The project needed an online UPS which could ensure interruption free work for the microcontroller / card computer. The board was to support up to 2A draw at 5V. The board also needed to work without a battery if required.
A fast switchover circuit was designed which activates in less than 10ms. To ride over that gap, a capacitor bank is used which also works to stabilize the voltage. A low forward voltage drop diode is used to prevent feeding power back to the main circuit.