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  • Making a PSU

    So I was going to try to make the newest Sproggy (2.5) PSU but found the transfomer expensive a a little hard to find.
    I was all set to peice together something from examples on numerous site but then i found the sproggy 2.0 (older).
    So i cut and pasted on the power good section from the 2.5, changed an IC to one that was readily available, added a capacitor or two and called it the 2.23.

    So here is what i have. Is there any big ugly errors that are going to fry my car battery?
    Any thing else i should consider?

    [SIZE=1]'91 Nissan Stanza

    [XXXXXXXXXXXXXXXXXXXX] XX% Completed -
    Car Totaled and i bought a 20G mp3 player

    http://machs-fuel.tk
    a DIY video projector page

  • #2
    Hi

    I don't see anything wrong with what you've done. It should work fine. :-)

    Comment


    • #3
      the 7812k is only rated at 1.5amps http://www.microsemi.com/corporate/c...p?PARTID=43969

      thats not enough imo

      cheers pcman
      donate to my team in the ****box rally all proceeds go to the cancer council http://www.everydayhero.com.au/dodgy_mechanics

      Comment


      • #4
        Yep the 7812 isn't going to cut it for most systems. You'd be better off using a switching regulator for the 12V. You'll more current out and it'll be much more efficient.

        Comment


        • #5
          yeah
          or use 3 or 4 of em and run each thing of a sep 12v reg

          cheers
          pcman
          donate to my team in the ****box rally all proceeds go to the cancer council http://www.everydayhero.com.au/dodgy_mechanics

          Comment


          • #6
            The only thing wrong with the design is you will have to have the car running to give you 12V correctly.

            Think about using the LM2577T for the 12V and run the input from the 5V supply.
            This way the car can be off and you can still use the pc.

            more info on website

            cheers

            andi
            Andi

            http://www.andicorp.com
            Setup: P233MMX, 32MBRAM, 8.4GB HD, CUSTOM DC2DC, 40x2 LCD.

            Comment


            • #7
              So would one LM2577 (3amps) be about enough for a basic system (MoBo, HD and character LCD?)
              [SIZE=1]'91 Nissan Stanza

              [XXXXXXXXXXXXXXXXXXXX] XX% Completed -
              Car Totaled and i bought a 20G mp3 player

              http://machs-fuel.tk
              a DIY video projector page

              Comment


              • #8
                Originally posted by Machs_FueL:
                <STRONG>So would one LM2577 (3amps) be about enough for a basic system (MoBo, HD and character LCD?)</STRONG>
                The 2577 will only give you around less than one amp of output current for a given design. It says 3 amps, but that is the current it can sink through the inductor.

                On my box I am using a laptop power supply. 1 amp from 12 volts will run a low power mobo, and hard drive. (not including the 5 volt line)


                There are other linear regulators other than the 7812 that can do 5 amps. You still need to satisfy the input voltage of 1 volt higher than the desired output.

                Jeff_
                MPEGBOX - Plexiglass Computer
                www.mpegbox.com

                Comment


                • #9
                  Originally posted by andicorp:
                  <STRONG>

                  Think about using the LM2577T for the 12V and run the input from the 5V supply.
                  This way the car can be off and you can still use the pc.


                  andi</STRONG>
                  Wouldn't it make more sense to take the input to the LM2577 from the 8-16 volt input rather than from the output of the 5 volt MAX787 ?

                  How much current can you get out of the 2577 anyway?

                  Jeff_
                  MPEGBOX - Plexiglass Computer
                  www.mpegbox.com

                  Comment


                  • #10
                    Ya i was thinking having the LM2577 right off the Vin, because that would give the PSU the ability to operate with out the car on

                    hit reload and the diagram should change showing what i was thinking
                    [SIZE=1]'91 Nissan Stanza

                    [XXXXXXXXXXXXXXXXXXXX] XX% Completed -
                    Car Totaled and i bought a 20G mp3 player

                    http://machs-fuel.tk
                    a DIY video projector page

                    Comment


                    • #11
                      Originally posted by Machs_FueL:
                      <STRONG>Ya i was thinking having the LM2577 right off the Vin, because that would give the PSU the ability to operate with out the car on

                      hit reload and the diagram should change showing what i was thinking</STRONG>

                      If I'm not mistaken, I think the output of the 2577 has to be more than the input by a volt or two. In the case where the powersupply doesn't have to work very hard the input goes directly to the output through that inductor. In the case where it does work, the inductor gets charged up and then its voltage adds to the input to make the output voltage. I'm not sure what would happen if you tried to make the output less than the input ie. 13.8 in and 12 out.

                      Jeff_
                      MPEGBOX - Plexiglass Computer
                      www.mpegbox.com

                      Comment


                      • #12
                        Without complicating the answer let me say that it wount work.
                        From your description i understand that LM2577 is step-up regulator which means the input voltage should be lesser then the output for atleast 1.5v~ volts.
                        SO basicly connecting the input to the unregulated 12V wont work!
                        However you could connect the input to +5volts but in this case you will need a 5Volt regulator to produce atleast 10amps to run the +5v rail of the computer as well as power the +12v regulator...
                        Take a look at the LM2587 regulator... It uses flyback design which is best suitable in this case... however you will need a transformer to go with it!

                        I dont get it... how people trying to design their own PSU without knowing this basic stuff about linier and switch mode regulators.
                        Fosgate

                        System Comp V3 - In progress.
                        Low power MB with C7 CPU, DC-DC PSU, car ECU link, USB TV, GPS, 7" TFT, Wireless, Voice.

                        Comment


                        • #13
                          Oh i see what you mean..

                          Sorry but it is the quickest way to learn

                          what about using a step down IC infront of an LM2577 ?
                          [SIZE=1]'91 Nissan Stanza

                          [XXXXXXXXXXXXXXXXXXXX] XX% Completed -
                          Car Totaled and i bought a 20G mp3 player

                          http://machs-fuel.tk
                          a DIY video projector page

                          Comment


                          • #14
                            Originally posted by Fosgate:
                            <STRONG>
                            However you could connect the input to +5volts but in this case you will need a 5Volt regulator to produce atleast 10amps to run the +5v rail of the computer as well as power the +12v regulator...
                            Take a look at the LM2587 regulator... It uses flyback design which is best suitable in this case... however you will need a transformer to go with it!

                            I dont get it... how people trying to design their own PSU without knowing this basic stuff about linier and switch mode regulators.</STRONG>
                            Ya, so you can cut severely into your 5 volt supply to get to plus 12 (very wasteful) or you use the 12 volt input to get 15 volts (or whatever you think the limit should be) and then use a linear regulator to get back down to 12. The whole thing will be just as efficient as going through two switch mode stages, plus you can get better filtering with the linear regulator. Chances are that with the LM25XX as the output stage (as a boost switch), you will have &gt;100 mV of ripple. Also, you can use the LM2587 or LM2577 as a fly-back or as a boost (which does not require a transformer, just an inductor.)

                            I don't get it, people who think they know everything but really still don't. Dude! There's a lot I don't know either, everyone has to start somewhere. There’s no better way than trying and getting your feet wet.

                            Jeff_
                            MPEGBOX - Plexiglass Computer
                            www.mpegbox.com

                            Comment


                            • #15
                              Dont want to make this a big argument after all we all here to help eachother right!
                              Just few words on your comments Jeff Mucha.

                              I guess my last post didnt clearly state that getting the +12v from the 5v rail is not as efficent... What i was pointing at with LM2587 is that it will take the input from the unregulated +12v and produce +12v @ 2Amp. In this case you dont need to touch the 5volt rail. LM2587 is around +89% efficent however it requires a transformer which lots of poeple here dont want to deal with.
                              Jeff Mucha the way you sugested by increasing the voltage to +15v then drog it down with linier reg... it will work however it wont be as efficent as using the LM2587 of the +12 input. As we all know the linier regs are working on 60-70% effiecentcy plus you will need a step-up regulator which again is gona get it share of wasting current in to a heat.
                              But if you were going to go that path you might as well convert the unreg +12 in to 30AC and then put it through a trasformer to produce all the required output voltages. In this case you wont need a seperate regulator for each rail plus your efficency will go as high as +90%.
                              Fosgate

                              System Comp V3 - In progress.
                              Low power MB with C7 CPU, DC-DC PSU, car ECU link, USB TV, GPS, 7" TFT, Wireless, Voice.

                              Comment

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