This work has been conducted for Ericsson Radio Systems AB. This work aimed at constructing a switched mode power supply, which would minimise weight and size in the application without disturbing the other modules. Unfortunately we can not communicate what kind of application the unit will supply with power due to the obligation of preserving secrecy. The application will from now on be referred to as "svarta lådan". Through measurements the work resulted in us becoming familiar with disturbances and the problems these can cause. We have also arrived at a construction, which will be further studied after we have built a prototype of it. The report describes some of the converters available. Buck, buck-boost and flyback are some of them. The dimensioning of the components has been made as a flyback implementing a switch-regulator, TOPSwitch 227Y. The report also describes the emergence of electromagnetic induction and how to reduce these. A series of measurements has been done on a laboratory circuit provided by Power Integrations. The series of measurement clearly points to the noise on the exit caused by the electromagnetic induction.