EMI FILTER DESIGN FOR SITNCHED-MODE POWER SUPPLY2

hjp · 发表于 2007-9-27 13:34:40

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Combining the last two equations, the optimum damping resistance value Rd is equal to:<wrapblock><shapetype id="_x0000_t75" stroked="f" filled="f" path="m@4@5l@4@11@9@11@9@5xe" o:preferrelative="t" o:spt="75" coordsize="21600,21600"><stroke joinstyle="miter" /><formulas><f eqn="if lineDrawn pixelLineWidth 0" /><f eqn="sum @0 1 0" /><f eqn="sum 0 0 @1" /><f eqn="prod @2 1 2" /><f eqn="prod @3 21600 pixelWidth" /><f eqn="prod @3 21600 pixelHeight" /><f eqn="sum @0 0 1" /><f eqn="prod @6 1 2" /><f eqn="prod @7 21600 pixelWidth" /><f eqn="sum @8 21600 0" /><f eqn="prod @7 21600 pixelHeight" /><f eqn="sum @10 21600 0" /></formulas><path o:connecttype="rect" gradientshapeok="t" o:extrusionok="f" /><lock aspectratio="t" v:ext="edit" /></shapetype><shape id="_x0000_s1028" style="MARGIN-TOP: 0px; Z-INDEX: 3; MARGIN-LEFT: 0px; WIDTH: 277.5pt; POSITION: absolute; HEIGHT: 42pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C

OCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image001.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> <wrapblock><shape id="_x0000_s1029" style="MARGIN-TOP: 1.8pt; Z-INDEX: 4; MARGIN-LEFT: 3.6pt; WIDTH: 41.25pt; POSITION: absolute; HEIGHT: 16.5pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C

OCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image003.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> With the blocking capacitor Cd equal to four times the filter capacitor C.Figures 5 and 6 shows  the output impedance and the transfer function of the parallel damped filter respectively. <wrapblock><shape id="_x0000_s1036" style="MARGIN-TOP: 0px; Z-INDEX: 11; MARGIN-LEFT: 0px; WIDTH: 409.8pt; POSITION: absolute; HEIGHT: 221.4pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C

OCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image005.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> <wrapblock><shape id="_x0000_s1037" style="MARGIN-TOP: 0px; Z-INDEX: 12; MARGIN-LEFT: 0px; WIDTH: 403.8pt; POSITION: absolute; HEIGHT: 239.4pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image007.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock>     SERIES DAMPED FILTER: Another way to obtain a damped filter is with a resistance Rd in series with an inductor Ld, all connected in parallel with the filter inductor L. (figure 7)At the cutoff frequency, the resistance Rd has to be a higher value of the Ld impedance. <h2 style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: left" align="left"> </h2><h2 style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1040" style="MARGIN-TOP: 10.2pt; Z-INDEX: 15; LEFT: 0px; MARGIN-LEFT: 46.8pt; WIDTH: 270.75pt; POSITION: absolute; HEIGHT: 150.75pt; TEXT-ALIGN: left" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image009.png" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> </h2><h2 style="MARGIN: 0cm 0cm 0pt">Figure 7 : Series damped filter</h2> The output impedance and the transfer function of the filter can be calculated the same way as the parallel damped filter:  <wrapblock><shape id="_x0000_s1027" style="MARGIN-TOP: 7.2pt; Z-INDEX: 2; MARGIN-LEFT: -7.2pt; WIDTH: 358.5pt; POSITION: absolute; HEIGHT: 54pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image011.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> <wrapblock><shape id="_x0000_s1026" style="MARGIN-TOP: 3.45pt; Z-INDEX: 1; MARGIN-LEFT: 21.6pt; WIDTH: 143.25pt; POSITION: absolute; HEIGHT: 46.5pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image013.wmz" /><wrap type="topAndBottom" side="right" /></shape><shape id="_x0000_s1041" style="MARGIN-TOP: 49.65pt; Z-INDEX: 16; MARGIN-LEFT: -3.6pt; WIDTH: 304.5pt; POSITION: absolute; HEIGHT: 94.5pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image014.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> From the approximated transfer function of the series damped filter, the damping factor can be calculated as: <wrapblock><shape id="_x0000_s1030" style="MARGIN-TOP: 0px; Z-INDEX: 5; MARGIN-LEFT: 0px; WIDTH: 87pt; POSITION: absolute; HEIGHT: 31.8pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image016.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock>  The peaking is minimized with a damping factor :<wrapblock><shape id="_x0000_s1031" style="MARGIN-TOP: 0px; Z-INDEX: 6; MARGIN-LEFT: 0px; WIDTH: 128.4pt; POSITION: absolute; HEIGHT: 30pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image018.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> The optimal damped resistance is:<wrapblock><shape id="_x0000_s1032" style="MARGIN-TOP: 0px; Z-INDEX: 7; MARGIN-LEFT: 0px; WIDTH: 234pt; POSITION: absolute; HEIGHT: 37.8pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image020.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> The disadvantage of this damped filter is that the high frequency attenuation is degraded. (See figure 10 ).  MULTIPLE SECTION FILTERS: Most of the time a multiple section filter allows higher attenuation at high frequencies with less volume and cost, because if the number of single components is increased, it allows the use of smaller inductance and capacitance values . (figure 8)<wrapblock><shape id="_x0000_s1042" style="MARGIN-TOP: 11.4pt; Z-INDEX: 17; MARGIN-LEFT: 46.8pt; WIDTH: 330.75pt; POSITION: absolute; HEIGHT: 150.75pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image022.png" /><wrap type="topAndBottom" side="right" /></shape></wrapblock>  <h2 style="MARGIN: 0cm 0cm 0pt">Figure 8 : Two section input filter </h2> <wrapblock><shape id="_x0000_s1043" style="MARGIN-TOP: 46.05pt; Z-INDEX: 18; MARGIN-LEFT: 3.6pt; WIDTH: 226.5pt; POSITION: absolute; HEIGHT: 75.75pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image024.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> The output impedance and the transfer function can be calculated from the combination of each block impedance:  <wrapblock><shape id="_x0000_s1033" style="MARGIN-TOP: 10.2pt; Z-INDEX: 8; MARGIN-LEFT: -8.4pt; WIDTH: 439.2pt; POSITION: absolute; HEIGHT: 39pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image026.wmz" /><wrap type="topAndBottom" side="right" /></shape><shape id="_x0000_s1034" style="MARGIN-TOP: 126.45pt; Z-INDEX: 9; MARGIN-LEFT: 3.6pt; WIDTH: 446.4pt; POSITION: absolute; HEIGHT: 35.4pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image027.wmz" /><wrap type="topAndBottom" side="right" /></shape><shape id="_x0000_s1044" style="MARGIN-TOP: 61.65pt; Z-INDEX: 19; MARGIN-LEFT: 3.6pt; WIDTH: 304.5pt; POSITION: absolute; HEIGHT: 58.5pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image028.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> Figures 9 and 10 show the output impedance and the transfer function of the series damped filter compared with the undamped one.<s></s>The two-stage filter has been optimized with the following ratios:<wrapblock><shape id="_x0000_s1035" style="MARGIN-TOP: 0px; Z-INDEX: 10; MARGIN-LEFT: 0px; WIDTH: 265.2pt; POSITION: absolute; HEIGHT: 34.8pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image030.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock> The filter provides an attenuation of 80dB with a peak filter output impedance lower than 2<span lang="EN-US" style="FONT-SIZE: 12pt; FONT-FAMILY: Symbol; mso-bidi-font-size: 10.0pt; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman"; mso-char-type: symbol; mso-symbol-font-family: Symbol">W. <wrapblock><shape id="_x0000_s1038" style="MARGIN-TOP: 11.1pt; Z-INDEX: 13; MARGIN-LEFT: -3.6pt; WIDTH: 409.8pt; POSITION: absolute; HEIGHT: 215.4pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image032.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock>  <wrapblock><shape id="_x0000_s1039" style="MARGIN-TOP: 0px; Z-INDEX: 14; MARGIN-LEFT: 0px; WIDTH: 409.8pt; POSITION: absolute; HEIGHT: 239.4pt" o:allowincell="f" type="#_x0000_t75"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image034.wmz" /><wrap type="topAndBottom" side="right" /></shape></wrapblock>   The switching power supply rejects noise for frequencies below the crossover frequency of the feedback control loop, and higher frequencies should be rejected from the input filter. To be able to meet the forward filtering with a small solution, the input filter has to have the corner frequency around one decade below the bandwidth of the feed back loop.  CAPACITOR AND INDUCTOR SELECTION: Another important issue affecting the final performance of the filter is the right selection of capacitors and inductors. For high frequency attenuation capacitors with low ESL and low ESR for ripple current capability must be selected. The most common capacitors used are the aluminum electrolytic type.To achieve low ESR and ESL the output capacitor could be split into different smaller capacitors put in parallel to achieve the same total value.Filter inductors should be designed to reduce parasitic capacitance as much as possible, the input and output leads should be kept as far apart as possible, and single layer or banked windings are preferred. At the National Semiconductor web site, <a href="http://power.national.com/">http://power.national.com</a>, one can find all the information and tools needed to design a complete switching power supply solution.  On the web site are datasheets, application notes, selection guides, and the WEBENCH power supply design software.   REFERENCE:1.      Rudolf P. Severns, Gordon E. Bloom “Modern DC to DC switchmode power converter circuits”.2.      R.D. Middlebrook, “Design Techniques for preventing Input Filter Oscillations in Switched-Mode Regulators”.3.      Robert W. Erickson “Optimal Single Resistor Damping of Input Filters”.4.      H. Dean Venable “Minimizing Input Filter”.5.      Jim Riche “ Feedback <place w:st="on">Loop</place> Stabilization on Switching Power Supply”.6.      Bruce W. Carsten “Design Techniques for the Inherent of Power Converter EMI”.

lvjianqi101 · 发表于 2008-11-27 21:36:19

zhe shi shen me ya ?

speedstarmix · 发表于 2009-11-17 14:53:43

書上的內容? 沒圖?

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EMI FILTER DESIGN FOR SITNCHED-MODE POWER SUPPLY2

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