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Additional pass through transistor or bigger reg?

Discussion in 'General Electronics Discussion' started by Balrock, Aug 7, 2012.

  1. Balrock

    Balrock

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    Mar 1, 2012
    I have been moving forward with my Bench PSU project and had a look today at increasing its current output. My design (still in breadboard stage) uses LM317 and LM337 regulators so it can provide about 1.5 amp. I was looking at increasing this to around 3 amp.

    One option I have looked at is using the same regulators with the addition of pass through "power" transistors. The other option is to use higher rated regulators. What are the pros and cons of each approach.

    Thanks for any help given, Paul
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    Hi Paul
    The LM338 will happily do up to 5 Amps, dont forget to heatsink it.
    messing around with lower rated regulator will work well its just a heck of a lot more work and higher component count.
    There's no point with pass transistors unless you are wanting over 5Amps, why complicate things more ?? :)

    Dave
     
  3. Balrock

    Balrock

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    Mar 1, 2012
    Hi Dave. Thanks for the quick reply. Yes I looked at the LM338 but they don't make a negative version of it as my PSU is Dual Rail.

    However, I am using 2 x transformers wired together (as I got them cheap) in place of one single unit so would I be correct in saying that if I separate (isolate) and use one transformer per LM338 rail I could wire the + output of the second LM338 to GND (0v) of the first and I would get a dual rail + GND - type configuration.

    I hope that made sense!
     
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    ahhhh ok, you didnt state anything about a split rail supply in your first post ;)

    Dave
     
  5. davenn

    davenn Moderator

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    Sep 5, 2009
    OK here's one example along the lines of what you were thinking
    NOTE there is NO connection between the secondaries of the transformer

    [​IMG]

    this came from the www site, down the page a little way .....
    http://www.tcaas.btinternet.co.uk/jlhesl.htm

    cheers
    Dave
     

    Attached Files:

  6. alfa88

    alfa88

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    Dec 1, 2010
    Take a look at my project log. I just posted it a couple of days ago. It uses 2- lm338s. As long as the 2 secondaries are not connected to each other; who needs a negative regulator? I might have gone a little overboard on the heatsinks but that's what I had laying around .
     
  7. davenn

    davenn Moderator

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    yup thats what the circuit does that I posted before your post lol ;)

    Dave
     
  8. duke37

    duke37

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    Jan 9, 2011
    The bridge rectifiers must be connected correctly. It would be better to rotate the diode symbol a quarter turn to the left.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Well spotted.
     
  10. Balrock

    Balrock

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    Mar 1, 2012
    Thanks all! I love this forum! What sweet headache relief it brings :D

    Sorry Dave, but in my defense I did quote "uses LM317 and LM337 regulators" ;)

    I will forge ahead to my next tangled web of confusion. Thanks again guys.

    "NOTE there is NO connection between the secondaries of the transformer" is ok for me Dave as I am actually using 2 smaller transformers anyway.
     
    Last edited: Aug 8, 2012
  11. davenn

    davenn Moderator

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    Sep 5, 2009
    yeah till i googled the LM337 I didnt realise it was a neg rail regulator .... never had the need to use one lol

    D
     
    Last edited: Aug 8, 2012
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