New developments for the improvement of high voltage rectification with silicon series string

Vacuum Tubes. The earliest practical generation of high voltage by rectification was provided by vacuum tubes. In fact, the discovery of the significance of the vacuum tube itself was related to its one way conduction of electrons emitted from a hot filament. The use of hard vacuum tubes and the more recently developed mercury vapor and ionized gas tubes have in common certain difficulties which still hamper designers. One such common difficulty is caused by the use of a hot cathode to supply electrons, either to conduct the current directly, as in hard vacuum tubes, or to start conduction in mercury vapor or a low pressure gas. The filament supplies required to sustain cathode temperatures reduce overall efficiency, increase the heat to be dissipated by the rectifier, and add considerable bulk to a high voltage power supply. The requirements for insulation and/or isolation for the operation above ground potential of the filament supply required by bridge circuits and voltage multipliers as well as the unwieldly shape and nature of the tube makes it difficult if not impossible to suppress corona. Other problems are high forward impedance, especially for hard vacuum types, difficulty of cascading units for higher voltages, time lag for filament warm up, and limited service life. On the other hand, they are readily available in a wide variety of designs, have a low initial cost, can stand off high voltage, obviating the necessity of series strings when voltages are not too high, are without any troublesome recovery phenomena, and have the ability when properly designed to stand a reasonable amount of abuse.