LM317 basic switch mode supply

Discussion in 'General Electronics Chat' started by rbg5k, Jan 26, 2010.

  1. rbg5k

    Thread Starter New Member

    Jan 26, 2010
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    You can set up an LM317 as a constant current supply with a simple power resistor between the output pin and adj pin to set current and take your CC output from the adj pin.

    Now, if I wanted to also have a switch mode (and constant current) supply, can I simply switch the input voltage on/off at the LM317 input?

    Say 100khz or so with an on/off pass transistor at the LM317 input?

    And I suppose a choke on the output?
     
  2. rbg5k

    Thread Starter New Member

    Jan 26, 2010
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    I know there are other. more suitable parts designed for smps but I have a bunch of boards with Lm317 already that I'd like to utilize.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    There are a couple of schematics in National Semiconductor's datasheet for the LM117/LM317 on page 18. The "Low Cost 3A Switching Regulator" didn't simulate well; it just acted as a linear regulator.

    Didn't try simulating the 2nd one.
     
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
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  5. rbg5k

    Thread Starter New Member

    Jan 26, 2010
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    Ok thanks. I have a ton of lm317.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Perfect for LEDs then. :D Seriously, this is not a bad thing.
     
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