I have put up a small LTC3108 breakout board based on Robert’s design that I also tested out. A re-cap for those that didn’t follow my energy harvesting posts:
The LTC3108 is a highly integrated DC/DC converter ideal for harvesting and managing surplus energy from extremely low input voltage sources such as TEGs (thermoelectric generators), thermopiles and small solar cells. The step-up topology operates from input voltages as low as 20mV. Using a small step-up transformer, the LTC3108 provides a complete power management solution for wireless sensing and data acquisition. The 2.2V LDO powers an external microprocessor, while the main output is programmed to one of four ﬁxed voltages to power a wireless transmitter or sensors. The power good indicator signals that the main output voltage is within regulation. A second output can be enabled by the host. A storage capacitor provides power when the input voltage source is unavailable. Extremely low quiescent current and high efﬁciency design ensure the fastest possible charge times of the output reservoir capacitor.
My purpose was to make it a bit smaller, then add couple solder jumpers to enable selecting the VOUT between 2.35V, 3.3V, 4.1V or 5V and switched the transformer from Coilcraft to Würth as those are more available. Here is how it looks:
Check my posts here and here on ways to use the LTC3108, also the datasheet is pretty resourceful.
I will put up some documentation and make these available in the shop these days.