Electrothermal modeling and characterization of SiC Schottky and silicon PiN diodes switching transients

Abstract

Schottky diodes are known to have lower conduction and switching losses compared to PiN diodes, however, are prone to ringing in the output characteristics. In this paper, analytical models have been developed to calculate the turn-off switching energy of SiC Schottky and silicon PiN diodes. The models account for the reverse recovery current and diode voltage overshoot in the case of the PiN diode as well as the output oscillations for the Schottky diodes. PiN diodes during turn-off exhibit significant reverse current which increases with the switching rate and temperature whereas Schottky diodes exhibit output oscillations due to RLC resonance in the circuit. By combining these models with thermal networks derived from transient thermal impedance curves of the diodes, a fast and accurate method of predicting the temperature transient for different switching frequencies and electrical time constants has been developed. These models can be used by application engineers to predict the energy dissipation when designing converters and can take account of temperature and switching rate dependencies of the diodes.

Improvement of an electro‐thermal model of SiC MPS diodes

“…Temperature is not represented in (17) because it has little effect on the capacitive turn-off charge [18] and on the related energy dissipation [8].…”

“…Thus, by integrating (16) from 0 to − V R , one can obtain a formula for the capacitive turn‐off charge Q c of the MPS diode, i.e. the charge evacuated during its switching off to a reverse voltage of V R : Temperature is not represented in (17) because it has little effect on the capacitive turn‐off charge [18] and on the related energy dissipation [8].…”

“…While the temperature dependence of electrical parameters is taken into account in many models, there is often no feedback to the thermal domain [7]. On the other hand, those models that include electro-thermal coupling through RC networks are not fully valid as they assume constant thermal resistance [8] or they relate thermal resistance to power dissipation [4]. In reality, thermal resistance varies with the junction-to-ambient temperature difference [9].…”

“…Some works tend to disregard SiC MPS dynamics due to their turn‐off charge being much lower than for silicon PIN diodes [4]. Indeed, the turn‐off energy is about one order of magnitude lower for the former [8], but this just means that dynamic power becomes significant for frequencies one order of magnitude higher which have already been demonstrated [10]. Most MPS models include device dynamics through a voltage‐dependent capacitance, but dynamic validation is limited to C – V curves [11, 12] while it is switching energy (dependent on the turn‐off charge) that is crucial in power converter applications.…”

Physics‐based spice model on the dynamic characteristics of silicon carbide Schottky barrier diode

“…There have been many researches on modelling SiC SBD. However, the diode resistances are always treated as constants in these models, and regardless of the impact of the MOS switch [15][16][17][18][19]. A significant deviation is observed between their simulation outputs and experimental measurements, especially on the ringing frequency and amplitude, which means the inaccuracy of switching features of the diode, like the switching time, the overshoot of current/voltage and the calculation of switching losses.…”