Soft-switching Flyback Converter Research Articles

A New Soft-switched Flyback Converter with a Minimum Number of Elements and High Efficiency

Background: This paper proposes a new soft-switching flyback converter with a simple structure and high efficiency. The proposed converter has zero current switching conditions for the turning-on distance and zero voltage switching conditions for the turning-off distance of the switch. Objective: With a minimum number of elements, a soft switching condition is created for all semiconductor devices, and high efficiency is obtained. Methods: To create the ZCS condition, an inductor is used, and when the switch is turned on, the current due to the existence of this inductor increases slowly. But when the switch is turned off, this inductor has an energy that suddenly discharge on the switch, which is then controlled by a capacitor and discharged in capacitor. Then when the energy is discharge in capacitor, this capacitor is connected to the switch, which increases the voltage of the switch slowly and ZVS condition is stablished. Also the energy of leakage inductance in this state is discharged in that same capacitor which eliminates destructive effect of this inductor. Results: A prototype of the proposed converter is implemented and tested in 60 W power. The experimental results verified theoretical analysis and shown that soft switching condition is established. Also 92% efficiency at full load is obtained, which shows the efficiency has increased. The current of the diodes in experimental results shows that when the diodes are turned off, ZCS condition is created, therefore reverse recovery problem of the diodes does not exist. Conclusion: Therefore, the proposed converter has high efficiency and simple structure, which is suitable to convert AC voltage to DC voltage for the devices power supply.

A soft-switched flyback converter with leakage recovery snubber for class 2 LED driver

This work presents a soft-switching flyback converter with active leakage recovery snubber suitable for use in high-performance class 2 LED lamp drivers. The proposed converter enjoys the features of simple circuit structure, improved switching performance, high efficiency and high power density. Transformer leakage energy of the flyback converter is recovered using an active auxiliary circuit, which also helps in soft-switching transition of the switches and power diodes. Switching turn-on and turn-off of its main switch occurs under ZVZCS and ZVS conditions respectively, whereas ZCS turn-on and ZVZCS turn-off of the auxiliary switch are also achieved in this converter. The detailed steady-state operating principle with mathematical equations, design guidelines and loss analysis are presented in this work. Finally, the converter feasibility is thoroughly tested through laboratory experimentation on a hardware prototype. The experimental results have successfully validated the theoretical analysis and real-time behavior of the converter.

Family of Soft-Switching Single-Switch PWM Converters with Lossless Passive Snubber

To increase the power conversion density, decrease switching losses and electromagnetic interference (EMI), and provide safe operating area for a switch, applying snubber circuits which provide soft-switching conditions is inevitable. Among different types of snubber circuits, passive snubbers, due to their simplicity and robustness, are preferred. These snubber circuits can obtain soft-switching conditions without any additional switch. Thus, gate drive and control circuits remain simple. In this paper, a simple lossless passive snubber circuit which can be applied on isolated and nonisolated converters is introduced. The proposed snubber circuit provides zero-current-switching and zero-voltage-switching conditions at turn-on and turnoff instants, respectively. The proposed snubber is applied on a boost converter and analyzed. Also, in order to prove the effectiveness of the proposed snubber circuit from the converter efficiency and EMI viewpoints, a 200-W prototype boost converter is implemented, and experimental results are presented. Also, the simulation results of a soft-switched flyback converter with the proposed snubber cell are presented.

소프트 스위칭 기법을 이용한 1단 PFC-flyback 컨버터

The flyback converter has been applied widely in isolated DC/DC power converters because this converters employ a single MOSFET switch. The leakage inductance should be minimized for high efficiency of flyback converter. but in reality, it is very difficult. Namely, The Snubber circuit is essential to recover the leakage inductance stored energy when the switch is turn off. Flyback Converter typically operates in DCM mode and when switch is turn off in hard switching, this hard switching action results in a high power losses and switching stresses. In order to overcome these problems, a novel soft switching flyback converter using resonant snubber circuit is proposed in this paper. The resonant snubber circuit is composed of the transformer leakage inductance and a capacitor. To verify and confirm the proposed resonant snubber circuit, PSIM simulation and hardware prototype are implemented. Simulation and Experimental results indicate that the proposed resonant snubber circuit is effective.

An improved two-switch flyback converter with regenerative clamping

A novel soft-switching two-switch flyback converter is proposed in this article. This converter is composed of two active power switches, a flyback transformer and two passive regenerative clamping circuits. The proposed converter has the advantages of a low-cost circuit configuration, a simple control scheme, high efficiency, and a wide operating range. The circuit topology, analysis, design considerations and experimental results of the new flyback converter are presented.

A Single-Stage Soft-Switching Flyback Converter for Power-Factor-Correction Applications

This letter presents a single-stage soft-switching Flyback converter for power-factor-correction (PFC) applications. High power factor and high conversion efficiency can be achieved by a simple single-stage circuit with soft-switching features. The operation principles and design criteria for the studied PFC converter are analyzed and discussed. A laboratory prototype is also built and tested. Finally, the experimental waveforms for this prototype circuit are shown to verify the feasibility of the proposed scheme.

Multi-mode controller IC for soft-switched flyback converter with high efficiency over the entire load range

This paper presents a multi-mode control scheme for a soft-switched flyback converter to achieve high efficiency and excellent load regulation over the entire load range. At heavy load, critical conduction mode with valley switching (CCMVS) is employed to realize soft switching so as to reduce turn-on loss of power switch as well as conducted electromagnetic interference (EMI). At light load, the converter operates in discontinuous conduction mode (DCM) with valley switching and adaptive off-time control (AOT) to limit the switching frequency range and maintain load regulation. At extremely light load or in standby mode, burst mode operation is adopted to provide low power consumption through reducing both switching frequency and static power dissipation of the controller. The multi-mode control is implemented by an oscillator whose pulse duration is adjusted by output feedback. An accurate valley switching control circuit guarantees the minimum turn-on voltage drop of power switch. The prototype of the controller IC was fabricated in a 1.5-μm BiCMOS process and applied to a 310 V/20 V, 90 W flyback DC/DC converter circuitry. Experimental results showed that all expected functions were realized successfully. The flyback converter achieved a high efficiency of over 80% from full load down to 2.5 W, with the maximum reaching 88.8%, while the total power consumption in standby mode was about 300 mW.

Adaptive off-time control for variable-frequency, soft-switched flyback converter at light loads

The soft switching of a flyback converter can be achieved by operating the circuit in the critical conduction mode. However, the critical-mode operation at light loads cannot be maintained due to a very high switching frequency and the loss of the output voltage regulation. A control which regulates the output down to the zero load and maintains soft switching at light loads is proposed. The proposed control scheme was implemented in the 380 V/19 V, 65 W flyback DC/DC converter.