Homemade USB-charger

Discussion in 'The Projects Forum' started by Alfanano, Feb 16, 2009.

  1. Alfanano

    Thread Starter New Member

    Feb 16, 2009
    Hi. I'm working on a little project that I decided to do after I bought 2 USB-chargers who got there power from AA/AAA batteries but I have ran into some problems and hoped that you could help me a bit.

    The components are:
    Battery pack for 4*R06 (generates 6 Volts)
    1 +5VDC regulator (LM2940T)
    1 100uF capacitor
    1 USB type A contact

    They are all connected like this:

    Checking with a voltmeter I get 4.95 V out but when I connect a USB product like cellphone or Ipod, it only reacts to that something is being connected but no charger icon comes up. So I guess that I have to do something with the to remain pins on the USB-port (D+ and D-). I read that using a 100k resistor and connecting it in a special way could trigger the units to charge but I have no idea of how
    So hopefully someone of you can help me what I should add to my circuit and how to make this work sucessfully.
  2. iONic

    AAC Fanatic!

    Nov 16, 2007
    Don't quote me, but I think this might be the way to accomplish the task.
  3. Alfanano

    Thread Starter New Member

    Feb 16, 2009
    Thank you for your answer iONic. Took some time today and made a more professional wiring diagram then the last one. Put in the suggestion from iONic and the result became this:


    Do any of you think it will work or fry everything I connect?
  4. spectrum123

    New Member

    Nov 2, 2013
    I made a USB charger with a 9 Volt battery connector and a 5 volt regulator with a USB port. That charges everything I have.
  5. wayneh


    Sep 9, 2010
    First a quibble - it's convention to put the higher voltage towards the top of the schematic.

    It won't fry if the polarity is right (I didn't check) but I don't think that will work. It puts full voltage on the data pins, albeit through the 10k. Most solutions I've seen require a voltage divider so that a specific voltage is applied to each pin. This fools the device into thinking it has been connected to a proper charger. The voltages required may (I'm not sure) vary amongst devices. So it may take some tinkering.

    Look up the Minty Boost project and I think you'll find all the info you need.
  6. Experimentonomen


    Feb 16, 2011
    Not even a LDO regulator will work with just one volt above the output, you need ATLEAST 8 volts for ANY 5V regulator to work.
    absf likes this.
  7. Oldi

    New Member

    Nov 1, 2013
    These is not true. LM 2940 Typically Dropout Voltage at 1A is 0.5V. http://www.ti.com/lit/ds/snvs769i/snvs769i.pdf
    For charging USB device it's better to have higher voltage, let say 5,3V - because of voltage drop on USB cable.