9V to USB Charging

Discussion in 'The Projects Forum' started by cold.man.1, Jul 24, 2012.

  1. cold.man.1

    Thread Starter New Member

    Jul 24, 2012
    3
    0
    Hey, im kinda new to building circuits and just wanted to know how to charge a usb device via 9v battery... ive mocked up a simple design wanted your feedback on it.

    [​IMG]

    Just to clarify 2 things: 1) "7805" is the voltage regulator i have been told works.. 2) the usb component is the "female" usb part (i dont know the technical term for it :p)

    also would it be possible to make it a rechargable 9v battery circuit? If so, what would it look like?

    Thanks in Advance
     
  2. mcasale

    Member

    Jul 18, 2011
    210
    12
    I think your USB charger will work, but I would add a dummy load resistor on the output of the 7805 to prevent it from rising above 5v at "no load". You might also need a 0.1uF ceramic capacitor at the same place to ensure it doesn't oscillate.

    A rechargeable battery would be nice, but the circuit can get tricky. You need to limit current into the battery and then shut it down when it gets fully charged.

    As always, the devil's in the details.
     
    RamaD likes this.
  3. cold.man.1

    Thread Starter New Member

    Jul 24, 2012
    3
    0
    Wow...i wasn't expecting a reply so quickly :D

    Im a total noob at this and have no idea how to position or connect a "dummy resistor" or capacitor :p . Also, and i know this might be in the wrong place, but how do i design a pcb so that it can be printed. I know it can be done by a company but i find that that is really expensive and i need to keep this low cost.

    I also found another circuit design online... does this one better suit USB charging or is the difference in output mininal?
    [​IMG]
     
  4. mcasale

    Member

    Jul 18, 2011
    210
    12
    I don't know what your USB device is, but I suspect you can just not connect the two data lines to anything.

    For simple PCB designs I have used www.expresspcb.com They have FREE tools for schematics and layout artwork. The company will send you unloaded boards, so you have to do the soldering yourself.

    I attached a schematic to get you started.
     
  5. cold.man.1

    Thread Starter New Member

    Jul 24, 2012
    3
    0
    GREAT! thanks so much. Most USB devices need a small current through the data pins though... im not sure how much...
     
  6. RamaD

    Active Member

    Dec 4, 2009
    254
    33
    That is a very useful tip, as it is not mentioned in datasheet. All specs mention only about loads of 5mA - xxx, but never mention that you can have output voltages exceeding the specified voltage, almost equal to the input voltage, potentially frying up your load. Dont ask me how I know! That seems to happen with some makes only, observed more in negative voltage regulators, maybe because the load on this is low.
    However, the load resistor can be reduced to 1K to keep it within the datasheet specification!
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    I don't know if I agree that "most" do, but I can agree with "many". And I think it's more a matter of the voltage you place on the pin than the current. That's the purpose of the resistor voltage dividers in the schematic you posted.

    If you know what devices you want to charge, spend some time researching what they need on the data pins. Many require no special action. You can find a lot of info on i-devices (which need to see voltages) and other popular models.

    If you can't find the info you need online, it's safe to just try a simple charger with nothing at all on the data pins, and I believe it's safe to try a range of voltages as long as the resistors are, say, 10k or more to limit any current.
     
Loading...