Introduction: Battery USB Device Charger

Picture of Battery USB Device Charger

OK, this is a very simple design, very few parts are required. The hardest part is probably adjusting the variable resistor. This is an effective circuit for devices that require 5v to charge.

Also everything I just said is somewhat misleading, this circuit for some reason works more like an external battery rather then charger.  If someone could point out why Ipod's say charged when this is plugged in rather then charging please let me know and I will update accordingly.

On the last step at the bottom also tells you how to get the same USB plugs I use free.

*I was looking at the Minty Boost Instructable page and it said a 9v battery with a 5v regulator aren't efficient because the regulator gives off lots of energy as heat.  I haven't calculated the efficiency of this circuit but it should be fairly efficient because the transistor, unlike the regulator, looses almost no energy as heat.  If someone decides to calculate the efficiency please let me know what it is, I would like to know but will never get around to calculating it myself.  Thanks.*

NPN circuit is on the last page.

Also this instructable may help get the Ipod to charge:

How to get your iPod to charge with your homemade charger.

Its about the data pins and uses 4 resistors.

Step 1: Parts

Picture of Parts

- 9v Battery
- 9v battery clip
- 2N4403 PNP transistor (Circuit can be modified for a NPN fairly easily)
- 5k variable resistor or trim pot (I used a trim pot because I had the right size lying around)
- 100 - 330 ohm resistor
- LED (color is up to you, I suggest green cause it looks more power, circuit working, good kind
of look to it, where as red looks like STOP! theres a problem! type of thing, if you know what I
- a ceramic or tantalum capacitor (last step I have a question about tantalum caps, Please
- a 6 to whatever volt 220uF cap (I used a 50v cap which is a little over kill)
- Female USB plug or other plug
- perf board or you can etch you own with copper clad

- soldering iron and stand (stands optional but handy)
- solder
- side snips
- a dremel or other tool to cut perf or copper clad board

Step 2: Circuit

Picture of Circuit

The circuit consists of a transistor used as a regulator to get the desired 5v. I thought it would be easier to take 9v down to 5v then take 3v up to 5v like the minty boost (not that they are bad but this seemed...easier). The LED is optional but is nice to have. 

Also the third picture is a board layout if you want to etch a custom board.

Also when using the electrolytic cap and if you use tantalum cap make sure polarity is correct, positive is the long lead, negative is the short lead.

Step 3: Solder

Picture of Solder

Solder it up! Make all the connections as necessary. Before soldering the USB port in, make sure the circuit has the correct pins lined up (data-, data+,-, and +) which ever order they go in. Make sure that its a FEMALE not a MALE USB connector or you'll have problems. Also use you multi-meter or volt meter to check the output from the transistor, and adjust the 5k ohm variable resistor accordingly. When your happy you may want to glue in place to be safe.

Step 4: Questions

Picture of Questions

As I said earlier I have a quick question about tantalum capacitors. I didn't have any ceramic caps at the moment and I always put a cap in to absorb shocks that the battery may give off. I usually use ceramic caps but as I said earlier I used tantalum cap. I have the polarity correct but just wanted to know if this will drain the battery more, less, the same or if there would be any other side effect from using this. This is the first time I actually used tantalum caps, I never really knew what they were used for. Any help would be appreciated.


Here is how to get the female USB plugs free, the same ones I have:

Look under connectors at SamTec, that's where I got mine. Click on Samples and put in:


in the part number box and change quantity to 5.

If you can't get to website from above then use this URL:

Then just copy paste:


into the item #1 box below the form

Don't forget to fill in all the information.

Step 5: NPN Transistor Circuit

Picture of NPN Transistor Circuit

The picture below is for an NPN Transistor instead of a PNP.  I would suggest a 2N4401 or 2N3904 should work.  I haven't built this one so it may need a little fiddling.


aakashsunkari (author)2014-08-14

The newer apple iPads need a 12 volt charger, but who would bring an iPad to a camping trip? Great job! 5 stars!

Robert Powell (author)2014-06-21

If your iPod is from apple then to make it charge you have to connect the two data pins together or put a 200 ohm resistor between them. Apple has a charging circuit inside the device that so only a wall charger can charge it but if if you connected the data pins it will charge. :-)

Robert Powell (author)2014-06-21

If your iPod is from apple then to make it charge you have to connect the two data pins together or put a 200 ohm resistor between them. Apple has a charging circuit inside the device that so only a wall charger can charge it but if if you connected the data pins it will charge. :-)

jcksparr0w (author)2013-09-12

What is the average battery life of the 9V when charging the iPod?

max1zzz (author)2012-02-25

I have been playing with the NPN circuit in simulation, it works well, except for one thing, when i attach a load the voltage drops (from around 12.5 i had it set to output to around 2.5) Dose this happen in real life? or is it just that the simulation is less than realistic (which wouldn't surprise me)

Wesley666 (author)max1zzz2012-02-25

It shouldn't, someone in the comments below tried it and said it worked exactly the same as the PNP circuit. I would trust simulators, I have used them before and they have shown a circuit not to work like I wanted it to, but I built it anyhow and it worked fine.

max1zzz (author)Wesley6662012-02-25

Thanks for the quick reply, i thought it probably was, the program i am using (Circuit wizard) doesn't always work too well (FET's and OP-Amps are very good examples of this), i will be adding the parts to make a few of these to my next order from rapid ;)

max1zzz (author)max1zzz2012-02-25

Incase anyone is interested, here's my version of the npn circuit (in PCB forum)
based on a BFY51 transistor (R1 is meant to be 330 ohm, not 1k)

Wesley666 (author)max1zzz2012-02-25

Nice circuit board design. Ya, most circuit simulators don't work worth a pinch.

Ririshi (author)2012-02-24


Does it drain battery when not using it with an iPod or other device?
If it does, can I make a switch on it? (I'm totally new to electronics)


Ririshi (author)Ririshi2012-02-24

Another question: Will this work with the 2N3906, which is misplaced on step 2?

Wesley666 (author)Ririshi2012-02-24

Yes, 2N3906 will work. It will drain the battery a bit from the LED and such, so if you want to leave your battery attached even when not in use put in a switch right after the negative terminal on the battery. So the negative wire should go to the switch, then the other side of the switch should go to capacitor and variable resistor (trim pot), then there should be no battery drain (If you leave the battery for years, it will still go dead, but that is regardless of whether its connected to a circuit or not, but without the switch it would be considerably faster)

gen.badger (author)2011-09-29

Hey, the npn circuit works just as good as the PNP one! good job!

Wesley666 (author)gen.badger2011-09-30

Oh, thank you! I had never tried it, I still haven't gotten PNP circuit to charge, it still works as an external battery, but it works fine that way. I am happy to know that the NPN circuit works as well though! :D

gen.badger (author)Wesley6662011-10-02

The NPN circuit does work but its touchy. I used a 10k ohm variable resistor and brought the voltage down to 5v. The issue is that the amperage is only 200 - 300mv where it should be at 1v (1000mv). I used a 9 volt battery which sucks for MAH (around 900) and a 7.4v LiPo rated for 4500 MAH which works really well. I am terrified to use them though as their want to explode when something goes wrong...

If I can get some PNP transistors I will construct a circuit and trouble shoot. I couldn't find a way to order the PNP transistors from a site on the sample site list though.. Any ideas?

-gen.badger of

Wesley666 (author)gen.badger2011-10-02

Do you live near a Radioshack, or Source By Circuit City if you are in Canada? If you do, they carry some components, usually expensive, $5 for 20 transistors, but its great if you need only one part, and want it right away. Otherwise try Texas Instrument, they give away samples and should have what you are looking for.

And yes, LiPo are the scariest batteries around, I don't like having them around even, but I have a few things that use them and need them removed to charge and I always sit and watch them charge so they don't burst into flames or explode and such.

gen.badger (author)Wesley6662011-10-02

I live in Florida but I have relatives in Canada... I could ask for a favor or two... and yes Radioshack is ridiculous with their prices. I think I will hit up TI for a sample and if I like them I will buy maybe 100 or so just to have in stock. In reference to the LiPo cells... One of mine just ballooned up... Looks like i have to retire that battery. I will most likely run a controlled burn with it.

Wesley666 (author)gen.badger2011-10-02

If you can't get samples and have to buy, try Electronics Goldmine, if you buy in bulk they usually have discounts. Transistors will come in rolls and it will say buy 1 for $0.20, 100 for $5 or $1000 for $10, or something along those lines.

gen.badger (author)Wesley6662011-10-03

Wow.. That is great. I will definitely check Electronics Goldmine out. I buy in bulk just because of this reason. Thank you for the advice, it is very helpful!

Wesley666 (author)gen.badger2011-10-02

Also, the Canadian store (The Source) is just as ridiculous. They are handy though if you need something on the fly though.

Andrew_48 (author)2011-06-07

you can add a 10k resistor in the data pins like shown it the photo

Crimson-Deity (author)2010-07-12

Will a 6volt 220µF capacitor work?

Wesley666 (author)Crimson-Deity2010-07-13

Oops! Thought this was a different 'Ible! Almost gave the wrong advise! However, if you are substituting it for the 50v 220uF, then yes, since there is only 5v there, but then make sure when adjusting the trimm pot that you start with the most resistance and lower resistance, other wise you will start with more then 6v and kill the cap (Explode). If you want to use that for the Tantulum (The little yellow one) then no, because it would have to be or be above 10v. Also if you have a breadboard, or are making this on a breadboard, you should add a 100K or at least a 10K ohm resistor in series with the 5K Trimm pot between the the Trimm pot and the base of the transistor. It should work exactly the same, but use less power overall. If you are just building it to perfboard, or printed circuitboard then nevermind, just in case. I would, but I am on vacation for 2 more weeks and I will probably forget by the time I get home! :D Hope this helps!

Adam Manick (author)Wesley6662010-09-13

Can I use a higher voltage and current input source?

Wesley666 (author)Adam Manick2010-09-13

Yes, then when you adjust the Trimm Pot, adjust it so the output is 5v. Make sure your caps voltage rating is above whatever you are plugging into it.

Adum24 (author)2010-05-24

Will this work with newer ipods

Wesley666 (author)Adum242010-05-25

It should, I was testing it with a 2nd and 4th generation Nano.  Haven't tried it with anything newer then that though...

Jodex (author)2009-11-11

Thank you, along with this and some other instructables I learnt where you can put ceramic and electrolytic capacitors. I'm also gonna make this with a bit modded schematic.

trunkmonkey4345 (author)2009-10-23

i have an electolyte capacitor and i was worndering id that would work it being within the guidelines

and also i had trouble finding the right transistor it is ok to usee something about a hindred digits off and npn

could you also tell me how to wire the npn?

thanks this is a great project keep up the great work

I just added another step with the NPN Circuit.  Also there is a link on the first slide for the data pins for charging.

thanks im not very good at electroics yet.
i appreciate the help

No Problemo.

First thanks.  Also the electrolytic cap should be fine as long as its over, I always use at least 1volt over whatever your putting through it.  As long as its 10 volts or above it will work because this circuit with the variable resistor adjust with the lowest resistance it can will put out almost 9 volts, so its kind of a safety net.  Also one under about 1000uF would be best just because above that the caps can start getting large, but its not critical.  I will post another step at the end for the NPN Transistor circuit.  I haven't tested it so you would have to test a bit.  It also doesn't have to be the exact transistor I use, but one with similar qualities.  You could use a 2N3906, I usually just use the ones I have on hand and base my circuit that way, but the variable resistor is there so you can dial in on the right voltage so most transistors should work, as long as they can be dialed in to 5 volts.  Breadboards work good for testing.

jasongroupindustries (author)2009-10-13

In certain site, I found that they use resistors that are connected to pin 2 and 3.
Try to use it.

Didn't work.  Post a link on the first slide that may have the answer.  I haven't tried but its off an actual apple charger so it should do the trick.

Thanks will try that, I haven't tried a 150k or 10k ohm resistor yet.  This could work yet!

laxchamp1111 (author)2009-10-22

 short the data pins son it will know its connected to a legit device

Wesley666 (author)laxchamp11112009-10-23

Didn't work.  Post a link on the first slide that may have the answer.  I haven't tried but its off an actual apple charger so it should do the trick.

Wesley666 (author)laxchamp11112009-10-22

Never heard that answer before.  Will definitely try it.

imakethings (author)2009-10-19

can u post a charger which charges i pods with 2 AA batteries?!

Wesley666 (author)imakethings2009-10-20

I could but that's called a minty boost and its already been done.

clarenz0527 (author)2009-10-17

what is the value of the tantalum or the ceramic capacitor shud i use?

Wesley666 (author)clarenz05272009-10-18

I used a 15v 22F tantalum cap but a ceramic cap with a value 9 or greater volts and I usually use a 220pF ceramic cap.

imakethings (author)2009-10-16

what is the difference between charger using 7805 and this?

Wesley666 (author)imakethings2009-10-17

I thought this would be more efficient.  The 7805 is supposed to loose lots of energy through heat so at best its only 75% efficient but it usually only averages 65% efficiency.  This should reduce the waste energy from the heat alot because since I built it I have never had the transistor or other component heat up at all.

newtonn2 (author)2009-10-14

 Cool multimeter! they ast forever! 

Great instructable!

About This Instructable




More by Wesley666:Cypress Devices Intro (Part 2)Cypress Devices Intro (Part 1)PS2 Controller Interfacing
Add instructable to: