Lifetime Extension of Power Semiconductor Devices by Closed-Loop Junction Temperature Control

The lifetime of power semiconductor devices is mainly affected by the thermal stress they are exposed to. Especially temperature swings damage these devices due to different coefficients of thermal expansion of the material layers inside the device. This leads to mechanical strain between these layers. This paper proposes a closed loop junction temperature control system, which is able to reduce occurring temperature swings in order to reduce the damage and to extend the expected lifetime. An online junction temperature measurement is required in order to obtain information about the real-time temperature. This is realized by measuring the temperature sensitive on-resistance of the used MOSFET. Then, the junction temperature is estimated with a calibration curve. Another requirement is the possibility to influence the junction temperature during operation. Therefore, the switching frequency is varied to affect the switching losses. This influences the junction temperature. In addition, a set-value generator is presented, which generates suitable set values to reduce temperature swings.