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Forward characteristics of switching power supply output filter analysis and simulation

In Electronic Infomation Category: F | on April 14,2011

Abstract: In this paper, a forward switching power supplys output I CR combination of filter characteristics in-depth analysis, comparative analysis of the basis of some previous studies, from the time domain and TC75S51FU datasheet and frequency domain simulation of the LCR function of the filter combination zero frequency performance and TC75S51FU price and the key to guide the converter loop compensation design.

0 Introduction

Switching power supply and TC75S51FU suppliers and power electronic converters, and requests the input parameters and output parameters in the case of changes in output load to maintain stability, and other disturbances from the south in the control loop in the nonlinear elements, will cause response and phase shift between the input, so the design is a very important aspect of the entire power control loop to compensate for the power output characteristics of many of the design with the control loop is closely related to the merits, such as in a variety of output stability conditions, dramatic changes in the input and output load transient response under, as well as resistance to all kinds of noise, electromagnetic interference. It can be said control loop compensation design and magnetic design and power electronic converter switching power supply design of the core of the difficulties, the literature there are some design guidelines and examples.

Therefore, requires the designer of the entire loop in all aspects of the frequency response and loop compensation design, only the analysis clearly every detail of the loop may cause the amplitude frequency, phase frequency transfer characteristics of change, it clearly in the debug parameter to adjust each component may be caused by changes in power characteristics. In general, the loop may cause significant changes in the phase-frequency characteristics of the place only two, one part of the output filter, error amplifier compensation is another link. Depth analysis of the clear part of the output filter, to be able to accurately design a good part of the compensation required to achieve the desired design requirements. Analysis of the contrary are not allowed if the output filter links, misleading link in the error compensation design, the control characteristics of the product unexpected results will occur.

1 forward converter output filter characteristics of the conventional theory and problems

In a forward converter, because the transformer end of the initial level at the same time conveying the same name as the reasons for the energy, the output need to configure the inductors and capacitors to form LC filters. Because the existing conventional electrolytic capacitor equivalent series resistance (ESR) of the entire output filter frequency response will appear an extra zero frequency, the two ends of the zero frequency will be a 40 dB / dec and a 20 dB / dec of amplitude-frequency characteristic slope, loop compensation design must be based on characteristics of the output filter design of appropriate compensation.

In the past some of the literature (Figure 1), gives the characteristics of conventional LC output filter and a brief analysis of each frequency to determine the inflection point formula, first appeared Lc filter characteristic frequency inflection point, after the amplitude-frequency characteristics of this frequency to a 40 dB / dec slope down to a phase frequency characteristics of the 180 phase shift. Later, with increasing frequency, the impedance of shunt capacitor smaller and smaller, start capacitor equivalent series resistance in the filter characteristics in the performance of p gradually clear that when the frequency increased in that time, this time Rcsr = 2fecsrL, increased 45 phase . When the frequency continues to rise, the output filter circuit into a LR circuit, the slope into a 20dB/dec by attenuation, phase shift tend to lag 90 .


Figure 1 Conventional LC filter amplitude-frequency characteristics

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