In this paper, a high-efficiency high power density LLC resonant converter with a matrix transformer is proposed. A matrix transformer can help reduce leakage inductance and the ac resistance of windings so that the flux cancellation method can then be utilized to reduce core size and loss. Synchronous rectifier (SR) devices and output capacitors are integrated into the secondary windings to eliminate termination-related winding losses, via loss and reduce leakage inductance. A 1 MHz 390 V/12 V 1 kW LLC resonant converter prototype is built to verify the proposed structure. The efficiency can reach as high as 95.4%, and the power density of the power stage is around 830 W/in 3 .

The demand for the future power supplies that can achieve higher output currents, smaller sizes, and higher efficiencies cannot be satisfied with the conventional technologies. There are limitations in the switch performance, packaging parasitics, layout parasitics, and thermal management that must be addressed to push for higher frequencies and improved power density. To address these limitations, the utilization of Gallium-Nitride (GaN) transistors, 3-D integrated technique, low-profile magnetic substrates, and ceramic substrates with high thermal conductivity are considered. This paper discusses the characteristics of GaN transistors, including the fundamental differences between the enhancement mode and the depletion mode GaN transistors, gate driving, and the deadtime loss, the effect of parasitics on the performance of high-frequency GaN point-of-load (POLs), the 3-D copackage technique to integrate the active layer with low profile low temperature cofired ceramic magnetic substrate, and the thermal design of a high -density module using advanced substrates. The final demonstrators are three 12-1.2-V conversion POL modules: a single-phase 20 A 900 W/in 3 2-MHz converter using enhancement mode GaN transistors, a single-phase10-A 800 W/in 3 5-MHz converter, and a two-phase 20-A 1100 W/in 3 5-MHz converter using the depletion mode GaN transistors. These converters offer unmatched power density compared to state-of-the-art industry products and research.

The Gallium Nitride (GaN) transistors offer the capability of high efficiency at high operation frequency. This paper will discuss the characteristics of enhancement mode and depletion mode GaN transistors; the high frequency GaN converter design considerations include gate driving, reducing dead-time loss, minimizing parasitics inductance, and the three dimension (3D) technology to integrate the active layer with low profile low temperature co-fired ceramic (LTCC) magnetic substrate to achieve high power density. The final demonstrations are two 12 V to 1.2 V conversion integrated point of load (POL) modules: a single-phase10A 800W/in 3 5MHz converter, a two-phase 20 A 1000 W/in 3 5 MHz converter using the depletion mode GaN transistors. These converters offer unmatched power density compared to state-of-the-art industry products and research.

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