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LM1084 Regulator

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  • LM1084 Regulator

    All,

    I've seen a lot of posts about these, saying that they could be suitable (in parallel) for giving power to the 60W DCDC PS for the Epia.

    I have 3 questions regarding them.

    1. If the car supply is exactly 12 volts (doubtfull, but stick with me) - won't the regulators dropout reduce the output to 11.something volts? Is that healthy for the PS?

    2. If the input voltage is below 12 volts, then the LM1084 doesn't boost to 12 volts. What does it do, just pass the lower voltage? If so, is this healthy for the PC?

    3. Are these things safe to put into parallel, are there any loading issues?

  • #2
    Well, currently I am using four in parallel to power the 60 watt DC-DC power supply. It works great with the car on or off. At 12 volts in, I measured 11.75 volts out. It will not allow you to start the car while the pc is on. It barely even gets warm when watching dvd's. As I understand it, the only non regulated voltages that come out of the 60 watt dc-dc power supply is 12 volts and because I am not running any 12 volt accessories (except the fan) I dont think it matters that 12 volts is not solid... I have ran everything with the car both on and off and so far I dont see a problem with it...

    Good Luck,

    Mike

    1999 voyager pontoon boat
    (soon to be computerized)

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    • #3
      I was just thinking... the main issue with these 60W power supplies is that they can't drive things like standard CD rom drives.

      from a different forum power consumption for a standard dize CDrom is given to be between 15W and 23W.

      A little math shows me that on a 5V supply rail (for a CDROM) you'd need 5A to be safe (25W).

      Couldn't you get a few linear regulators in parallel wired up? shove anything up to 15V into them, and get a nice flat 5V +/- 2% out.

      This has probably been discussed to hell and back, but i just thought i'd try and reason whilst i typed

      Cheers

      R

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      • #4
        well, you probably want to use a laptop hdd and a laptop dvd drive as they run off 5 volts and use less power to operate...

        My slim slot Imac drive only uses 1.8 amps at 5 volts and my ibm travelstar 40 gig laptop hdd only uses 1 amp at 5 volts.

        Mike
        1999 voyager pontoon boat
        (soon to be computerized)

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        • #5
          mike,

          Where did you get the adaptor for the imac slot loading drive? I picked up one of those, but the JAE 50pin adapter on it is upside down when compared to other slim drives on the market. Thus my $10 adapter from idot.com is useless It sticks out the side of the drive instead of going down the rear of the drive. Any ideas?

          Thanks.

          --Dima

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          • #6
            It is on here somewhere... Do a search on it and you will find the information.. It is a mac part number that you can buy online...

            1999 voyager pontoon boat
            (soon to be computerized)

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            • #7
              How exactly did you put 4 regulators in parallel? Were they matched perfectly?

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              • #8
                I just hooked up four of these in parallel with a cap between input and ground...

                http://www.fairchildsemi.com/ds/KA/KA78R12.pdf
                1999 voyager pontoon boat
                (soon to be computerized)

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                • #9
                  Just remember that linear regulators are extremely ineffecient (i.e. the'll use more source current, and generate huge amounts of heat).

                  Assuming you are fine with those two problems there is nothing wrong with that method. It does make power supply design and implementation a heck of a lot easier compared to switching supplies.

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                  • #10
                    yeah, but in this application, there are only burning off a maximum of 2.2-2.4 volts usually. With a good heat sink everything will be fine
                    [H]4 Life
                    My next generation Front End is right on schedule.
                    It will be done sometime in the next generation.
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