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Thread: NooB Question about powering a laptop using M2-ATX

  1. #11
    Newbie
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    Mar 2009
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    13
    @DigitalVampire : Then what should be the best way to do it?

  2. #12
    Constant Bitrate
    Join Date
    Dec 2006
    Location
    India
    Posts
    213
    Quick and easy.

    Use a LM7812 based regulator just for the screen. Being linear regulators, 7812 regulators are not very efficient, but will get the job done dirty cheap. Don't forget to heat sink the 7812 chip. Small downside is that when the car is not started, ie when battery voltage is ~12V, 7812 will output only ~10.5V. See if your screen is tolerant to that low voltage. In general, slightly lower voltage should not lead to any problems. When the car is running, the battery voltage goes up to 14.4V and 7812 will regulate the output to solid 12V as required by the screen. Since the voltage differential is not that high, the heat dissipation should not be high either.

    IIRC, LM317 is better in terms of drop-out voltage than LM7812 and should help the above idle situation better. LM317 being an adjustable linear regulator, requires 2 resistors to set the output voltage though.

    PS: All above assuming that your screen takes less than or equal to 1A current.

    Powering 7812/317 from the 19V rail would solve the idle power issue completely, but it would be too inefficient again.

    See what suits your situation better.

  3. #13
    Newbie
    Join Date
    Mar 2009
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    13
    @DigitalVampire : Do you have any schematics to this?
    I am not that good when it comes to electronics.

    Or should i google it ?

    Thanks again

  4. #14
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    Mar 2009
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    @DigitalVampire : I think the screen would need 1A. It would be Lilliput EBY701. So according to you, i should power my laptop using DC-DC adaptor and power the screen using LM317 regulator. Right?

  5. #15
    Constant Bitrate
    Join Date
    May 2008
    Posts
    223
    Do you already have an M2-ATX or just planning on getting one?

  6. #16
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    Mar 2009
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    I am planning to buy.

  7. #17
    Constant Bitrate
    Join Date
    May 2008
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    223
    Then if you have a need for 5v, 12v, and 19v regulated output, I would suggest something like a CNX-P1900 with an add-on CNX-P5V.

    Yes, it's more expensive, but it's the right way to do it.

  8. #18
    Newbie
    Join Date
    Mar 2009
    Posts
    13
    @Sicarius : Actually my Acer Laptop is very old and i dont expect it to run longer. As far as i have learned, Carnetix CNX-P1900 would not help me in case some time later i go for a PC based Carputer. Am I right?

  9. #19
    Constant Bitrate
    Join Date
    May 2008
    Posts
    223
    Correct, the Carnetix is more for laptops and things like Mac Minis with a single voltage power input plus some accessories.

    If you're looking to future-proof your install then what you have in your first post should still work just fine.

  10. #20
    Newbie
    Join Date
    Mar 2009
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    13
    @Sicarius : Thanks a lot for clarifying my doubts.

    As all the guys are pointing out that two DC-DC converters in series is not efficient. I redesigned the wiring.


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