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9 volt usb charger

Discussion in 'General Electronics Discussion' started by jacobk, Mar 29, 2012.

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  1. jacobk

    jacobk

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    Mar 29, 2012
    hello i am trying to make a USB charger for my phone that outputs 5.1 volt at 750mA, i was looking at a product that does this (which gave me the idea to do this), the url is below. It uses a 9v dry cell, is there any way to convert the input of 9v volts down to 5.1 750mA.
    thank you for the help
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Getting 750mA from a 9V battery for any length of time will be a problem.

    However, for maximum efficiency what you'd be looking for is a switchmode regulator with an input voltage that includes 9V and a fixed or variable output that can be set to 5V
     
  3. jacobk

    jacobk

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    Mar 29, 2012
    The kit includes a 7805 ic would that work
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It would, but not for long. (What kit?)

    You are throwing away almost half the power in the battery as heat.
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    No,
    this kit includes the 7805T regulator which is a linear regulator with all the drawbacks already noted.
    Jameco doesn't seem to have switch mode 7805 compatible regulators in stock.
    Google >7805 switch mode< will give you lots of results, if you're lucky one of your favorite retailers has something similar to the on eI posted first in stock.

    Harald
     
  7. jacobk

    jacobk

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    Mar 29, 2012
    Thank you and could you list some of your favorite retailers just so i can have better chance of finding needed parts in the future
     
  8. GonzoEngineer

    GonzoEngineer

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    Dec 2, 2011
    I don't know if you are in the USA, but Micropower Direct.com has just what you need!
     
  9. jacobk

    jacobk

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    Mar 29, 2012
    I am in the us, i am kinda new to actually building the circuits, i just usually do book work. So which model would you recommend.
     
  10. KJ6EAD

    KJ6EAD

    1,114
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    Aug 13, 2011
    Adafruit has been selling the Mintyboost kit for a couple of years. It uses 2 AA batteries which works better and is more economical than a 9V battery.

    http://www.adafruit.com/products/14
     
  11. jacobk

    jacobk

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    Mar 29, 2012
    Current amplification

    I am doing a project where around 750mA is need, how can i amplify the current while maintaining the voltage. I read a forum that said i should use a Darlington transistor, is this correct? And if so how would i do so?
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You'll have to describe more of what you want to do.

    If you have a signal that provides a max of (say) 10mA and you need to switch something that draws 1A, then yes, a transistor may be what you need.

    If your power supply is only capable of 100mA and you need 750mA, then there's no way to do that. You need a power supply rated for a higher current.
     
  13. jacobk

    jacobk

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    Mar 29, 2012
    If you remember i posted about using a nine volt battery and a 7805to charge my phone through a usb jack. Well i have done tbat but the current is not high enough, jt chafges but at like 4 or 5 times slower than if i used my charger. I cannot get a higher current power supply, but could i use another 9volt battery and an op amp or transistor?
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Not really. It may be better to tell me where that thread is and I'll move your new post to it so we have some context for your question.

    I guess we may have suggested that the current you'll get out of a 9V battery isn't very high, and that the phone may require certain indications to be present to charge at high speed.

    We may also have suggested that a linear regulator means that you'll be wasting a substantial amount of power as heat.
     
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