AA to USB

Over a couple of posts, I'll be describing a little project I've been working on. When all is said and done, this device will take a pair of AA batteries and use them to power a USB port, something called a boost converter. What's that good for? It could be used as a backup power source for something that is powered or recharged over USB, such as an ipod. My iphone gets about 4 hours of video playback on a full charge - this device I'm making could be used to augment or recharge the iphone battery to double that playback time - good for long flights.

Now, the end result will be useful, but is hardly the point of the project. If I was actually interested in having such a device, I could just buy one. If I wanted something cooler than store-bought, I could purchase a Minty Boost kit, a tin of Altoids, then have a fun for an hour with a soldering iron.

No, the point of this project is the design of it and the doing of it. I haven't done much electronics work since I left college, so it's nice to dabble in it again. Partly I wanted a little side project. Another part of it was that, while looking over the development and design of the Mint Boost, I thought that I could do a better job. It's a cool piece of work, and the Altoids tin gives it some geek chic, but there were two things I wanted to improve on. The first is a limitation on current. The chip at the heart of the Minty Boost, a MAX756, is spec'ed for only 200 mA at 5 V. The USB specification is to be able to supply up to 500 mA at 5 V. I'm not sure what the power draw of an iPod is while it is playing something and recharging, but I figure I may as well try and satisfy the spec. The second limitation is efficiency. The Minty Boost does better than most DIY designs, but is only about 85% efficient. I figured I could do better.

Tune in next time for the start of the design, and oh so tiny components...