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Thread: Designing New DC-ATX Power Supply

  1. #1
    Maximum Bitrate Raas's Avatar
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    Post Designing New DC-ATX Power Supply

    Hi there, I'm playing with this thought for a while now because.

    • The maxim components in SPROGGY's design aren that easy to obtain as thought, besides that they are expensive, if you can obtain them .. (here in The Netherlands I can only obtain 1 of the 2 needed in SPROGGY's design)
      and I think not all of the components used are to easy to get
    • I someone heard about the sproggy supply that this thing wasn't powerfull enough when you are really expanding your system
    • I don't want DC-AC-DC
    • I don't want a pre-made unit like the one from keypower, just because it's way to expensive


    I'm absolutely no electronics expert, but I asked a couple of friends of mine for some help.

    The goal for this is: designing a power supply that is easy to make, and the parts used are available to almost everyone in the world because I think we all want this...

    I was looking through National Semiconductor's webpage and found the LM338. which is an adjustable regulator with the following characteristics:


    LM338T / LM338K
    5a adjustable regulator
    7a peak
    12a short peak
    Vin 4.2 - 40
    Vout 1.2 - 32 V

    and these were very cheap (something like $1.1 each, and like $0.6 for 10 of them)

    I readed the datasheet that is on the website, and it stated that the ouput voltage could easily adjusted with only 2 resistors.

    They also could be assebled in series to produce more amps (like 10a or 15a or maybe even 20a)

    I think that when we use these for all of our positive voltages, the supply could even run at 5v (so the computer will continue to run, even when cranking the car, or with a very bad battery)

    Also a friend of me told me that when he's got the positive voltages, he could easily make the needed negative voltages...
    Is this true ??? (as i don't know too much about electronics, but i want to figure out a decent power supply)

    I haven't looked to the power-good-feature, but I think i can easily adopt this one from the sproggy power supply...

    The supply I was thinking of would supply the following voltages:

    +5v @ 20a (28a peak)
    +3,3 @ 15a (21a peak)
    +12v @ 10a (14a peak)
    -5v @ 1-2a
    -12v @ 1-2a

    According to this, it would be like a ca. 200w supply

    What do you guys think of this,
    Any ideas, suggestions, criticism, whatever is welcome...

    Maybe we could get this of, with globally available components, and every one can build his own power supply very easy !!

    Greets
    Raas - The Netherlands
    ME: VIA epia m10000, lilliput 7', opus 150w, 80gb<br>
    GF: IBM Thinkpad 380, ext. 3.5 80gb, 40x4, PB-IR

  2. #2
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    go for it!

  3. #3
    Variable Bitrate
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    He's prolly using the same parts as Sproggy but have you checked this cat's Dc/Dc ATX supply out? Be forewarned, he IS using Maxim components.
    http://home.primus.com.au/bravo/Carp...bjcarputer.htm
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  4. #4
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    They also could be assebled in series to produce more amps (like 10a or 15a or maybe even 20a)
    did you mean in series or parallel? I think you mean the later dont you??? If you have any luck be sure to post the circuit. I think you might have problems with the 12 volts rails though using these regulators. The supply will need to maintain about 13.5Volts at all times. Thus your car will need to have a good alternator and be running!

    Good luck anyway!
    Project - GAME OVER :(

  5. #5
    Maximum Bitrate Raas's Avatar
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    Sorry Magnetik, I wasn't to clear about this, but thanks for correcting me.

    I think you might have problems with the 12 volts rails though using these regulators. The supply will need to maintain about 13.5Volts at all times.
    I'm a bit confused now.
    In the datasheet there are some examples which will produce like more volts than their input is...
    So for the 12v rail, I don't need an input higher than 12v.
    The regulator should be able to produce 12v with even a 7v input,

    If not, I have to find another sollution, but I think that these regulators are a very good base for my power supply

    If you have any luck be sure to post the circuit.
    Don't worry when things work out i will build a DIY-webpage about this supply.

    Greetz...

    BTW.
    If anyone also has ideas about this, please post them, (as like the 3000 eyes of our 1500 members will see a lot more than only my 2 )

    Greetz
    Raas - The Netherlands
    ME: VIA epia m10000, lilliput 7', opus 150w, 80gb<br>
    GF: IBM Thinkpad 380, ext. 3.5 80gb, 40x4, PB-IR

  6. #6
    Maximum Bitrate Raas's Avatar
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    He's prolly using the same parts as Sproggy but have you checked this cat's Dc/Dc ATX supply out? Be forewarned, he IS using Maxim components. http://home.primus.com.au/bravo/Carp...bjcarputer.htm
    Thanks for the info Tony S I have looked at it, and maybe i will adopt the Power Good feature.

    Thanks.
    Raas - The Netherlands
    ME: VIA epia m10000, lilliput 7', opus 150w, 80gb<br>
    GF: IBM Thinkpad 380, ext. 3.5 80gb, 40x4, PB-IR

  7. #7
    Retired Admin Aaron Cake's Avatar
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    Cool

    Originally posted by Raas:
    I was looking through National Semiconductor's webpage and found the LM338. which is an adjustable regulator with the following characteristics:
    5a adjustable regulator
    7a peak
    12a short peak
    Vin 4.2 - 40
    Vout 1.2 - 32 V
    and these were very cheap (something like $1.1 each, and like $0.6 for 10 of them)
    Wow I never realised how cheap they were wholesale. My local electronics store sells them for $14.99.

    I readed the datasheet that is on the website, and it stated that the ouput voltage could easily adjusted with only 2 resistors.
    True, but this regulator is totally unsuitable for this purpose...read below.

    They also could be assebled in series to produce more amps (like 10a or 15a or maybe even 20a)
    You mean parallel. But you can't parallel voltage regulators and expect it to work very well for very long.

    I think that when we use these for all of our positive voltages, the supply could even run at 5v (so the computer will continue to run, even when cranking the car, or with a very bad battery)
    This regulator will not work for the 12V supply. It requires an input voltage of at least 14V in order to produce 12V out. This will work when the car is running, but not when it is turned off.

    Also a friend of me told me that when he's got the positive voltages, he could easily make the needed negative voltages...
    Is this true ??? (as i don't know too much about electronics, but i want to figure out a decent power supply)
    Yes. It is relativly easy to make a negative voltage from a positive voltage. There are two schematics on my website that will do this.

    I haven't looked to the power-good-feature, but I think i can easily adopt this one from the sproggy power supply...
    Power good is easy. Just a simple RC network.

    +5v @ 20a (28a peak)
    +3,3 @ 15a (21a peak)
    +12v @ 10a (14a peak)
    -5v @ 1-2a
    -12v @ 1-2a
    According to this, it would be like a ca. 200w supply
    This is an insane amount of power, and with a linear circuit heat would become a big problem. I shudder to think of the size of heatsinks required. Also, making -5V and -12V at 2A is no trivial matter.

    Your best bet would be to design a switching power supply, with an output of around 100W or so. Much more manageable.
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  8. #8
    Maximum Bitrate Meatballman's Avatar
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    This may be a dumb suggestion from someone who knows nothing about electronics, buy why don't you just see what Keypower uses in their supply and make a similar design? There are a couple guys that have it that could post a pic of the board.

    Just a thought.

  9. #9
    Maximum Bitrate Raas's Avatar
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    Wow I never realised how cheap they were wholesale. My local electronics store sells them for $14.99.
    I looked at the Farnell's website.

    You mean parallel. But you can't parallel voltage regulators and expect it to work very well for very long.
    Why not ?? the datasheet even has some examples of 10a or even 15a schematics which produce a continious output. I don't think they would show/reccomend these designs if they weren't build to last, wouldn't they ?
    Please look at the datasheet, there are some very simple 10a and 15a examples. The only thing about them is, that they require a minimum load of 100ma

    This regulator will not work for the 12V supply. It requires an input voltage of at least 14V in order to produce 12V out. This will work when the car is running, but not when it is turned off.
    Okay, I probably have to figure out something else for that to have a decent and strong enough 12v supply. Someone probably has done this, so maybe I could learn/addapt something from that.

    Yes. It is relativly easy to make a negative voltage from a positive voltage. There are two schematics on my website that will do this.
    Okay, Thanks Man, I will look at them , and maybe use them... Thanks !!!!

    This is an insane amount of power, and with a linear circuit heat would become a big problem. I shudder to think of the size of heatsinks required. Also, making -5V and -12V at 2A is no trivial matter.

    Your best bet would be to design a switching power supply, with an output of around 100W or so. Much more manageable.
    Yes, true, this psu Probably will have a lot of overkill, but I someone heard that the sproggy power supply wasn't powerfull enough. So why not build an extra powerfull psu, like the one your standard desktop pc has. Q. Why does the Keypower PSU have such great capacity ???

    This might sound dumb, But I actually didn't read anything about a heatsing required. The regulator comes in 2 different styles.

    • TO-3 Steel, metal can package
      Which has only 2 pins (Vin,ADJ) and it's case is the output.
      A Heatsink can't be attached to this one
    • TO-220, Plastic package
      This one has 3 pins (Vin,ADJ,Vout) and has this thing where you probably want to attach a heatsink. only thing is, that this thing also functions as an output (Vout) so this regulator has 2 (the same) outputs.
      And we can't put these all on the same heatsink, because the voltages would screw up


    So I don't think these things require heatsinks... (altough I must say, I do find this a bit strange....)

    Meatballman
    This may be a dumb suggestion from someone who knows nothing about electronics, buy why don't you just see what Keypower uses in their supply and make a similar design? There are a couple guys that have it that could post a pic of the board.
    This would be very nice.. Now only thing we have to do is wait 'till someone would like to do that..

    But then... they most likely will use parts that aren't globally available or something..


    Maybe I'm just going to a bit of the sproggy design, but instead of the maxim chips which are for 3,3v and 5v, I will use some own design using the LM338 regulator..
    (because, the only thing which blocks me from buildign sproggy's design is that I can't find the required maxim chips.)


    [sorry for the long post guys]
    Raas - The Netherlands
    ME: VIA epia m10000, lilliput 7', opus 150w, 80gb<br>
    GF: IBM Thinkpad 380, ext. 3.5 80gb, 40x4, PB-IR

  10. #10
    Maximum Bitrate Raas's Avatar
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    This regulator will not work for the 12V supply. It requires an input voltage of at least 14V in order to produce 12V out. This will work when the car is running, but not when it is turned off.
    Maybe someone has a good idea how to produce Vout=12v@5a from Vin=7-16v

    Or maybe there just a simple part that will product Vout &gt; 14v @ 5a
    and then I still can use the LM338 to get a decent 12v

    Does anyone of you have an idea about this ?

    TIA
    Greetz
    Raas - The Netherlands
    ME: VIA epia m10000, lilliput 7', opus 150w, 80gb<br>
    GF: IBM Thinkpad 380, ext. 3.5 80gb, 40x4, PB-IR

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