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Supercap question

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Discussion in 'General Electronics Discussion' started by harryhair5, Jun 20, 2013.

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  1. Jun 20, 2013 #1
    harryhair5

    harryhair5

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    Jun 20, 2013
    Hi - I'm new here and still learning how to design my own small circuits. I'm playing around with a small GPS receiver (http://www.gtop-tech.com/en/product/PA6C-GPS-Module/MT3339_GPS_Module_03.htm) and the sleep current draw is 20ua.

    Could you theoretically power the 20ua standby with a supercap? What would you guess the size would be in order to provide standby power for 15 minutes?
     
  2. Jun 21, 2013 #2
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Yes, and the size depends on the voltage drop you could handle.

    At a constant current of 20uA, the voltage will drop of 20uV per second per Farad.

    Assuming you had a 0.033F capacitor (I have some of them and they are pretty small) and it started at 5V, then after 900 seconds the voltage would have fallen to 4.45V.

    If you had a 1F supercap, it would take a little over 7.5 hours to fall to the same voltage.
     
  3. Jun 21, 2013 #3
    harryhair5

    harryhair5

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    Jun 20, 2013
    Very cool. Thank you for your input.
     
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