Derrick J. Page

Some Advances in High Power, High dI/dt, Semiconductor Switches

The design and operation of modern high power thyristors is outlined and some of the limitations of present designs are detailed. Two new methods of turning on power semiconductor switches which overcome these limitations are described. The first method involves the use of special emitter shunt patterns which are used in conjunction with laterally directed junction charging current to achieve a large area of turn-on. In this mode of operation the device is turned on by a high rate of change of anode voltage. The second method employs a neodymium doped YAG laser to produce, instantaneously, a high density of electrons and holes within the base regions of the device. Both of these methods enable rates of rise of current in power semiconductor switches that are significantly higher than those available in conventional thyristors. Rates of rise of 20,000A/μsec, rising to 3000 amperes, have been achieved to date using the laser triggering technique. These devices are ideal for series operation due to the isolated nature of the triggering source. Series strings of ten laser-fired devices have been operated successfully to date. Due to the extremely high switching rate, the dynamic voltage equalization networks customarily used to protect high voltage series strings of power devices can be significantly reduced in complexity. High-power thyristors with fast turn-on capability are likely to be applied in circuits requiring the switching of large currents and voltages with moderate duty cycle.