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[Sproggy PSU] T6 replacement

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  • [Sproggy PSU] T6 replacement

    After my request in <a href=http://www.mp3car.com/ubb/Forum2/HTML/002159.html>this</a> thread, I have decided to go for the <a href=http://www.sproggy.com>sproggy</a> PSU. I have all the parts now, except for the flyback regulator transformer. (T6 in the wiring diagram.)

    It turns out Coilcraft is not shipping it as free sample anymore... On their website they say they have received thousands of requests in the past few months and will not send it to anyone making an mp3-player.

    So I am looking for a replacement regulator. Is there anyone with a good enough understanding of switching mode power supplies who can point out a replacement? It doesn't have to have the same pin-out, as I can make another PCB layout. If I do so, I will post the new layout so everyone will benefit from it. Please help me, otherwise I will be stuck with a DC-AC inverter.

    [edit] Pushed Submit waaaaayyy too early [/edit]

    [This message has been edited by Shaper (edited 03-16-2001).]

  • #2
    Gudday,
    Well i am not using sproggy's -12v circuit, instead I am using the max776, puts out 500mA and doesn't need any hard to source parts...go to their homepage www.maximic.com and search for the above datasheet...they have some usefull circuits at the end on page 10 of datasheets.

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    • #3
      AussieGuy,

      After checking up on the MAXIM datasheet, I have the following ideas/conclusions/questions:

      <UL>[*]I suppose you use the MAX775 instead of MAX776, which puts out 12V negative.</LI>[*]If you don't use the T6 transformer and the LM2587 at all, what part(s) do you use to get the 12V with enough amps?</LI>[*]You drive the MAX775 with the +5V generated from the MAX787-circuit? (Since it needs 3-8V input voltage.)</LI>[/list]
      It seems I will be designing my own PSU after all... So far I am looking at these specs for it:

      <UL>[*]+5V from MAX787 at max. 5A (Maybe 2 pieces in parallel like sproggy)</LI>[*]+3.3V from MAX788 at max. 5A, maybe two of them to get to 10A (Again like sproggy)</LI>[*]-12V from MAX775 at max. 1A</LI>[*]-5V from 7905 at max. 0.5A</LI>[*]+12V no idea yet!</LI>[/list]
      Any suggestions as to what to use for +12V? (No regulators, they won't cut it with a car battery's voltage swings.)

      Thanks,

      Shaper

      Comment


      • #4
        You can try using MAX1771. It's DC-DC step-up controller,so it can work with voltages below 12v. Use bootstraped mode,as shown in datasheet.Every one of it can supply about 1A without overloading the circuit.
        I also used Sproggy's DC-DC PSU,I got all the parts,including T6.The problem was that 12v section couldn't supply enough current for Hard-Disk spin-up,which requires about 2.5A at startup for about 3 sec. After searching the web and consulting with engineers in my work I decided to go with MAX1771. If you look on his datasheet you'll see that the only problem is that you need powerful chokes and diode (about 3A - to be safe),and powerful MOSFET,probably with heatsink on it,depends how much current you'll use.
        Enjoint life!

        Comment


        • #5
          While back when i designed my DC-DC converter i used the LM2587 Flyback regulator with 1:1 transformer which was available as a sample from coilcraft. After testing the design it was clear that it could handle power load of up to 2 Amps. I ran some tests using a 6Gig Fujitsu HD and a 12x CD-ROM. The test system was P166 based.
          Considering the input voltage which can be 8-15 volts the flyback regulations is most suitable design you can use.
          MAX1771 is a Step-up regulator .... which means it will work if the input voltage is less then the output voltage. However Maxim claims that Max1771 will operate from 5 to 16 volts... i havent tested this but as far as i know this only can be achived using Flyback regulations. MAX1771 might have integrated Step-up and Step-down regulators in which case it will work as long as the input voltage is less then or above the output voltage... but what if the input voltage is +12 (+-0.5v)?
          Dima have you tested the MAX1771 IC ? what was the results like ....


          ------------------

          Fosgate
          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


          • #6
            Ok,to understand what I'm gonna say here you need to look on its datasheet.
            There are two possible modes for operating MAX1771: bootsrapped and non-bootstrapped.Bootstarpped mode is more effective in our case,cause we need to suck more current.Use the circuit as shown at figure 2a.For input I'm using 5v,which is taken from MAX787 output (up to 5A!).Also,you can use bigger inductor,about 47uH,that can handle 2A at least.Now,R-slnsl,that in figure is 40mOhm,determines the maximum output current.I'm using 20mOhm,and output current that I get is 1.2A. I'm using two MAX1771,so I have 2.4A for +12v,it's enough for me.
            One more thing,I tested the circuit also with 12v input instead of 5v,it worked pretty well and gave me about 1.7A,but the MOSFET became very hot.After checking the currents I came to conclusion that I need more powerful MOSFET that can handle about 3A.After checking the prices I discovered that it's a quite expensive (about 6$ here),and you also need 2 ot these for more current,so I decided to use 5V as input (MAX787 is free!).
            I also checked the circuit in figure 6.If the input voltage is more than 12v (situation when the engine is running - voltage raises to about 15-16v),more powerful MOSFET required.
            So after all,I decided to stay with bootstrapped mode with 5v input.
            Fosgate,when I used LM2587 circuit with T6,I could only get about 0.8A,without using -12V output.How did you managed to get 2A from it?
            Enjoint life!

            Comment


            • #7
              Dima my design of the DC converter was bit different from Sproggy's. I'm using another transformer from Coilcraft it was 1:1 ratio and was only used for +12 volt. For -12 i was using an inverting step-up convertor from Maxim. Im pretty sure you have the schematic of my design if not i can send it to you, it in Protel format. Its pretty much a standard design from the datasheet of LM2587... nothing special ... with Big heatsink and a fan on it it can handle power output up to 2 amps without any problem ... and it doent get hot at all (well there is a fan on it with a heat sink). Thats about it i guess.
              I might play around with Max1771, see if its any better ... it sayes its pretty efficient.
              Anyway i will keep you posted.
              By the way what MOSFET did you use with MAX1771 Dima?



              ------------------

              Fosgate
              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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