Help building a Variable Hi amp power supply

Discussion in 'The Projects Forum' started by sparkfishes, May 20, 2012.

  1. sparkfishes

    Thread Starter New Member

    Oct 19, 2009
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    0

    I have been looking at this "need" for several weeks and - like most things I do I wanted not just to build the supply but learn more .
    I want about 15 Amps out of the supply 20A would be better
    I have read about the various Higher amperage regulators and about putting regulators in parallel but I really wanted to make this circuit




    There are several similar ( PNP) circuits on the net and they all have the same values

    I don't understand how the LM317 t controls the voltage of the by-pass transistors
    The input of the transistors is Supply voltage ( 29.6) The out put is straight to the out put terminal and the base is at 29V and 296mA

    Any way I can not get the circuit below ( or the six other I have built) to vary . The LM317 side works OK but as soon as I add the 2955's the output goes to 32.6V


     
    Last edited: May 20, 2012
  2. paulktreg

    Distinguished Member

    Jun 2, 2008
    611
    120
    I can't see any of your schematics?
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    Did you thing of the big brother of the LM317, the LM338?
    Here is a schematic for a 15A regulator using 3 X the LM338 (from the datasheet):

    [​IMG]

    I also have attached the full datasheet for the LM138/LM338.

    Bertus
     
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  4. sparkfishes

    Thread Starter New Member

    Oct 19, 2009
    16
    0
    That is because I can not find out how to upload them I have read the instructions but I still can not do it
    I have up loaded the circuit but it will not display it
    The circuit is a jpg file and only 18mB
    Time zone BST
     
  5. sparkfishes

    Thread Starter New Member

    Oct 19, 2009
    16
    0
    Thanks for the circuit but is not really what I want to do
    I want to get my circuit working and understand why it does not work - where I am making my mistakes
    The Lm 388 are expensive and I would need to get theop amp when I have theother componet here.
    I don't want to appear ungrateful, but I want to learn, not just make A power supply
     
  6. sparkfishes

    Thread Starter New Member

    Oct 19, 2009
    16
    0
    If you could explain HOW iget them to display I would be very grateful- YES i have read the instruction but I can not get te SMALL JPG file to diplay
    They upload - I think
     
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    How to upload an attachment.

    To attach a document or picture to a post

    Click "Go Advanced" at the bottom of your post,

    One of several options will pop up,

    Click "Manage Attachments" much further at the bottom of your post,

    To upload a file from your computer click "Browse", then select the file.

    Schematics should be .gif or .png format, pictures should be .jpg. .jpg formats will fuzz out schematics, and should not be used for that purpose.

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

    If you want to display this file there is an old thread I made,

    How to Display Attachments Full Size
     
    sparkfishes likes this.
  8. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Last edited: May 20, 2012
    sparkfishes likes this.
  9. sparkfishes

    Thread Starter New Member

    Oct 19, 2009
    16
    0
    The circuit is not from the LM317 data sheet although the p[art that is just for the voltage regulation is as per data sheet and that side works OK.
    It is only when I put the TRS in the circuit it does not regulate the voltage
    Thanks to Bill MarstonI have now uploaded the circuit- I swear I did the same instruction before I asked for help and it did not show up!
     
  10. evilclem

    Member

    Dec 20, 2011
    118
    16
    High amp variable.png

    Try using the 317 to drive the base of the transistors.

    At the moment you have no control on the transistors and the 317 is doing nothing (as it's output is saturated by the transistors bypassing it).
     
  11. sparkfishes

    Thread Starter New Member

    Oct 19, 2009
    16
    0
    That is exactly what I thought but there are at least TWO circuits on the web that have the same configuration
    I have been doing this almost constantly for 5 day I am going to ak a break and come back to it - thanks
     
  12. sparkfishes

    Thread Starter New Member

    Oct 19, 2009
    16
    0
    That is EXACTLY the circuit I am trying to replicate
    This is the circuit I used
     
  13. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    The link I gave in post #8 also contains the explanation of the circuit.
    Driving the PNP transistors with the output of the LM317 will not work.

    Bertus
     
  14. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Would not a LM723 approach be better in this case? The circuit posted by Bertus look quite complicated. Compared to using 1 LM723 and some support circuits
     
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