I found myself constantly needing a circuit that could charge a lithium polymer battery and provide 5V for my projects. I didn’t want to spend $15 every time I needed one, so I decided to design my own and manufacture it.
The first step I took was creating a circuit schematic that included each of the features I needed. The image shown on the right is a representation of the schematic. I decided on an MCP3831 charge controller to function as the charging module. The data sheet can be found here.
After completing the schematic, I used Eagle PCB designer to make a PCB layout. This proved to be the most challenging aspect of this project. I learned about various design constraints such as track width, pad connection angle, and designing for rapid prototyping with a CNC mill.
The final stage of this project was manufacturing the circuit board. Using a PCB prototyping service called PCB Way I had my design fabricated into an FR-4 circuit board. An image of the finished board is depicted on the right. The circuit produced a reliable 5V +- 100mV output and a safe charging feature that paused charging when the battery reached full capacity. It also included an over-discharge protection feature.