9v DC to 1.5v DC

Discussion in 'General Electronics Chat' started by smithy1776, May 26, 2011.

  1. smithy1776

    Thread Starter New Member

    May 26, 2011
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    What resistor values would I need to use with an LM317 to step 9v DC down to 1.5V DC? Are the two capacitors in the data sheet diagram absolutely necessary?
     
  2. muthukumar_ece2004

    New Member

    May 20, 2011
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    Use R2=47E and R1=220E;
    Yes, two capacitors should be used!
     
  3. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
    90
    According to the datasheet, the LM317 requires as much as 10ma of current to flow from Vout to the ADJ pin for proper operation. R1 is normally about 120Ω to get that.
    With a smaller R1 you will need a different R2. Use the formula on your drawing.

    LM117's are different, they only need 5ma.
     
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  4. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
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    Be aware that, depending on the current you draw, you may dissipate quite a bit of power and may need a good heat sink.
     
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  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you are using a PP3 "transistor" battery, it will have a short life, and you will spend a lot of money buying new batteries. Most of the power (~83%) will be dissipated in the regulator as heat instead of doing useful work in the load (~17%).

    You would be much better off to use different batteries. AA Alkaline batteries would not even require a regulator - unless you really need 1.5v exactly.
     
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  6. nigelwright7557

    Senior Member

    May 10, 2008
    487
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    You really need a buck converter to efficiently convert the voltage.
     
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  7. iONic

    AAC Fanatic!

    Nov 16, 2007
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    With r1 @ 240 ohms, R2 should be 48 ohm for 1.50V.
     
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