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  • Power Supply design questions...

    Morning everyone,

    I am currently trying to design my own little DC/DC power supply based on the LT1074 since the MAX778 and MAX787 aren't available (as samples) any more.

    The problem I have right now is that the LT1074 us a Buck style regulator and my setup won't 'survive' the crank, at least on the 12V line. Does anyone have a efficient! solution for that? I was thinking about using a boost converter first and then the LT1074. Any opinions?

    Code:
    12V DC from car --> Boost Converter (24V) --> Buck Converter (LT1074 for 12/5V)
    Lilliput 7" TS TFT, ASRock K7VM2, Duron 1,3 GHz, 512 MB DDR RAM, 30 GB Seagate HDD @ 5.400 rpm, WLAN w/ 500mW booster, Toshiba Slimline DVD-ROM Drive, D-Link USB Radio

    Download the German Voicepack 1.0 for FreeDrive now!

  • #2
    There are two ways of thinking here. You can go down to 5V then up to 12V or up to say 15V then back down to 12V.
    I do have a design lying around here that I thought up ages ago and it goes up to 15V then down to 12V. At the time I thought it was the best way to go, but that is my opinion.
    Never let the truth get in the way of a good story

    Comment


    • #3
      Originally posted by meddler
      There are two ways of thinking here. You can go down to 5V then up to 12V or up to say 15V then back down to 12V.
      I do have a design lying around here that I thought up ages ago and it goes up to 15V then down to 12V. At the time I thought it was the best way to go, but that is my opinion.
      Thanks for the input. Going 15 or 24V first an then 12V seems the better idea to me as well. If you could post your design I'd be thanksful, since it might save me some work. Don't wanna re-invent the wheel
      Lilliput 7" TS TFT, ASRock K7VM2, Duron 1,3 GHz, 512 MB DDR RAM, 30 GB Seagate HDD @ 5.400 rpm, WLAN w/ 500mW booster, Toshiba Slimline DVD-ROM Drive, D-Link USB Radio

      Download the German Voicepack 1.0 for FreeDrive now!

      Comment


      • #4
        I have done some research on this. By far, the most efficient design I have seen is the desgin base on Linear Technology's LTC3780. It doesn't buck and then boost or boost and then buck. It switches between those mode in real time which is the most efficient way. The DSATX and DSX12V are based on this chip for the regulated 12V.

        If you are just designing one only for yourself, it might be cheaper just to buy the existing ones.

        Andy

        Comment


        • #5
          Originally posted by Jeeve5
          Morning everyone,

          I am currently trying to design my own little DC/DC power supply based on the LT1074 since the MAX778 and MAX787 aren't available (as samples) any more.

          The problem I have right now is that the LT1074 us a Buck style regulator and my setup won't 'survive' the crank, at least on the 12V line. Does anyone have a efficient! solution for that? I was thinking about using a boost converter first and then the LT1074. Any opinions?

          Code:
          12V DC from car --> Boost Converter (24V) --> Buck Converter (LT1074 for 12/5V)
          If your going to boost, don't boost to any higher than you have to. The further you go, the more power you loose. I'd go to 15-16 volts then buck down if your going to go this route..
          MPEGBOX - Plexiglass Computer
          www.mpegbox.com

          Comment


          • #6
            Originally posted by 20div0
            I have done some research on this. By far, the most efficient design I have seen is the desgin base on Linear Technology's LTC3780. It doesn't buck and then boost or boost and then buck. It switches between those mode in real time which is the most efficient way. The DSATX and DSX12V are based on this chip for the regulated 12V.

            If you are just designing one only for yourself, it might be cheaper just to buy the existing ones.

            Andy
            Yeah, I have ordered 4 samples of the LTC3780 since I work at a university. Hopefully they will arrive next week and I can start making the PCB layout for my first test board.

            I will make one with the LTC3780 for 12V and the LT1074 for 5V and another board with the LT1074 with a LT1370 infornt for 12V and a LT1074 for 5V.

            We'll see how it works out
            Lilliput 7" TS TFT, ASRock K7VM2, Duron 1,3 GHz, 512 MB DDR RAM, 30 GB Seagate HDD @ 5.400 rpm, WLAN w/ 500mW booster, Toshiba Slimline DVD-ROM Drive, D-Link USB Radio

            Download the German Voicepack 1.0 for FreeDrive now!

            Comment


            • #7
              Originally posted by Jeeve5
              Thanks for the input. Going 15 or 24V first an then 12V seems the better idea to me as well. If you could post your design I'd be thanksful, since it might save me some work. Don't wanna re-invent the wheel
              Most of my work was towards making of a shutdown controller. I'll see if I can dig up my PSU stuff. My design was based on the SG3525 chip. they were quite hard to get at the time and that's why I stopped developing it. If you want some more info, send me a pm.
              Never let the truth get in the way of a good story

              Comment


              • #8
                Originally posted by meddler
                Most of my work was towards making of a shutdown controller. I'll see if I can dig up my PSU stuff. My design was based on the SG3525 chip. they were quite hard to get at the time and that's why I stopped developing it. If you want some more info, send me a pm.
                Thanks for the offer, but if I read the datasheet correctly, the SG3525 only supplies .5A which is way less than I am looking for

                Please correct me if I am wrong though
                Lilliput 7" TS TFT, ASRock K7VM2, Duron 1,3 GHz, 512 MB DDR RAM, 30 GB Seagate HDD @ 5.400 rpm, WLAN w/ 500mW booster, Toshiba Slimline DVD-ROM Drive, D-Link USB Radio

                Download the German Voicepack 1.0 for FreeDrive now!

                Comment


                • #9
                  I had a pair of IRFZ44 mosfets hanging off the output of the chip to increase the current abilities. The SG3525 is the controller.
                  Never let the truth get in the way of a good story

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