通過USB為NiMH電池充電

圖1. USB供電的單節NiMH電池開關模式充電器

雖然表面上Li+電池已經占據整個便攜世界，但NiMH電池并沒有被完全遺棄。令人吃驚的是，盡管單位重量的能量仍然有較大差距，但其單位體積的能量僅比Li+電池低大約15%。NiMH電池的最大缺點是自放電率較高，混合型NiMH電池在很大程度解決了這一問題，例如SANYO? Eneloop?電池，靜態下一年之后仍然能夠保留85%的電量。NiMH電池的(de)吸引力在于成(cheng)本(ben)低、安全性高、用(yong)戶(hu)更換方(fang)便等(deng)，至少(shao)標準電(dian)池具(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。充電器開關頻率大約為150kHz，電池充電電流為1.1A (典(dian)型(xing)(xing)AA型(xing)(xing)NiMH電(dian)(dian)(dian)(dian)(dian)池在大(da)約(yue)0.5°C條件下(xia))。由(you)于降壓(ya)轉換器將(jiang)5V、500mA轉換成電(dian)(dian)(dian)(dian)(dian)池充(chong)電(dian)(dian)(dian)(dian)(dian)時(shi)(shi)的(de)(de)1.5V、1.1A，電(dian)(dian)(dian)(dian)(dian)路供給(gei)電(dian)(dian)(dian)(dian)(dian)池的(de)(de)電(dian)(dian)(dian)(dian)(dian)流(1.1A)大(da)于從USB接(jie)口(kou)(kou)獲得的(de)(de)電(dian)(dian)(dian)(dian)(dian)流(500mA)。需要注(zhu)意的(de)(de)是，由(you)于在低(di)充(chong)電(dian)(dian)(dian)(dian)(dian)速率下(xia)不能(neng)正(zheng)確(que)判斷(duan)充(chong)電(dian)(dian)(dian)(dian)(dian)終止，只(zhi)能(neng)采用500mA或更大(da)功率的(de)(de)端口(kou)(kou)進(jin)行充(chong)電(dian)(dian)(dian)(dian)(dian)。所以，當枚舉確(que)定(ding)只(zhi)有(you)100mA電(dian)(dian)(dian)(dian)(dian)流可(ke)用時(shi)(shi)，不應激活(huo)充(chong)電(dian)(dian)(dian)(dian)(dian)。系統通過關閉TMR上的(de)(de)Q2，使定(ding)時(shi)(shi)器電(dian)(dian)(dian)(dian)(dian)阻懸空，停止充(chong)電(dian)(dian)(dian)(dian)(dian)。

該充電器另外一項特別有用的功能是：通過檢測電池阻抗確定接入的是否為堿性電池或故障電池，檢(jian)測(ce)到這種(zhong)狀況(kuang)時(shi)將(jiang)禁止充(chong)電。這就(jiu)允許用(yong)戶在緊(jin)急情(qing)況(kuang)下插入堿(jian)性電池，無需擔心意(yi)外(wai)充(chong)電。