USB Charging Circuit
A handy DC to USB assembled circuit that we use to make our Solar USB Chargers. You can use it too. Takes DC power from as low as 2V and bumps it up to the 5V USB needs at around 600mA (0.6A) of current.
This circuit works fine with most simple USB devices, however many modern phones or tablets require a much higher sustained amperage than what this circuit can output. For best results use a lithium or alkaline based battery source.