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單節NiMH電池開關模式充電器電路

 

                                             

圖1. USB供電的單節NiMH電池開關模式充電器

       雖然表面上Li+電池(chi)(chi)(chi)已經占(zhan)據整個便攜世界(jie),但NiMH電池(chi)(chi)(chi)并沒有(you)被完全遺棄(qi)。令人吃驚的(de)是(shi),盡管單位重量(liang)的(de)能(neng)(neng)(neng)量(liang)仍然有(you)較(jiao)大差距,但其單位體積的(de)能(neng)(neng)(neng)量(liang)僅比(bi)Li+電池(chi)(chi)(chi)低(di)大約15%。NiMH電池(chi)(chi)(chi)的(de)最大缺點是(shi)自放電率(lv)較(jiao)高,混合型NiMH電池(chi)(chi)(chi)在很大程(cheng)度(du)解決了這一問題(ti),例如SANYO? Eneloop?電池(chi)(chi)(chi),靜態下(xia)一年之后仍然能(neng)(neng)(neng)夠保(bao)留85%的(de)電量(liang)。NiMH電池(chi)(chi)(chi)的(de)吸引(yin)力在于(yu)成本低(di)、安全性高、用戶更換方便等,至少標準電池(chi)(chi)(chi)具(ju)備這些優勢。

      圖1所示便攜設備由一節AA型NiMH電池供電,利用USB充電。DS2710充電器開(kai)關(guan)頻率(lv)大約為150kHz,電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)為1.1A (典型AA型NiMH電(dian)(dian)(dian)(dian)池(chi)在(zai)大約0.5°C條件下)。由于降壓轉(zhuan)換器(qi)將5V、500mA轉(zhuan)換成電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)時的(de)(de)1.5V、1.1A,電(dian)(dian)(dian)(dian)路供給電(dian)(dian)(dian)(dian)池(chi)的(de)(de)電(dian)(dian)(dian)(dian)流(liu)(1.1A)大于從USB接口獲得的(de)(de)電(dian)(dian)(dian)(dian)流(liu)(500mA)。需要注(zhu)意的(de)(de)是,由于在(zai)低充(chong)電(dian)(dian)(dian)(dian)速率(lv)下不能正確判斷充(chong)電(dian)(dian)(dian)(dian)終止,只能采用500mA或更大功率(lv)的(de)(de)端口進行充(chong)電(dian)(dian)(dian)(dian)。所以,當枚舉確定(ding)只有100mA電(dian)(dian)(dian)(dian)流(liu)可用時,不應激活充(chong)電(dian)(dian)(dian)(dian)。系統通過關(guan)閉(bi)TMR上的(de)(de)Q2,使(shi)定(ding)時器(qi)電(dian)(dian)(dian)(dian)阻懸空,停止充(chong)電(dian)(dian)(dian)(dian)。

     該充電(dian)(dian)(dian)器另(ling)外(wai)一項特別(bie)有用的功(gong)能是:通過(guo)檢測電(dian)(dian)(dian)池(chi)(chi)阻抗確定接入(ru)的是否為(wei)堿性(xing)電(dian)(dian)(dian)池(chi)(chi)或故障電(dian)(dian)(dian)池(chi)(chi),檢測到這(zhe)種(zhong)狀況(kuang)時將禁止充電(dian)(dian)(dian)。這(zhe)就允許用戶在緊急情況(kuang)下插入(ru)堿性(xing)電(dian)(dian)(dian)池(chi)(chi),無需(xu)擔(dan)心(xin)意外(wai)充電(dian)(dian)(dian)。

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