low voltage power source

Discussion in 'General Electronics Chat' started by sotinam, Jun 21, 2016.

  1. sotinam

    Thread Starter New Member

    Apr 20, 2016
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    Hi all,

    I have a circuit which needs an adjustable voltage source of ~1.5 V (It should be able to be adjusted on any number between 1 V and 1.8 V). One option might be using a voltage regulator based circuit (https://www.sparkfun.com/products/526) that provides a fixed 3.3V output and then using a voltage divider (with one potentiometer and one fixed resistor) to reduce the output to desired voltage. I was wondering if somebody knows a better/simpler (with less needed input power) way to do it?

    Any advice is appreciated,
    S
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,869
    1,393
    The LM317 will regulate down to 1.2V.
     
  3. EM Fields

    Member

    Jun 8, 2016
    167
    28

    How much current will the adjustable source be required to deliver, and will the load presented to the adjustable source vary once the voltage is set?
     
  4. sotinam

    Thread Starter New Member

    Apr 20, 2016
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    Maximum 20 mA
     
  5. EM Fields

    Member

    Jun 8, 2016
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    Once the voltage is set, what variations in load current will the source be expected to support while keeping its output voltage constant?
     
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  6. sotinam

    Thread Starter New Member

    Apr 20, 2016
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    I honestly don't know
     
  7. EM Fields

    Member

    Jun 8, 2016
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    Sorry, I worded the question badly.

    What I'm asking is that if the load on the source varies from zero milliamperes to 20 milliamperes, what change in the source voltage, over that range of current, can you tolerate?
     
  8. hp1729

    Well-Known Member

    Nov 23, 2015
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    Design 439 voltage sources.PNG
    Op Amp with a pot on the input. Voltage follower circuit.
     
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  9. wayneh

    Expert

    Sep 9, 2010
    12,120
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    I think the LM317 is a viable option if you don't want to use the op-amp above (which is a good solution). Shift the bottom voltage up with a diode, so that the LM317 controls down to 1.2-0.7 =0.5V. Do the calculations to choose a pot giving full scale adjustment over the the required range. Use a dummy load to ensure the regulator is always loaded to at least ~10mA. (Check the data sheet for the minimum required load.)

    The diode voltage drop is not fixed or entirely predictable, so if you need great precision, this wouldn't be so hot. If ±0.1V is OK, then it's fine.
     
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  10. sotinam

    Thread Starter New Member

    Apr 20, 2016
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    Thank you so much guys
     
  11. hp1729

    Well-Known Member

    Nov 23, 2015
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    LM317LZ (TO-92 package for that low a current) is a good choice. If you take the reference circuit down to -1.2 V instead of ground you can get the LM317 to go down to zero volts. It takes a little creativity because it throws things off.
    The diode idea is predictable if you know how much voltage that diode will drop at what current.
     
  12. hp1729

    Well-Known Member

    Nov 23, 2015
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    Design 495 LM317 down to zero 7660.PNG [QU
    OTE="hp1729, post: 1012327, member: 298400"]LM317LZ (TO-92 package for that low a current) is a good choice. If you take the reference circuit down to -1.2 V instead of ground you can get the LM317 to go down to zero volts. It takes a little creativity because it throws things off.
    The diode idea is predictable if you know how much voltage that diode will drop at what current.[/QUOTE]

    LM317 taken down to zero.

    It is made for 0 to +12 V or so. You may have to make adjustments for a lower voltage only.
     
    Last edited: Jun 22, 2016
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