Recently, the demand for miniaturized and fast transient response power delivery systems has been growing in high-voltage industrial electronics applications. Gallium Nitride (GaN) FETs showing a superior figure of merit (R ds, ON X Q g ) in comparison with silicon FETs [1] can enable both high-frequency and high-efficiency operation in these applications, thus making power converters smaller, faster and more efficient. However, the lack of GaN-compatible high-speed gate drivers is a major impediment to fully take advantage of GaN FET-based power converters. Conventional high-voltage gate drivers usually exhibit propagation delay, t delay , of up to several 10s of ns in the level shifter (LS), which becomes a critical problem as the switching frequency, f sw , reaches the 10MHz regime. Moreover, the switching slew rate (SR) of driving GaN FETs needs particular care in order to maintain efficient and reliable operation. Driving power GaN FETs with a fast SR results in large switching voltage spikes, risking breakdown of low-V gs GaN devices, while slow SR leads to long switching rise time, t R , which degrades efficiency and limits f sw . In [2], large t delay and long t R in the GaN FET driver limit its f sw to 1MHz. A design reported in [3] improves t R to 1.2ns, thereby enabling f sw up to 10MHz. However, the unregulated switching dead time, t DT , then becomes a major limitation to further reduction of t de!ay . This results in limited f sw and narrower range of V IN -V O conversion ratio. Interleaved multiphase topologies can be the most effective way to increase system f sw . However, each extra phase requires a capacitor for bootstrapped (BST) gate driving which incurs additional cost and complexity of the PCB design. Moreover, the requirements of f sw synchronization and balanced current sharing for high f sw operation in multiphase implementation are challenging.

16.7 A 20V 8.4W 20MHz four-phase GaN DC-DC converter with fully on-chip dual-SR bootstrapped GaN FET driver achieving 4ns constant propagation delay and 1ns switching rise time

This paper presents an ac-dc LED driver that consists of two-parallel inverted buck converters. To buffer the twice-line-frequency energy, one inverted buck converter (also known as a floating buck converter) conveys energy to a storage capacitor, simultaneously performing the power factor correction. The other inverted buck converter regulates the LED current to maintain a constant brightness in the LEDs for reducing the light flicker to low-risk levels. The proposed architecture reduces the voltage stress and the size of the storage capacitor, enabling the use of a film capacitor instead of an electrolytic capacitor. Considering the power factor and the flicker standards, a design procedure to achieve a high power factor, while minimizing the storage capacitance and the LED current ripple, is presented. A prototype of the proposed LED driver has been implemented with an on-chip controller IC fabricated in a 0.35-μm CMOS process and its functionality and performance have been verified experimentally. It demonstrates a power factor of 0.94 and a peak power efficiency of 85.4% with an LED current ripple of 6.5%, while delivering 15 W to the LEDs.

An AC-DC LED Driver with a Two Parallel Inverted Buck Topology for Reducing the Light Flicker in Lighting Applications to Low-Risk Levels

Dual-output gate drivers for switched-mode power supplies require low-side reference signals to be shifted to the switch-node potential. With the move to ultra-fast switching GaN converters, there is a commercial need to achieve switch-node slew-rates exceeding 100 V/ns, however, reported level shifters do not simultaneously achieve the required power supply slew immunities and sub-ns propagation delays. This paper presents a novel design technique to achieve the first floating voltage level shifters that deliver slew-rate immunities above 100 V/ns and sub-ns delay in the same circuit. Step-by-step transistor-level design methods are presented. This technique is applied to improve a reported level shifter, and experimentally validated by fabricating this level shifter in a 180 nm high-voltage CMOS process. The final level shifter has zero static power consumption, and is shown to have a sub-nanosecond delay across the whole operating range, a 200 V/ns positive power-rail slew tolerance, and infinite negative slew tolerance. The measured propagation delay decreases from 722 ps with the floating ground at −1.5 V, to 532 ps for a floating ground of 45 V, and the power consumption is 30.3 pJ per transition at 45 V. It has a figure of merit of 0.06 ns/( $\mu $ mV), which is an $1.7\times $ improvement on the next best reported level shifter for this type of application.

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A New Design Technique for Sub-Nanosecond Delay and 200 V/ns Power Supply Slew-Tolerant Floating Voltage Level Shifters for GaN SMPS

Gallium nitride (GaN) transistors enable efficient and compact high-voltage power converters. In the state-of-the-art enhancement mode GaN-on-Si technology, a 650-V power transistor is formed as a lateral structure enabling monolithic integration with a driver and analog control circuits on one die. Offline power converters show a trend toward a higher level of integration, shifting from monolithic silicon (CMOS) to various integration levels in GaN technology. In this article, a monolithic, self-biased GaN buck converter for offline operation is presented, supporting both 110- and 230-V ac line voltage and providing up to 29-W output power. The converter shows a superior efficiency of 95.6 % and a very high level of integration in a 650-V p-GaN gate e-mode GaN-on-Si technology. Analog design techniques for GaN integration, such as an auto-zero comparator and a high-voltage supply regulator, are discussed. Experimental results of stand-alone circuit blocks and the full buck converter confirm the viability of monolithic GaN integration as a path toward compact and efficient offline power converters.

A Monolithic GaN-IC With Integrated Control Loop for 400-V Offline Buck Operation Achieving 95.6% Peak Efficiency

This paper presents a novel switching-converter-free ac–dc light-emitting diode (LED) driver with low-frequency-flicker reduction for general lighting applications. The proposed driving solution can minimize the system size as it enables the monolithic integration of the controller and power transistors while both the bulky off-chip electrolytic capacitors and magnetics are eliminated. Moreover, the driver can effectively reduce the harmful optical flicker at the double-line-frequency by employing a novel quasi-constant power control scheme while maintaining high efficiency and a good power factor (PF). The proposed driver is implemented with a single controller integrated circuit chip, which includes the controller and high-voltage power transistors, and the off-chip diode bridge and valley-fill circuit. The chip is fabricated with a 0.35- $\mu \text{m}$ 120-V high-voltage CMOS process and occupies 1.85 mm2. The driver can provide up to 7.8-W power to the LED and achieves 87.6% peak efficiency and an over 0.925 PF with only 17.3% flicker from a 110-Vac 60-Hz input.

An AC Input Switching-Converter-Free LED Driver With Low-Frequency-Flicker Reduction

With the advent of reliable, high brightness and high efficacy LEDs, the lighting industry is expected to see a significant growth in the near future. However, for LEDs to completely replace the traditional incandescent and CFL bulbs, the power converters within the LED drivers need to be miniaturized. Superior figure of merit (Rds,ONxQg) of Gallium Nitride (GaN) FETs over Silicon FETs [1] can enable both high efficiency and high frequency operation, thereby making power converters smaller, more efficient and reliable. By using integrated controllers and drivers, the number of components on the driver PCB can be reduced, further miniaturizing the driver. This work focuses on demonstrating a small form factor, high efficiency offline LED driver using GaN FETs with an integrated gate driver and controller circuit implemented on a 0.35μm CMOS process with 3.3V/15V voltage handling capability.

D. Freeman

Papers

90.6% efficient 11MHz 22W LED driver using GaN FETs and burst-mode controller with 0.96 power factor