EnergyHarvesting

TI BQ25504

BQ25504 Nano Power, suitable for WSN
Maximum power point tracking (MPPT) is implemented in bq25504 in order to maximize the power extracted

from an energy harvester source.

When operating as a charger, the main storage elements must be connected to VBAT pin. Many types of

elements can be used, such as capacitors, super capacitors or various battery chemistries

More on BQ25504

TI TPS61200 boost converter

LiPower - Boost Converter from Sparkfun at $1
Input voltage 0.3-5.5V
Output voltage 3.3 or 5V
5V @ 600mA max
3.3V @ 200mA max
Undervoltage lock out at 2.6V
Quiescent current, less than 55uA
LiPo JST connector or 2-pin header power input\
Inductor: 4.7uH, 1.2A Sumida CDRH2D18
Over temperature protection

Linear technologies LTC3108

OpenHarware LTC3108 board Bob's sensors blog Go easily from 20 mV to 3.3V
Eagle files Here: I've posted the Eagle files and the component library for the LTC3108 breakout board (both DFN and SSOP) on my public github site
Linear Technology product page
LTC3108 datasheet
LTC3108EGN#PBF IC VOLTAGE CONVERTER 16-SSOP digikey $6.28@1pc, $3.58@100pcs

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.

digikey training module

LTC3108 TRANSFORMER

The LTC3108 utilizes a depletion mode N-channel MOSFET switch to form a resonant step-up oscillator using an external step-up transformer and a small coupling capacitor. This allows it to boost input voltages as low as 20mV high enough to provide multiple regulated output voltages for powering other circuits. The frequency of oscillation is determined by the inductance of the transformer secondary winding and is typically in the range of 20kHz to 200kHz. For input voltages as low as 20mV, a primary-secondary turns ratio of about 1:100 is recommended. For higher input voltages, a lower turns ratio can be used. These transformers are standard, off-the-shelf components, and are readily available from many magnetic suppliers. The compound depletion mode FET is what makes 20mV operation possible. Linear Technology has optimized the FET in ways not possible with discrete designs that result in much better harvesting efficiency.