Fast temperature sensing for GaN power devices using E-field probes

The material properties of GaN enable high-voltage devices to be manufactured in very small packages. This reduces device footprint and parasitics. However, it also increases thermal impedances which makes thermal management increasingly challenging, negatively affecting reliability. One way to increase reliability is to monitor device junction temperature, and subsequently modify converter operation to hold the temperature in safe bounds. This paper demonstrates a method of sensing the instantaneous junction temperature of GaN power devices, using a low-cost capacitive E-field probe and analogue circuitry. For the first time, the use of the extremely fast turn-on dv/dt of GaN devices to determine instantaneous junction temperature is reported. The dependency of the sensor output on load current is shown, and a circuit demonstrated that provides an alert for temperatures above a chosen threshold. The circuit detail, operation, response times, and alternative approaches to take care of the dependency on load current are presented, with a view to helping designers to develop integrated and discrete temperature sensing methods for GaN devices. This new temperature sensing technique could be integrated into a smart power module or added to large power devices as an auxiliary circuit.