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(dian)池(chi)已經占據整個便攜世(shi)界，但NiMH電(dian)池(chi)并沒有(you)被(bei)完(wan)全遺棄。令人吃驚的(de)(de)(de)是(shi)，盡管單位重量(liang)的(de)(de)(de)能量(liang)仍(reng)然有(you)較(jiao)大差距，但其單位體積的(de)(de)(de)能量(liang)僅比(bi)Li+電(dian)池(chi)低(di)大約15%。NiMH電(dian)池(chi)的(de)(de)(de)最大缺點是(shi)自放(fang)電(dian)率(lv)較(jiao)高(gao)，混合型NiMH電(dian)池(chi)在很大程(cheng)度解決了這一問題，例如SANYO? Eneloop?電(dian)池(chi)，靜態下一年之后仍(reng)然能夠保留85%的(de)(de)(de)電(dian)量(liang)。NiMH電(dian)池(chi)的(de)(de)(de)吸引力在于成本(ben)低(di)、安全性高(gao)、用戶更換方(fang)便等(deng)，至少標準(zhun)電(dian)池(chi)具備這些優勢。

      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(pin)率大(da)約為150kHz，電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)為1.1A (典(dian)型(xing)AA型(xing)NiMH電(dian)(dian)(dian)池(chi)在大(da)約0.5°C條件下(xia))。由于降壓(ya)轉換器(qi)將5V、500mA轉換成電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)時的(de)1.5V、1.1A，電(dian)(dian)(dian)路(lu)供給電(dian)(dian)(dian)池(chi)的(de)電(dian)(dian)(dian)流(liu)(liu)(1.1A)大(da)于從USB接口獲得(de)的(de)電(dian)(dian)(dian)流(liu)(liu)(500mA)。需要(yao)注意的(de)是，由于在低充電(dian)(dian)(dian)速(su)率下(xia)不能正(zheng)確判斷充電(dian)(dian)(dian)終止，只能采用500mA或(huo)更大(da)功率的(de)端口進行充電(dian)(dian)(dian)。所以，當枚舉(ju)確定(ding)只有100mA電(dian)(dian)(dian)流(liu)(liu)可用時，不應激活充電(dian)(dian)(dian)。系統通過關(guan)閉(bi)TMR上的(de)Q2，使定(ding)時器(qi)電(dian)(dian)(dian)阻懸(xuan)空(kong)，停止充電(dian)(dian)(dian)。

     該充電(dian)器另外一項(xiang)特別有用的功(gong)能是：通(tong)過檢(jian)測電(dian)池阻抗確定(ding)接入(ru)的是否(fou)為堿(jian)性電(dian)池或故障電(dian)池，檢(jian)測到這(zhe)種狀況時將禁(jin)止充電(dian)。這(zhe)就允許(xu)用戶在(zai)緊急情況下插入(ru)堿(jian)性電(dian)池，無(wu)需擔心意外充電(dian)。