An Active Gate Driver Addressing GaN HEMT Gate-Source Voltage Overshoots for Both Turn-on and Turn-off Periods

Compared with traditional Si MOSFETs, GaN HEMTs have faster turn-on and turn-off speeds and are often used in high-frequency applications. However, the high dv/dt generated by high-frequency switching causes displacement current to flow into the gate drive circuit through the Cgd. High di/dt generates EMI (electromagnetic interference) that also affects the drive circuit, and it is also present in the gate drive circuit. Both of these can cause serious interference in the drive circuit, resulting in positive or negative spikes in the gate-source voltage. These spikes can easily break down the gate, which challenges the safety of GaN HEMTs. To address this problem, we have designed an active gate driver addressing GaN HEMT gate-source voltage overshoots for both turn-on and turn-off periods. The reliability of GaN HEMT applications is improved by connecting a gate capacitor at the right moment to absorb the forward or reverse spikes. In the double pulse test (DPT), at 400 V/16 A, the positive gate-source voltage spike was reduced by 51.5% relative to CGD when the turn-on time was only 3.5 ns. The negative gate-source voltage spike was reduced by 47.6% relative to CGD when the turn-off time was only 5.2 ns. This effectively proves the effectiveness of the designed AGD.