FUNCTIONING FEATURE ANALYSIS OF VOLTAGE LIMITERS BASED ON A COMBINED VARISTOR-POSISTOR STRUCTURE

Abstract

Modeling and analysis results concerning the influence of the electrical and thermal conditions on the functioning of series-connected and thermally contacted layers of varistor ceramics and a posistor composite are presented. Such structures may be useful for the development of a promising limiter of constant and slowly varying voltages. The main attention is paid to the behavior of their functional electrical and thermal characteristics with changes in the internal resistance of the input voltage source and in heat flow intensity to the environment as well as in its temperature. It is shown that a change in the internal resistance of the input voltage source can only lead to a shift towards higher input voltage values ensuring the posistor element actuation. At a low intensity of heat exchange between such a voltage limiter and the environment, it may operate at voltages lower than the classification voltage of the varistor layer, and thus the device under consideration is not capable of fixing a constant voltage at the output and can function as a self-resetting high voltage fuse. In the case of an increase in the ambient temperature (up to the temperature of the phase transition in the posistor layer material), the temperature of the structure and the output voltage of the device change insignificantly around the temperature limitation point, and the current value and dissipation power of the structure are much reduced. For structures based on varistor ceramics with a strong temperature dependence of low-voltage resistance (high activation energies of its temperature sensitivity), the output voltage decrease (to values of one volt order) takes place.