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  • +12v circuit

    I am trying to make a +12v circuit because the sproggy didnt give enough juice for my hard drive. I have drawn a quick circuit that uses 2x max1771 based on the diagram from the max 1771 data sheet. Will this circuit work? Is there a better way of doing it maybe using less components? Also i am having trouble selecting the correct FET, so any part numbers or farnel order codes would be much appriated.

  • #2
    Call me stoopid (I don't know any electronics, so I shouldn't really bother about this), but why do you use 5V input?

    Why not use a regulator in some circuit that takes 8-15 input (or whatever) from the car el-system and give 12V stable?

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    • #3
      It might have worked if you didn't short the input directly to the output.
      MPEGBOX - Plexiglass Computer
      www.mpegbox.com

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      • #4
        LOL

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        • #5
          Re: +12v circuit

          Originally posted by cheesyhoward
          I am trying to make a +12v circuit because the sproggy didnt give enough juice for my hard drive.
          What else were you trying to run from the supply? and what were you using to power the sproggy? 2amps @ 12volts SHOULD be enough for most HD/MOBO combinations... Perhaps you could use a low drop out 12volt reg to run the HD, I did this, and it worked fine..
          2 week temp ban (spam and complaining about deleted posts)
          register another account and you're gone for good.

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          • #6
            The circuit in the datasheet is shorted as well (page 8 fig 2a). So i just stuck 2 of them together. I admit I am rubbish at electronics thats why I posted the circuit before attempting to build it. The reason I am building this circuit is because it was suggested to me by Dima since he was having the same problem as me with the Hard disk requiring a lot of power to spin up.

            http://www.mp3car.com/vbulletin/show...&threadid=9195

            Could someone post or give me a link to the low drop out 12v regulator circuit? Would a low drop out 12v regulator keep the hard disk spinning when I crank the engine? This is why i was planning to run the max1771 off the 5v output on the sproggy since the chip can supply 12v output on a lower input and hence keep the hard disk spinning while cranking.

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            • #7
              Originally posted by cheesyhoward
              Would a low drop out 12v regulator keep the hard disk spinning when I crank the engine? This is why i was planning to run the max1771 off the 5v output on the sproggy since the chip can supply 12v output on a lower input and hence keep the hard disk spinning while cranking.
              Ahh, no.. sorrry.
              2 week temp ban (spam and complaining about deleted posts)
              register another account and you're gone for good.

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              • #8
                I've actually found that most 7200 rpm hard drives need a lil' more than 2 amps to spin up.

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                • #9
                  well any circuit diagrams would be much appriated

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                  • #10
                    Originally posted by cheesyhoward
                    The circuit in the datasheet is shorted as well (page 8 fig 2a).
                    It isn't shorted. The 5 volts only goes to the coil and the input Cap. THe output goes to V+ and the input doesn't. When you draw these things, you have to be consistant when you use dots to indicate intercetions. You have dots in some places and not in others..

                    Figure 2a would work just fine. if you read the datasheet, you can probabaly get enough current out of this device by using the right external parts, smaller sence resistor, beefier transistor, more filter caps.. etc..
                    MPEGBOX - Plexiglass Computer
                    www.mpegbox.com

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                    • #11
                      ok i have modified my diagram, is this one correct?

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                      • #12
                        Originally posted by cheesyhoward
                        ok i have modified my diagram, is this one correct?
                        It might work, or one might hog all the current. I would just use diode with a higher current rating, a larger mosfet, and more output caps and save yourself the 3 bucks of the second regluator. You will also need a smaller sense resistor.
                        MPEGBOX - Plexiglass Computer
                        www.mpegbox.com

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