| Abstract |
A GaN half-bridge, suffering from high turn-off overvoltage preventing further load current increase, is improved by paralleling GaN-HEMTs (Gallium Nitride - High Electron Mobility Transistor). To compare both designs, a method combining 3D-FEM and SPICE simulations is presented and validated by measurements of the initial half-bridge's switching characteristic. This method is then applied to the half-bridge with parallel HEMTs. The simulation of commutation paths in the parallel connection verifies the layout's symmetry, proven by measuring the switching behaviour using these paths. Switching tests of the entire parallel half-bridge demonstrate the successful reduction of the overvoltage peak for the application's desired load current. They further show a basically even load current distribution, with an almost identical slew-rate of the current transients rebalancing after an unbalanced time. From the analysis of this time, it is concluded that its reason should be an effect on the gate-source behaviour with a relatively long time constant, not only explainable by static threshold voltage (Vth) differences between the parallel transistors. By manipulating the static Vth difference in the SPICE simulation to a higher value than measured the current distribution can be described including the unbalanced behaviour. |
