During the past few years, in more and more countries, the control of noise or RFI is being changed. The major changes that are being made besides lowering the permitted emission levels, are applying emission control to more products and increasing the frequency over range which emission control is necessary. The total power supply market growth is about 500 million dollars per year or 20% per year, clearly a very significant increase.1 In recent years, there has been a rapid shift from linear to switching power systems. The current rate of switching technology growth is about 35% of the total power supply market2 per year.