Project Overview & Function.

This project is an independent implementation and layout redesign of the "Tiny Solar Supply" circuit originally designed by Clemens Valens for Elektor Labs. The purpose of this board is to harvest energy from a small solar panel to charge a single 1.2V Ni-MH AA/AAA battery during the day. When the sun goes down, it automatically boosts and regulates that low battery voltage up to a clean, stable 3.3V output—making it ideal for powering low-power microcontrollers or wireless sensor nodes.

While commercial solar garden lights often output an unregulated voltage that sags under load, this design utilizes an active step-up converter to maintain an exact 3.3V output rail.

Why I Chose This Project.

I chose to build the Tiny Solar Supply because it addresses a very common limitation found in standard solar-powered hobby projects: unregulated voltage drops. Most basic solar setups experience massive voltage fluctuations as the sun changes or under varying circuit loads. By choosing a design centered around an active, micropower step-up switching regulator, I wanted to master the engineering principles behind creating a truly stable, efficient 3.3V power rail from a single 1.2V battery cell.

 How it Works.

• Daytime Charging & Auto-Shutdown: While the solar panel receives sunlight, it charges the battery through diode D2. Concurrently, it pulls up the gate of the 2N7002 N-channel MOSFET (T1). This forces T1 to conduct, pulling the shutdown pin (/SHDN) of the converter IC low to keep the boost circuit completely turned off while charging.

• Nighttime Activation: When the solar panel output drops in the dark, T1 turns off. This releases the shutdown pin, allowing the step-up converter to switch on and deliver power to the load.

 Key Hardware Features.

• Core DC/DC Converter: Diodes Inc. AP3015 / AP3015A micropower step-up switching regulator, capable of starting up from input voltages as low as 1.0V to 1.2V. 
• Output Voltage Formula: The output is precisely tuned to ~3.3V using the feedback resistor divider ratio:

V (out) = 1.23 * [1 + (R1 / R2)]

• Form Factor & Custom Layout: Unlike the original design tailored for a specific enclosure, this PCB layout was built from scratch in KiCad 10 with a unique component placement optimized for standard breadboard prototyping and general-purpose projects.

 Beginner's Learning Journey & Derivative Modifications.

• Custom Component Placement: I completely reorganized the physical layout compared to the original Elektor design files. The components were arranged to minimize the high-frequency switching loop area between the AP3015 IC, the 10µH inductor (L1), and the SS14 rectifier diode (D1) to improve efficiency and minimize noise.
• What I Learned: Through this design, I learned how to handle micro-power switching regulators, read a professional circuit manual, configure custom net classes in KiCad 10 for power rails, and manage automatic state-switching using a small-signal MOSFET.