This is my circuit which charges the supercapacitors. The problem with the circuit is the minimum input voltage require to get 3.3 volts output. Once the input voltage goes below the certain level ( i guess ~4.2 volts ) then breakout board does not give 3.3 volts as an output. As per the circuit, I do need 3.3 volts constant.

Should I use boost converter from 2.7 volts to 3.3 volts?

Please give some suggestions of IC or circuits.


simulate this circuit – Schematic created using CircuitLab


Energy Harvester


This project is about powering few LEDs (let's say 3 LEDs) with the solar panel. LED specs are 2.6 volts and 2 mA. The solar panel could be of any voltage and dimension. I prefer to use 5, 6 or, 9 volts small panels. I used LDR to sense the presence of the light with the LM393 comparator and TI SPST switch IC for switching. My original goal is to be able to use it for a long time at least 16-18 hours. Thus, I used super caps to store energy.

Temperature range: -20 to 52 deg C

LED: 2.65 volts and 2 mA datasheet

Solar PV source power: 0.6 W Amazon

desired load power: 0.02 W

work time: 24 hours (after 'power-bank' is fully charged and LEDs are triggered by the sensor)

sensor: LDR (I would love to use other sensors like current as LDR could give false detection with some occlusion)

project time: 30 days

  • \$\begingroup\$ I see two initial problems so far, 1) the LTC3588 is designed for piezoelectric energy harvesting (short high voltage pulses) so it's not ideal for solar (which has kinda the opposite requirements) and 2) what's to stop your caps from exploding if you're feeding 9V into a 5.4V supercap bank? \$\endgroup\$
    – Sam
    Feb 19, 2017 at 22:27
  • \$\begingroup\$ Converting a low current Solar Panel @ 9V to a charge 2 capacitors from 0 to 2.7V (x2 with balancing) then buck-boost to blue LED @ 3.1V at constant current is probably the worst application (in terms of efficacy, size, cost, complexity, impedance matching etc.) of using two 50 F supercaps. Consider a 1 or 2 LiPo 18650 cells (3.3 to 3.7V) , it will be 10x more efficient and smaller with 1 or 2 LEDs or some other application. PV efficiency drops with load voltage below 82%Voc. Boost converters cannot make use of all the charge to 0V. \$\endgroup\$ Feb 19, 2017 at 23:12
  • \$\begingroup\$ @Sam For (1) what would you suggest for solar application? I need to drive 3 LEDs using solar and supercaps. (2) While designing, I thought that diode would block the current once the caps are fully charged. \$\endgroup\$
    – Mat_python
    Feb 20, 2017 at 0:31
  • \$\begingroup\$ @TonyStewart.EEsince'75 Thank you. I thought of using super caps as they can store more energy and I do not need to replace them for a long time. My application requires having a solar panel as input and 3 LEDs as output. It should work for at least 10 years. What would you suggest? \$\endgroup\$
    – Mat_python
    Feb 20, 2017 at 0:35
  • 1
    \$\begingroup\$ I would suggest you list ALL the specs and requirements \$\endgroup\$ Feb 20, 2017 at 1:27


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