I recently came across the Minty Boost project and instantly knew that was a piece of hardware I wanted to have, in order to extend battery life of my Nintendo DS (using an USB charger cable I bought the other day) and of my Creative MuVo. The only problem with the Minty Boost though is, that I wasn't able to find the used IC at my electronic parts vendor of choice, Reichelt. So I searched for a substitute and came across the LT 1073 CN8. In it's datasheet I quickly found an example circuit for my application - namely converting the voltage supplied by two AA in series (3V) into the 5V expected from the USB port. Some merge of the example circuit and the Minty Boost, and this one was born:

The parts used were the following:

I first built the prototype on a test board and checked it thoroughly.

As I was planning to put the circuit into an old Penguin Peppermints tin lying around (someone in this household really likes them ), I implemented the circuit on a piece of breadboard fitting into the tin together with battery mount and usb connector. And this is the end result (click to enlarge):

The finished pack	The finished packs interior
My NDS charging from the pack	Same as before
Creative MuVo running from the pack	Same as before

Instead of the LT 1073 CN8 I used in the circuit above, you can also use the LT 1073 CN8-5 like Andi did, which already includes the right resistor combination for an output voltage of 5V. In order to make it work though, you'll need a slightly different circuit – just omit R2 and R3 and instead directly connect the output of the diode with pin 8 of the IC: