Dave Clausen of NYC Resistor wanted a powerful battery pack to recharge his energy-hungry iPhone 3GS and myriad ham radio equipment, so he designed the Mintybuck to handle the job with ease. Rather than using AA batteries and a boost converter to raise the output voltage to 5v, he swapped in a 12v lithium cell and a LM2674-5.0-based buck converter to efficiently drop the voltage down to 5v. The chip is spec’d for 500 mA, and can convert power with >90% efficiency. Not bad for a little charger!