Proof-of-Concept Study of Variable Resistor for Overvoltage Compensation Due to Impedance Mismatch

In numerous pulsed power applications, such as flash X-ray radiography, the voltage pulse shape plays a critical role to guarantee reliable and correct system operation. In particular, for flat-top pulses, the quality of the voltage plateau can be crucial to ensure optimum operating conditions. It can only be obtained if, first, the generator itself delivers a well-shaped pulse and, second, the assembly formed by the transmission line and the load has a matched impedance. However, certain factors, such as high-power levels or high signal frequencies, may introduce variations in the impedance at the load, resulting in a global mismatch. This article puts forward a new approach to mitigate impedance variations that degrade the voltage plateau at the load level. An original solution based on a variable resistor, which is comprised of surface-mount device (SMD) resistors combined with power transistors that operate as on–off switches, is proposed. These enable the device’s impedance to be adjusted dynamically. This article elaborates on the conceptual framework and design decisions that led to the development of an experimental prototype. It also presents initial experimental results in which a deliberately degraded voltage plateau, characterized by a peak reaching 1 kV, is corrected. This correction allows the original plateau quality to be restored with an accuracy of approximately2%.