Gallium Nitride FETs Research Articles

Characterization of GaN HEMTs' Aging Precursors and Activation Energy Under a Wide Range of Thermal Cycling Tests

In this paper, 650 V / 7.5 A rated enhancement-mode (E-mode) Gallium Nitride (GaN) high-electron-mobility-transistors (HEMTs) with integrated gate drivers are characterized under thousands of accelerated thermal cycles (ATC) at different junction temperature stresses. This research helps in developing fundamental insights into GaN HEMTs' aging characteristics through the degradation of ten devices under ATC tests. For over 20,000 thermal cycles, the forward and reverse conduction losses, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> GSS, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> oss, and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RDS</i> on are experimentally measured to identify the parameter shifts and the corresponding precursors. Results indicate that both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IGSS</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> oss do not deviate much, but the values of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RDS</i> on, the forward and reverse conduction losses vary considerably with device aging. This paper also presents an empirical method to estimate the correlation between the acceleration factors of the GaN FETs' degradation process and the thermal cycling conditions. The value of the activation energy of the tested GaN HEMT devices is also derived using the empirical equations to be about 1.13 eV under the applied stress factors. This study finds that the degradation process of GaN HEMTs with age facilitates a reasonable correlation with different failure mechanisms, which further helps in reliability improvement.

Cascode GaN FET 기반 EV용 V2x DAB 컨버터의 경부하 효율 분석

In this paper, the light-load efficiency of cascode gallium nitride (GaN) FET-based V2x dual active bridge (DAB) converters for electric vehicles(EVs) is analyzed. High efficiency and high power density are required when an on-board charger(OBC) is used in EVs. To this and a zero voltage switching (ZVS) topology, such as that observed in DAB converters, is widely applied. As for the converter requiring current enough to achieve the ZVS condition of the efficiency characteristics vary depending on whether ZVS operated or not. Therefore, in this study, the efficiency in the hard switching section is improved by applying a cascode GaN FET to a DAB converter. The ZVS characteristic is analyzed by considering the parasitic output capacitance of the switching device. Compared to the Si device, the cascode GaN FET with low parasitic output capacitance realizes ZVS under a lower load condition. To verify this, a load test is performed by applying it to a 3-kW DAB converter. The experimental results confirm that ZVS is achieved when the cascode GaN FET is applied. Moreover, a shorter dead time can be applied owing to excellent dv/dt and di/dt characteristics, which improves the overall efficiency. In conclusion, the use of GaN FET in DAB converters can improve efficiency at light loads.

Improved Circuit Design and Adaptive Burst Mode Control in PSFB Converters for Higher Efficiency Over a Wide Power Range

This paper presents an improved circuit design of Gallium Nitride (GaN) based phase shifted full bridge (PSFB) converters along with a new adaptive burst mode control strategy, to achieve high efficiency over a wide power range, including light loads. The main challenges of PSFB converters addressed in this paper are: load-dependent zero-voltage switching (ZVS), transformer saturation, and secondary side ringing. Since switching losses of GaN FETs are dominant at light loads, adaptive burst mode control can be employed to improve the efficiency at lower output power. By periodically switching output current between 0 A and minimum ZVS current, adaptive burst mode control can enable both smaller effective switching frequency and lower switching losses. A correction factor ‘k’ is adopted in the adaptive burst mode control’s current loop PI calculation so that the output current can switch fast without any overshoot that increases switches’ current stress. To verify the effectiveness of the proposed circuit and controller design, a 375 V input, 70 V output, 800 W PSIM simulation model as well as experimental prototype are developed and tested. The experimental results demonstrate the practical benefits of the proposed adaptive burst mode control.

Modeling of Conducted EM Emissions of Synchronous Buck Converters for Different Voltage Conversion Ratios

Large voltage conversion ratios of switching power converters operating at frequencies in the megahertz range are difficult to achieve because of the short pulses of the control signals for the transistor switches, and a multistage topology is a common solution to overcome this problem. A synchronous buck converter based on gallium-nitride FET switches is designed to analyze the effects of different voltage conversion ratios on the conducted electromagnetic (EM) emissions at the input of the converter. The input and output voltage and power levels are set to reproduce the operating conditions of the front-end and load converter in a multistage buck converter topology. The relationship between the generated conducted EM emissions and the voltage conversion ratio of the designed buck converter is approximated by the quadratic regression model. The synchronous buck converter with silicon transistor switches is designed to validate the proposed regression model. The extracted model allows accurate estimation of the conducted EM emissions generated by the buck converter for different voltage conversion ratios.

Low-Voltage GaN FETs in Motor Control Application; Issues and Advantages: A Review

The efficiency and power density improvement of power switching converters play a crucial role in energy conversion. In the field of motor control, this requires an increase in the converter switching frequency together with a reduction in the switching legs’ dead time. This target turns out to be complex when using pure silicon switch technologies. Gallium Nitride (GaN) devices have appeared in the switching device arena in recent years and feature much more favorable static and dynamic characteristics compared to pure silicon devices. In the field of motion control, there is a growing use of GaN devices, especially in low voltage applications. This paper provides guidelines for designers on the optimal use of GaN FETs in motor control applications, identifying the advantages and discussing the main issues. In this work, primarily an experimental evaluation of GaN FETs in a low voltage electrical drive is carried out. The experimental investigation is obtained through two different experimental boards to highlight the switching legs’ behavior in several operative conditions and different implementations. In this evaluative approach, the main GaN FETs’ technological aspects and issues are recalled and consequently linked to motion control requirements. The device’s fast switching transients combined with reduced direct resistance contribute to decreased power losses. Thus, in GaN FETs, a high switching frequency with a strong decrease in dead time is achievable. The reduced dead time impact on power loss management and improvement of output waveforms quality is analyzed and discussed in this paper. Furthermore, input filter capacitor design matters correlated with increasing switching frequency are pointed out. Finally, the voltage transients slope effect (dv/dt) is considered and correlated with low voltage motor drives requirements.

Full Custom Design of an Arbitrary Waveform Gate Driver With 10-GHz Waypoint Rates for GaN FETs

Active gate driving of power devices seeks to shape switching trajectories via the gate, for example, to reduce EMI without degrading efficiency. To this end, driver ICs with integrated arbitrary waveform generators have been used to achieve complex gate signals. This article describes, for the first time, the implementation details of a digitally programmable arbitrary waveform gate driver capable of a 10-GHz waypoint rate, including comprehensive design considerations for critical high-speed subsystems that codify the tradeoff in flexibility, speed, and area. The design, which is taped out in a 180-nm high-voltage CMOS process, utilizes buffers that switch up to ten times in a single clock cycle to overcome the limited achievable clock speed of high-voltage silicon integrated circuits and a fully digital architecture to provide robustness under high slew rates of the ground rail. The driver IC has networks of 100-ps delay elements that are configured prior to a switching transient, to selectively control an array of fast, parallel-connected drivers with different output impedances. Key to the high timing resolution are high-speed asynchronous circuits for memory readout, output buffering, and pulse generation. The driver IC is experimentally evaluated to have a 100-ps resolution and to operate reliably in a 400-V gallium nitride (GaN) bridge leg, under ground-rail voltage slew rates peaking at over 100 V/ns. Design rules are provided to obtain an architecture with the least area for a given set of timing and impedance resolution requirements. The reported design methods enable complex driving waveforms to be applied during nanosecond-scale transients of GaN power devices and demonstrate how digitally programmable active gate drivers for GaN power FETs can be designed to meet a given set of application requirements.

GaN-Based Tri-Mode Intelligent Solid-State Circuit Breakers for Low-Voltage DC Power Networks

The purpose of this article is to provide a comprehensive and integrated discussion on the basic concept and general design methodology of a gallium nitride (GaN)-based, tri-mode, intelligent solid-state circuit breaker, referred to as iBreaker. The iBreaker concept explores the use of GaN devices in the low-voltage (<; 1000 V), mΩ-resistance SSCB designs and new SSCB topology and control techniques beyond the commonly used on/off switch configuration in order to integrate more intelligent functions without increasing component count. The iBreaker adopts a distinct pulsewidth modulation (PWM) current limiting (PWM-CL) state in addition to the conventional on and off states to facilitate soft startup, fault authentication, and fault location functions. Key design elements, such as use of wide bandgap (particularly GaN) switches, tri-mode operation, combined digital and analog control, and universal hardware/software architecture, are discussed in detail. In particular, the bidirectional buck topology, changes among operation states, variable PWM frequency control, fault locating techniques, GaN FET hardware, and thermal design are discussed. Two iBreaker prototypes, rated at 380 V/20 A and 1000 V/10 A, respectively, are built and tested to validate the proposed SSCB design concept. 99.95% transmission efficiency, passive cooling, and μs-scale response time are demonstrated experimentally.

92.5% Average Power Efficiency Fully Integrated Floating Buck Quasi-Resonant LED Drivers Using GaN FETs

LEDs are highly energy efficient and have substantially longer lifetimes compared to other existing lighting technologies. In order to facilitate the new generation of LED devices, approaches to improve power efficiency with increased integration level for lighting device should be analysed. This paper proposes a fully on-chip integrated LED driver design implemented using heterogeneous integration of gallium nitride (GaN) devices atop BCD circuits. The performance of the proposed design is then compared with the conventional fully on-board integration of power devices with the LED driver integrated circuit (IC). The experimental results confirm that the fully on-chip integrated LED driver achieves a consistently higher power efficiency value compared with the fully on-board design within the input voltage range of 4.5–5.5 V. The maximal percentage improvement in the efficiency of the on-chip solution compared with the on-board solution is 18%.

Micro-sized Cryocooler Controllers for Space

The explosion in SmallSat and CubeSat deployments has led to a need for miniaturized cooling solutions for sensors that require cryocooling. Since there are limited opportunities for miniaturization in the thermal mechanical unit (TMU) portion of the cryocooling system, much of the pressure to reduce size falls on the cryocooler control electronics (CCE). In the world of digital electronics, continuous size reduction is the expected norm, however, in the world of power electronics this is not the case. The number of components and their variety is greatly limited when selecting space grade electronics, typically resulting in designs that make space grade electronic solutions much larger than an equivalent circuit made of commercial grade electronics.One way to reduce the size of the power components is to switch at a higher speed. The current generation CCE devices built by Iris Technology utilize MOSFET power transistors to perform power conversion. The characteristics of the power MOSFETs limit the switch rate to something on the order of 100 kHz, thus driving the energy storage requirements of the capacitors and inductors. If we could switch faster we reduce the required energy storage and thus the size of the inductors and capacitors.One solution to the switching frequency problem is the use of Gallium Nitride (GaN) FETs which can be switched on the order of 1 MHz. GaN FETs are inherently radiation tolerant, however recently GaN FETs have become available with space grade packaging. The space grade packaging is available with an integral radiation hardened high/low side driver. This integrated part provides further size reduction to the electronics design.Recently, high performance space grade microcontrollers have become available. These parts offer another integration opportunity, as the FPGA and ADC functions can be combined into a single smaller chip. Space grade GaN FETs when combined with the space grade microcontrollers provide an opportunity for significant reduction in the volume required for the CCE portion of a cryocooler system.

GaN FET 적용한 동기식 부스트 컨버터에 관한 연구

Si FETs (Silicon FETs) have been widely used as power switches for DC-DC converters. However, in recent years, GaN FETs (Gallium Nitride FETs), which have better electrical characteristics than Si FETs, have been commercialized and they have gradually replaced Si FETs. The superior electric characteristics of GaN FETs over Si FETs is analyzed in this paper. Among the various superior electric characteristics of GaN FETs, the absence of reverse recovery current and the capability of reverse conduction can reduce the conduction loss and the reverse recovery loss of a diode. which is the main power loss of the DC-DC boost converter operating in the CCM (continuous conduction mode). Therefore, a synchronous DC-DC boost converter, which can use two GaN FETs, was studied as a method to improve the power efficiency of the DC-DC boost converter. To verify the superiority of the proposed boost converter, a prototype with a input voltage of 12V, an output voltage of 24V, an operating frequency of 300kHz, and an output power of 35W was fabricated and compared with a conventional DC-DC boost converter using a MOSFET and a diode. The experimental results show that the power efficiency of the synchronous boost converter using two GaN FETs is higher than that of the conventional boost converter in the entire output power ranges and the maximum efficiency improvement is 4.9% at the output voltage of 35W.

Design Approach for a Self-Oscillating Resonant Converter Operating in High Frequency for LED Applications

In this paper, a design approach for the self-oscillating command circuit (SOCC) as a driver for a resonant converter operating in high frequency for LED applications is proposed. This proposal, conceived from the proposed methodologies, contemplates the influence of the Cascode gallium nitride (GaN) FET input and output capacitances, making it relevant to higher switching frequencies, where such parasitic elements lead to increased errors. In conjunction with higher efficiency levels, series resonant inverters like the zero-voltage switching half-bridge are known to have potentially reduced size on its reactive components when operated at higher frequencies, resulting in smaller and lighter systems. Combined to the ‘simplicity and low cost of the SOCC, these advantages translate into a simple and cost-effective high-power-density application. The self-oscillating resonant converter (SORC) accurate design is based upon the describing function method as a linearization tool and the extended Nyquist stability criterion that evaluates whether or not the system can oscillate around given predicted frequency. Practical input capacitance measurement data for different silicon MOSFETs and a Cascode GaN FET are compared and considered in order to obtain a high-frequency design approach for an SORC. Simulation and experimental results for an SORC with Cascode GaN FET operating at 1 MHz for a 10-W LED are shown based on the design procedure described.

An Auto-Zero-Voltage-Switching Quasi-Resonant LED Driver With GaN FETs and Fully Integrated LED Shunt Protectors

An auto-zero-voltage-switching (ZVS) quasi-resonant LED driver with gallium nitride (GaN) FETs for general lighting applications is presented. The proposed LED driver switches at high frequency to minimize the inductors to microhenry range. ZVS can be automatically achieved with the proposed controller to eliminate switching loss. The GaN FETs enable high-frequency operation and improve the power efficiency. A fully integrated LED shunt protector is proposed to bypass the failed LEDs in series-connected LED strings. The overall lifetime of the LED strings can be improved, and the maintenance cost can be reduced. The characteristics of the ZVS quasi-resonant LED driver with small inductors and the conditions for ZVS are also discussed in detail. The LED driver is fabricated with a 0.35- $\mu \text{m}$ 120-V high-voltage process. It can provide up to 25-W power to the LED with $2 \times 3.3\,\,\mu \text{H}$ inductors and achieves 91.4% peak efficiency and a 0.973 peak power factor from 60-Hz 100- to 120- $\text{V}_{\mathrm {ac}}$ input.

A High-Frequency CLCL Converter Based on Leakage Inductance and Variable Width Winding Planar Magnetics

A CLCL resonant DC/DC converter based on the transformer leakage inductance is proposed in this paper. With the adoption of leakage inductance, the system volume and magnetic losses can be greatly reduced. The optimal design method of the proposed converter is analyzed in detail. Also, the advantages of the CLCL converter are depicted compared with LLC circuit. The design of variable width winding planar magnetics is depicted in detail, which can reduce the winding losses and parasitic capacitance. A 1-MHz prototype using gallium nitride FETs is built to verify the feasibility of the proposed resonant converter and design method.

Utilizing Sequential Action Control Method in GaN-Based High-Speed Drive for BLDC Motor

This paper presents a hybrid model–based control algorithm that combines Model Predictive Control (MPC) and Sequential Action Control (SAC) deployed in a high-speed drive for Brushless DC (BLDC) motor by using a DC-DC converter with Gallium Nitride (GaN) switches. GaN FETs are selected because of their higher speed and lower power loss as compared with traditional Si switches. In the proposed framework, SAC processes the initial values of the control variables as well as their time of application and their duration in MPC loop. After receiving the underlying estimation of future contribution from SAC, MPC consolidates it with current input and predicts future control values by using the system state space model. This hybrid control conserves control effort and reduces sensitivity to initial conditions. In this way, converter’s output voltage is controlled to produce the reference speed at the motor output. National Instrument PXIe-6356 module is utilized as the interface between software and hardware that is a multi-function, LabVIEW-compatible data acquisition device. The viability of the proposed hybrid optimization for the high-speed drive is confirmed numerically by utilizing MATLAB/Simulink and approved experimentally using a Gallium Nitride (GaN) half-bridge DC-DC converter.

(Invited) 650 Volt GaN Commercialization Reaches Automotive Standards

With its proven ability to reduce size (form factor) and save energy (high efficiency) Gallium Nitride (GaN) is now no longer a nice to have, it is a must-have for power conversion. High voltage (HV) GaN HEMTs (also called GaN FETs) in the range of 650 to 900 volts are becoming the next standard for power conversion. GaN provides cost-competitive, easy-to-embed solutions that reduce energy loss by >50 percent, shrink system sizes by >40 percent, to simplify power converter/inverter design and manufacturing. These benefits are being realized today in various markets: Consumer, Industrial, Server, Servo Motors and Drives, Solar, Telecommunications, and recently Hybrid and Electric Vehicles. Having successfully completed JEDEC qualification and commercialization of HV-GaN, we will now review the first ever Automotive (AEC Q101) Qualification for GaN and discuss in detail results for highly stressed robustness tests, FIT rates & lifetime testing.

Design and Implementation of a GaN-Based, 100-kHz, 102-W/in3Single-Phase Inverter

High power density is a desirable feature of power electronics design, which prompts economic incentives for industrial applications. In this paper, a gallium nitride (GaN)-based 2-kVA single-phase inverter design was developed for the Google Little Box Challenge, which achieves a 102-W/in $^{3}$ power density. First, the static and dynamic temperature-dependent characteristics of multiple SiC and enhancement-mode GaN FETs are investigated and compared. Based on the device testing results, several topologies of the inverter stage and different power decoupling solutions are compared with respect to the device volume, efficiency, and thermal requirements. Moreover, some design approaches for magnetic devices and the implementation of gate drives for GaN devices are discussed in this paper, which enable a compact and robust system. Finally, a dc notch filter and a hard switching full-bridge converter are combined as the proposed design for the prototype. A 2-kVA prototype is demonstrated, which meets the volume, efficiency, and thermal requirements. The performance of the prototype is verified by the experimental results.

Active Detuning of MRI Receive Coils with GaN FETs

Here, we present the use of Gallium Nitride (GaN) FETs as a replacement for PIN diodes in active detuning circuits for magnetic resonance imaging (MRI) receive coils at 63.6 MHz. We use simulated circuit models, benchtop measurements, and imaging experiments to show that GaN FETs perform comparably with a common MRI-compatible PIN diode. The GaN FET-based circuits require orders of magnitude less bias current to operate, effectively eliminating ${\rm B}_{0}$ distortion resulting from biasing.

GaN FET을 이용한 토템폴 구조의 브리지리스 부스트 PFC 컨버터

The superiority of gallium nitride FET (GaN FET) over silicon MOSFET is examined in this paper. One of the outstanding features of GaN FET is low reverse-recovery charge, which enables continuous conduction mode operation of totem-pole bridgeless boost power factor correction (PFC) circuit. Among many bridgeless topologies, totem-pole bridgeless shows high efficiency and low conducted electromagnetic interference performance, with low cost and simple control scheme. The operation principle, control scheme, and circuit implementation of the proposed topology are provided. The converter is driven in two-module interleaved topology to operate at a power level of 5.5 kW, whereas phase-shedding control is adopted for light load efficiency improvement. Negative bias circuit is used in gate drivers to avoid the shoot-through induced by high speed switching. The superiority of GaN FET is verified by constructing a 5.5 kW prototype of two-module interleaved totem-pole bridgeless boost PFC converter. The experiment results show the highest efficiency of 98.7% at 1.6 kW load and an efficiency of 97.7% at the rated load.

Si MOSFET과 GaN FET Power System 성능 비교 평가

This paper carries out a series of analysis of power system using Gallium Nitride (GaN) FET which has wide band gap (WBG) characteristics comparing to conventional Si MOSFET-used power system. At first, for comparison of each semiconductor device, the switching-transient parameter is quantitatively extracted from released information of GaN FET. And GaN FET model which reflect this dynamic property is configured. By using this model, the performance of GaN FET is analyzed comparing to Si MOSFET. Also, in order to enable a representative assessment on the power system level, Si MOSFET and GaN FET are applied to the most common structure of power system, full-bridge, and each power systems are compared based on various criteria, such as performance, efficiency and power density. The entire process is verified with the aid of mathematical analysis and simulation.

Classification and Comparative Evaluation of PV Panel-Integrated DC–DC Converter Concepts

The strings of photovoltaic panels have a significantly reduced power output when mismatch between the panels occurs, as, e.g., caused by partial shading. With mismatch, either the panel-integrated diodes are bypassing the shaded panels if the string is operated at the current level of the unshaded panels, or some power of the unshaded panels is lost if the string current is reduced to the level of the shaded panels. With the implementation of dc-dc converters on panel level, the maximum available power can be extracted from each panel regardless of any mismatch. In this paper, different concepts of PV panel-integrated dc-dc converters are presented and their suitability for panel integration is evaluated. The buck-boost converter is identified as the most promising concept and an efficiency/power density ( η- ρ) Pareto optimization of this topology is shown. Based on the optimization results, two 275 W converter prototypes with either Silicon MOSFETs with a switching frequency of 100 kHz or gallium nitride FETs with a switching frequency of 400 kHz are designed for an input voltage range of 15 to 45 V and an output voltage range of 10 to 100 V. The theoretical considerations are verified by efficiency measurements which are compared to the characteristics of a commercial panel-integrated converter.