Multiple output Volts from 1 power source

Discussion in 'The Projects Forum' started by garcijon, Aug 19, 2014.

  1. garcijon

    Thread Starter New Member

    Aug 19, 2014
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    0
    Hi All,

    I am new to the forums and new to working with electronics. I am working on a project for my lab involving the use of servos and arduino - tilting platform for rodents.

    I am using a Futaba S9353HV servo, Arduino Uno, LM317 and LM7815 voltage regulators and 3 Omega load cells (detect downward force).

    I need to supply the load cells with 15V regulated input and am currently using the LM317 to give the arduino ~9V and using the 5V output pin from it to power the servo.

    When I connect a multimeter to the output/ground from the LM7815 I notice that it is fixed at 15.08 which is fine but then when the servo begins to move it downs down as low as 13 V. I have a capacitor on the input/output of the LM7815 and LM317.

    On the output of the LM7815 I have a small clay capacitor (it says 474) which is believe is .1 uF. The input has a 1uF capacitor. I have the same setup on the LM317.

    Can anyone please help me figure out how to get a fixed ~15V from an LM7815 even while the servo is moving?

    Also almost forgot to mention. The power supply is 15V 200nA.



    Edit:

    I immediately realized that I was not taking into account the dropout voltage (with the help of google) for the LM7815. The operation range of the load cells is from 10-15 V so I changed to an LM7812 but the setup is all the same. I notice on the multimeter that the power is still not fixed once the servo starts moving.

    Could this be due to the low Amps on the power supply?
     
    Last edited: Aug 19, 2014
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    Hi,
    Do you mean 200mA.?

    I would say your power supply cannot supply the required current to the servo and so the 7815 Vout will drop.

    E
     
  3. garcijon

    Thread Starter New Member

    Aug 19, 2014
    4
    0
    Yes I do mean 200 mA, sorry.
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    380
    no problem.:)

    Use a voltmeter to check the Input voltage to the 7815 , while the servo is running and not running, post what you measure.
    Eric
     
  5. garcijon

    Thread Starter New Member

    Aug 19, 2014
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    When the servo is not running it gets 17.11 V as input. When the servo starts moving it fluctuates between 13-16 V depending on how long the servo moves for.

    I have a 12V power supply that is 1.5 A. I noticed that there is less fluctuations even while the servo is running using the LM7812 but the output is not fixed because the input is too low.

    I guess is it safe to say that the issue is the amps on the 15V power supply?

    Thank you very much for you help
     
  6. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi,
    The 7815 requires at least 17V to 17.5V input to ensure a 15Vout.
    The 7812 requires ~ 14.5V input for a 12Vout.

    E
     
  7. garcijon

    Thread Starter New Member

    Aug 19, 2014
    4
    0
    Thank you very much for your help. I got a 15V 1 A power supply and everything seems to be working fine with the 7812.
     
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