With this tiny thing you can charge almost all devices that are charged via USB, like iPods or mobile phones, with only two AA-Cells!

Step 1: Having the Idea

So why should i build this?
The reason is quite simple: I am bored of empty batteries (Ipod, mobile phone) while I'am on the go. And the solution with the linear regulator like the "7805" is in fact very simple, but very unefficient, because: firstly you need a supply that provides about 3 volts more than you need for usb and secondly in most cases the difference between input voltage and output voltage is lost in heat.

The solution for the problem comes from Linear Technology. The most important compenent of the cicuit presented in the next steps is the "LT1301". This is a small step up converter for to build switching mode power supplys with only a few external components.

Step 2: Parts You Need

What you need:

->The LT1301 and a ic socket (8DIP)

->2 electrolyte caps WITH! low ESR (6,3V 100uF)

->one inductor with a very LOW! DCR (around 0,03R) with 10uH should be able to handle switching
currents at about 1,5 Amperes.

->one schottky rectifier like "SB130" or "1N5817" (important if you can't get one of the two proposed
rectifiers:low forward voltage drop, fast switching capability and it should be able to handle
currents of 1 Ampere.)

-> A switch(on/off), an usb connector, a circuit board, a LED with resitor (limit led current to 2mA!, don't loose your mA by pumping them throu the LED) and don't forget the battery holder

Step 3: The Circuit in Detail

What is important when building?

The input capacitator should be as close as possible to pin 6 (Vin) of the LT1301!
Keep all cicuit traces short!
Directly tie Pin1(GND) Pin8 (PGND) and Pin3 (Shutdown) togheter and connect it to ground.
Avoid long soldering times for to prevent destruction of components by overheating...

For the detailed placement of the components on the circuit board you can use your own creativity...

Step 4: Finished!

So now its done, but before connecting it to any usb device, be sure that it works properly! (the voltage should be 5 volts, the LED only should glow,etc...) When all is checked and you are sure that everything works you can (if you like it) start to put hot melt around it as kind of protection. In case you don't like hot melt you can put the device into a match box or everything you want...

on the left side of the picture you see an older version on the right you see the newer smaller, enhanced version

Some Technical data:
Input: 1,5 to 3 volts
Output: 5 Volts @ 200mA max. (really enough to charge an iPod mini or a mobile phone, trust me ;-) )
Watts and efficiency:
In: 0,95W at 2,5 V
Out: 0,875W at 5 V
loss: 0,075W
8 percent loss
92% efficiency