Hacks
USB Battery Pack
I recently came across the Minty Boost project and instantly knew that was a piece of hardware I wanted to have, in order to extend battery life of my Nintendo DS (using an USB charger cable I bought the other day) and of my Creative MuVo. The only problem with the Minty Boost though is, that I wasn't able to find the used IC at my electronic parts vendor of choice, Reichelt. So I searched for a substitute and came across the LT 1073 CN8. In it's datasheet I quickly found an example circuit for my application - namely converting the voltage supplied by two AA in series (3V) into the 5V expected from the USB port. Some merge of the example circuit and the Minty Boost, and this one was born:
The parts used were the following:
| Name | Description | Reichelt ID | Approx. price per piece |
|---|---|---|---|
| R1 | 100 Ohm Resistor | 1/4W 100 | 0.10€ |
| R2 | 47 kOhm Resistor | 1/4W 47K | 0.10€ |
| R3 | 2.2 kOhm Resistor | 1/4W 2,2K | 0.10€ |
| C1 | 100µF Capacitor (axial) | AX 100/16 | 0.14€ |
| C2 | 100µF Capacitor (axial) | AX 100/16 | 0.14€ |
| D1 | 1N5818 Diode | 1N 5818 | 0.06€ |
| L1 | 68µH Inductor | SMCC 68µ | 0.19€ |
| IC1 | LT 1073 DC/DC Converter | LT1073 CN 8 | 4.80€ |
| X1 | Female USB A Connector | USB AW | 0.25€ |
| Mount for 2 AA Batteries | HALTER 2xUM3-DK | 0.23€ | |
| Battery clip for the mount | CLIP 9V | 0.09€ | |
| Breadboard | H25PR050 | 0.61€ | |
| Total cost | 6.81€ | ||
I first built the prototype on a test board and checked it thoroughly.
As I was planning to put the circuit into an old Penguin Peppermints tin lying around (someone in this household really likes them 
), I implemented the circuit on a piece of breadboard fitting into the tin together with battery mount and usb connector. And this is the end result (click to enlarge):
 The finished pack |  The finished packs interior |
 My NDS charging from the pack |  Same as before |
 Creative MuVo running from the pack |  Same as before |
Variation
Instead of the LT 1073 CN8 I used in the circuit above, you can also use the LT 1073 CN8-5 like Andi did, which already includes the right resistor combination for an output voltage of 5V. In order to make it work though, you'll need a slightly different circuit – just omit R2 and R3 and instead directly connect the output of the diode with pin 8 of the IC:
Discussion
Hi!
I like the circuit - Cool - just would like to use a smaller packaging and AAA batteries … I am sure I can come up with something …
But one question beforehand: is the voltage of 3V regulated? How does USB react on voltage that is unregulated?
looking at the prices on reichelt.de it looks like the whole thing must basically be done for fun - not to save money. These boxes can be bought for almost that price …
Am I right that you can actually change the voltage if you use the upper layout and replace the voltage devider (made up of the 2 resistors) with a potentiometer. This way you could also connect other outputs to the device that require other voltages. Or maybe in that case it would be better to use a shift for different voltages … or … connect a voltmeter also
best regards Daniel - also from Germany
PS.: you do not seriously expect people to put in their Emailaddress there?
Just saw this comment, sorry for the belated answer.
Regarding input voltage regulation, the capacitor parallel to the input is supposed to stabilize the input. In my experience, that is sufficient for satisfying results when charging a Nintendo DS or running a Muvo.
The potentiometer thing should work, although I wouldn't want to fumble around with something like this on the run. A switch for changing between common resistor combinations might be an option though.
And I don't care whether people put in their email addy here, I would certainly not use it for anything (despite maybe sending a reply on a comment by email as well if it takes some time, like now), but it comes in handy for gravatars. So do what you like, but please don't put me in the spammer category, I'm kinda allergic to such things ;)
what is the input voltage of the USB charger
As indicated in the schematic: 2×1.5V = 3V, output is 5V
Could it charge an ipod?
answer
question.
If the ipod works with a regular USB connection and does not need any currents on the data lines – maybe. I have no idea, I don't have an ipod, and I don't ever plan to get one (or anything from that fruit computer company that is).
Hi em i really want one of this USB Batterie Pack what should i do ?
Hi.
I like the circuit, I want to adjust it to work like phone charger, but I need information for output current.
Salute.
Hey,
This is another way of doing it for the non electricians.
Network Security, Performance, Wireless and more
I put this together on a breadboard using a 68uH inductor from futurlec.com and it didn't work, but the inductor was a really tiny skinny axial one (looked smaller than a 1/8W resistor). I had some “fatter” ones that were 100uH, so I put that in and everything worked fine (using fresh AA's). I also had some 82uH ones (that looked like a fat ceramic disc cap), and they worked as well, giving me 4.72V.
So am I destroying the efficiency by using a larger valued inductor? I'm guessing the tiny one was being saturated, so did not work. I'm going to test the larger ones with some nearly dead AA's (1.5v - 2v total) to make sure it still works at the lower threshold, and if everything looks fine I'll solder it up.
Also, I plan on using a 2K resistor instead of the 2.2k, so I'll get an output of ~5.1/5.2v instead of ~4.72/4.74v.
Thanks for the site. It'll be nice to have a portable charger for my DS.
This is were I must pass on answering, sorry
My electronic skills are not sufficient for completely understanding what happens in this chip in dialogue with the circuit, besides that the datasheet implied using the indicated inductor. My educated guess would be that the difference of 32µH won't lead to any trouble though.
is it possible if i want to produce 12V (output) from 3V (input)
Should be in the datasheet. I do remember something like this, but the max output current was quite low, so it depends on your intended application.
I want to try the circuit from http://www.reuk.co.uk/DC-Voltage-Multiplier-Circuit-Plans.htm that using Max756 to boost from 0.7 to 5 volt. Will that circuit work with the USB too? Can anyone tell me how to interface the USB.
Thanks
First of all, none of those circuits “from reuk.co.uk” are actually from reuk.co.uk but only “collected” from all over the internet (without any attribution to the author I might add, what by itself I find quite close to “stealing”). I even had to tell them to stop stealing my bandwidth by hotlinking to my images and the datasheet of the LT1073 as provided on this page.
Second, I have no idea of the MAX756 – as you might have read above, I wasn't able to get my hands on one, so this is probably the wrong place to ask about application details of that chip.
If I were you, I'd try my luck at the creator of the most famous application of a MAX756 step-up-converter, namely ladyada/adafruit. They also have a forum there. Converting 0.7V up to 5V sounds like a bad idea though, as the available amps then would be very low and simply not be sufficient for anything useful (you not just only need 5V, as to my experience you also need at least 100mA current to do anything charging related via USB).
Firstly, thanks for replying my question. Secondly, It really sounds like a bad idea, but i have to handle an input of 0.7V and i need an output of 5V. By using Max756 I can get another option of getting 3.3V, by modifying the circuit i could possibly get 3V output. Just want to ask you if it's possible to use your circuit after a 3V output from mine, so the result will be 5V output. It sounds silly though. But will the current be large enough >100mA in order to charge via USB?
thanks for your time Jim