The rapid development and advancement in the microelectronics field has ledmany electronics apparatus to become smaller in size. However the size of the apparatus depends strongly on its power part. If the power part of theapparatus, which consumes the most space in the electronics apparatus isnot modified, the size of the apparatus is limited.Owing to this, research on high frequency switching power supply is alsoknown to grow with the advancement of the microelectronics. The high frequency switching power supply is efficient, lightweight and low cost at certain power rating, compared to the conventional linear power supply.There are many topologies of the high frequency off the line ac to dcconverter. This thesis concentrates on the flyback topology in fabricatinga high efficiency off the line ac to dc converter. The power rating of the converter is 100W and it is to regulate an output dc voltage of 14V from a 210V ac input.