IN Brief:
- The AEM15820 integrates separate low- and high-power boost converters for hybrid photovoltaic sources.
- Cold start begins from 275mV with approximately 5µW available from the source.
- One controller can manage products moving between dim indoor illumination and substantially stronger outdoor light.
e-peas has expanded availability of its AEM15820 energy-harvesting power-management IC, which manages photovoltaic sources operating across dim indoor illumination and substantially higher outdoor power levels.
The device integrates separate low- and high-power boost-converter paths and switches between them as the available source energy changes. This arrangement avoids forcing one conversion stage to cover both microwatt-level indoor harvesting and the larger power available when the same cell is exposed to strong daylight.
Cold start is supported from an input of 275mV when approximately 5µW is available, allowing a depleted system to begin charging without an already active controller. Once operating, the PMIC manages a dynamic source range extending from microwatts towards watts, depending on photovoltaic area, cell technology, illumination, and configuration.
The AEM15820 includes a regulated output covering 0.6V to 3.3V, with output current up to 100mA, and supports batteries and lithium-ion capacitors as storage elements. GPIO and I²C configuration covers source regulation, storage protection thresholds, thermal behaviour, and load-output settings, while a 5V input allows faster charging from an external supply.
Applications include remote cameras, asset trackers, wireless sensors, smart locks, wearable equipment, and connected building devices. Products that move repeatedly between indoor and outdoor environments place particularly broad demands on the harvesting circuit because the available photovoltaic output can change by several orders of magnitude.
Source conditions rarely remain steady
Photovoltaic harvesting is often described through a fixed power figure, although actual installations seldom provide one. Indoor output depends on the type of lighting, distance from the fixture, orientation, occupancy controls, and the spectral response of the cell; outdoors, cloud, shade, contamination, angle, and temperature introduce further variation.
A converter designed for extremely low input power may reach its current or voltage limits in stronger light, whereas one optimised for greater output may consume too much quiescent power to start from an indoor cell. Dividing the conversion task between two boost paths preserves low-power sensitivity while allowing the system to collect more energy when source conditions improve.
Source regulation remains central to overall performance because a photovoltaic cell’s optimum operating point shifts with illumination, temperature, and load. Drawing excessive current collapses the cell voltage, while a conservative operating point leaves energy unused. The controller must regulate the source without consuming a disproportionate share of the power it is attempting to collect.
Cold-start behaviour deserves separate consideration from normal conversion efficiency. A device can operate efficiently once its storage element has reached a suitable voltage yet fail to recover after prolonged darkness if its start-up circuit demands more power than the cell can provide. Board leakage, storage-element condition, and the behaviour of downstream loads determine whether the source can reach the specified starting threshold.
Storage selection changes the balance between energy density, peak current, leakage, temperature, and cycle life. Rechargeable batteries store more energy within a limited volume but require protection and controlled charging, while supercapacitors tolerate frequent cycling and large current pulses at the cost of greater self-discharge. Lithium-ion capacitors occupy an intermediate position and still require careful voltage management.
The load must operate against an available-energy budget rather than a nominal supply alone. Sensor sampling, local processing, radio transmission, and firmware updates may need to reduce as stored energy falls, while a system that continues attempting an expensive wireless connection can enter a repeated reset cycle and consume the remaining reserve.
Photovoltaic integration also shapes the enclosure because the cell needs a useful exposed area, predictable orientation, and protection from moisture, cleaning chemicals, impact, and ultraviolet ageing. Electrical conversion cannot compensate for a cell obscured by installation hardware or a surface that accumulates dirt during service.
The AEM15820 reduces the number of conversion devices required to span a wide illumination range, while the complete product remains dependent on accurate environmental characterisation, low board leakage, suitable storage, and firmware capable of adapting activity to the energy available at any moment.
