In situ characterisation of non linear capacitors

Multilayers ceramic capacitors (MLCC) presenting non linear behaviours of their C(V) characteristics may have interesting applications in power electronics. Most of them have already been described. Nevertheless, the choice of a particular type instead of another one is all the more so difficult since, on one hand the physical mechanisms able to explain this behaviour is far from being understood. On the other hand, C(V) characteristics are in general obtained for low voltage values different from the ones they are going to be involved in. In this paper, direct in situ characterisations of different BaTiO3 based capacitors commercially available are achieved. The role of the capacitors' type (X7R,Z5U), of the temperature and of the voltage waveform (and more particularly its polarity) is demonstrated. Temperature values up to 200 degreesC are measured during normal operations in a RCD dissipative snubber without any alterations of the C(V) characteristics. All these results are discussed as regards the main physical properties of the constitutive materials in order to reach an optimisation of their use through an appropriate dimensioning.