diy PSU design

Discussion in 'General Electronics Chat' started by adamclark, Feb 19, 2014.

  1. adamclark

    Thread Starter Member

    Oct 4, 2013
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    hello all.. I have started a thread on this a while back and got plenty of info that I needed on parts and good insight on design. But now I think ive got all the parts necessary to start my build. Ive chose a transformer its an old Marantz with a sec hv coil that is center tapped and from the center to each side it is 44.5 vac. I have that figured to make 62.47 VDC. What I want to do with my psu is make it 0-24vdc variable with 10a current. I plan on using an mb354-w bridge rectifier that's rated at 100vdc@30a. I plan on using each side of the hv sec. coil to make +/- vdc. I plan on using 3 lm317's with a 3055 on each as a pass transistor to achieve the ampherage. I think I have a rough schematic ive drawn ill try to attach. My xformer also has 2 other coils, 1 at 8.1ac and another at38.5 vac. I hope to use these somehow for other features. I also have 3 nte2050's and 12 green 7seg displays that I plan to use to make digital displays for +vdc,-vdc, and amps. What I don't have yet is the correct potentiometers for the rough tunin and fine tuning knobs, I will need some help for those. I have plenty of heatsinks from small to very big and a few fans so keeping things cool shouldn't be a problem. Ill try to attach my drawings so far. please keep in mind that im just a step above but below intermediate. Ive built rough dirty psus befor but nothing this complex. I hope to use this for years to come. I appreciate your critique, suggestions and advise. thank you. I think yhe one labeled new supply is mt latest but without the pass transistors.. please give me your advisw as im finally ready to build. thanks
     
  2. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
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    Whats do D1 or D2 do? ??
     
  3. adamclark

    Thread Starter Member

    Oct 4, 2013
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    on which schematic? these were drawn as part of a learning process and none is accurate. I have more that ive drawn just cant find them at the moment, I will try the rest. What I really need is to know where to place the 3055 on each 317 and to verify that I can actually achieve what I want to do with what Ive got. ill also try to find a link to my other thread so you can see the actual thought process.. I know I really need to refine my schematic and I knoe I have a more complete one somewhere ill find. Im not pressed to add the meters as I know they will require a completely separate circuit to function. I just need advise. Ill find the rest and put them up. but any info you can give would help. I think that even with all ive got drawn, a whole new schematic will be necessary. I should say that a lot of the schematics I show have been givin from other members here.. im just trying at the moment to come up with a solid idea to start my build with.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,986
    3,729
    D2 is backwards. On far right document (on the LM337). The arrow should point to the more positive potential.
     
  5. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    http://forum.allaboutcircuits.com/showthread.php?t=90938 this is the original thread but its quite long.. it ended up with others trying to push ideas instead of helping with mine.. but it will show you where I was at.. But after some consideration, ive considered starting fresh since ive got most of the components and fell that what I want can be achieved with what ive got.. It got confusing.so perhaps a fresh start is necessary. I don't want it done for me, I want to understand everything going on. this started as a learning experience for me.
     
  6. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    ive also got an nte996 that I think replaces the lm308 but I might be wrong.. I had to take a couple month break due to family reasons
     
  7. adamclark

    Thread Starter Member

    Oct 4, 2013
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    I think ive givin a decent explanation af what I want and from the other thread I believe I got what I need... I kind of feel that a complete restart might be needed as ive lost my train of thought from the first attempt... I do know that the transformer to rectifier has to be the way ive got it, but right after that I started getting mixed opinions. thought I had my way through it, but it seems half my notes are missing
     
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    That transformer is completely wrong for your design. If the max output voltage desired is 24, the input unregulated DC should be not more than about 30V. With 44V and the desired current of 10A, that gives you 440 Watts of power dissipation at low values of Vout which is impossible to heatsink.

    Even at 30V in, you could have up to 300W which is extremely difficult to heatsink. It would have to be divided across about 6 transistors mounted to a massive fan cooled heatsink assembly.

    You also need a design with a good current limit capability or you will just be building a giant fuse that will need to be repaired all the time.


    FYI: The 317 + pass transistor is probably the worst possible choice for a usable power supply. Take it from somebody who knows. Anything else would be better. Even the old LM723 based design would be better.

    As a note: a 240W linear adjustable power supply is a long dying breed because of the massive power dissipation problem. Much better approach to use a switcher.
     
    Last edited: Feb 20, 2014
  9. bance

    Member

    Aug 11, 2012
    315
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    I think you need to clearly define what you are trying to achieve. There are many features that can be added to a simple linear PSU to make it much more useful.

    The plus side is that you already have the expensive parts (enclosure,transformer,heat-sinks.)

    So you could start with a basic design, something straight off the data-sheet, as you have in post #1, and then add the extras as you need them.

    These extras often offer protection to your 'powered circuits' which can be invaluable when things aren't wired correctly (we all make mistakes:D)

    Have a look at this thread for fundamentals.

    HTH Steve
     
  10. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    I just want to build my own psu, I have already purchased many things from discussion in other threads.. I have 3 NTE2050's for a +v meter and -v meter and an ammeter, I have 12 NTE3054 7 segment displays for this, I have a dozen lm317t's and as many 2n3055's. not that I intend on using them all... I have the center tapped transformer. I have an NTE996 but I have lost most my drawings, I believe its supposed to replace the lm308? maybe from a design in another thread.. All I really need is +16 and 5a of current, but I want to get the most out of what I have..I can remember that the NTE996 is important for me. I have plenty of heatsink and fans. So this is what Ive got so far, and Ive stated what I need. Also from what ive gathered this type of supply is much cleaner than a switching psu. I test a lot of car audio equipment and I really don't want much hum and the higher the current I can have is better for this...
     
  11. adamclark

    Thread Starter Member

    Oct 4, 2013
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    this is my first drawing and the one im still trying to stick to but adding the pass transistors on the 317's.. It should supply the current and variable voltage right?
     
  12. bance

    Member

    Aug 11, 2012
    315
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    Why don't you build it and find out if it works?

    Oh! and if I were you I'd use the 38.5V tap first....
     
  13. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    I intend to build it,,lol.. no offence meant, However Im trying really hard to understand how it all works together so once built if it doesn't work I will be a little more ready to troubleshoot.. and I still haven't completely chosen a design yet.. If I used the 38.5v tap how would I get +v and -v.. I thought that required a center tapped transformer?
     
  14. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
    6
    Ok,, I found a couple schematics one is just a basic 317t with the pass transistor. I got it right from the lm317t datasheet.. Im assuming I would have to put one on each of the 317's in my main drawing. the other I just found and it shows a 317 with 2 3055's in a different configuration that's supposed to do 15a but I cant tell if its adjustable or not.....But I think as far as my tranformer and components I already have go, It seems almost like its right along the lines of my thoughts and it also seems a little to simple..lol
     
  15. adamclark

    Thread Starter Member

    Oct 4, 2013
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    oh, and I believe the NTE2050 chips im using for the meters require -v and +v, which is why I even considered a dual supply,,, plus Ive recently started to work with microcontrollers (pic and arduino) so I thought it would be a nice feature to my psu..
     
  16. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    can somebody please explain to me in newbie terms how the second picture in post 14 works also please?
     
  17. bance

    Member

    Aug 11, 2012
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    This goes back to my original reply:-
    Do you want a 0-24V supply or a 24-0-24V (+/-24V) supply?
    Do you need current limiting?... Soft start?... Voltage limiting?

    The design in post #11 simply won't work, at least the way drawn, which is why I suggested using the 38.5V tap.

    You will quite probably need a completely separate supply for your meters, if they are to work!

    Designing is an iterative process, make a start and then improve upon it..... and so on.
     
    Last edited: Mar 5, 2014
  18. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    I got ya,,, yea I want 0-24 +/- supply and be able to set each voltage separately. My transformer also has another tap that's 8.1vac which should work out to 11.37vdc that I intended to use for my meters and such. Ive thought about a case temp meter too, but ill add all that after I have a working adjustable psu in its case,,, I really am trying to take all of your advice and Im going to start to build right as soon as I figure out what im building.. I plan on starting small and adding the pretty and cool stuff after Im making good clean adjustable power that meets my current demands. and ive seen a working psu somewhere that the guy ran the lights for the switches and other aesthetics off the power filter caps to burn off some extra current to keep the heat down at the regulators..
     
  19. adamclark

    Thread Starter Member

    Oct 4, 2013
    472
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    And one of the reasons I want to use the center tapped coil, other than the +/-vdc was because it is my understanding that I will lose 3 volts at the rectifier bridge and and additional 3vdc per lm317 and I plan on using 3 of them.. So that's 15vdc down from where I started..
     
  20. bance

    Member

    Aug 11, 2012
    315
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    OK, why do I think the post #11 supply won't work? (Hint read the data-sheet for the LM317, the bit about "ABSOLUTE MAXIMUM RATINGS")

    The Data-sheet is your friend.:D
     
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