EMC analysis of current source gate drivers

The prevention of electromagnetic emissions (EME) in bridge applications is of major importance, especially in automotive applications. Current source gate drivers are a popular approach to improve the performance in electromagnetic compatibility (EMC). Despites, their EMC performance has rarely been investigated in detail. Starting with the differences in the gate drive transients versus a conventional hard switching driver this paper presents a study regarding the EMC behavior. Different application cases are considered: Switching time, direction of load current, different load current levels. Experimental evaluation boards were prepared for both driver methods, results are provided for various cases. In order to identify the potential of current source gate drivers, the influence of the dv/dt and di/dt at bridge output were studied based on simulation. The di/dt turned out to be more important, a 5dBμV improved EMC was achieved by extending the duration of the current slope from 82ns to 92ns. The simulation setup also allowed to analyze the turn-on and turn-off transitions separately regarding EMC. Mainly due to the reverse recovery the turn-on transition gives 10dBμV worse EMC noise compared to turn-off. As an overall result, EMC improvements due to current source gate drivers in general are very case dependent.