Electrical consumption, especially direct or variable frequency currents, has strongly increased over 50 years in industry. This situation explains the growth of power electronics. At the beginning, when rectifiers replaced DC machines, only diodes and thyristors were used. Then power transistors appeared and enabled the extension of smaller power applications for domestic use. New research topics were developed around converters and power devices. For all these years, circuit specialists used available components but did not try to improve them; a lot of progress in device manufacturing proceeded from microelectronic tecnology