V.I. Kazantsev - Ph. D. (Eng.), Associate Professor, Leading Engineer, JSC «Pluton» (Moscow)
S.A. Platonov - Head of Laboratory, JSC «Pluton» (Moscow). E-mail: s.platonov@pluton.msk.ru

In modern equipment for receiving high-powered microwave oscillations are used microwave vacuum devices working, as a rule, in a pulsed mode. It is necessary to generate high-voltage pulses on relevant outputs of generating device to create required microwave oscillations. This function is performed by a special device - modulator with its main elements - high voltage keys. Currently, these keys are based on diagram of series connection of many (more than 5) transistors. In the general case, because of individual circuit elements parameters spread, it is possible the appearance of overvoltage on individual transistors. For over coming such overvoltage and avoiding break down of individual devices, each transistor is connected in parallel with equalization circuitry. A rule of thumb states that significant impact on operation of such schemes have parasitic stray capacitance of individual elements to keys body. The most important capacitance is parasitic stray capacitance of individual transistors to keys body. Based on the analysis of simplified equivalent circuit of composite key for an open state it was identified the dependence of voltage, applied to the individual transistors, place of inclusion and values of parasitic parameters. In what connection the closer the cell is located to the load, the larger is applied voltage. For elimination this voltage dependence it was proposed voltage equalization method by applying additional capacitors connected between output electrodes of transistors. The capacitance of each capacitor is determined in accordance with location of transistor in the circuit and magnitude of parasitic capacitance of transistor to the body.