Thermistor modelling

Please see our lab session circuit description files on http://fides.fe.uni-lj.si/~zigar/CAO/FILES/. Firstly, we created a subcircuit, where temperature was one of the input parameters. The resistance of the NTC was calculated from parameter b and the temperature using a known formula for NTC modeling. A special element - non-linear voltage source BR was used to model the resistance changes according to temperature.

Thermistor self-heating

Since power dissipation of the NTC causes the element to heat-up, its resistance changes also on self-behalf. We changed the model in such manner, that input parameter temp is no-longer needed, but is calculated during the transient analysis. The self-heating part is a circuit which models the temperature change (the temperature is represented by the node T voltage!). The current in this circuit actually represents dissipated power (v(p,n)*i(Vi)). The independent voltage source represents the initial temperature (25 degrees C). There are also thermal resistance and thermal capacity, which are properties of NTC body and environment. Using this configuration we modeled changes in NTC resistance during time, when pulses are applied to the NTC. (See http://fides.fe.uni-lj.si/~zigar/CAO/FILES/).