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(yin)力在于成(cheng)本低(di)、安全性高、用戶更換方便等，至少標準電池具備(bei)這些優(you)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)AA型(xing)NiMH電(dian)(dian)(dian)(dian)池(chi)在大約0.5°C條件下)。由于(yu)降壓(ya)轉換(huan)(huan)器將5V、500mA轉換(huan)(huan)成電(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)時(shi)的(de)1.5V、1.1A，電(dian)(dian)(dian)(dian)路供給電(dian)(dian)(dian)(dian)池(chi)的(de)電(dian)(dian)(dian)(dian)流(liu)(1.1A)大于(yu)從USB接(jie)口(kou)獲(huo)得的(de)電(dian)(dian)(dian)(dian)流(liu)(500mA)。需要注意的(de)是，由于(yu)在低充(chong)電(dian)(dian)(dian)(dian)速(su)率下不能正(zheng)確判(pan)斷充(chong)電(dian)(dian)(dian)(dian)終(zhong)止，只能采用(yong)500mA或更大功率的(de)端口(kou)進行充(chong)電(dian)(dian)(dian)(dian)。所(suo)以，當枚舉確定(ding)(ding)只有100mA電(dian)(dian)(dian)(dian)流(liu)可(ke)用(yong)時(shi)，不應激活充(chong)電(dian)(dian)(dian)(dian)。系統通過關閉TMR上的(de)Q2，使定(ding)(ding)時(shi)器電(dian)(dian)(dian)(dian)阻懸空，停止充(chong)電(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(dian)(dian)(dian)池(chi)，檢測到這(zhe)種狀況(kuang)時將(jiang)禁止充電(dian)(dian)(dian)。這(zhe)就允(yun)許(xu)用戶在緊急(ji)情況(kuang)下插入堿性電(dian)(dian)(dian)池(chi)，無需擔心意外充電(dian)(dian)(dian)。