I created the minty boost that can charge an iphone, which was a kit from Adafruit. The input has 3 volts. In order for the output to have 5 volts, the entire circuit acts as a boost converter. The input is the batteries and the output is the USB port. A boost converter is a power converter whose output voltage is greater than its input voltage. Some parts of the circuit is the capacitors, which stores electrical charge, and a diode that limits the flow of current in one direction. However, the most important part of the minty boost is the chip. The chip has a complex structure, which helps boost the voltage.