Design and development of surge protection device for serial communication interface of high voltage power supply

Operation of any cyclotron system, like the K-130 Room Temperature Cyclotron of VECC, requires various high voltage power supplies for its different subsystems. Typical examples are Anode Power Supply, Screen Grid Power Supply of RF Systems, Deflector Power Supply etc. These power supplies are remotely controlled and monitored from the control room. For the purpose, interfacing between these high voltage power supplies and the low-voltage communication electronics becomes critical. Depending on situations, those power supplies can become potential sources of high voltage surges. Some of the phenomena causing generation of high voltage surges are earth fault, arcing at load sides etc. The surges, if coupled to low-voltage electronics through different coupling channel by resistive and/or inductive and/or capacitive coupling, can cause disruption in operation or even failure or damage of the low voltage electronics. Therefore, Surge Protection Devices (SPDs) are needed to protect the low-voltage circuits during these scenarios. The paper illustrates the design, simulation and development of SPD for the serial communication interface of a high voltage power supply. A hybrid type SPD has been designed incorporating Gas Discharge Tube and Transient Voltage Suppressor Diodes to devise a two stage protection strategy. The components are chosen to ensure the protection of the affected equipment from surge as per IEC 61000-4-5. Further analysis has been carried out to assess and reduce the level of distortion of the communication line voltage waveforms due to inclusion of SPD during normal condition. The final circuit has been fabricated and tested for its frequency response and response to pulse train. The test results are compared with the analytical results to validate the design. (author)