Power Supply

Discussion in 'The Projects Forum' started by ajm113, Aug 14, 2013.

  1. ajm113

    Thread Starter Member

    Feb 19, 2011
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    Hello everyone! I'm designing a very basic bench top power supply for my lab I'm building in the future. It's a 12v 2A variable power supply with short circuit prevention. I dont want to buy a dual high voltage power supply yet anyways, since most of my projects dont require more then 12v and aren't doing anything that require a very filtered output.

    I'm looking for any flaws in my design or perhaps ideas to add to it to make it more efficient.

    Sorry if the schematic is a bit hard to read, I love to design with pen and clean it up in Photoshop for further annalist.
     
  2. #12

    Expert

    Nov 30, 2010
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    There are a dozen ways to do this. The LM723 chip is designed to produce a voltage and regulate overcurrent. An LM317L chip has a built in 100ma current limit and voltage can be adjusted with external resistors. An op-amp can regulate the output voltage so it does not vary because of interference from the current limit circuit until the overcurrent limit is needed.

    Get specific about what qualities are important to you, then design the circuit.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    For both Voltage and Current regulation you could use an L200 regulator,
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    What you have drawn can't work. I have a basic lab supply design you can take.
     
  5. Jony130

    AAC Fanatic!

    Feb 17, 2009
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  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    That looks like a well-intended but simplified version of the design I posted which I actually did about 25 years ago.

    The problem I see with the circuit above is the LM358 opamp has ground as it's negative rail which limits how low it can pull. U2A is not going to be able to pull low enough to cut T3 off very well, which it must do to be able to limit the current.

    I avoid that problem in my design because the op-amps drive in the positive direction. I also use a better voltage reference. Using a 7805 as a voltage ref will give garbage grade performance over temp changes.
     
    Last edited: Aug 15, 2013
  7. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
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    Care to explain the flaws with my design bountyhunter? Just so I know what I did wrong. lol
     
  8. wayneh

    Expert

    Sep 9, 2010
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    I don't see a need for the diode coming off the rectifier, unless you're intentionally using it to burn off voltage.
     
  9. ajm113

    Thread Starter Member

    Feb 19, 2011
    176
    5
    Actually that was supposed to just be a output arrow. But for some reason I was like... "eh screw it, just keep drawing the connection." I forgot to remove that arrow in Photoshop. <_<
     
  10. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I'll do the biggest one: look at how the NPN darlington is connected that is supposed to drive the load and see if it can supply load current.

    OK, one more: the thing on the return side of the negative output which looks like current limit: you have a 1K pot into the base of the NPN transistor. How much current will that base get from that 1K pot and how are you ever going to get the NPN to sink 2A?
     
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