Personnel

FICs - Prof. Philip K. T. Mok

Description

The emerging use of Gallium Nitride (GaN) device is leading a high speed revolution for high voltage (HV) power circuits. Compared to their conventional slow silicon counterparts, GaN devices simultaneously offer fast switching and improved efficiency due to the significantly reduced parasitics. Thus, power adapters, chargers, LED drivers and other power circuits that use GaN can be smaller and lighter. Depletion-mode (D-mode) GaN transistors, which feature higher robustness and lower fabrication cost than enhancement-mode GaN switches, are widely used in HV applications. However, these D-mode transistors have a negative threshold voltage and lack a body diode for reverse current operation. Therefore, a special GaN driving circuit is necessary to ensure the fast and completed turning-on and turning-off of the transistor and to provide reverse current conduction with low energy loss. The direct driving scheme, with a negative voltage to turn off the D-mode GaN transistor, is an effective solution for driving the main switch of the power converters because it provides high reliability and almost zero reverse recovery loss. However, it is not suitable to configure the GaN as a power diode with this scheme to conduct reverse current, due to the high voltage drop on the GaN device. In addition, it is challenging to operate HV GaN-based power converters in a synchronized configuration with accurate dead-time control, because of the delay in signal level shifting. In this project, a novel D-mode GaN driver will be developed to address the above issues together with a proposed pseudo-synchronous scheme in which the turning the rectifier switch on/off will be determined locally without HV signal level shifting. In addition, techniques for precise switching timing control will be investigated to achieve almost perfect dead time in different operation modes. These techniques will help to further improve the system efficiency for a variety of GaN-based switching power converters with high operation frequency. A closed-loop HV bidirectional buck converter will also be implemented with the proposed GaN drivers to verify the effectiveness of the proposed techniques.

Source: RGC | ITF