A gallium nitride (GaN) field effect transistor can provide superior performance over a Si- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> due to its low <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance and low junction capacitances. However, a GaN-based converter exhibits higher dead time loss during reverse conduction. Thus, to improve the efficiency, dead time optimization is required. This article proposes simple models for dead time optimization in a GaN-based buck converter under different load conditions. The proposed models are analytical in nature compared to the conventional models available for Si-based converters. A buck converter prototype is designed using a 100 V GaN device (GS61008P from GaN Systems) and the proposed analytical model-based dead time optimization techniques are validated experimentally. The proposed modeling techniques can be extended for other GaN-based dc–dc converters. 

Dead Time Optimization in a GaN-Based Buck Converter

The active clamp flyback (ACF) converter utilising gallium nitride (GaN) devices with high-switching frequency and high efficiency is impressive in system miniaturisation for AC–DC adapters. Owing to poor reverse conduction of GaN devices, the improper dead time between two switches can cause large power consumption in high frequency. This study proposes a dynamic dead time optimisation technique for GaNs ideal zero-voltage switching (ZVS) to address the issue. It adjusts the clamp switch on time to avoid large reverse conduction voltage stress on the main switch in different loads conditions. In addition, a new control scheme for clamp switch is introduced for enhancing efficiency in light to medium load. These techniques are experimentally verified on a 45 W (20 V/2.25 A) prototype of an ACF converter with a field-programmable gate array. The controller enables the system to operate at 1 MHz and dynamically modulates the dead-time under universal input and full load. With the light load ZVS control scheme, the system can achieve a maximum efficiency of 94.12 and 80.23% in the worst case. The prototyped converter can achieve power density (exclude case and controller) of 18 W/in
 3
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https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2020.0464

Digitally controlled GaN-based MHz active clamp flyback converter with dynamic dead time optimisation for AC–DC adapter

High switching frequency, high efficiency and high power density are critical in portable AC-DC adapters. The active clamp flyback (ACF) converter can achieve zero voltage switching (ZVS) and recycle leakage energy of transformer to maintain high efficiency in high frequency operation. This paper presents a digital PWM control method of secondary resonant ACF converter. A proposed adaptive period modulation is used to choose the optimum period under different conditions which can contribute to efficiency improvement. Meanwhile, a digital PI compensator is adopted to regulate the output voltage. A 65W prototype of ACF converter with digital microcontroller is implemented. With proposed digital control method, the prototype operates with 500-900 kHz frequency range and realizes maximum efficiency of 91.2% which is 2% better than control method at fixed frequency.

Digital PWM Control Active Clamp Flyback Converter with Adaptive Period Modulation

Portable electronics devices (PEDs) are one of the most promising sources for information-exchange in this Information Age. Their performance is becoming very much sensitive to power consumption. Rechargeable batteries are the prime source of energy for PEDs and a key to their desired performance stability. With the remarkable progress in battery charging technologies and USB standards, multifunctional PEDs have constantly been able to meet the requests of our daily life conveniently. But these PEDs charge their rechargeable batteries at different voltage and power levels thus each requires a different kind of a battery charger. In this paper concept of universal USB charger has been explored i.e a single USB charger for all the PEDs. To realize this universal USB charger first, a comprehensive overview of USB standards and specifications has been outlined. Next GaN-based active clamp flyback converter has been discussed along with some possible architecture for single-port and multi-port universal chargers.

Concept of Universal USB Charger

Direct AC LED drivers have advantages over conventional LED drivers in size and cost because of no need for bulky and expensive inductive components. However, none of conventional direct AC LED drivers researched so far support triode AC switch (TRIAC) compatibility at low percent flicker. This paper achieves both TRIAC dimmer compatibility and low percent flicker by correlating a phase-cut ratio to luminance and using always-on multi-arrays, respectively, without the need of a dedicated IC. The proposed LED driver consists of a phase-cut/DC converter, a switch controller, a current regulator, and three LED arrays. The experimental results based on commercial 15W LEDs show that the percent flicker of 18.6% @ 120 Hz is achieved with an efficiency of 84.7% and a power factor of 97.3% @ 120 V.

/pdf/a-low-flicker-triac-dimmable-direct-ac-led-driver-for-always-3f4zki6ykx.pdf

A Low Flicker TRIAC Dimmable Direct AC LED Driver for Always-on LED Arrays

This paper presents a complete digital pulse-width modulation (PWM) controller for MHz active clamp flyback (ACF) converter with gallium nitride (GaN) devices. A proposed model based on state-space averaging is used to predict the dynamic behavior of ACF converter. With the model, a digital PID compensator is introduced to achieve high-speed dynamic response. Meanwhile, a high-resolution digital pulse-width modulator is employed to meet the requirement of tight output voltage regulation. The implementation techniques are experimentally verified on a 45 W (20 V/2.25 A) prototype of ACF converter based on FPGA. The proposed digital control scheme enables the system operates at the switching frequency of 1 MHz and obtains less than 200 us recovery time in case of load transient (2-0.2 A). The AC-DC adapter's prototype can achieve the maximum efficiency of 91.34% and power density (exclude case) of 18 W/in3.

A Digital PWM Controller of MHz Active Clamp Flyback with GaN Devices for AC-DC Adapter

The invention discloses a dynamic compensation control circuit for a synchronous rectification power converter. The dynamic compensation control circuit comprises a zero-crossing comparison module, a dynamic compensation module, and a synchronous rectification logic control module. The control circuit determines whether an advanced switch-on case exists by detecting the lower overshoot of a switching node, adjusts the input offset voltage of the zero-crossing comparison module according to a detection result so as to achieve accurate synchronous rectification control. The dynamic compensation control circuit, while ensuring control and detection functions, improves the accuracy of a synchronous rectifier tube gate control signal, and is simple in structure, easy realize, low in cost and high in precision. Further, the dynamic compensation control circuit can compensate the input offset voltage of the zero-crossing comparison module and the loop delay introduced by the synchronous rectification control logic and the comparison module, and further improve the accuracy of the synchronous rectifier tube control signal, thereby reducing the on-state loss of the output end and increasing the efficiency of the power converter.

Dynamic compensation control circuit for synchronous rectification power converter

The invention discloses a digital control device of an active clamping flyback AC-DC converter based on a gallium nitride device, replaces a traditional silicon-based device with a gallium nitride device with a higher quality factor, adds a clamping tube and a clamping capacitor with controllable power to a flyback circuit, and utilizes an active clamping circuit for replacing a passive absorptioncircuit. The digital control device samples the information such as the peak current, an auxiliary winding voltage, an output feedback voltage and the like, digitally modulates output voltage changeand the dead time between a main power tube and a clamping tube, clamps the maximum reverse current of a primary side current, maintains the main power tube to be just in zero-voltage conduction, andovercomes the defect of high reverse conduction loss of a gallium nitride device. A light load control scheme is optimized, so zero-voltage conduction of the two power tubes can be realized under anycondition. Due to soft switching and light load efficiency optimization technologies under all working conditions, the device can work at the relatively high working frequency, and efficiency and power density can be greatly improved when the device is applied to an adapter.

Digital control device of active clamping flyback AC-DC converter based on gallium nitride device

A dimmable and power-compensated AC direct LED driver with high efficiency for lighting applications is presented. A Source-Coupled Pair (SCP) is adopted to realize the soft self-commutating. There is no additional sensing or control circuitry, which lower the system power dissipation. A pulse-width modulation (PWM) dimming technique is applied in regulating the LED's brightness. Furthermore, the driver includes a Power Compensation module which enables the output power of LEDs approximately constant under various line voltage. The LED driver IC is designed and implemented in CSMC's 700 V 1 um BCD process. The post-layout simulation results show that under 220 V|rms AC voltage, the driver has a high efficiency of 90.28% and realizes dimming with a 90% duty ratio, 10 KHz dimming signal. The output power compensated only changes 4% under a 10% variation in input voltage.

Donglie Gu

Papers

A Digital PWM Controller of MHz Active Clamp Flyback with GaN Devices for AC-DC Adapter

Digitally controlled GaN-based MHz active clamp flyback converter with dynamic dead time optimisation for AC–DC adapter

Dynamic compensation control circuit for synchronous rectification power converter

Digital control device of active clamping flyback AC-DC converter based on gallium nitride device

A dimmable and power-compensated AC direct LED driver with high efficiency