The design of a switching power supply is an iterative process which involves many variables that have to be adjusted in order to obtain an optimized solution. However, there are trade-offs which allow for a simple low cost, low component, single sided board design method. This application note provides a simple approach to designing a converter utilizing the ON Semiconductor NCP1055 high voltage switch regulator. The easy-to-follow step-by-step procedure guides the user into designing the different blocks that constitute the power supply, mainly the input block, the power stage, the magnetics, the snubber, the output block, and the feedback loop. The circuit diagram, bill of material, and PCB layout are also included at the end of the application note. This power supply is specifically designed for a 5.0 V, 2.0 A output and a maximum duty cycle of 48%. It meets IEC and UL requirements. EMI is minimal and a 70% achievable efficiency or greater is possible. The NCP1055 is a family of monolithic high voltage switching regulators designed to work in rectified AC line sources and flyback converter applications. They are capable of providing an output power ranging from 6.0 W to 40 W with a fixed AC input of 100 V, 115 V, or 230 V and 3.0 W to 20 W with a variable AC input ranging from 85 V to 265 V. This device features an on-chip 700 V SENSEFETTM power switch circuit, an active startup regulator circuit which eliminates the need for an auxiliary bias winding on the converter transformer, fault logic with a programmable timer for converter overload protection. Protective features provide power switch current limiting, input under voltage lockout with hysteresis, thermal shutdown, and restart fault detection. For more information, please contact an ON Semiconductor sales representative or log on to www.onsemi.com.