The UPS delivers uninterrupted power to the ac load. It consists of the following functional blocks: AC mains section contains filter, transformer and rectifierIt receives ac supply, filters it with the help of line filters and rectifies it to the desired level of the load. Battery charger with circuit and battery. It converts the ac supply to the desired dc levels and charges the battery. It has special protection to prevent overcharging of batteries. Static switch / contactor. In the event of power failure the inverter is connected to the load with the help of switch. The inverter changes from the battery to ac of constant frequency and amplitude. It also has synchronization circuits for smooth change-over from mains to inverter ac avoid waveform distortion.