Battery USB Device Charger





Introduction: 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

- 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

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

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

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

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.



    • Science of Cooking

      Science of Cooking
    • Pro Tips Challenge

      Pro Tips Challenge
    • Pocket-Sized Contest

      Pocket-Sized Contest

    We have a be nice policy.
    Please be positive and constructive.




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

    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. :-)

    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. :-)

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

    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)

    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.

    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 ;)

    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)

    Screen shot 2012-02-26 at 00.38.39.pngScreen shot 2012-02-26 at 00.38.52.png

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


    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)