Usually when someone asks me how to build a USB charger I point them to Jason Striegel’s USB battery v2. It’ll work for a lot of things that only need 5V. Unfortunately [ian] has a 3G firewire iPod so he decided to build a switch mode power supply to generate the 8-30V required by firewire. The device is powered by 3 AA batteries and uses a PIC 12F683 microcontroller to regulate the output voltage. The device can power a dead 3G iPod, but it can’t charge it, so Ian is looking for some input from the community. Some have already suggested using FETs with a lower turn on voltage.