Energy Harv
An energy-harvesting power-management circuit helps turn a suitable transducer's output into stored energy and a useful supply. Light, heat differences and vibration need different transducers and sometimes different input conditioning. One IC does not automatically accept every source.
The source must first provide enough voltage and power to start the circuit. Once running, a converter may work at a lower input voltage. BQ25570, for example, specifies a typical 600 mV cold-start voltage but can continue harvesting from inputs as low as 100 mV after startup. Its boost charger stores energy, and a separate buck converter supplies a regulated output. Its maximum-power-point tracking samples the source's open-circuit voltage and uses a programmed fraction of that voltage.
In plain terms
A rain barrel fills a little at a time, then supplies a bigger watering burst. The electronics do the same with energy: collect, store, and wait until there is enough for the next task.
Why designers use it
- Collect small amounts of energy from a compatible source instead of wasting them.
- Store energy between intermittent measurements or radio transmissions.
- Reduce reliance on battery replacement when the complete energy budget supports the application.
Best for
- Low-duty-cycle sensors
- Small solar-powered circuits
- Appropriate thermoelectric harvesting systems
Key specifications
- Cold start versus running: Different input requirements (BQ25570 Rev G: 600 mV typical cold start; harvesting down to 100 mV after startup. Required power and other datasheet conditions still apply.)
- Energy budget: Source, losses, storage and load (Check average operation as well as short load bursts and periods without input energy.)
- Source interface: Match the actual transducer (Polarity, conditioning, input limits and source loading are design requirements.)
- Storage and output: Device-specific configuration (Follow battery/capacitor voltage limits, load-isolation guidance and output settings.)
When not to use it
- When available energy, storage capacity and conversion losses cannot support the load over time.
- When the source cannot meet startup requirements, even if its voltage appears adequate for already-running operation.
- When source polarity, voltage or current is outside the IC's input requirements without suitable conditioning.
Common mistakes
- Confusing the minimum running input voltage with the cold-start requirement.
- Checking voltage but not the input power needed to charge storage and overcome leakage.
- Connecting an AC or bipolar transducer directly to an input intended for suitable DC.
- Allowing the system load to consume the stored energy before startup completes.
- Promising battery-free operation or a fixed shelf life without measuring the complete energy budget.
Where you will find it
- The BQ25570 datasheet documents harvesting from small photovoltaic and thermoelectric sources, with rechargeable battery or capacitor storage. The source and storage must meet the stated electrical requirements.
- A sensor can accumulate energy between measurements and draw from storage during a short burst. This is a design pattern, not a guarantee of a particular transmission interval, output power or battery-free lifetime.
A short history
Energy-harvesting systems combine a transducer, power management and often storage. The BQ25570 datasheet explains one implementation for high-impedance sources such as small photovoltaic or thermoelectric generators. Its cold-start circuit, boost charger, storage management and buck output have different jobs. Other harvesting ICs need not use the same architecture or thresholds.
Good to know
- A circuit may keep running on an input too small to start it from an empty reservoir. Startup and steady operation are different tests.
- A large storage capacitor does not create energy. It changes how much energy can be saved for later, while leakage and startup time still matter.