LLC resonant DC-to-DC power converter with synchronous rectifiers using high- and medium-voltage gallium nitride-based transistors

The design demands for compact and low-profile power supplies are rapidly growing due to the preference for smaller and thinner appearance of industrial and consumer electronics. In this study, practical design methods for a high-density and low-profile DC-to-DC power converter are proposed. The prototype board of a 24 V/20 A LLC resonant converter was implemented. Given that a half-bridge circuit on the primary side operated with zero-voltage switching, the nominal operating frequency was further increased to 300 kHz. Notably, when an LLC series resonant converter with a low output voltage and high load current operates at a high switching frequency, several practical design considerations are required. A synchronous rectifier on the secondary side was configured to reduce the conduction losses. Gallium nitride-based transistors with high- and medium-voltage ratings were applied to the input and output sides due to their superior switching properties. A multi-layered PCB substrate was introduced to facilitate the design of the devices. Finite-element analysis of the PCB layout and thermal design was empirically conducted through computer simulation techniques. The parallelly connected gallium nitride-based transistors achieved a reliable operation and superior performance. Through a magnetic analysis, the design of a low-profile integrated transformer was optimized for high-frequency operation. Regarded as the most critical issue in gallium nitride-based transistors operating at high frequencies, the performance in electromagnetic interference was verified through effective measurements of conducted and radiated noises.