Shu Ji

High-Frequency High Power Density 3-D Integrated Gallium-Nitride-Based Point of Load Module Design

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/in3 2-MHz converter using enhancement mode GaN transistors, a single-phase10-A 800 W/in3 5-MHz converter, and a two-phase 20-A 1100 W/in3 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.

High frequency high power density 3D integrated Gallium Nitride based point of load module

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 800 W/in3 5 MHz converter, a two-phase 20 A 1000 W/in3 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.

Three-level driving method for GaN power transistor in synchronous buck converter

The emerging Gallium-Nitride (GaN) based power transistors offers the potential to achieve higher efficiency and higher switching frequencies than possible with Silicon MOSFETs. This paper will discuss the GaN device characteristics, and based on this, the driving method will be discussed. Then a three-level driving method is proposed to overcome the high reverse conduction loss issue of the GaN power transistor. Finally, a 12V to 1.2V Synchronous Buck converter with a full load current of 20A is built to verify the proposed method. The experimental results show that the proposed method is necessary and effective for efficiency improvement in high switching applications of GaN power transistor.

Multi-channel constant current (MC 3 ) LLC resonant LED driver

Multi-channel LED drivers are required in many applications, such as display backlighting, indoor lighting and street lighting. The LED driver should have the capability of providing multiple constant current source regardless to the LED forward voltage variations. Moreover, how to achieve current sharing between multiple LED channels is also challengeable in these applications. In this paper, a multi-channel constant current (MC3) LLC resonant LED driver is proposed. The LLC converter is controlled to operate as a constant current mode LED driver. By employing the multiple transformer structure, one single-stage driver can drive multiple LED channels, simplifying the driving scheme and circuit complexity. A DC block capacitor is utilized to balance the currents between two LED channels driven by the same transformer. After considering LEDs i-v characteristic, the LLC current gain characteristic is proposed and derived to describe a LLC converter with current-controlled output. Instead of constant resistive load considered in LLC voltage gain characteristic derivation, a non-linear LED load is modeled and used in AC equivalent circuit to derive LLC current gain characteristic. A design methodology for MC3 LLC LED driver has been developed based on the proposed LLC current gain characteristic. A 100kHz, 200W, 4-channel MC3 LLC LED driver is designed and simulated to verify the proposed circuit and design method.

Multi-channel constant current (MC 3 ) LED driver

High-brightness light emitting diodes (LEDs) are promising for various lighting applications, such as the backlighting of liquid crystal display (LCD) panels and the street lighting. Many backlighting and street lighting applications require the multi-channel constant current (MC3) driver to achieve better performance and higher reliability. The purpose of this paper is to introduce a simple and effective MC3 LED driver and explain its control concept and mechanisms. Coupled inductor concept is employed in the drivers circuit to improve the output current cross regulation. This paper also provides a general model to describe the current cross regulation (CCR) among multi-channel outputs mathematically. By using this model, factors that affect cross regulation can be easily located and analyzed. Simulation results are provided to verify the concept.

Matrix transformer for LLC resonant converters

In this paper, a high efficiency high power density matrix transformer structure for LLC resonant converters is proposed. Matrix transformer is help to reduce leakage inductance and the AC resistance of windings. Flux cancellation method is utilized to reduce core size and loss. Synchronous Rectifier (SR) devices and output capacitors are integrated into secondary windings to eliminate termination related winding losses, via loss and leakage inductance. An 1.6 MHz 390 /12 V 1kW LLC resonant converter prototype is built to verify the proposed structure.

LLC resonant converter with matrix transformer

In this paper, a high efficiency high power density matrix transformer structure for LLC resonant converters is proposed. Matrix transformer is help to reduce leakage inductance and the AC resistance of windings. Flux cancellation method is utilized to reduce core size and loss. Synchronous Rectifier (SR) devices and output capacitors are integrated into secondary windings to eliminate termination related winding losses, via loss and leakage inductance. A detail design procedure is proposed. A 1MHz 390V /12 V 1kW LLC resonant converter prototype is built.