Multi-Time Scale Thermal Simulation Simulation-Assisted Lifetime Prediction of Power MOSFE T in LED Driver

Abstract

Power MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) has become one of the reliability-critical components in LED (lighting-emitting diode) driver applications. The failure types, which are stressed by temperature variations, are the dominant mechanisms of discrete power MOSFETs. During the operation of LED drivers, the thermal cycles come from different time constants, ranging from microseconds (caused by MOSFET switching losses) to minutes/hours (caused by the changing of ambient temperature and loads). In order to comprehensively understand thermal behaviours of power MOSFETs, this paper proposed a multi-timescale thermal modelling method for the stress analysis and lifetime prediction of power MOSFETs considering its operating mission profile. For the small timescale (device switching), an electro-thermal transient thermal simulation of MOSFETs is proposed, where the electrical simulation and thermal simulation are carried out in SABER to evaluate the turn-on/turn-off losses and ANSYS Icepak to analyze thermal stresses, respectively. For the large timescale, the system-level thermal model of the LED driver is built to evaluate the converter-level stresses. Afterward, considering two typical mission profiles of street lighting, the lifetime of the power MOSFET is predicted by using this multi-time scale model. This method can provide a more realistic way to predict the lifetime of power MOSFETs under different operation profiles.