Stability of Over-Voltage Diode Characteristics in Exploitation Conditions

The wide-spread use of over-voltage diodes for non-linear over-voltage protection results in a variety of possible working conditions. It is therefore essential to have a thorough insight into their reliability in various exploitation environments. The aim of this paper is to investigate the influence of temperature variation, aging and radiation exposure on over-voltage diode characteristics. Behaviour of over-voltage diodes in the temperature range from -50degC to 150degC was investigated. Aging caused by exploitation was investigated by applying 1000 consecutive double exponential over-voltage pulses to the diode. Radiation effects of californium-252 combined neutron/gamma radiation were examined. Volt-ampere characteristics, volt-ohm characteristics, and the value of breakdown voltage were used to characterize over-voltage diode operation. Nonlinear coefficient, defined from the volt-ampere curve, was also used as a diode parameter. Over-voltage diodes showed severe deterioration of protective characteristics after being exposed to radiation or elevated temperature, while on the other hand they proved to be highly resistive to aging. Results are presented with the accompanying theoretical interpretations of the observed changes in over-voltage diode behaviour.