Active Thermal Control of GaN-Based DC/DC Converter

The new packaging technologies used for gallium nitride (GaN) devices avoid wire bonds and leads in order to completely utilize their switching performance. This also means that thermomechanical fatigue that used to exist within the device may no longer be a reliability problem. And one of the main bottlenecks for reliability will be the solder joints between the device and the printed circuit board (PCB). To limit the thermal cycling induced failures in these points, an active thermal control scheme using a two step gate driver designed for GaN is presented in this paper. In contrast to the active thermal control techniques employing variable switching frequency control, this method does not alter the converter operation frequency; instead, it merely controls the GaN device slew rates. A simple temperature control algorithm that actively varies the device losses with the objective to minimize thermal cycling is proposed. The solder fatigue due to thermal cycling has been discussed. The effectiveness of this active thermal control scheme has been analyzed also in comparison with losses and validated with analysis, simulation, and experimental results.