Design of a switching mode power supply with UPS features

The proposed circuit integrates a flyback converter and a buck converter to provide a switch-mode power supply (SMPS) with uninterruptible power supply (UPS) features. It can accept a high voltage of main power input and a low voltage of backup battery input. It uses one PWM IC-controller for the normal and backup modes of operation so that it does not require a synchronization and a detection circuit for power failure. Therefore, the cost and circuit size will be reduced together. High efficiency can be obtained due to the use of a single DC-DC conversion topology from input to output over the conventional UPS. It can also provide full isolation among the high voltage main power input, the low voltage backup battery input and the voltage output. The prototype circuit was built, and the circuit operation and the experimental results of this converter are presented.