Flyback Power Factor Correction Converter Research Articles

An Adaptive Off-Time Controlled DCM Flyback PFC Converter With Unity Power Factor and High Efficiency

Constant duty cycle controlled discontinuous conduction mode (DCM) flyback power factor correction (PFC) converter has the advantage of high power factor (PF) and the disadvantage of low efficiency. While, constant on-time (COT) controlled critical conduction mode (CRM) flyback PFC converter has the exact opposite features, besides its switching frequency varies in a line cycle, and the variation range is very large, which complicates the electromagnetic interference (EMI) design. In order to obtain both benefits of these two control methods, an adaptive off-time (AOT) control technique for DCM flyback PFC converter is proposed in this paper. By utilizing the output voltage and the amplitude of line voltage to adjust the off-time of the main switch, the magnetizing current of transformer exactly operates in CRM when the rectified input voltage gets the peak. Thus, the root-mean-square (RMS) current of the main switch and the diode, as well as the conduction loss can be effectively reduced, and high efficiency can be obtained. The proposed control technique also can achieve theoretical unity PF over universal input voltage range of 90~264VAC. Moreover, its variation range of switching frequency is greatly reduced compared to that of COT control. A 60W prototype has been fabricated and tested in the laboratory and experimental results are presented to verify the effectiveness of the proposed method.

Mitigation of CM conducted EMI in flyback converter using balancing capacitors

The offline Switched Mode Power Supply (SMPS) draw non-sinusoidal line current from the utility power supply, thereby introducing unwanted harmonics and also generate significant electromagnetic interference (EMI). Power factor correction (PFC) converters can be used to improve the power factor. But they also generate EMI in both Differential Mode (DM) and Common Mode (CM). In this paper, the EMI generated by the flyback PFC converter is addressed. A lumped circuit model for CM conducted EMI generated in a flyback converter, including the HF transformer's parasitics and the components, is considered. The parasitics of the HF transformer are calculated and measured experimentally. Using them, the resonant frequencies of the flyback converter are calculated for validation. A technique for determining the required balancing capacitor to mitigate CM conducted EMI is presented. A novel technique by splitting this balancing capacitor with their mid-point grounded for further reduction of this EMI is presented. This technique can eliminate the C y capacitors of the EMI line filter connected between line/neutral to the ground. Hence for the same amount of CM conducted EMI mitigation, the size and the cost of EMI line filters are reduced. Theoretical analysis, simulation results, and experimental verifications are presented.

Feed‐forward control scheme to improve light‐load power factor for single‐stage flyback PFC converters

In this Letter, the author proposes a new feed-forward controller for single-stage flyback power factor correction (PFC) converters. By compensating the phase-lead effect caused by input capacitor current, the proposed feed-forward control duty improves the displacement factor as well as the distortion factor, and so the flyback PFC converter has high power quality. By means of the synchronous rectification circuit, the flyback PFC converter can operate in reverse when the negative current is required. To confirm the theoretical analysis and validity of the proposed control scheme, the author demonstrated the proposed control algorithm with 80 W flyback PFC converter prototype.

Adaptive on Time Controlled Double-Line- Frequency Ripple Suppressor With Fast Dynamic Response and High Efficiency

Due to the input power and output power do not match in real time, single-stage power factor correction converters have large double-line-frequency ripple at the output voltage. The double-line-frequency ripple voltage will cause some electronic devices to work abnormally, and limit the control loop bandwidth of power factor correction converter. In order to reduce the output double-line-frequency ripple voltage, a single-stage Flyback power factor correction converter with Buck ripple suppressor is used in this paper, the Buck ripple suppressor can generate same magnitude but 180° phase shifted voltage as Flyback power factor correction converter output voltage ripple. Adaptive on-time control is adopted in the Buck ripple suppressor benefiting with its wider bandwidth and fast dynamic response. The switching frequency range and stability of Buck ripple suppressor under constant on-time control and adaptive on-time control are discussed. By establishing the input-output audio susceptibility model, the output double-line-frequency ripple suppression performance is analyzed. Buck ripple suppressor using adaptive on-time control can suppress double-line-frequency ripple voltage effectively with the fast dynamic response and high efficiency. Simulation and experimental results are given to verify the theoretical analysis.

CM Conducted EMI mitigation in flyback PFC converter

The switched mode power supplies offer many advantages in power conversion. But they offer low power factor and generate electromagnetic interference (EMI). The low power factor can be improved by a front-end power factor correction (PFC) unit. However, they also generate EMI in both differential mode and common mode (CM). The interwinding capacitance of the transformer and parasitic capacitance between the heat sink and ground are major contributors to CM noise. The traditional method to minimize the CM noise by using a line filter consists of CM choke and Y capacitor. But, CM noise causes leakage current to flow to the ground through the Y capacitor. This leakage current has to be restricted as per the standards for commercially used equipment and medical instruments. The technique proposed here reduces the values of Y capacitor thereby reducing the leakage current. This can be reduced by minimizing the predominant parasitic capacitances of the HF transformer used in the PFC converter. This paper presents a technique for reducing these parasitic capacitances by incorporating an additional parasitic capacitance noise cancellation winding (PCW). A flyback transformer winding capacitance model depicting the parasitic capacitances is considered, and a novel method to determine this parasitic capacitance is presented. Using this model, the CM Conducted EMI in a flyback PFC is determined by simulation and experimentation. These simulation and experimentation results are used to design an EMI line filter to reduce the Conducted CM noise to complaint levels. The value of Y capacitor now is reduced due to the addition of PCW thereby reducing the size and cost of the filter. This technique has been validated experimentally on a 30-W power factor correction flyback converter working in critical conduction mode.

Conducted Emi Model for Flyback PFC Converter

Power Factor Correction (PFC) units are used at the front end of Switched Mode Power Supply (SMPS) to improve the input power factor. However, they generate Electromagnetic Interference (EMI) which needs to be mitigated to compliant levels prescribed by International Standards. The Electromagnetic Compatibility (EMC) standards have set regulations which require expensive instruments and environment for their measurement. Hence there is a need for predicting Conducted EMI by simulation before the product is tested for full compliance to reduce the complexity of the circuit design and cost. To estimate the Conducted EMI, it is important to identify the main noise sources and their conduction paths. This can be achieved by simulating the circuit using the exact models of the transformer, capacitor, PCB trace, and the switching semiconductors. In this paper these components of PFC flyback converter are modelled using SPICE models, datasheet defined component parameters and experimental measurements. The theoretical analysis and simulation results show that the method discussed can predict and analyse the Conducted EMI. This is tested experimentally on a Flyback PFC converter working in Critical Conduction Mode. A line filter is designed and used to bring the noise to compliant levels. Simulation and Experimental results after using the line filter are also presented.

Evaluation and Suppression of a Low-Frequency Output Voltage Ripple of a Single-Stage AC–DC Converter Based on an Output Impedance Model

A single-stage ac–dc converter with high power factor (PF) usually suffers from a significant output voltage ripple at double line frequency. In order to suppress such low-frequency output voltage ripple and maintain high PF, a series compensation circuit (SCC), which generates the same magnitude but 180° phase shifted low-frequency voltage ripple, is connected in series with the output of a power factor correction (PFC) converter. In this paper, an output impedance model of the SCC is established and the relationship between the output impedance of the SCC and the low-frequency output voltage ripple of an ac–dc converter is analyzed. Based on the proposed output impedance model, a low-frequency output voltage ripple can be evaluated. To further reduce the low-frequency output voltage ripple, an output impedance shaping method with a virtual impedance is presented. The implementation of the virtual impedance of the SCC with average current mode control is studied. A flyback PFC converter with a buck SCC is implemented for the study of the suppression of the low-frequency output voltage ripple. A prototype is designed to verify the analysis results.

Analysis and design of a novel tri-state Flyback PFC converter with high load power

A novel tri-state pseudo-continuous conduction mode (PCCM) Flyback power factor correction (PFC) converter and its corresponding control strategy are proposed to improve load power. The proposed converter is built with double MOSFET formed half bridge and operated in PCCM, which provides an additional degree of control freedom for simplifying the PFC controller. The tri-state PCCM Flyback converter can improve the load power effectively compared with the conventional DCM Flyback PFC converter at constant switching frequency. Analyses and 200W prototypes of the tri-state PCCM Flyback PFC converter and conventional DCM Flyback PFC converter have been presented. The results show that the proposed tri-state PCCM Flyback PFC converter is suitable for heavier load power compared with conventional DCM Flyback PFC converter.

Single‐stage soft‐switched PWM flyback power factor correction with reduced dead angle

This study proposes a single-stage zero-voltage transition pulse width modulation (PWM) flyback power factor correction converter. The bulk capacitor voltage is controlled by using negative magnetic feedback (NMF) without any input current dead angle. In the proposed circuit, the main and auxiliary switches turn on and off under zero-voltage switching and zero-current switching conditions, respectively. The proposed auxiliary circuit provides soft switching condition while eliminating the dead angle caused by NMF winding. Thus, high-efficiency and high-power factor is achieved. Experimental results obtained from a 160 V/300 W circuit are provided to verify that the proposed structure can suppress the dead angle at zero crossing and soft switching of all switches can be achieved properly.

Variable-On-Time Control to Achieve High Input Power Factor for a CRM-Integrated Buck–Flyback PFC Converter

A variable-on-time (VOT) control scheme for a critical conduction mode (CRM) integrated buck–flyback power factor correction (PFC) converter with high power factor (PF) and low total harmonic distortion (THD) is proposed in this paper. By utilizing the input and output voltage to modulate the on-time of both buck and flyback switches, the input current harmonics can be eliminated and high PF will be obtained. The operating principles of both the conventional constant-on-time (COT) control and VOT control for the CRM buck–flyback PFC converter are analyzed. A 100-W prototype has been built and tested in the lab. The experimental results demonstrate that the THD and PF of the converter with VOT control are greatly improved compared to those with COT control.

Design of Single-Stage Flyback PFC Converter for LED Driver

A light emitting diode (LED) driver based on single-stage power factor correction (PFC) is presented in this paper. The designed LED driver using flyback topology can achieve power factor correction and constant-current drive LED in boundary conduction mode. The circuit principle is described in detail, the formulas for MOS switch-on time, switching frequency and the main impact factor of power factor are proposed. The experiment results show that the designed LED driver has high power factor, stable output and it can drive the LED with high efficiency.

A Two-Stage Output Current Ripple-Free Flyback-Buck AC-DC LED Driver with High Power Factor

A two-stage output current ripple-free flyback-buck AC-DC LED driver with high power factor is presented. The first stage is a flyback power factor correction (PFC) converter and the second stage is a ripple-free zero-voltage-switching (ZVS) synchronous buck converter. Nearly unity input power factor can be obtained by using a flyback PFC converter. In the second stage, the output capacitor is eliminated because the output current ripple is completely removed by utilizing additional circuit composed of a coupled inductor, a series inductor, and a series capacitor. Thus, the proposed circuit is suitable to long-lifespan LED driver. Moreover, by using synchronous switch, ZVS condition is satisfied in the main switches and also the reverse recovery problems in the body diode of switch are solved. Therefore, the efficiency, lifespan and the stability for LED driver is improved. A prototype LED driver for 80W is built up to verify theoretical analysis and experiment results are presented.

An Average Current Modulation Method for Single-Stage LED Drivers With High Power Factor and Zero Low-Frequency Current Ripple

Conventional single-stage light-emitting diode (LED) drivers with a high power factor (PF) contain a significant LED current ripple at twice the ac line frequency, and would require large energy storage capacitors to limit the effect on LED light. Conventional designs and novel control techniques aim to power LED loads with a dc voltage to ensure a limited low-frequency LED current ripple. This paper proposes an average current modulation method that is designed to operate in conjunction with single-stage PF correction (PFC) circuits that contain significant ac voltage ripple, while maintaining zero low-frequency current ripple. This allows the energy storage capacitance of the PFC stage to be reduced, avoiding the need for electrolytic-type capacitors and prolonging the life of the LED driver. The average current modulation circuit requires a single low-voltage MOSFET, a current sense resistor, and a simple control circuit. By requiring no additional magnetic components, the cost of the current modulation circuit is very low and has minimal impact on the efficiency of the overall LED driver. Two experimental prototypes, an 8.75-W system with a buck–boost PFC converter and a 25-W system with a flyback PFC converter, have been built to verify the capability and excellent performance of the proposed driving technique.

Peak current‐controlled CRM flyback PFC converter with square of line voltage‐compensated primary current envelope

A peak current control technique for a flyback power factor correction (PFC) converter operating in critical conduction mode (CRM) is proposed. By using the square of the line voltage to compensate the peak current envelope of the primary current, the input current distortion of the traditional peak current-controlled CRM flyback PFC converter can be eliminated, and the unity power factor and low total harmonic distortion (THD) can be obtained. The operating principles and characteristics of the proposed peak current-controlled CRM flyback PFC converter are analysed. Experimental results of a 30 W prototype show that the power factor and THD of the proposed peak current-controlled CRM flyback PFC converter are better than those of the traditional peak current-controlled CRM flyback PFC converter.

Variable-On-Time-Controlled Critical-Conduction-Mode Flyback PFC Converter

A variable on-time (VOT) control strategy for a critical conduction mode (CRM) flyback power factor correction (PFC) converter with low total harmonic distortion (THD) and high power factor (PF) is proposed in this paper. By using input voltage and the voltage across the auxiliary winding of the flyback transformer to modulate the turn-on time of the switch of the CRM flyback PFC converter, the PF and THD of the converter can be improved. The operation principles of the traditional constant on-time (COT)-controlled CRM flyback PFC converter and VOT-controlled CRM flyback PFC converter are analyzed. The experimental results show that the PF and THD of the VOT-controlled CRM flyback PFC converter are better than those of the COT-controlled CRM flyback PFC converter.

A cost‐effective PWM dimming method for LED lighting applications

AbstractThis paper presents a novel cost‐effective pulse‐width‐modulation (PWM) dimming method for light‐emitting diode (LED) lighting applications. High efficiency, high power factor, circuit simplicity, and low cost can be achieved by a Flyback power factor correction converter with the studied adaptive PWM dimming method. The operation principles and design considerations of the proposed LED dimming method are analyzed and discussed. A 45 W laboratory prototype has been built and tested to verify the feasibility of the proposed scheme. Copyright © 2013 John Wiley & Sons, Ltd.