Recent advances in bipolar transistor technology have been considerable. Transistors can now be applied economically and reliably to a wide range of power switching applications, many of which were impossible with other power semiconductors. The authors discuss the characteristics and application of transistors as high frequency power switches operating from supplies up to approximately 575V AC (1000V DC link maximum). Both standard triple Darlington bipolar transistors ('Triplingtons') and the newer insulated gate bipolar transistors (IGBT) are considered. >