Design of a switching mode power supply with UPS features

The proposed circuit integrates an isolated capacitive idling Cuk converter [1] and a buck converter to provide a switch-mode power supply with uninterruptible power supply (UPS) features. From the unique topology of capacitive idling Cuk converter, the input voltage regulation can be obtained on the primary side, while the load current regulation can be performed on the secondary side. In this arrangement, complete isolation can be achieved, and a wider difference in voltages between input mains and a low-voltage backup battery input. In addition, the separation of control provides further advantages such as independent short circuit protection and each output can be regulated independently for multiple output system. High efficiency, low cost and small size can also be achieved compared with the traditional UPS because it requires only DC-DC conversion in each mode.