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HELP voltage regulator

  1. Feb 3, 2006 #1
    Hell oI am a car audio installer. we have a incar video monitor that has a voltage limitation of 12v +/- 15%. problem that arises is that below say 11.5 it wont turn on, if above say 13.8 It shuts off, If the voltage is low it gets lines running through it, if there is enough to allow it to turn on.

    Is there some type of simple voltage reggulator or any type of suggestion you would have that i can do to get the voltage to regulat at these tight parameters?

    We currently wired 6amp diodes to lower the voltage as to not ruin the monitors(4 of them) we wired them in series to limit the 14.4 volts when running down to 13.8, but if the car isnt running the shut off or have l lines

  2. jcsd
  3. Feb 3, 2006 #2


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    Well if the video monitor does not have a good, tolerant power supply, then you would need to connect a tolerant power conditioner of some sort yourself in series with the car power. One way to do it (not great) is to connect a 110VAC inverter to the car power, and add an AC to 12V adapter after that. The upconversion to 110VAC and then downconversion to 12V should allow the 12V output to be pretty flat. You'll need to check the power consumption needed by the camera, and size the inverter and 12V regulator accordingly. You can probably buy those things at Radio Shack to try them out.

    The better solution would be to build your own power isolator, which could either be a boost-to-linear regulator (which does the same thing as what I mentioned above, but only up to maybe 15-20VDC, not 110VAC), or you can use a combo boost-buck switching regulator topology. The boost-buck topology can keep the output regulated, regardless of whether the input is above or below the desired output voltage.
  4. Feb 3, 2006 #3


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    Depending upon the current needed by the monitors, you can buy off-the-shelf 12V buck converters from places like Digi-Key that will regulate the battery's 13.8 down to 12V. You'd have to look up the current consumption specs of the monitor for us to help you pick one. Keep in mind that most voltage regulators need > 1V of "head room" to function. If you're trying to get 12V out, you'll typically need to give them 13+V in. This shouldn't be a problem in an automobile, as long as you don't have bad wiring with high resistivity.

    I wouldn't use berkeman's solution unless there is already an inverter in the vehicle.

    - Warren
  5. Feb 3, 2006 #4


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    Yeah, that's why I said it's not a great solution. Lots of noise that wasn't there before. But the OP can't just use a buck, because he has to deal with sag of the input voltage as well. Really, a buck-boost DC-DC converter would be his best solution. Hey, I wonder if any of the pre-packaged DC-DC converter bricks would work for him.....

    Time for a little google fun....back in a couple.....
  6. Feb 3, 2006 #5


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    Holy smokes! I googled "dc-dc converter" +module, and got a bzillion hits. This page even lists "car 12 power supplies for computers"!! I guess it must be a pretty common requirement to make a clean 12V from the noisy and wide-ranging car power. Check this one out and some of the others:



    Comparison Chart:
    Last edited: Feb 3, 2006
  7. Feb 3, 2006 #6
    thanks for the quick replys guys
  8. Feb 3, 2006 #7


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    You may also run into issues with noise if the power supplies are not isolated well. Commonly referred to as a 'ground loop' and "alternator whine" it can easily happen with inexpensive gear and video is almost as prone as audio. 120V AC Inverters are typically quite bad in this regard for lines on the screen if the DC adapter on the other end doesn't have adequate filtering, and a true-sinewave inverter is much more expensive.

    The Jacob's Accuvolt is a pretty common supply that could be used for this.

    Or there are others designed for use in situations where you would otherwise not be able to use a regular boost/buck that wouldn't have enough isolation on its outputs. But they are far from cheap.
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