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

Image Notes1. LT13012. Input Cap (100uF 6,3V LOW ESR)3. Inductor (10uH 0,03R 2,4A)4. Schottky Rectifier (SB130> 1A @ 30V)5. LED with Resistor (390R, LED current limited to 8mA to avoid to much outputlost by the LED, LED is connected to 5V output)6. Output Cap (100uF 6,3V LOW ESR)7. USB Con8. Power Switch9. To Batteries (2xAA Nihm rechargeable batteries or alkaline (not recomended,they provide not enough current, and they are not environmentally friendly...)

step 1: Having the ideaSo 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 verysimple, 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 betweeninput 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 stepup converter for to build switching mode power supplys with only a few external components.

step 2: Parts you needWhat 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 switchingcurrents at about 1,5 Amperes.

->one schottky rectifier like "SB130" or "1N5817" (important if you can't get one of the two proposedrectifiers:low forward voltage drop, fast switching capability and it should be able to handlecurrents 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 forgetthe battery holder

step 3: The Circuit in detailWhat 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 ischecked 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 thedevice 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 voltsOutput: 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 VOut: 0,875W at 5 Vloss: 0,075W8 percent loss92% efficiency