For another project I wanted to use a Li-Ion or Li-Po battery charger and controller that gave a 3V3 and 5V output. The power demands were not high. After searching the internet a few days I did not found any controller that fit my demands: USB connector, small form factor, stay on even when very low current is drawn from the battery.

I tried to combine a 5V controller and charger and combine it with a 3V3 regulator. This did not work when the battery was empty, the power switched on and off before it became stable.

So I designed my own power supply controller.

The size is 26.5 x 20.2 mm. Maximum power output is about 500mA. This is not checked yet, I use it for low power applications. Charge current is 500mA max. Output voltage 5.1V and 3V3. LED will signal when battery is fully charged. You can connect a 3.7V Li-Ion or better a 3.7V Li-Po cell with charge and discharge protection.

For more information and resources: https://www.iot-lab.org/blog/502/