Power factor correction using merged flyback-forward converters

A single stage isolated PFC converter is obtained merging flyback and forward topologies. Thus, the flyback section allows power transfer while the line rectified voltage is not high enough to enable the forward stage operation. By this way, optimal correction is feasible. Also, this approach allows sharing of the transformer and the power transistor     

Power-factor correction using Cuk converters indiscontinuous-capacitor-voltage mode operation

The characteristics of Cuk power converters in discontinuous-capacitor-voltage mode operation are studied. A Cuk power converter in this mode of operation is an inherent power-factor corrector and features soft turn-off switching. Simulation and experimental results are reported to verify the theoretical analysis. In addition, the advantages and disadvantages of power factor correction circuits using Cuk power converters in discontinuous-inductor-current mode operation and Cuk power converters in discontinuous-capacitor-voltage mode operation are discussed     

Quasi-optical measurement of carcinotron phase noise at 350 GHz

Phase noise of a single carcinotron operating at 350 GHz, at offset frequencies in the range 10⁵-10⁷ Hz, from the carrier has been measured. A quasi-optical analogue of the delay line frequency discriminator method was used, demonstrating a simple method capable of measuring phase noise in the (sub)mm region. The results obtained are of practical use in the design of phase locked systems, in the wavelength region used     

Closed-loop binary phase correction of an LCTV using a pointdiffraction interferometer

A point diffraction interferometer was used to examine the phase nonuniformity of a liquid-crystal television (LCTV). The resulting interference pattern was then binarized and written back onto the LCTV for phase compensation. A binary phase joint transform correlation experiment was performed using the binary phase corrected LCTV to demonstrate the applicability of this technique     

相位差法用于拼接镜piston相位检测的实验研究

为了在实验的基础上研究相位差法在拼接镜piston波前探测中的性能,本文在球面镜上放置两个合成口径分别为200 mm和50 mm的拼接形光阑,进行了模拟拼接实验。依据相位差法的基本原理,通过优化计算可得piston误差分别小于25 nm和1 nm,以此验证了相位差法在拼接镜piston波前探测中的能力,并为将相位差法用于实际拼接镜系统波前探测打下了一定的基础。     

用双平面反射镜构成位错产生光学漩涡

我们给出了一种简单的产生光学漩涡的方法,当一束高斯光束对称地照射在两块略微相互倾斜的平面反射镜上时,实验显示在远场形成了涡旋光束。我们给出了产生该涡旋光的机理和产生涡旋的条件,并且进行了数值模拟。该方法简单易行,不受波长限制,转换效率高。     

相位共轭镜和相位共轭腔

本文使用矩阵光学方法,分析了下述论题:1.相位共轭镜的两类变换矩阵及其物理意义;2.相位共轭腔与常规稳定腔的比较;3.相位共轭腔的模参数;4.有频移的相位共轭腔;5.相位共轭腔的稳定性,并提出了一些问题加以讨论。     

Methods of calibration and correction of analog-to-digital converters (review)

In this review, systems for calibration and correction of the main classes of analog-to-digital converters, notably, parallel, pipe-line, successive approximation register, and based on delta-sigma modulators are considered. Among other problems, the questions of the circuit design with redundancy and self-calibration are analyzed. Technical characteristics of modern converters in general are presented and promising development directions are singled out.     

Comparison between current-driven resonant converters used forsingle-stage isolated power-factor correction

The aim of this paper is to analyze the power factor correction capability of isolated current-source resonant converter topologies with two energy storage elements, which takes advantage of the leakage inductance of the HF transformer. These converter topologies are studied and modeled. Computer simulation results are also given. Thanks to its interesting characteristics, a converter topology is chosen and a converter prototype is built in order to validate theoretical study. Using this converter topology, a very good power factor is achieved     

Flyboost power factor correction cell and a new family of single-stage AC/DC converters

A novel power factor correction (PFC) cell, called flyboost, is presented. The proposed PFC cell combines power conversion characteristics of conventional flyback and boost converters. Based on the flyboost PFC cell, a new family of single-stage (S/sup 2/) ac/dc converters can be derived. Prominent features of newly derived S/sup 2/ converters include: three power conversions, i.e., boost, flyback, and another isolated dc/dc power conversions are simultaneously realized that typically uses only one power switch and one simple controller; part of the power delivered to the load is processed only once; bulk capacitor voltage can be clamped to the desired level; and capable of operating under continuous current mode. Experimental results on example converters verify that while still achieving high power factor and tight output regulation, the flyboost PFC cell substantially improve the efficiency of the converter.     

Optical phase difference measurement and correction using AlGaAs integrated guided-wave components

A Y-junction interferometer phase measurement technique that is independent of the power or power ratio in the input arms has been developed. The technique is intended for use in the basic module of a proposed integrated optical system for use at GaAs wavelengths that produces a flat-phase output wavefront. A proof-of-concept AlGaAs guided-wave Mach-Zehnder interferometer was used to demonstrate measurement and correction of a phase difference between the arms using this phase measurement technique. Results have been obtained for the cases of successive steps in the phase difference between the interferometer arms, of random phase differences, and of a power imbalance of up to 30% between the arms.<>     

A full-wave rectifier using a current conveyor and current mirrors

The realization of a full-wave rectifier using a current conveyor and current mirrors is presented. The proposed rectifier is composed of a voltage-to-current converter, a current mode full-wave rectifier, and a current-to-voltage converter. A voltage input signal is changed into a current signal by the voltage-to-current converter. The current mode full-wave rectifier rectifies this current signal resulting in the current full-wave output signal that is converted into a voltage full-wave output signal by one grounded-resistor. The theory of operation is described. The simulation and experiment results are used to verify the theoretical prediction. Simulated results show that the proposed rectifier yields the minimum voltage rectification to 94µV. Experimental results demonstrate the performance of the proposed rectifier for 50mV_peak signal rectification.     

Single phase power factor correction: a survey

New recommendations and future standards have increased the interest in power factor correction circuits. There are multiple solutions in which line current is sinusoidal. In addition, a great number of circuits have been proposed with nonsinusoidal line current. In this paper, a review of the most interesting solutions for single phase and low power applications is carried out. They are classified attending to the line current waveform, energy processing, number of switches, control loops, etc. The major advantages and disadvantages are highlighted and the field of application is found.     

Single-switch parallel power factor correction AC-DC converters with inherent load current feedback

Single-stage power factor correction (PFC) ac-dc converters usually suffer from high bulk capacitor voltage stress and extra switch current stress. Bulk capacitor voltage feedback with a coupled-winding structure can dramatically alleviate the stresses. However, this type of feedback is indirect because the feedback only occurs after the bulk capacitor voltage increases. This paper presents a family of single-switch single-stage parallel PFC ac-dc converters with inherent load current feedback. Unlike the bulk capacitor voltage feedback, which utilizes the decreased duty ratio and the increased bulk capacitor voltage to reduce the input power at light load, the load current feedback can reduce the input power automatically at light load while maintaining an unchanged duty ratio. The proposed converters combine the advantages of simple topology, low bulk capacitor voltage, and no extra current stress across the switch. The concept is verified using an ac-dc converter with universal-line input and 5-V, 60-W output power. The input current harmonics meet IEC1000-3-2 Class D requirements.     

Constructing the phase converters consisting of arbitrary number oftranslucent surfaces

An effective analytical method of synthesis of an artificial anisotropic structure has been developed. At a design frequency, it ensures perfect match and a phase shift given. The structure may be formed by arbitrary number of inductive and capacitive grids. The method has been applied to constructing circular polarizers and twist polarizers. The geometrical parameters of the polarizers were found in the explicit form. Analytical criteria for an estimate of the bandwidth of the devices have been derived. Performance of the polarizers over a frequency band was studied. A circular polarizer has been proposed which consists of both a cascade of two inductive grids and a cascade of two capacitive grids. The polarizer can be used when very high axial ratio is needed. It ensures more than 10% bandwidth for 0.99 axial ratio. Measurements have been presented that prove adequacy of the mathematical model for real inductive and capacitive screens     

自泵浦位相共轭镜耦合到环形染料激光器的特性

本文叙述在电场作用下,自泵浦位相共轭镜耦合到环形染料激光器时的波长自扫描特性和共轭反射率随波长变化的特性。实验表明,当波长朝短波方向自扫描时,沿c轴施加的电场能有效地控制波长扫描速率和方向;共轭反射率随波长自扫描朝长波方向增加。     

Flyback DC-DC converters stabilized by using ripple

An instructive block diagram for development of the flyback DC-DC converters is given. Two derived examples, one from 5 V to 2000 V and another from 3 V to 7.5 V are presented. The converters use output ripple for direct determination of operating frequency which compensates all instabilities in the circuit except a change of a reference voltage. This approach is suitable for development of the supply for detectors and electronics in radiation protection instrumentation and other applications where load and source voltages are variable.