In this thesis an approach of computer aided design, simulation and implementation of a microprocessor based variable output voltage flyback switched mode power supply is investigated. The design, of the 15 Watt prototype with variable output voltage is achieved such that it can be easily extended to higher power ratings. The implemented microprocessor controller can be used, with very slight software modifications, to control - many power converters regardless of their type, power rating, output voltage level or the input voltage limits. The designed power stage of the power system is based on the power bipolar transistor as the main switching device with simple protection networks used to ensure safe operation. The system behavior and performance is simulated and examined under many desired operation conditions. The results are demonstrated in chapter five. From these results it is found that switched mode power supplies are efficiently used to provide variable output voltage level power supplies.