Analysis of the noise and efficiency characteristics in a quasi-resonant converter
A quasi-resonant converter using flyback topology can realize soft switching with relatively simple circuit. However, a switching device with high withstand voltage is necessary to achieve complete zero voltage switching when the input voltage is high and it causes decrease of efficiency because a switching device with high withstand voltage has relatively high on voltage. Therefore, we analyzed efficiency and noise of a quasi-resonant converter with a low breakdown voltage and low on voltage switching device under the condition of non-zero voltage switching. As a result of the analysis, it is found that high efficiency and low noise are achieved with non-zero voltage switching.
An Adaptive Blanking Time Control Scheme for an Audible Noise-Free Quasi-Resonant Flyback Converter
The quasi-resonant (QR) control scheme is widely adopted in a Flyback converter to maximize its efficiency by reducing the switching loss. The switching frequency increases with decreasing load or increasing input voltage. In order to limit electromagnetic interference noise and improve light load efficiency, the maximum switching frequency should be limited. However, the maximum switching frequency limitation adopted in QR control will cause audible noise due to the frequency hopping phenomena at certain load and input condition, which is related to the intrinsic output characteristic of the control scheme. This paper presents a simple solution to eliminate the frequency hopping in the QR Flyback using an adaptive blanking time circuit. The proposed method changes the blanking time automatically to keep the output characteristic smooth that eliminates the audible noise in the transformer. The detailed operation principle and design considerations are presented. The experimental results from a 16 V/4 A prototype are provided to validate the effectiveness of the proposed solution.
Physical Processes in Inorganic Scintillators
BASIC PRINCIPLES AND PROCESSES Physical Mechanism of Scintillation Creation of Electron Hole Pairs Excitation and Emission of Luminescence Centers Scintillation Materials Halides Oxides and Oxide Systems Chalcogenides Glasses Interaction of Ionizing Radiation with Scintillators High Energy Photons Charged Particles Neutral Particles General Characteristics of Inorganic Scintillators Light Yield Duration of Scintillation Pulse Afterglow Temperature Response Optical Properties Radiation Hardness Density Emission Spectra Mechanical and Chemical Properties Physical Parameters Cost Consideration Scintillator Requirements in Various Applications High Energy Physics Intermediate Energy Physics Positron Emission Tomography Gamma Spectroscopy Energy Resolution Intrinsic Scintillator Resolution Nonproportional Response Time Resolution Low Energy Quanta and Electrons CONVERSION OF ELECTRONIC EXCITATIONS IN SOLIDS Charge Carrier Behaviors Delta Rays Secondaries Excitation of Luminescence Centers Effect of Ionization Density Energy Losses Simple Phenomenological Model Plasmon Model Polaron Model Scintillation Yield Spectra Vacuum Ultraviolet Region Ultrasoft X-Rays X-Rays Gamma Rays Heavy Ionizing Particles INTRINSIC LUMINESCENCE OF INORGANIC SCINTILLATORS Excitonic Luminescence Alkali Halide Crystals Alkaline-Earth Fluorides Ternary Halide Compounds Excitonic-Like Luminescence Cesium Iodide Tungstate and Molybdate Phosphors Core-to-Valence Transitions First Evidence for Radiative Core-to-Valence Transitions Excitation Spectra Emission Spectra Experiment Theory Luminescence Kinetics Experimental Theoretical Investigations Temperature Dependence of Luminescence Parameters Conditions of Detection Prospects for Research EXTRINSIC LUMINESCENCE OF INORGANIC SCINTILLATORS Thallium-Activated Halide Scintillators Crystals with NaCl-Type Structure Crystals with CsCl-Type Structure Other Thallium-Based and Thallium-Doped Crystals Crystals Containing Other ns2 Ions Bismuth Germanate (BGO) Sodium-Activated Cesium Iodide Rare-Earth-Activated Crystals General Considerations Europium-Activated Crystals Cerium-Activated Compounds Preliminary Comments LaF3-CeF3 Systems Cerium Chloride Barium Fluoride Gadolinium-Containing Crystals Lu- and Y-Containing Crystals Nd- and Pr-Activated Crystals DEFECT FORMATION BY IONIZING RADIATION Effect on Scintillator Characteristics Mechanisms of Defect Formation Efficiency of Defect Production Geometrical Factor Separation between F and H Centers Temperature Dependence of Production Efficiency Role of Halogen Ion Impurities Effect of Cation Impurities Formation Time of F-H Pairs Closing Comments References Index