Energy Harvesting Devices: How DC-DC Converters Enable IoT and Wireless Sensor Networks

The Internet of Things (IoT) promises a world where billions of sensors monitor everything from factory machinery to forest ecosystems. Yet one fundamental problem remains: how do you power a sensor stuck on a remote pipeline, inside a concrete wall, or on a shipping container in the middle of the ocean? Batteries die. Solar panels need light. The answer lies in energy harvesting — scavenging tiny amounts of energy from the surrounding environment — and the unsung hero that makes it all possible: the DC-DC converter.

The Battery Problem

Wireless sensor networks (WSNs) suffer from a major design limitation: limited battery energy availability. Batteries require regular recharging and replacement due to their limited lifespans and storage capacities. For large-scale IoT deployments, the cost and logistics of changing thousands of batteries is simply impractical. As an alternative, energy harvesting emerges as a viable solution to power sensor devices sustainably.

Energy Harvesting 101: Where Does the Power Come From?

Energy harvesting involves scavenging energy from the surrounding environment, with common sources including vibrations, light, thermoelectricity, and radio frequency (RF) energy. Each source presents unique electrical characteristics — and unique challenges.

The DC-DC Converter: The Critical Enabler

Raw energy from harvesters is rarely usable directly. A piezoelectric element generates AC voltage. A TEG produces a few tens of millivolts — far too low to power a microcontroller. A solar cell’s voltage fluctuates wildly with light intensity. This is where DC-DC converters come in.

The DC-DC converter in an energy harvesting system performs several essential functions:

• Voltage boosting: Steps up millivolt-level inputs to useful voltages (3–5V)
• AC-to-DC conversion: Rectifies piezoelectric or RF inputs
• Maximum Power Point Tracking (MPPT): Extracts the maximum available power from the harvester
• Energy storage management: Safely charges batteries, supercapacitors, or thin-film cells

For wireless sensor networks powered by energy harvesting, the DC-DC converter usually resides at the last stage of the whole energy harvesting system just before the empowering sensor node. Its efficiency directly determines whether a sensor node wakes up at all.

Ultra-Low Power Converter ICs: Enabling the Impossible

The past decade has seen remarkable advancements in ultra-low power converter ICs designed specifically for energy harvesting. These devices can start up from vanishingly small voltages and operate with nanoamp quiescent currents.

Texas Instruments BQ25570: A highly integrated energy harvesting nano-power management solution that can start from VIN as low as 600 mV and continuously harvest from inputs as low as 100 mV. It features an ultra-low power DC-DC boost charger, a nano-power buck converter, and programmable MPPT. Its full operating quiescent current is just 488 nA typical, and ship mode draws less than 5 nA from battery. The buck converter achieves up to 93% efficiency and supports peak output current up to 110 mA. This IC can extract energy from solar panels, thermal and piezoelectric generators without collapsing those high-impedance sources.

STMicroelectronics SPV1050: An ultra-low power and high-efficiency power manager embedding four MOSFETs for boost or buck-boost DC-DC converter configurations. An internal high accuracy MPPT algorithm can be used to maximize the power extracted from PV panels or TEGs. It requires only 550 mV and 30 μA to cold start in boost configuration; after first start-up the input voltage can range between 150 mV and VEOC. Two fully independent LDOs (1.8V and 3.3V) are embedded for powering MCUs, sensors or RF transceivers.

e-peas AEM30940: A high-efficiency energy harvesting PMIC that maximizes power extraction from intermittent sources, DC sources, RF and AC sources with adapted rectifiers. It can harvest from just 50 mV after cold start, extracting up to 110 mA from the harvester. RF input power from -18.5 dBm up to 10 dBm (typical). It features configurable MPPT ratio, dual-cell supercapacitor balancing, and primary battery support.

EnOcean ECT 310: An ultra-low-voltage DC/DC converter, which converts low input voltage upwards of 20 mV into conventional electronic output voltage of 3 to 4 V, enabling batteryless wireless modules to use heat as their power source.

MPPT: Squeezing Every Microwatt

Maximum Power Point Tracking is critical for efficient energy harvesting. Without MPPT, a converter might draw power at a voltage far from the harvester’s peak power point, wasting precious energy.

The BQ25570 includes programmable MPPT to provide optimal energy extraction from a variety of energy harvesters. The SPV1050 offers selectable enable/disable MPPT functionality with programmable MPPT by external resistors. More advanced designs use digital MPPT controllers; one recent converter achieved a tracking efficiency higher than 90% for source voltages ranging from 50 mV to 200 mV, with a peak end-to-end efficiency of 87.6%.

Efficiency at Microwatt Power Levels

Efficiency is everything in energy harvesting. But traditional efficiency metrics can be misleading: a converter that achieves 90% at 1W may drop to 10% at 1 μW. The challenge is maintaining high efficiency across a 1000:1 power range.

A 300-nW sensitive DC-DC converter designed for sub-μW power sources harvests energy whenever the available power is more than 0.3 μW. Efficiency at 0.3 μW is 25%, at 0.5 μW is 37% and at 1 μW is 48%. The complete IC consumes just 50 nA for internal operations and the input voltage can be as low as 70 mV. For comparison, a dual-source reconfigurable DC-DC converter achieved a peak conversion efficiency of 88.1% with a maximum output power of 10 mW at VOUT=1.2V, using a series pile-up synchronized harvesting technique to improve efficiency at low input voltage.

Real-World Applications

Energy harvesting powered by advanced DC-DC converters is already enabling real-world deployments:

• Building automation: EnOcean’s heat-powered wireless modules use the ECT 310 converter to harvest energy from radiators, machinery, and even the human body to power batteryless switches and sensors.
• Industrial monitoring: Wireless sensors powered by vibration harvesting can monitor machinery health without wiring or battery changes.
• Medical implants and wearables: TEG-based harvesters can power body-worn sensors using body heat, eliminating the need for battery replacement.
• Remote environmental monitoring: Solar-powered WSN nodes with efficient DC-DC converters and supercapacitor storage can operate for years in remote locations.

Researchers have successfully powered a commercial temperature sensor at -27 dBm using RF energy harvesting with nanoscale spin-rectifiers.

The Future: Battery-Free, Self-Sustaining Networks

State-of-the-art battery-free, wireless sensing nodes can become energy self-sufficient using ambient energy harvesting and wireless power transfer techniques. These nodes use low-power communication protocols with a focus on energy efficiency, sustainability and security issues.

The scalability of wireless sensor networks for vast numbers of sensors is currently hindered by the impracticality of relying on batteries to power them. Energy harvesting directly addresses this bottleneck. With ongoing advances in ultra-low power converter ICs — including cold-start voltages dropping below 50 mV and quiescent currents approaching 10 nA — the vision of trillions of batteryless IoT sensors is rapidly becoming reality.

Summary

For engineers designing wireless sensor nodes, the selection of the right DC-DC converter is as critical as the sensor itself. The converter must start from the harvester’s minimum voltage, track the harvester’s MPP efficiently across all expected conditions, and consume negligible quiescent current. With the latest generation of ultra-low power converter ICs, truly self-sustaining wireless sensor networks are finally within reach.

Resources

• BQ25570 Datasheet: Ultra Low Power Harvester Power Management IC (Texas Instruments)
• SPV1050 Datasheet: Ultra low power energy harvester and battery charger (STMicroelectronics)
• AEM30940 Datasheet: High-efficiency RF MPPT boost PMIC (e-peas)
• ECT 310 Datasheet: Ultra-low-voltage DC/DC converter (EnOcean)