Techniques for reducing distortion in input and output terminals of switching power supplies

Pao Yue-kong Library Electronic Theses Database

Techniques for reducing distortion in input and output terminals of switching power supplies

 

Author: Poon, Ngai-kit Franki
Title: Techniques for reducing distortion in input and output terminals of switching power supplies
Degree: Ph.D.
Year: 2003
Subject: Hong Kong Polytechnic University -- Dissertations
Electric distortion -- Prevention
Electromagnetic interference -- Prevention
Switching power supplies
Department: Dept. of Electronic and Information Engineering
Pages: 142 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1732940
URI: http://theses.lib.polyu.edu.hk/handle/200/4032
Abstract: This thesis addresses the techniques for reducing the voltage or current distortion measured across the input and output of switching power supplies. The ideal input characteristic of a power supply at steady-state condition is linearly resistive, i.e., a pure dc input voltage will result in a pure dc input current. The ideal output of a dc power supply is also a pure dc voltage. However, problems arising from electromagnetic interference (EMI), ripple voltage, ripple current, non-resistive input characteristic, spiking under load transient of a switching power supply will make the power supply's input current and/or output voltage deviate from ideality. Such deviations eventually manifest themselves as input current distortion and rather long output transient. In this thesis, distortion is treated in a unified manner. The main philosophy of this thesis is that the problem of eliminating distortion can be solved in a unified manner, resorting to treatment-based elementary circuit theory. Also, a unified synthesis approach is proposed to eliminate EMI, ripple current, ripple voltage as well as output spikes under load transient. The specific contributions of this thesis are as follows: I.The origin of distortion caused by the switching behavior of a switching converter is investigated. A modeling technique for generating a complete circuit schematic is developed for effective analysis. This technique "inks out" the irwisible components whose existence is due to the presence of subtle non-contact coupling paths, thus enabling handy prediction of the extent of distortion caused by the switching behavior of the switching converter. II.A general approach for eliminating distortion by using an add-on circuit approach is proposed. This involves the use of a circuit synthesis technique for generating passive and active filters for eliminating distortion caused by the switching behavior of the switching converter. An add-on circuit that eliminates unwantd signal coupling from one part of the circuit to another is used. This method is applicable to all types of converters. III.A prudent application of the same synthesis technique is demonstrated for drastic reduction of the output voltage spikes under load transient. IV.An application circuit for achieving a resistive input characteristic converter without the use of feedback or duty cycle control is demonstrated. The thesis colltains seven chapters, beginning with an overview of the basic concepts of the lumped element approach and the various problems relevant to the study of distortion in switching power supplies. The main contributions are described in three core chapters. The last chapter concludes and provides some clues for we developments.

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