Need help doing that.

Discussion in 'General Electronics Chat' started by Lightfire, Jun 7, 2011.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    Hello,

    I am planning to make a converter of a DC to DC.:D(I guess, I can't) But it would greatly help me if somebody will post a schematic for it.;)

    My input will be so far 12 V DC /as for the AH/maH I don't know (maybe as small current as possible). And the output will be DC 5.0 V@ 350mA.;)

    If somebody posted me a schematic for it or circuit diagram for this converter, I would greatly appreciate that. Even though, i can't do but I want to see the schematic, promise I will appreciate that and promise, if I think I can't do, I won't do. I just want to see the schematic for this converter.

    Thank ya very much.
    Lightfire
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    That one is actually easy, and safe. A simple voltage regulator will do it, something like a 7805. You will need the same current in as out. You will also need some small capacitors on the input and output.

    Another way to create 5V is to use a 6V battery and hang a diode after it, to drop 0.6V and create a 5.4 V power supply.
     
  3. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    Okay.

    What kind of 7805 do I need to buy to get this kind of outputs, 5.0VDC at 350 maH?

    Any help would be greatly appreciated.
     
  4. #12

    Expert

    Nov 30, 2010
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    search for LM7805 or LM 7805
    Thats all the numbers you need.
    You will find many brands that make that chip.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    and the datasheet will tell you everything you need. Might want to grab a small heatsink too to attach to the 7805
     
  6. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    Ok... thanks
    Okay. Is this regulator will regulate also the ampere? Or the output ampere will just be the same?
    Thanks
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    It depends on the specific part. There are light weight versions only rated for 0.1A, but most of them are rated for 1.0A. Look for the TO220 case styles.

    Note: at .35A they will get hot, very hot.
     
  8. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    The amperes will be regulated by the fact that the load consumes 350mA at 5V. There is a current limit in those things like Bill said, but that is a limit and not regulation per se.
     
  9. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    Will resistor works fine:confused: :D
     
  10. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    I don´t really understand your question. You said that the circuit you want to power draws 350mA maximum when powered with 5V. That´s what it does, no resistors needed anywhere.
     
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  11. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    OK.

    Um, ok. now. i need the item lists and schematic.

    Oh, pls. pls. pls. im begging. a lot................
     
  12. kubeek

    AAC Fanatic!

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  13. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    But the current.:(I want the current output is 350maH
     
  14. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    You want the output current to be exactly 350mA, or to be no more than 350mA?

    Maybe you should post what device you are trying to supply, because this is getting very confused.
     
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  15. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    A cellphone. :) Nokia. :D
     
  16. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Instead of a charger or battery?
     
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  17. #12

    Expert

    Nov 30, 2010
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    The cell phone will use the amount of current it wants. Just give it 5 volts.
     
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  18. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    From the charger?????
    Nope. Maybe the cellphone will explode.:eek:
     
  19. Wendy

    Moderator

    Mar 24, 2008
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    OK, this is where Ohm's Law comes in. If you haven't studied it this is the time. It will be forever useful, and always needed.

    The load pulls what it needs, dictated by Ohm's Law. A power supply circuit does not provide current, it provides voltage. You wanted 5V with a max of 350ma. If there is no load there is no current. Loads are variable, this is a given. So the lowest resistance this circuit would provide for (using Ohm's Law)

    V=IR
    R=V/I
    I=V/R

    R = V/I = 5V/0.35A = 14.28Ω

    P = Power = VI = V²/R = V²/I
    P = 5V * 0.35A = 1.75W

    If the cell phone needs 5V that is ALL that is important. The current number sets itself, according to Ohm's Law.
     
  20. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    The charger specs of outputs are. 5.0vdc / 350 mah as said. but the cellphone's batetry specs are 860maH/3.7V/3.2W. EH????
     
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