Isolated high-output current DC/DC converters are critical for future data center power architecture. LLC converters with matrix transformer are suitable for these applications due to its high efficiency and high power density. Different matrix transformer structures are investigated in this paper. To improve the current design practice, a high-frequency transformer loss model is developed and a detailed design methodology is proposed. Moreover, a novel matrix transformer structure is proposed to integrate four elemental transformers into one magnetic core with simple four-layer print circuit board windings implementation and further reduced core loss. By pushing switching frequency up to megahertz with GaN devices, the proposed matrix transformer can achieve high efficiency, high power density, and automatic manufacturing for magnetic components. A 1-MHz 380 V/12 V 800-W LLC converter with GaN devices is demonstrated. The prototype achieves a peak efficiency of 97.6% and a power density of 900 W/in3.

High-Efficiency High-Power-Density LLC Converter With an Integrated Planar Matrix Transformer for High-Output Current Applications

This paper presents the development of a simulation model for high-voltage gallium nitride (GaN) high-electron-mobility transistors (HEMT) in a cascode structure. A method is proposed to accurately extract the device package parasitic inductance, which is of vital importance to better predict the high-frequency switching performance of the device. The simulation model is verified by a double-pulse tester, and the results match well both in terms of device switching waveform and switching energy. Based on the simulation model, an investigation of the package influence on the cascode GaN HEMT is presented, and several critical parasitic inductances are identified and verified. Finally, a detailed loss breakdown is made for a buck converter, including a comparison between hard switching and soft switching. The results indicate that the switching loss is a dominant part of the total loss under hard-switching conditions in megahertz high-frequency range and below 8~10 A operation current; therefore, soft switching is preferred to achieve high-frequency and high-efficiency operation of the high-voltage GaN HEMT.

Package Parasitic Inductance Extraction and Simulation Model Development for the High-Voltage Cascode GaN HEMT

This paper presents a historical and philosophical perspective on a possible future for power electronics. Technologies have specific life cycles that are driven by internal innovation, subsequently reaching maturity. Power electronics appears to be a much more complex case, functioning as an enabling technology spanning an enormous range of power levels, functions and applications. Power electronics is also divided into many constituent technologies. Till now, the development of power electronics has been driven chiefly by internal semiconductor technology and converter circuit technology, approaching maturity in its internally set metrics, such as efficiency. This paper examines critically the fundamental functions found in electronic energy processing, the constituent technologies comprising power electronics, and the power electronics technology space in light of the internal driving philosophy of power electronics and its historical development. It is finally concluded that, although approaching the limits of its internal metrics indicates internal maturity, the external constituent technologies of packaging, manufacturing, electromagnetic and physical impact, and converter control technology still present remarkable opportunities for development. As power electronics is an enabling technology, its development, together with internal developments, such as wide bandgap semiconductors, will be driven externally by applications in the future.

On a Future for Power Electronics

The current state of wide bandgap device technology is reviewed and its impact on power electronic system miniaturization for a wide variety of voltage levels is described. A synopsis of recent complementary technological developments in passives, integrated driver, and protection circuitry and electronic packaging are described, followed by an outline of the applications that stand to be impacted. A glimpse into the future based on the current technological trends is offered.

Wide Bandgap Technologies and Their Implications on Miniaturizing Power Electronic Systems

The high-brightness white-light-emitting diode (LED) has attracted a lot of attention for its high efficacy, simple to drive, environmentally friendly, long lifespan, and compact size. The power supply for LED also requires long life, while maintaining high efficiency, high power factor, and low cost. However, a typical power supply design employs an electrolytic capacitor as the storage capacitor, which is not only bulky, but also with a short lifespan, thus hampering performance improvement of the entire LED lighting system. In this paper, a novel power factor correction (PFC) topology is proposed by inserting the valley-fill circuit in the single-ended primary inductance converter (SEPIC)-derived converter, which can reduce the voltage stress of the storage capacitor and output diode under the same power factor condition. This valley-fill SEPIC-derived topology is, then, proposed for LED lighting applications. By allowing a relatively large voltage ripple in the PFC design and operating in the discontinuous conduction mode (DCM), the proposed PFC topology is able to eliminate the electrolytic capacitor, while maintaining high power factor and high efficiency. Under the electrolytic capacitor-less condition, the proposed PFC circuit can reduce the capacitance of the storage capacitor to half for the same power factor and output voltage ripple as comparing to its original circuit. To further increase the efficiency of LED driver proposal, a twin-bus buck converter is introduced and employed as the second-stage current regulator with the PWM dimming function. The basic operating principle and analysis will be described in detail. A 50-W prototype has been built and tested in the laboratory, and the experimental results under universal input-voltage operation are presented to verify the effectiveness and advantages of the proposal.

A Novel Valley-Fill SEPIC-Derived Power Supply Without Electrolytic Capacitor for LED Lighting Application

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/in3.

LLC Resonant Converter With Matrix Transformer

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 3-D Integrated Gallium-Nitride-Based Point of Load Module Design

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.

LLC resonant converter with matrix transformer

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/in3 5MHz 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.

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

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 LED's 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.

Shu Ji

Papers

LLC Resonant Converter With Matrix Transformer

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

LLC resonant converter with matrix transformer

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

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