AC-DC Adapter Research Articles

A High-Efficiency QR Flyback DC–DC Converter with Reduced Switch Voltage Stress Realized by Applying a Self-Driven Active Snubber (SDAS)

In this paper, a QR flyback converter using a self-driven active snubber (SDAS) was proposed to solve the problem of voltage surge in the switch of QR flyback converters. In the proposed converter, the SDAS consisting of a clamping capacitor and an active switch can be configured in parallel with the main switch or transformer to reduce the voltage surge in the switch. To confirm the steady-state characteristics of the QR flyback converter to which the proposed SDAS is applied, equivalent circuits for each state were constructed, and the equations and characteristics for each state were determined. A 60 W class small AC–DC adapter was constructed to confirm the effectiveness of the proposed converter and the control circuit method, and the experimental results were analyzed. The size of the experimental AC–DC adapter was 74×29×23 mm, and it had a high power density of 20 W/in3 or more. The experimental circuit was limited to the high power conversion efficiency of up to 91.56%, and the maximum voltage surge in the switch was approximately 450 V. One of the reasons for such high efficiency is the SDAS circuit, which sufficiently reduces the voltage surge of the QR flyback switch, compared with the RCD clamp circuit, and does not consume power in principle.

A Modulation Method for Capacitance Reduction in Active-Clamp Flyback-Based AC–DC Adapters

Recent developments of fast-charging power delivery protocols are driving ac–dc adapters to 100-W power ranges. Conventional solutions in this power range employing a two-stage topology and a big twice-line frequency buffer capacitor are generally costly and bulky. This article presents a patent-pending modulation method for an active-clamp flyback converter, allowing for a single-stage adapter design with reduced capacitance requirements and higher efficiency. This is achieved by exploiting the inherent energy storage capability of the clamping capacitor while turning it into an active power buffer. No hardware modifications are needed, while all salient features of active-clamp flyback converter, i.e., soft switching and leakage recycling, are retained. Operating principles and detailed controller design are discussed, and a 100-W laboratory prototype is built. The prototype achieves 94% peak efficiency and up to 92% size reduction of the buffer capacitor. The experimental evaluation shows that the new single-stage solution enabled by the proposed modulation method is superior to the conventional two-stage and single-stage solutions in terms of cost, conversion efficiency, and power density.

A deep learning-driven low-power, accurate, and portable platform for rapid detection of COVID-19 using reverse-transcription loop-mediated isothermal amplification

This paper presents a deep learning-driven portable, accurate, low-cost, and easy-to-use device to perform Reverse-Transcription Loop-Mediated Isothermal Amplification (RT-LAMP) to facilitate rapid detection of COVID-19. The 3D-printed device—powered using only a 5 Volt AC-DC adapter—can perform 16 simultaneous RT-LAMP reactions and can be used multiple times. Moreover, the experimental protocol is devised to obviate the need for separate, expensive equipment for RNA extraction in addition to eliminating sample evaporation. The entire process from sample preparation to the qualitative assessment of the LAMP amplification takes only 45 min (10 min for pre-heating and 35 min for RT-LAMP reactions). The completion of the amplification reaction yields a fuchsia color for the negative samples and either a yellow or orange color for the positive samples, based on a pH indicator dye. The device is coupled with a novel deep learning system that automatically analyzes the amplification results and pays attention to the pH indicator dye to screen the COVID-19 subjects. The proposed device has been rigorously tested on 250 RT-LAMP clinical samples, where it achieved an overall specificity and sensitivity of 0.9666 and 0.9722, respectively with a recall of 0.9892 for Ct < 30. Also, the proposed system can be widely used as an accurate, sensitive, rapid, and portable tool to detect COVID–19 in settings where access to a lab is difficult, or the results are urgently required.

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

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/in3.

Development of a vacuum cleaner robot

Modern households are becoming more automated thereby delivering convenience and reducing time spent on house chores. While vacuum cleaners have made home cleaning easier, they are largely noisy and bulky for everyday use. It is therefore sine qua non to improve the technology of vacuum cleaning to reduce these deficiencies. Here, we report the development of a compact and efficient vacuum cleaner robot for potential office and home use. The developed robot is disk-shaped, equipped with vacuuming and cleaning technology and controlled by Arduino mega microcontroller. It sucks dirt via a retractable dustbin on top of which a cooling fan is mounted, and two sweepers each driven by a 3 V DC motor. The robot navigates via two motor shield controlled rear wheels and a front caster wheel which also governs its turning. Four ultrasonic sensors, placed at 90° apart, detect obstacles and subsequently help the robot navigate. The robot is powered by 3 batteries (28.8 V DC), rechargeable via an embedded AC-DC adapter. It is 12 cm wide and 9 cm tall making it easy for maneuvering its environment. Because of the light weight battery, cardboard based dustbin and small blower used, its weight is about 1.5 kg. The total current consumed is ∼1102 mA. When fully charged, a 2200 mAh-capacity battery works continuously for two hours and cleans floor efficiently. With this capability, the device will be deployed for office and home use thereby making cleaning a fully autonomous duty.