High voltage solid state switches for space applications

A considerable saving in satellite weight is available if loads such as ion thrusters can be operated directly from high voltage solar cell supplies. Such operation raises the need for a high voltage switch for changing loads and reconfiguring the array at different stages of the mission, Silicon p-n junctions can theoretically be made with very high breakdown voltages but processing technology limits switching devices to a few thousand volts. It is shown that increasing the blocking voltage leads to a corresponding increase in the on state conduction loss for a given current density and that the most efficient use of silicon is made by blocking the voltage over several reverse-biased junctions in series. For off-on d.c switching capability series transistor configurations are superior to series thyristor configurations. Control electrodes of the series transistors will be at widely separated potentials when the switch ie off leading to the selection of optoelectronic triggering methods. A conceptual switch design based on the study uses thyristors in the transistor bias supply to minimize the number of power supplies required.