AAA Battery Booster
This idea (and Mike's interest in voltage boosting) is due to Ted Hullar.
Ted has some LED headlamps that take 3 alkaline AAAs apiece. A few problems with this:
- Alkaline batteries are expensive, he'd rather use NiMH, but:
- NiMH batteries have enough juice over time, but the voltage is too low to keep white LEDs happy, and
- Batteries are bought and charged in pairs!
I have stuff like this too.
His suggestion: A voltage booster IC and attendant passives in the shape of an AAA battery. This replaces one of the three batteries. The remaining two NiMH batteries add up to 2.4V, much lower than 3 alkalines' initial voltage of 4.8V. But NiMH batteries can deliver more current, which the boost IC can turn to higher voltage. The version of the chip that I had (MAX756 I think) delivered 5V, which we decided was perfect to slightly overdrive LEDs that were probably wired to tolerate 4.8V. (His light had PWM dimming, but the max setting was still simple DC with ballast resistors.)
It can fit between the positive end of the two batteries and the positive power terminal of the light. It needs a connection to ground; this can be a discreet wire and tab wedged into ground between the battery and the negative power terminal of the light.
I prototyped it. It worked. It busted the same night. I promised I'd design an IC. Many weeks later...
Here's the pre-draft: