12v from a 7805 - help please!

Discussion in 'Modding and Hacking - Consoles and Electronics' started by bacteria, Jan 9, 2010.

  1. bacteria

    bacteria I am the Bacman

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    According to this site: http://www.rason.org/Projects/regulator/regulator.htm

    you can get 12v from a 7805 (which normally outputs 5v).

    I have tried this circuit with a 7.4v battery and a 12v battery, and I just get 5v still. In other words, it doesn't seem to work.

    Ideas? I just want a simple low amperage (500mA max) step-up regulator.

    I am ideally wanting to get 12v out of a 7.4v battery, other ideas?
     
  2. ASSEMbler

    ASSEMbler Administrator Staff Member

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    Not all 7805 are same capability, it varies by mfg afiak.
    78XX, maybe you want 7812?
     
    Last edited by a moderator: Jan 9, 2010
  3. bacteria

    bacteria I am the Bacman

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    No, 7812 converts a higher voltage down to 12v, a 7805 converts a higher voltage down to 5v, a 7905 to -5v.

    Those are step-down converters, I need step-up; ie lower voltage in higher out.

    I made a small error on my board, I actually get 7v out of 7.7v in from the 7805; I need 12v!
     
  4. marshallh

    marshallh N64 Coder

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  5. bacteria

    bacteria I am the Bacman

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    Got 11v out of 12.6v

    I think I misread what the document was I originally saw - when it said 12v out of a 7805 I took it as a step-up regulator as opposed to what it normally is, a step-down regulator. All this circuit is therefore, is a way to reduce the voltage to a circuit by a little not increase it, via a 7805.

    I got confused!
     
  6. Jamtex

    Jamtex Adult Orientated Mahjong Connoisseur

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    Er yes, feed in more then 13.6V and you should get 12V...there are chips that can do DC voltage step up, like the LM2577 which will take a voltage from 3V to 20V and convert it to 12V 800ma...

    here is a simple circuit that will take 6V to 10A (requires 12W which is about 2A for 6V) and outputs 12V at around 850ma...

    Requires parts that can be bought from most electronic stores and a simple wound inductor.

    http://www.aaroncake.net/Circuits/6-12conv.asp
     
    Last edited: Jan 10, 2010
  7. bacteria

    bacteria I am the Bacman

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    I sent an enquiry to the Technical Support on SparkFun electronics - they said you can get a negative voltage by running voltage into a regulator (eg 7805) and then wiring positive to negative and negative to positive.

    Logical, and does, but is that safe or will it generate a short?

    If it is right, it is a very easy and cheap way to achieve this!

    Comments?
     
  8. ASSEMbler

    ASSEMbler Administrator Staff Member

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    Something burning? lol
     
  9. bacteria

    bacteria I am the Bacman

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    So it would make a short then?

    This was the reply I got from that company:

    "To get -5VDC you can regulate the output of the batteries with a voltage regulator and connect the polarity in a 'backwards' fashion. So you'd tie GND to + and 5V to -. Here's a voltage regulator which might work: http://www.sparkfun.com/commerce/product_info.php?products_id=107 "
     

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