Var. pw. supply help

Discussion in 'The Projects Forum' started by Ronaldn0519, Jan 4, 2014.

  1. Ronaldn0519

    Thread Starter New Member

    Jan 3, 2014
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    Hi guys I'm new here so let me introduce myself. My names Ron an i have a pretty good background in electrical/electronics. This is the first time I'm actually going to try an build a circuit. I would like to build a variable power supply from an existing computer power supply. I would like to build this for aluminum anodizing. It doesn't have to be a 5 amp supply, the minimum would be about 3 amps. i don't need a lot of current for my application. i have some questions/opinions about this build. i have found a diagram for a 1.2-36v 5amp dc build schematic.
    here are my concerns.
    this schematic doesn't show Vin from supply and Vout? (Vout threw RV1?)
    what is J1 &J2 TBlock-m2? (my guess is a terminal block/ banana plug?)
    What are your opinions on this build? (from what it look it should work but the question is will it produce up to 5 amps?
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    That circuit is right off the LM317 applications section. Go to TI's web site and download the datasheet and ApP notes for an LM317.

    The minimum input voltage will have to be about 2.5V higher than the output voltage. If the input is say 30V, and the output is set to say 5V, and the load current is say 3A, then the power dissipation in Q1 will be huge [(30-5)*3 = 75Watts]. You will need about a square yard (or square meter, since you didn't list your country when you signed up) of aluminum heatsink!
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
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    I think I have read some place in this forum. About modifying a ATX power supply to adjustable. By some simple circuit board modifications. This is not something I have done my self. So I may be on thin ice here. And I also have a roasted chicken ready to eat
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Haha, great news. I hope it doesn't look like your avatar. :p
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    The Vin is from J1, the output is from J2.

    J1 and J2 just a connector as power plug, your can using the type you want.

    Refer to the 12V/30A Power Supply, you can using the LM317 to replace the 7812, and using the circuit of LM317, for the heat problem that you just using the TIP147 less than 1.5A and 4 pcs, and using each 2N2955 for 2A for 3 pcs.

    If you provide the IC numbers of your pc power, maybe you got the chance to modify the circuit from inside of the power, and unnecessary to using the circuit of LM317, but it just maybe.

    How high the voltages do you need?
     
    Last edited: Jan 4, 2014
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    That's true, but I have never been a fan of that kluge. The power transistor has no current limit protection and no over temp protection. As my boss used to remind me: any power supply that has no effective current limiting isn't really a power supply, it's a FUSE.

    If all you need is 3A, there are many integrated regulator IC's available. Try the Linear Technology web site, they have a ton of linear regs.
     
    #12 likes this.
  7. #12

    Expert

    Nov 30, 2010
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    LOL! That is one of the reasons I jumped at the chance to leave my job in the power supply factory. The, "real" engineers kept sending in designs that taught me to recognize, "the familiar crackle of exploding thermoplastic".

    "But I have a BSEE and the datasheet says...":D
     
  8. Ronaldn0519

    Thread Starter New Member

    Jan 3, 2014
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    Sorry it took me so long to reply. It's been a busy day. I got pictures of the power suppy specs and also the inside just for reference. The voltage isn't s factor in anodizing but I need the amps to control the process. I could do with 3 amps rather then try an get the 5 amp circuit to work. I won't be able to anodize lager parts.
     
  9. Ronaldn0519

    Thread Starter New Member

    Jan 3, 2014
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    For some reason it isn't allowing me to upload 3 images so I had to do it this way so please bear with me
     
  10. Ronaldn0519

    Thread Starter New Member

    Jan 3, 2014
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    And here is the last image
     
  11. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Here you go:

    http://www.ti.com/lit/ds/symlink/lm350-n.pdf
     
  12. #12

    Expert

    Nov 30, 2010
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    The pot is oversized because it is cheaper that way.
    The part numbers are www.mouser.com
     
    Last edited: Jan 5, 2014
  13. ScottWang

    Moderator

    Aug 23, 2012
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    What's the model's ID number?
     
  14. ScottWang

    Moderator

    Aug 23, 2012
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    The picture is not clear, did you see the 16 pins IC number?
     
  15. Ronaldn0519

    Thread Starter New Member

    Jan 3, 2014
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    #12 & BountyHunter thanks! so thats all i would have to do #12 to make it a 3am supply. I always end up overlooking things an thinking to far ahead of something that can be done so simple.

    Scottwang what do u mean by the 16 pin ic?
     
  16. #12

    Expert

    Nov 30, 2010
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    Keep in mind that my drawing is only a close up of the regulator resistors and where to buy them. You have to add the capacitors, the main supply voltage, the heat sink, the amp meter, etc.
    You have to put it all in a nice box where the fumes won't get at it!
     
  17. ScottWang

    Moderator

    Aug 23, 2012
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    ATX Power supply using the PWM ic inside, the ic almost has 16 pins.
     
  18. Ronaldn0519

    Thread Starter New Member

    Jan 3, 2014
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    yea i was just thinking about that. I have ltspice on my computer for messing around with circuits. i can figure out how big/many of capacitors will need to be put in via oscilloscope feature on there.
     
  19. #12

    Expert

    Nov 30, 2010
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    Also read the datasheet. 3 terminal regulators can oscillate if you don't follow instructions.
     
  20. Ronaldn0519

    Thread Starter New Member

    Jan 3, 2014
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    Are you talking about the big connector that connects to the motherboard?
     
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