LM317 300mA vairable power supply

Discussion in 'General Electronics Chat' started by RodneyB, Jul 7, 2015.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I want to make a small 300nA variable power supply and want to use the LM317L, which can handle a maximum current of 100mA.

    I would rather not use the LM317T because of the size. I was considering putting a transistor from the output of the LM317L to the base of the transistor and then switching the current through a transistor that can handle the current. But not sure of this or even which transistor to use.

    Any advice Greatly appreciated.
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    What output voltage range.? also what is the voltage driving the regulator.?

    E
    Did you mean 300nA.???

    EDIT:
    There are some smaller sized LM317 types. ref image.
     
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  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    The LM317 datasheet has applications circuits that cover adding an external transistor to increase the current capability. But by the time you go through all of that, the combo circuit will be larger than the TO-220 package. What is the regulator powering, and what about the size is important? Surface area on the circuit board? Component height above the board?

    ak
     
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  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Anything above a few volts output will have to dissipate ~1W or more, so a TO220 package is justified. You may also need a substantial heatsink.
     
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  5. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Thank you all firstly sorry about my mistake I meant 300mA. The Supply voltage is 24 Volts, I need an output voltage of 16.2 Volts. I was even considering building it with surface mount components as size here is the issue.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    That's 2.3 W total power that has to be dissipated somewhere. A TO-220 package standing up in free air and dissipating 2 W will get hot enough to melt fingerprints. It doesn't take much to cool it down to its operating temperature range, but you can't cheat fizix.

    ak
     
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  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    When getting rid of heat, size matters
     
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