In this paper the authors present the designing of an UPS using PSoC technology. Uninterruptible Power Supplies (UPS) play an important role in interfacing critical loads such as computers, communication system, medical/life support system, and industry control to the utility power grid. They are designed to provide clean and continuous power to load in case of failure of utility power condition. In this paper the UPS is designed using a single CY8C27443 Programmable System on Chip (PSoC). PSoC (Programmable System-on-Chip) is a family of mixed-signal arrays, featuring a microcontroller and configurable integrated analog and digital peripherals.