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Constant Current Regulator

  1. Jun 10, 2006 #1
    I've recently purchased a Magnavox 15" LCD-TV {15MF400T/37}
    which requires 12 volt, 3.5 Amp, DC input.
    I want to use this TV in my RV - on a Standard 12 volt,
    Deep Cycle, Vehicle Electrical System - where voltage can
    vary from 10 - 15 volts depending on the state of discharge
    or recharge, etc.

    Will it be necessary to regulate the current input (to the
    TV) with a constant current regulator, and/or voltage
    regulator ??
    Or can I just plug it Straight IN ??
    PS- The TV came with a 120 V. AC to 12 V., DC, 4.16 AMP
    converter and there's no documentation regarding vehicle
    usage and Magnavox Support says there's no accessory for 12
    volt DC to DC operation.
  2. jcsd
  3. Jun 10, 2006 #2


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    Gold Member

    It seems as if it isn't terribly picky about the current if the adaptor is that far off of the input specs. Maybe there's an internal regulator. I wonder if you can't just find an automotive adapter with the same specs, such as for a Gameboy or portable DVD player. They use LCD screens as well, so their specs must be somewhere in the same neighbourhood. Try asking a local TV repair shop.
  4. Jun 12, 2006 #3


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    Staff: Mentor

    Don't confuse current and voltage. The TV will have an input voltage requirement that should include the tolerance on the 12V input. When you supply the 12V input as required, some current will flow, and the maximum current that will flow is the 3.5A number that you mentioned. The TV will likely draw less than that maximum current most of the time. But your job in providing power is to be sure to supply a constant 12V (at least within the specs tolerance), and be sure to be able to hold that 12V even while supplying up to 3.5A. A constant current supply is a totally different animal.

    Having said that, I don't think it's a good idea to run the display below whatever its minimum input voltage is. Most likely, it's something like 12V-10% = 10.8V. If the supply drops below that minumum, I'd imagine that some bad things could happen. Like the EL backlight power supply might start to have problems....?
  5. Jun 12, 2006 #4


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    Staff: Mentor

    BTW, I thought I remembered an old thread where we talked about running 12V equipment in cars (where you need a better 12V supply than the car battery circuit provides). I used the PF search engine to find it. Check out my post part-way down the thread, where I found DC-DC converters for cars that clean up the 12V. This looks like the way the OP should go:

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