LM317 with automatic low cut off

Discussion in 'General Electronics Chat' started by bend94, Feb 15, 2016.

  1. bend94

    Thread Starter New Member

    Feb 15, 2016
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    Hi,

    I am building a simple DC 12v DC in 9v DC out.
    I have been using an LM317 and its been fine.

    Now I require the output to cut out if the input voltage drop below 10v.
    With a draxning please
    Thanks in advance for your help!
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    To do this you will have to add a comparator to the input. Why don't you sketch up a block diagram or schematic for us to review.

    Also, what do you mean by "cut out"? An LM317 has a minimum output voltage of 1.25 V. You can not turn the output down to zero volts without more modifications to the standard regulator circuit.

    ak
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
    3,242
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    The regulator will stop regulating before the input drops to 10V.
    upload_2016-2-15_12-56-2.png
     
  4. hp1729

    Well-Known Member

    Nov 23, 2015
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    I think what he is looking for is the output to go to zero, not just go unregulated or drop to 1.25. Disconnect the input if it drops below 10 V?
     
  5. crutschow

    Expert

    Mar 14, 2008
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    Is a minimum output of about 1.25V okay?
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Something you need to be aware of, the LM317 drops around 2V just doing its job. So if you have 10V in you will have 8V or less out.

    There are families of more modern 3 terminal regulators that drop a lot less voltage. A good resource on this site is Components Selection Guide.

    If you want I will draw something up to get you started. I suspect you need to address the other problem first though.

    Just a thought, a simple zener circuit might work better for the regulator, depending on what your current requirement for your circuit is.
     
  7. bend94

    Thread Starter New Member

    Feb 15, 2016
    13
    0
    Hi again

    Please find my actual electronic device that i am using
    I power my arduino with solar energy. it is working correctly till the battery has enough energy.

    My goal is to stop powering my arduino when to battery is to low
    Because with this actual LM317 when battery power is too low
    the arduino is powerup / powerdown / powerup / powerdown all the time.

    I want to stop when low power to avoid damage on my arduino.

    upload_2016-2-16_10-2-42.jpeg

    Please help

    thanks
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You can use a TL431 programmed zener and p_fet or opto coupler to turn off your Arduino, you set the desired voltage using two resistors.
     
  9. bend94

    Thread Starter New Member

    Feb 15, 2016
    13
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    thanks do you have a cabling scheme ?
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Do you want the Arduino power to stay off until the cut-off is manually reset?
     
  11. bend94

    Thread Starter New Member

    Feb 15, 2016
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    i will like arduino to stay off until sunshine and battery is recharged enough to power the arduino
    so not manually but if possible automatic

    thanks
     
  12. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    To do what you want requires two things, a comparator to sense the voltage out of the Regulator, and either a power switch or a control signal output that shuts down the system. What is the circuit or device inside the box called Regulator? If this has a shutdown control pin, it makes things easier.

    Automatic restart is not a problem. Do you want the system to restart as soon as the solar panel output is high enough to run the system, or wait until the battery is recharged enough?

    ak
     
  13. bend94

    Thread Starter New Member

    Feb 15, 2016
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    my device will be connected to the solar regulator output .
    This output deliver 12V DC . Well i would like to restart when the solar output is delivering 12V DC
     
  14. bend94

    Thread Starter New Member

    Feb 15, 2016
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    The Regulator is a solar regulator without any shutdown control pin

    >a comparator to sense the voltage out of the Regulator,
    Is it possible to do so, with a NE555 ?
     
  15. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    It's possible, but a comparator IC such as the LM339 would be much more convenient since it is easier to define reference voltages.
     
  16. bend94

    Thread Starter New Member

    Feb 15, 2016
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    ok for the LM339 . Have you got an example ? with a wire diagram.

    thanks
     
  17. bend94

    Thread Starter New Member

    Feb 15, 2016
    13
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    hi

    i will consider the LM339 way.
    For now, i had study a NE555 way.
    here it is !

    What do you think ?

    Regards my regulator.jpg
     
  18. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The NPN transistor will short the output of the regulator and cut the poser for the 555.
    This circuit will probably oscillate.

    Bertus
     
  19. bend94

    Thread Starter New Member

    Feb 15, 2016
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    And if i replace transistor by a relay?
     
  20. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Same problem with a relay, if you use it to short the output of the 7809.
    There is also some uncertainty as to the switching thresholds in that circuit, since if the 7809 input drops below the point where regulation fails, the 7809 output will drop too, and so the thresholds will be 2/3 of ??? and 1/3 of ???.
     
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