Germany’s Fraunhofer Institute for Applied Solid State Physics IAF says it has developed the world’s first 600-V half-bridge circuit monolithically integrated on one chip. Fraunhofer used gallium nitride (GaN) to do the job. The half-bridge circuit comprises two GaN high-electron mobility transistors (HEMT) and two integrated freewheeling diodes. The HEMTs have a breakdown voltage of more than 600 V and an on-state resistance of 120 mΩ. Use of a folded-chip layout enables the dc link capacitance to be tightly connected between the supply voltage and ground. Fraunhofer says this design creates an optimized power path and allows for clean, stable switching at high frequencies. The circuit has been demonstrated in a down converter going from 400 to 200 V at a switching frequency of 3 MHz.
Fraunhofer says the same GaN-on-silicon technology used in the half bridge has been used to devise a monolithically integrated multilevel inverter. In this topology, ten GaN power devices sit on one chip with an area of 2 x 3 mm2. Each switch has a breakdown voltage of 400 V in the off state and a resistance of 350 mΩ in the on state. This converter has been demonstrated in inverters operating at 120-V mains voltage levels.
Monolithically integrated half-bridge circuits have significantly better electronic properties than their discrete counterparts. For example, the switching frequency can be improved by a factor of around ten in comparison with conventional voltage converters. “A switching frequency of up to 3 MHz allows us to achieve a much greater power density. This is important in areas such as e-mobility, where many converters which are as efficient as possible have to be fitted in very little space,” says Richard Reiner, research associate at Fraunhofer IAF in the Power Electronics business unit.
Fraunhofer IAF is presenting its monolithically integrated half-bridge circuit at PCIM Europe in Nuremberg May 16–18, 2017.