Energy Harvesting Devices Add the Re-Introduction of Power for Devices

Wearable devices, small mobile devices, and any device that requires perpetual uptime can benefit from energy harvesting capabilities. This can be used to extend battery life or provide a useful backup power source if the primary power is disconnected. Possible applications can be found in IoT devices, military equipment, sensor networks, and even autonomous vehicles.

If you’re looking to maintain uptime, charge/extend batteries, or even create a primary power source, you’ll need to choose between three primary energy harvesting technologies. The right technology will depend on the environment where the device will be deployed, but judicious use of these devices can provide the extra power your device needs.

Energy Harvesting Methods for PCBs and Small Electronics

Much like modern power generation technologies, all energy harvesting devices convert some prevalent source of energy and convert it into electricity. In smaller electronic devices, the newest energy harvesting technologies are designed to convert mechanical, thermal, or background electromagnetic energy to electrical power. This power can then be used to charge a battery, or it can be stored in a capacitor.

When working in an environment where radio waves are used for communication between devices, there are times where that extra RF energy essentially goes to waste. Using an omnidirectional antenna for communication spreads RF energy everywhere. Devices that harvest this extra energy can be used to extend battery life while remaining mobile.

If you are working with equipment that produces a significant amount of wasted heat, you can use this waste heat to power electronic devices by exploiting the Seebeck effect. Thermoelectric generators are widely available and are useful for powering small electronics. The effectiveness of these generators depends on the temperature gradient between the heat source and the surroundings, and this should be considered when choosing the right thermoelectric generator.

Finally, you may have a device that will be mounted near a system that produces some mechanical vibration. You can convert this mechanical energy into electrical energy using a piezoelectric generator.

A thermoelectric generator module

Parameters to Consider When Choosing Energy Harvesting Devices

If you’re planning to include an RF or microwave energy harvesting module in your next device, you’ll need to consider the frequency band of the module. Most modules have narrow bandwidth and will have low power conversion efficiencies outside of the defined bandwidth. However, if you want to harvest over a broader range of frequencies, you can use multiple modules with different frequency responses. You’ll also need to consider the input impedance and layout requirements of the receiving antenna in order to avoid transmission line effects and feed loss.

Thermoelectric generators have a defined temperature range at which they are most efficient. Although the current harvested from these devices depends on the temperature gradient between the hot and cold sides of the device, there is a point where the electrical response from these devices becomes nonlinear. Exceeding the rated maximum temperature and temperature gradient will not produce significantly more current from the generator. Instead, the output current will start to saturate at some maximum value.

Piezoelectric generators have a similar nonlinear response once the vibration amplitude exceeds a certain value. They also have a defined response bandwidth that provides maximum power conversion efficiency. The vibrational environment in which these devices will be used should be carefully examined before choosing a piezoelectric generator. Thankfully, the bandwidth of most piezo rectification/regulation modules is much wider than the bandwidth of the piezo, so you’ll have some freedom with the module you choose.

Powercast, P1110B

The P1110B is a module that harvests background RF signals and converts them to a DC voltage. This surface-mounted IC has a small footprint and is ideal for use on a small PCB. The receiver can reach 70% conversion efficiency in the 902-928 MHz frequency band, although the module can still harvest energy outside this band.

Output power can be used to charge a battery directly rather than being stored in a capacitor. When placing this module on your PCB, make sure to design your RF feed line as a short 50 Ohm trace to ensure impedance matching and prevent feed losses. The RF input antenna and feed line should be isolated from the ground plane.

The P1110B converts RF energy to DC and provides the energy to the attached storage element. When an adjustable voltage threshold on the storage element is achieved, the P1110B automatically disables charging. A microprocessor can be used to obtain data from the component for improving overall system operation.

Typical application circuit from page 8 of the P1110B datasheet

Linear Technology, LTC3588EDD-1PBF

The LTC3588EDD-1PBF is specifically designed for collecting and power storage applications. This compact IC functions as a rectifier and voltage regulator for piezoelectric energy harvesting applications. The LTC3588-1 harvests ambient vibrational energy through a piezoelectric element and stores the rectified output with a capacitor. Higher frequency vibration will output a larger current, where moderate kHz vibrations will produce mA levels of current.

The LTC3588-1...is designed to interface directly to a piezoelectric or alternative A/C power source, rectify a voltage waveform and store harvested energy on an external capacitor, bleed off any excess power via an internal shunt regulator, and maintain a regulated output voltage by means of a nanopower, high efficiency, synchronous buck regulator.

Found on page 12 of the LTC3588EDD-1PBF datasheet

Linear Technology, LTC3107

The LTC3107 is a thermoelectric module packaged in an IC with a small footprint. Rather than powering a complete system, this IC is designed as a battery extender. This module harvests energy using a thermoelectric generator and outputs additional current, thus reducing demands on a battery.

A small step-up transformer can be used to manage power input from a thermoelectric generator. This device acts like a compact charge collector and voltage regulator all in one package. This IC is rated for battery voltages ranging from 2 to 4 V. Typical application examples include alkaline cells, 3 V lithium coin cell, or a 3.6 V Li-SOCl2 battery.

The LTC3107 is an ultra-low input voltage step-up DC/DC converter and power manager for extending the battery life of low power wireless sensors and other low power applications that utilize a primary battery. The LTC3107 intelligently manages harvested energy from sources such as TEGs (Thermo-Electric Generators) to service the output while minimizing battery drain, thereby maximizing battery life.

Found on page 1 of the LTC3107 datasheet

There is one set of energy harvesting devices that have not been mentioned here: photovoltaics. The number of photovoltaic components available to power electronics is great that it deserves more attention than can be provided here. If you want to supplement or completely replace your DC power source, using a photovoltaic cell is a great option to power your next electronic device.

You can greatly improve uptime for your next electronic device when you pair the right harvesting module with the right regulator. Some evaluation boards are available for energy harvesting modules, making it easy to build a prototype for your next product. If you’re thinking about adding energy harvesting and storage capabilities to your next electronic device, you can find the right options with our Similar Parts recommendations.

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