Abstract: A digital controlled bi-directional DC/DC converter adopting the Buck-Boost topology for power bank application is studied. The circuit principles and control method of converter's different operation modes are analyzed. The paper also analyzes the key parameters which effect the performance of digital controlled system and studys the method of implementation of digital controller. Finally, a 45W experimental prototype is built with dsPIC33 microcontroller to validate the design. The experimental results show that the design realizes energy conversion in bi-directional freely and has a good effect of constant voltage-constant voltage charging process.