Supercap question

[harryhair5]

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?

 

[(*steve*)]

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.

 

[harryhair5]

Very cool. Thank you for your input.