Power supply from USB connector?

Discussion in 'General Electronics Chat' started by Conrad007, Oct 24, 2011.

  1. Conrad007

    Thread Starter New Member

    Oct 24, 2011
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    Hello everybody,

    this is my first post on this forum - I am a "fresh" member :).

    I would just start with a question... I have an USB mp3 player (DK-Digital), powered by a single AAA battery. It has a form of an USB stick, 2GB internal memory and can be used as a mass storage device on any computer. My question is: is it possible to make some modifications in order to use the power from the USB connection of the PC, instead of the AAA battery, for playing music or listen to FM radio? The next question would be (conditioned by an positive answer to the first one) if I could also use the USB power to charge the AAA accumulator?

    Thanks in advance for all your answers!

    Best regards,
    Conrad
     
  2. nigelwright7557

    Senior Member

    May 10, 2008
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    I dont see why not so long as you dont take too much power from the usb. If i remember correctly you can take up to 200mA.
     
  3. chrisw1990

    Active Member

    Oct 22, 2011
    543
    41
    in short, id say no, as the overheads for the usb protocol specify how much current the usb device is going to take, i would assume they have specified around 100mA, not the full 500mA otherwise you could implement a trickle charge mod.,
    in short, id say no, but i might be wrong, im sure someone will point it out if not
     
  4. chrisw1990

    Active Member

    Oct 22, 2011
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    500mA if the overhead is set correctly
     
  5. Conrad007

    Thread Starter New Member

    Oct 24, 2011
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    Thank you for your answers.
    So would it be that simple - just 2 wires from the +/-5V contacts of the usb connector to the +/- contacts of the AAA battery (eventually with a interconnected diode)?
    I mean just for the power supply of the mp3 player / FM radio, the charging function for the accumulator would be (I believe) more complex...
     
  6. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Do you know the model #?

    It can plug directly into a USB hubt, O.K. Will it play with and/or without the AAA battery plugged in? Don't know. Will it charge the battery in the device being plugged in? Don't know.

    Yes.

    I'll assume here that an "AAA accumulator" is a battery....and in this case a rechargeable battery. This is hard to say without the users manual for the specific model you have. The USB hub can certainly be used to charge standalone batteries and other battery powered devices.
     
  7. Conrad007

    Thread Starter New Member

    Oct 24, 2011
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    Hello iONic,

    the exact model description is Dk-Digital MP 052 2GB. It will only play with the battery plugged in. Without battery and plugged in the USB Hub will only be available as storage device (MTP mode), so no mp3 player or FM function. It will not charge the battery while plugged in the USB.
    I would just like to know in the first place how to modify it to be able to use the mp3 player and FM without a battery, just plugged in a USB HUB (or maybe a USB charger / USB power supply).

    Conrad
     
  8. Conrad007

    Thread Starter New Member

    Oct 24, 2011
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    ...so could somebody explain me how to do practically the wiring in order to use the USB power instead the battery?

    Thanks in advance!
     
  9. iONic

    AAC Fanatic!

    Nov 16, 2007
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    You would have to step down the 5V to 1.5V and then find a way to connect the wires to the MP3 player. A couple of pics of how you access the battery compartment would be helpful.

    A voltage regulator that might work is.NCP1117LP
    http://www.onsemi.com/pub/Collateral/NCP1117LP-D.PDF
     
    Last edited: Oct 31, 2011
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    He would need a uC to negotiate and identify itself, then ask for more current. It isn't something that can be solved with adding some discrete components.

    Some USB Hubs, and even some USB Motherboards are now simply limiting each port to 500mA straight off, the negotiation is optional. USB 3.0 will put that limit back in place, but higher, 150mA unconfigured, 900mA for a configured device.
     
  11. iONic

    AAC Fanatic!

    Nov 16, 2007
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    I think he can get 200mA unchecked, which should be more than enough for his device.
     
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