Spontaneous Transistor Failures in Automotive Power Electronics 2014-01-0228
The amount of electronics in vehicles is increasing, so is the amount of power electronics circuits, like inverters for electric motor drives or dc/dc converters. The muscles of these circuits are power transistors like MOSFETs and IGBTs - in each circuit are several of them.
While MOSFETs and IGBTs have advanced over the years in terms of their performance, their wide product spectrum and feature spectrum as well as cost, they are still not unbreakable, but semiconductors which are more sensitive to electrical or thermal overstress than, a relay for instance.
Especially electrical overstress, like overvoltage or over current, may damage a power transistor within a short time frame. Hence, electrical overstress must be avoided when designing the power electronics circuit.
However, even a power transistor in a carefully designed power electronics circuit, may still be exposed to over current, short circuit, over voltage, over temperature and so forth. This may damage the power transistor and may have severe consequences for the application. Unfortunately, power transistors do not have an intrinsic self protecting mechanism. Therefore, it is recommended to monitor voltage, current, temperature, compare against thresholds and turn off when needed.
This paper will discuss types of failures, common causes of failure, voltage and current waveforms in normal operation and failure modes and suggest methods to avoid the failure (operate the power transistor within safe boundaries). Alternatively, detection methods and an appropriate response strategy is given after a failure is detected.