Gate-boosted Operation of a GaN-HEMT as Closing Switch

Gate-boosted operation enables a MOSFET to turn on with a much faster rise time than listed in the data sheet. Thereby, the gate boosting circuit comprises a capacitor in series to the inductance in the gate circuit and, hence, compensates the inductance such that the resonance frequency of this circuit is raised significantly resulting in a faster turn-on of the MOSFET switch. The gate driver needs to provide the gate charge required for tuming on the MOSFET. An extra voltage is needed to charge the additional series capacitor, which needs to be supplied by the driver in addition to the gate-to-source voltage. However, if a driver is too slow or not capable of providing sufficient power for charging the gate fast enough, it may limit the fall time of the gate voltage. In order to push such limitations towards a faster turn-on, a novel driver circuit for a GaN-HEMT based on a Marx configuration has been set up and tested.
A three-stage Marx circuit based on avalanche transistors acting as fast closing switches has been employed as a voltage source for the driver. lt has been operated at a stage voltage of approximately 280 V. The Marx circuit is connected to the capacitor inserted for compensating the inductance in series to the gate. ... mehrlt fonns a capacitive voltage divider in combination with the gate's voltage-dependent input capacitance, limiting the gate-source voltage.
The circuit has been set up and tested successfully connected to an essentially resistive load up to a drain-source voltage of 600 V at the GaN-HEMT. With a load of 50 n, when operating the device at 600 V a fall time of0.6 ns was measured for the drain-source voltage. A test with a load impedance of 16.6 n resulted in a respective fall time of0.7 ns.
In the contribution, selected design details of the circuit and measurement results will be presented.