1
\$\begingroup\$

I want to implement a momentary power backup in my circuit using a supercapacitor. I have come up with the following circuit. Am I right in implementing the super capacitor like this? Also, the input voltage is 5V. Should I have a capacitor rated above the input 5V? enter image description here

Increased the resistor value to 100R and added a Schottky diode parallel to the resistor. Supercapacitor rated at 10V.

enter image description here

\$\endgroup\$
3
  • 1
    \$\begingroup\$ How long of a time do you need to bridge with the cap and what does the circuit draw? Maybe a large electrolytic is sufficient ? \$\endgroup\$
    – tobalt
    May 7, 2021 at 7:13
  • \$\begingroup\$ The total consumption is unknown at the moment but expected to be under 200mA. Also, the output of the Buck stage is 3.3V. I expect a backup of less than 3 seconds. \$\endgroup\$
    – Adnan
    May 7, 2021 at 8:06
  • 1
    \$\begingroup\$ Then the supercap sure sounds good. As stated in my answer, if you don't need the cap to power the circuit very often, you can increase R23 substantially. The only drawback of that will be the time needed to charge the Supercap. \$\endgroup\$
    – tobalt
    May 7, 2021 at 8:09

1 Answer 1

Reset to default
1
\$\begingroup\$

Yes the cap need to be rated higher than Vin or it can be destroyed.

Also I would increase R23 much more, otherwise the cap will use significant current from the DC supply when not charged. then place a schottky which will allow easy discharge of the cap in parallel to R23. That way you don't waste all that energy as heat in R23 when powering the circuit off the cap.

\$\endgroup\$
2
  • \$\begingroup\$ can you please check the edited schematic and provide a feedback? thanks \$\endgroup\$
    – Adnan
    May 7, 2021 at 7:02
  • \$\begingroup\$ Yes that is what I had in mind. 100 R still seems small. The cap will draw 50 mA initially with 100R for ~minutes until its charged. Depends what your supply can offer if this is acceptable. This will also heat R23 a lot. Maybe 1k is a better value. Still pay attention to the voltage rating. \$\endgroup\$
    – tobalt
    May 7, 2021 at 7:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.