheng)度上取決于應用對(dui)充電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)的(de)(de)需(xu)求。變(bian)(bian)(bian)壓器(qi)(qi)是(shi)電(dian)(dian)(dian)路中尺(chi)寸最(zui)大(da)(da)(da)(da)的(de)(de)元件,由于開關控制器(qi)(qi)的(de)(de)工作頻率(lv)大(da)(da)(da)(da)于250kHz,允許系(xi)統選(xuan)(xuan)用小尺(chi)寸的(de)(de)變(bian)(bian)(bian)壓器(qi)(qi)。
上(shang)電(dian)時(shi),在開(kai)關控制器(qi)工作之前,U1調節器(qi)直接通過(guo)泄漏電(dian)阻(zu)R1、R2從整(zheng)流(liu)通路吸取少量的(de)(de)電(dian)流(liu),兩(liang)個(ge)電(dian)阻(zu)阻(zu)值保證每個(ge)電(dian)阻(zu)上(shang)的(de)(de)壓降不會超出每個(ge)電(dian)阻(zu)的(de)(de)容限,Vin引(yin)腳電(dian)壓不會超出其28V額定值(30V為(wei)絕對最(zui)大(da)值),U1在輸入(ru)電(dian)壓達到24V時(shi)開(kai)始開(kai)關操作,并(bing)吸取更大(da)的(de)(de)電(dian)流(liu)(高于R1、R2所能(neng)提供的(de)(de)電(dian)流(liu)),在變壓器(qi)副邊線圈能(neng)夠提供足夠的(de)(de)能(neng)量之前,額外的(de)(de)電(dian)流(liu)由Vin引(yin)腳的(de)(de)旁路電(dian)容供給。這種處(chu)理方式能(neng)夠適合較寬的(de)(de)輸入(ru)電(dian)壓范圍,對效率的(de)(de)影響也(ye)很小(xiao),這是因為(wei)在啟動(dong)過(guo)程中(zhong)只需(xu)極小(xiao)的(de)(de)供電(dian)電(dian)流(liu)(典型(xing)值為(wei)50uA)。
為了防止(zhi)U1的Vin引腳(jiao)(jiao)出現過壓,可以在Vin與地之間接一(yi)個26V至30V的齊(qi)納管,電(dian)壓值(zhi)需要(yao)高于欠壓鎖存電(dian)壓的最大值(zhi),低(di)于該(gai)引腳(jiao)(jiao)所允許的最大絕對(dui)電(dian)壓。如果器件沒有啟動正常的開關操作(zuo),則可認為電(dian)路發生了某些問(wen)題,所以,這一(yi)保護(hu)措施對(dui)于U1來(lai)說(shuo)并不是必需的。
U1是一款電(dian)(dian)(dian)流模式PWM控制器,具(ju)有(you)逐周期(qi)限流電(dian)(dian)(dian)路,必要時其占空(kong)比可(ke)以提高到75%,非常適合圖1所示的(de)反激拓撲。原邊開關電(dian)(dian)(dian)流檢測采用尺寸為1206的(de)1.78Ω電(dian)(dian)(dian)阻(zu)(R7),該電(dian)(dian)(dian)阻(zu)限制了變壓(ya)器原邊的(de)最大電(dian)(dian)(dian)流。固(gu)定開關頻率和(he)最大占空(kong)比限制使得最大限流具(ju)有(you)輸(shu)出(chu)短路保(bao)護功能。
一旦短路(lu)(lu)輸出造成電(dian)路(lu)(lu)達到(dao)了上(shang)述限(xian)制條件(jian),第(di)三組線(xian)圈將(jiang)無法提(ti)供(gong)10V以(yi)上(shang)的電(dian)壓(ya)(UVLO的低電(dian)壓(ya)門限(xian)),U1將(jiang)再次進入啟動狀(zhuang)態,停止開關操作(zuo)。短路(lu)(lu)故(gu)障解除(chu)后系統會自動恢復(fu)正常的工作(zuo)狀(zhuang)態。
電壓調節
變壓器副邊的電壓經過整流、濾波,然后由R4、R5分壓在并聯型穩壓器U3的調節點產生1.24V(對應于4.5V輸出)的反饋電壓。為保證電池充電器正常工作,4.5V是最低電壓(包括容差)。因為充電器采用的是線性結構,充電效率與輸入、輸出電壓的差值成反比,用最低電壓為充電器供電有助于(yu)降低功率損耗。
當(dang)調(diao)節(jie)點電(dian)(dian)(dian)壓(ya)高于(yu)1.24V時(shi)(shi),并聯型穩(wen)(wen)壓(ya)器(qi)將吸(xi)入(ru)電(dian)(dian)(dian)流(liu)(liu),導(dao)通(tong)光耦LED,原(yuan)邊的(de)(de)(de)(de)(de)光敏(min)晶(jing)體管將處于(yu)發光狀態。U1的(de)(de)(de)(de)(de)OPTO輸入(ru)引腳(jiao)用于(yu)直接(jie)連接(jie)光敏(min)晶(jing)體管,以(yi)極其簡單的(de)(de)(de)(de)(de)方(fang)式構(gou)成閉合環路。光敏(min)晶(jing)體管導(dao)通(tong)時(shi)(shi),OPTO引腳(jiao)被拉低(di),內部比(bi)較(jiao)器(qi)在(zai)(zai)(zai)它的(de)(de)(de)(de)(de)一(yi)個輸入(ru)端檢測(ce)到較(jiao)低(di)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)壓(ya),比(bi)較(jiao)器(qi)的(de)(de)(de)(de)(de)另一(yi)輸入(ru)電(dian)(dian)(dian)流(liu)(liu)檢測(ce)引腳(jiao)(CS)的(de)(de)(de)(de)(de)峰值(zhi)電(dian)(dian)(dian)壓(ya),OPTO引腳(jiao)的(de)(de)(de)(de)(de)低(di)電(dian)(dian)(dian)壓(ya)將在(zai)(zai)(zai)每個周期直接(jie)限(xian)制(zhi)功率MOSFETN1的(de)(de)(de)(de)(de)峰值(zhi)電(dian)(dian)(dian)流(liu)(liu)。由于(yu)U1是(shi)一(yi)個PWM控制(zhi)器(qi),電(dian)(dian)(dian)流(liu)(liu)限(xian)制(zhi)使得(de)電(dian)(dian)(dian)壓(ya)調(diao)節(jie)受作用在(zai)(zai)(zai)N1上的(de)(de)(de)(de)(de)占空比(bi)(導(dao)通(tong)時(shi)(shi)間與斷(duan)開(kai)時(shi)(shi)間的(de)(de)(de)(de)(de)比(bi)值(zhi))的(de)(de)(de)(de)(de)影響,環路穩(wen)(wen)定性通(tong)過調(diao)節(jie)R11和C12來保證(zheng)。R10和C5(連接(jie)在(zai)(zai)(zai)U3的(de)(de)(de)(de)(de)第3和第4引腳(jiao))可消除(chu)穩(wen)(wen)定工作情況下的(de)(de)(de)(de)(de)噪聲干擾。
U4的工作特點
U4是一款用于單節Li+電池充電、功能完備的充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器,采(cai)用線性充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)模式,內置調整管(guan)和電(dian)(dian)(dian)(dian)(dian)(dian)流檢測電(dian)(dian)(dian)(dian)(dian)(dian)路。另外,它還集成了一(yi)個(ge)反(fan)向抑制二極(ji)管(guan),在(zai)去掉輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)源時(shi)(shi)可(ke)防止(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)方(fang)向放電(dian)(dian)(dian)(dian)(dian)(dian)。接入一(yi)個(ge)深度放電(dian)(dian)(dian)(dian)(dian)(dian)的電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)時(shi)(shi),U4能夠檢測到(dao)低(di)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(低(di)于(yu)2.5V),這樣,U4將首先啟動涓流充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過程(cheng),在(zai)快(kuai)充(chong)(chong)(chong)周期的1/10時(shi)(shi)間段對電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)進行涓流充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian),直到(dao)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)壓上升(sheng)到(dao)2.5V以上。在(zai)涓流充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)到(dao)快(kuai)速(su)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)轉換時(shi)(shi),軟啟動電(dian)(dian)(dian)(dian)(dian)(dian)路迫(po)使(shi)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)流在(zai)3ms時(shi)(shi)間內緩(huan)慢上升(sheng),避免較大的浪涌電(dian)(dian)(dian)(dian)(dian)(dian)流拉低(di)輸(shu)入電(dian)(dian)(dian)(dian)(dian)(dian)源。
上(shang)述功能(neng)的(de)實施不需要微(wei)控制(zhi)器的(de)監(jian)管,而且,U4還具有可(ke)(ke)編程的(de)溫度限制(zhi)功能(neng),我們會在下面就這(zhe)一點進行詳細(xi)討論。用(yong)一個(ge)電(dian)(dian)(dian)阻設置(zhi)最大充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流,電(dian)(dian)(dian)阻兩端的(de)電(dian)(dian)(dian)壓與充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流成正比(bi),通過監(jian)視該電(dian)(dian)(dian)壓即可(ke)(ke)連續跟(gen)(gen)蹤(zong)充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流,更為(wei)復雜(za)的(de)系(xi)統也(ye)可(ke)(ke)以采用(yong)ADC跟(gen)(gen)蹤(zong)監(jian)視充(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流。
Maxim還(huan)提(ti)供有(you)另一款與MAX1507非常相似的充電(dian)(dian)(dian)器―MAX1555,這款IC能夠在沒有(you)交流(liu)電(dian)(dian)(dian)源(yuan)的情(qing)況下從USB主機(ji)獲得充電(dian)(dian)(dian)電(dian)(dian)(dian)源(yuan)。
電流調節
如果把Li+電(dian)(dian)(dian)(dian)(dian)池(chi)直接(jie)與一個低阻(zu)電(dian)(dian)(dian)(dian)(dian)壓源連接(jie),充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流將(jiang)不受任何限(xian)制,這種狀況(kuang)會對電(dian)(dian)(dian)(dian)(dian)池(chi)及其(qi)周圍環(huan)境造成災(zai)難(nan)性的損害,從Li+電(dian)(dian)(dian)(dian)(dian)池(chi)的安全性考慮,必須(xu)將(jiang)其(qi)充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流限(xian)制在額定范圍以內。U4根據(ju)連接(jie)在ISET(第5引腳)的電(dian)(dian)(dian)(dian)(dian)阻(zu)限(xian)制充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流,圖(tu)1電(dian)(dian)(dian)(dian)(dian)路中選用了一個1.87kΩ的電(dian)(dian)(dian)(dian)(dian)阻(zu),將(jiang)最(zui)大電(dian)(dian)(dian)(dian)(dian)流設(she)置(zhi)在780mA:
Ifast=1461V/Rset=1461/1870≈780mA
電(dian)池(chi)電(dian)壓最小時,由于(yu)輸入穩定在4.5V,U4輸入與輸出的壓差最大(da),如果(guo)此時電(dian)池(chi)是以最大(da)電(dian)流充電(dian),U4功耗將(jiang)達到最大(da)值(zhi)。例如,假設電(dian)池(chi)電(dian)壓為(wei)2.5V,則(ze)對(dui)應(ying)的功耗為(wei)：
P=IV=(0.78A)×(4.5V-2.5V)=1.56W
U4封(feng)裝(8引腳薄型(xing)DFN-EP,EP表(biao)示(shi)裸(luo)露焊盤(pan))在溫(wen)度(du)高(gao)(gao)達(da)(da)70℃時可以(yi)(yi)(yi)耗散的(de)最(zui)大功率(lv)是1.951W,這樣,在整個電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)范圍內(nei)以(yi)(yi)(yi)780mA的(de)電(dian)(dian)(dian)(dian)(dian)流(liu)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)應該沒有任何問(wen)題。但是,如果(guo)IC管芯由于較高(gao)(gao)的(de)環境(jing)溫(wen)度(du)或不良的(de)散熱(re)(re)條(tiao)件(jian)達(da)(da)到(dao)(dao)(dao)了(le)70℃,U4內(nei)部的(de)熱(re)(re)調節環路將自動(dong)降(jiang)低充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu),這一過程(cheng)有別于其它(ta)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)IC中(zhong)(zhong)的(de)“熱(re)(re)關斷(duan)”,“熱(re)(re)關斷(duan)”方式(shi)只是簡單地中(zhong)(zhong)止芯片(pian)(pian)中(zhong)(zhong)的(de)所有電(dian)(dian)(dian)(dian)(dian)路工作(zuo),直到(dao)(dao)(dao)晶(jing)片(pian)(pian)溫(wen)度(du)降(jiang)至規定的(de)數值。MAX1507所采用的(de)方案能(neng)夠(gou)保(bao)證在芯片(pian)(pian)溫(wen)度(du)不超出(chu)最(zui)大限制(zhi)范圍的(de)條(tiao)件(jian)下(xia)提供(gong)最(zui)快的(de)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)速率(lv),隨著電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)的(de)升高(gao)(gao),充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)在保(bao)持最(zui)高(gao)(gao)溫(wen)度(du)的(de)前提下(xia)逐漸升高(gao)(gao),直到(dao)(dao)(dao)達(da)(da)到(dao)(dao)(dao)最(zui)大充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)。在此之(zhi)后,充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)器(qi)在滿足芯片(pian)(pian)溫(wen)度(du)限制(zhi)的(de)條(tiao)件(jian)下(xia)將以(yi)(yi)(yi)最(zui)大充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)對電(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian),直到(dao)(dao)(dao)電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)達(da)(da)到(dao)(dao)(dao)內(nei)部設置的(de)4.2V±1%。電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)達(da)(da)到(dao)(dao)(dao)門限值后,U4將輸出(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)保(bao)持在4.2V,從而使充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)開(kai)始下(xia)降(jiang)。充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)降(jiang)低到(dao)(dao)(dao)快充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)10%時,充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)指示(shi)燈關閉(bi),表(biao)示(shi)充(chong)(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)周(zhou)期結(jie)束。
如(ru)果充(chong)電過程中輸出負載增大,例如(ru),用(yong)戶在(zai)電池充(chong)電時啟動了其(qi)它(ta)電路,U4允許返回(hui)到限流(liu)模式。
測試結果
圖1電(dian)路(lu)輸(shu)入為(wei)110V交(jiao)流(liu)(liu)電(dian)源,輸(shu)出(chu)為(wei)4.14V、740mA負載,效率可(ke)達到46%。當(dang)負載電(dian)流(liu)(liu)增大(da)使電(dian)池(chi)電(dian)壓(ya)(ya)降至2.7V時,電(dian)路(lu)將輸(shu)出(chu)電(dian)流(liu)(liu)限制在802mA,比(bi)設置的(de)780mA限流(liu)(liu)門限提(ti)高不到3%,在規(gui)定的(de)參數指標以內。MAX1507允(yun)許±8%的(de)變化。當(dang)電(dian)池(chi)電(dian)壓(ya)(ya)拉(la)至2.5V時,輸(shu)出(chu)電(dian)流(liu)(liu)降至76.1mA,在78mA(780mA的(de)1/10)的(de)3%以內。U4數據(ju)手(shou)冊中規(gui)定允(yun)許±5%的(de)范圍(wei)。輸(shu)出(chu)短路(lu)時電(dian)路(lu)還允(yun)許返回(hui)到該模式。
空(kong)載時(shi),輸出穩定(ding)在(zai)4.2V左右(you),形成一個三角(jiao)波(bo),在(zai)U4輸出接(jie)一個負載電(dian)阻可以消除這個偏(pian)差,保(bao)持其連續性,但會降低系(xi)統效率,但對(dui)于交流電(dian)供電(dian)系(xi)統來(lai)說(shuo),效率并不重要。
本文小結
利用電流模式PWM控制器(U1)構成隔離電源,結合Li+電池充電IC(U4)和其它元件可以構成一個由通用的交流電源供電的Li+電池充電器。該方案不(bu)需(xu)要(yao)任何額外的(de)控制(zhi)電路(如微控制(zhi)器(qi)的(de)干預),也不(bu)需(xu)要(yao)軟(ruan)件開發。硬件開發只需(xu)對Maxim提供的(de)標準評估板稍作修改即可,具(ju)有成本低、開發周期短等優(you)勢。
由于(yu)系(xi)統沒有60Hz的(de)隔(ge)離變壓器,具有尺寸小、輕便等(deng)特點,可用于(yu)手機或(huo)其它手持(chi)設(she)備(bei)(bei)的(de)充(chong)電。所有熱量(liang)均集中在交流適(shi)配(pei)器內,與內置充(chong)電器的(de)手持(chi)設(she)備(bei)(bei)相比(bi),不(bu)需要過多考慮散熱問題(ti)。