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Voltage Regulation

Discussion in 'General Electronics Discussion' started by Mastermind, Aug 25, 2011.

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  1. Mastermind

    Mastermind

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    Jul 29, 2011
    If I have a camera transmitter that requires 12 volt 500 ma and I have a battery that outputs 24 volt 75ah, how could I regulate it down to 12 volt so the transmitter gets the voltage it needs?
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    hi there :)

    yup, you can just use a 12V voltage regulator, say a LM7812. do a google search for a datasheet for that device and you will see the recommended capacitor values onthe input and output of the LM7812.

    cheers
    Dave
     
  3. Mastermind

    Mastermind

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    Jul 29, 2011
    Last edited: Aug 26, 2011
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    ok well for the higher current loads you are going to need a different regulator.
    wouldnt hurt to power the uPC off its own supply anyway.
    you could use a LM338 adjustable regulator (it can handle up to 5Amps) and use appropriate resistors to set the needed voltage have a look at its datasheet.

    or if you are consious of power requirements/drain you could look at a switching type DC -DC converter that would be somewhat more efficient that the LM338
    as you have linked to. If price was of concern then the LM338 option would be considerably cheaper.

    NOTE that one you linked to is 3Amp MAX if your uPC is drawing 3A ( and definately no current left over to supply the camera /TX) contineously then that
    supply probably will not do. you would need to have a bit of headroom say a PSU capable of at least 4 amps

    cheers
    Dave
     
    Last edited: Aug 26, 2011
  5. Mastermind

    Mastermind

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    Jul 29, 2011
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The linear regulator will provide 50% efficiency all day long :)
     
  7. Mastermind

    Mastermind

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    Jul 29, 2011
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Looks like it should work. It also should run pretty cool (at least compared with a linear regulator).

    Note that a linear regulator for the original spec was perfectly acceptable. As you increased the current requirements, a SMPS becomes more attractive.
     
  9. JoeyAVR

    JoeyAVR

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    Aug 25, 2011
    If that 24V is coming from the starter battery on a truck, you'll need to add some serious protection against transients and over voltage, or it could be bye-bye to your electronics quite quickly.
     
  10. Mastermind

    Mastermind

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    Jul 29, 2011
    I'm using it for a robot so it shouldn't be a problem. The reason I wasn't going to use that one was because of the efficiency.
     
  11. TheLaw

    TheLaw

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    Sep 27, 2010
    A switching design is a much better idea for a battery based power supply. Sure a 3A linear regulator would be very easy...but you'll loose maybe 40%+ of potential battery life by using a linear regulator. LM2576 is about as easy as it gets for switching designs. It's not THAT different compared to a linear design. A few more components, and you have to make sure you read the datasheet so you place the components correcty, as layout is critical to efficiency.

    But it's definitely not impossible.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    And here you are telling us more that you could have mentioned in your first post.

    Firstly you're asking for 12V @ 500mA for a camera transmitter.

    Later it comes out that you want 3A output, then efficiency becomes a huge concern, then we hear it's to be mounted on a mobile platform.

    Each change brings a different design suggestion.

    Do you have any more surprises?

    It is far better to summarise all the major requirements in your first post.
     
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