Would you like a compact power supply for small indoor IoT devices? With this DIY solar panel voltage converter project, which was published in 2015, you can harness energy from a solar panel in an indoor environment. The design operates with an input source as minuscule as 7.5 μW, enabling the use of a low-cost mini solar panel. Featuring an LTC3129 integrated circuit, this microcontroller-free solution offers a streamlined and efficient approach to powering indoor IoT devices using renewable energy sources.
Solar Panel converter PCB
Stores energy from indoor lighting. Solar panel Vout 5 V typ., 42 μA

Solar Panel Voltage Converter Circuit

The circuit exploits the unique ability of the LTC3129 and LTC3129‑1 to start up and operate from an input power source as small as 7.5 μW, making them capable of operating from compact, low-cost solar cells with indoor light levels below 200 lux. Various components need to be configured as a function of the IC that you select. Hardly a microwatt of solar power is wasted in this circuit.
Solar Panel Voltage Converter
At the heart of the converter is either an LTC3129 or an LTC3129-1 IC, depending on your choice.
“The circuit features battery backup circuitry around BAT1,” the author and designer Sunil Malekar explained in the original 2015 article. “A CR2032 backup battery provides power when solar power is insufficient. The LTC3129 is used in this case, allowing VOUT to be programmed for 3.2 V to better match the voltage of the coin cell. With 5 V input from the solar panel on connector K1 you can expect an output of 3.2 V on K2. The output voltage can be adapted to requirements by configuring the feedback resistor values in the case of LTC3129, or by setting the three programmable pins in the case of LTC3129-1. Provisions are made in the circuit to maintain the stability of the output voltage. The circuit can also operate without the coin cell battery.”
Solar Panel converter project
Since the circuit is designed for indoor use, a super-charge capacitor C10 stores the energy captured from daylight.

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Sunil Makejar’s article, “Solar Panel Voltage Converter for IoT Devices,” appeared in Elektor July/August 2015. As an Elektor Member, you can enjoy ElektorMag, a 10% Elektor Store discount on many products, and 24/7 access to Elektor’s online library, which includes this article and many others. If you don’t yet have a membership, take one out today and start reading through our thousands of projects and circuits.

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