W pracy zaproponowano nowy elektrotermiczny model cewki z rdzeniem ferromagnetycznym, bazujący na izotermicznym modelu Jilesa - Athertona. Opracowany model uwzględnia takie właściwości rdzenia ferromagnetycznego jak pętla histerezy, nasycenie rdzenia, temperatura Curie oraz samonagrzewanie, spowodowane stratami energii zarówno w rdzeniu, jak i w uzwojeniu. Nowy model zaimplementowano w programie SPICE w postaci podukładu i porównano wyniki obliczeń z danymi katalogowymi. Niezbędne wartości parametrów elektrycznych i termicznych wyznaczono na podstawie odpowiednich pomiarów oraz danych katalogowych materiałów ferromagnetycznych.
Coils are electronic devices which are often used in electronic small - power circuits, for example in filters, and also in high - power circuits, for example in switched dc-dc converters. The use of a ferromagnetic cores makes it possible to diminish the dimensions of a the coil, but is causes nonlinearity of their characteristics simultaneously. Due to the temperature effects, the strong temperature dependences of the coil characteristics are observed. In considerations presented in the paper the inner temperature of the coil, understood as the sum of the ambient temperature and the component resulting from selfheating, is taken into account. The aim of this paper is to formulate the model of the coil with the ferromagnetic core for SPICE. Unfortunately, the isothermal model (i.e. without selfheating taken into account) of the coil with the ferromagnetic core, used in the popular software SPICE for the analysis of electronic circuits, omits the influence of temoerature on the characteristics and the parameters of the core. In the paper the new electrothermal model of the coil with the ferromagnetic core (EMCR) designed for this software is proposed. The strategy of the formulation of EMCR model is the same as for the electrothermal models of semiconductor devices. According to this strategy, the coil isothermal model with the parameters dependent on temperature, based on the literature Jiles - Atherton model was elaborated at first. Next, the lumped thermal model which takes into account the power losses, both in the coil and in the core, resulting from selfheating in both coil components and additionally, the mutual thermal interactions between them was formulated. EMCR includes the most important properties of the ferromagnetic core, as the hysteresis of B(H) characteristic, the saturation of the core, Curie temperature and selfheating caused by energy losses, both in the core and in the coil, respectively. The new EMCR model was implemented into SPICE software using a proper constructed subcircuit. Because of the limitations of SPICE software, some dependencies, existing in EMCR describing for example the power losses in the core realised by the special subcircuits. The lumped thermal model is represented by its electrical analog, consisting of the current sources representing power dissipated in the core and in the coil, and RC networks representing own transient thermal impedances of the coil and of the core, and the mutual transient thermal impedances between them. At first, some isothermal calculations of the coil with the core characteristics using EMCR model and SPICE built-in model were performed with the ambient temperature as a parameter, without selfheating taken into account. The correctness of these calculations was compared with the catalogue data. The parameter values of the model were estimated on the basis of the catalogue data and the proper measurements. As it results from the investigations performed at the room temperature, the calculation results obtained with the use of both model fit well to the data, given in the catalogue. In the wide range of the ambient temperature only the results obtained with the use of EMCR fit well to the data, because SPICE built-in model of the ferromagnetic core does not include the influence of temperature on its characteristics and parameters. Additionally, the electrothermal analyses of the coil with the core characteristics using EMCR model were performed. The results of these analyses show the strong influence of selfheating on the characteristics of the coil with the ferromagnetic core. This influence is observed as the decrease of the value of the coil inductance or the loss of ferromagnetic properties of the core as the result of exceeding Curie temperature. Of course, the change of the characteristics and parameter values of the coil as the result of selfheating can influence the characteristics of switched dc-dc converters.