Many portable devices like mp3s players , ipods needs  to be connected at USB port to recharge their batteries , but sometimes you don’t have a PC where to connect it to charge . In that case you can use an external mp3 player charger power adapter circuit like this , which is based on the MC34063 circuit which  is a monolithic control circuit delivering the main functions for DC DC voltage converting.
The MC34063 mp3 player charger contains an internal temperature compensated reference, comparator, duty cycle controlled oscillator with an active current limit circuit, driver and high current output switch.
The output voltage of this MC34063 mp3 player charger will deliver a  5 volts output voltage at 660mA output current .
The output voltage is adjustable through two external resistors with a 2 % reference accuracy.

This IPOD , MP3 device charger circuit require an input voltage from 9 to 15 volts DC .
Modify the VR1 variable resistor you can adjust the output voltage at 5 volts .
The L1 coil has 75 turns of 0.5 mm enameled copper wire on a Neosid powdered iron core 17-732-22 .