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EMI FILTER DESIGN FOR SITNCHED-MODE POWER SUPPLY2

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发表于 2007-9-27 13:34:40 | 显示全部楼层 |阅读模式

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  <p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">Combining the last two equations, the optimum damping resistance value Rd is equal to:<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><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&#46;5pt; POSITION: absolute; HEIGHT: 42pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///COCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image001&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p /></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1029" style="MARGIN-TOP: 1&#46;8pt; Z-INDEX: 4; MARGIN-LEFT: 3&#46;6pt; WIDTH: 41&#46;25pt; POSITION: absolute; HEIGHT: 16&#46;5pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///COCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image003&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p /></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">With the blocking capacitor Cd equal to four times the filter capacitor C&#46;<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">Figures 5 and 6 shows<span style="mso-spacerun: yes">&nbsp; </span>the output impedance and the transfer function of the parallel damped filter respectively&#46;<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1036" style="MARGIN-TOP: 0px; Z-INDEX: 11; MARGIN-LEFT: 0px; WIDTH: 409&#46;8pt; POSITION: absolute; HEIGHT: 221&#46;4pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///COCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image005&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p /></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1037" style="MARGIN-TOP: 0px; Z-INDEX: 12; MARGIN-LEFT: 0px; WIDTH: 403&#46;8pt; POSITION: absolute; HEIGHT: 239&#46;4pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image007&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p /></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">SERIES DAMPED FILTER:<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">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&#46; (figure 7)<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">At the cutoff frequency, the resistance Rd has to be a higher value of the Ld impedance&#46; <p /></font></span></p><h2 style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: left" align="left"><span lang="EN-US"><p><font face="Times New Roman" size="3">&nbsp;</font></p></span></h2><h2 style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1040" style="MARGIN-TOP: 10&#46;2pt; Z-INDEX: 15; LEFT: 0px; MARGIN-LEFT: 46&#46;8pt; WIDTH: 270&#46;75pt; POSITION: absolute; HEIGHT: 150&#46;75pt; TEXT-ALIGN: left" o:allowincell="f" type="#_x0000_t75"><font size="3"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image009&#46;png" /><wrap type="topAndBottom" side="right" /></font></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /></h2><h2 style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US"><font face="Times New Roman" size="3">Figure 7 : Series damped filter</font></span></h2><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">The output impedance and the transfer function of the filter can be calculated the same way as the parallel damped filter:<span style="mso-spacerun: yes">&nbsp; </span><p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1027" style="MARGIN-TOP: 7&#46;2pt; Z-INDEX: 2; MARGIN-LEFT: -7&#46;2pt; WIDTH: 358&#46;5pt; POSITION: absolute; HEIGHT: 54pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image011&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p /></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1026" style="MARGIN-TOP: 3&#46;45pt; Z-INDEX: 1; MARGIN-LEFT: 21&#46;6pt; WIDTH: 143&#46;25pt; POSITION: absolute; HEIGHT: 46&#46;5pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image013&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape><shape id="_x0000_s1041" style="MARGIN-TOP: 49&#46;65pt; Z-INDEX: 16; MARGIN-LEFT: -3&#46;6pt; WIDTH: 304&#46;5pt; POSITION: absolute; HEIGHT: 94&#46;5pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image014&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p /></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">From the approximated transfer function of the series damped filter, the damping factor can be calculated as:<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1030" style="MARGIN-TOP: 0px; Z-INDEX: 5; MARGIN-LEFT: 0px; WIDTH: 87pt; POSITION: absolute; HEIGHT: 31&#46;8pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image016&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman"><span style="mso-spacerun: yes">&nbsp;</span>The peaking is minimized with a damping factor :<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1031" style="MARGIN-TOP: 0px; Z-INDEX: 6; MARGIN-LEFT: 0px; WIDTH: 128&#46;4pt; POSITION: absolute; HEIGHT: 30pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image018&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">The optimal damped resistance is:<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1032" style="MARGIN-TOP: 0px; Z-INDEX: 7; MARGIN-LEFT: 0px; WIDTH: 234pt; POSITION: absolute; HEIGHT: 37&#46;8pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image020&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">The disadvantage of this damped filter is that the high frequency attenuation is degraded&#46; (See figure 10 )&#46;<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">MULTIPLE SECTION FILTERS:<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">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 &#46; (figure 8)<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1042" style="MARGIN-TOP: 11&#46;4pt; Z-INDEX: 17; MARGIN-LEFT: 46&#46;8pt; WIDTH: 330&#46;75pt; POSITION: absolute; HEIGHT: 150&#46;75pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image022&#46;png" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p /></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><h2 style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US"><font face="Times New Roman" size="3">Figure 8 : Two section input filter </font></span></h2><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoBodyText2" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1043" style="MARGIN-TOP: 46&#46;05pt; Z-INDEX: 18; MARGIN-LEFT: 3&#46;6pt; WIDTH: 226&#46;5pt; POSITION: absolute; HEIGHT: 75&#46;75pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image024&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US"><font face="Times New Roman" size="3">The output impedance and the transfer function can be calculated from the combination of each block impedance:</font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman"><span style="mso-spacerun: yes">&nbsp;</span><p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1033" style="MARGIN-TOP: 10&#46;2pt; Z-INDEX: 8; MARGIN-LEFT: -8&#46;4pt; WIDTH: 439&#46;2pt; POSITION: absolute; HEIGHT: 39pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image026&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape><shape id="_x0000_s1034" style="MARGIN-TOP: 126&#46;45pt; Z-INDEX: 9; MARGIN-LEFT: 3&#46;6pt; WIDTH: 446&#46;4pt; POSITION: absolute; HEIGHT: 35&#46;4pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image027&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape><shape id="_x0000_s1044" style="MARGIN-TOP: 61&#46;65pt; Z-INDEX: 19; MARGIN-LEFT: 3&#46;6pt; WIDTH: 304&#46;5pt; POSITION: absolute; HEIGHT: 58&#46;5pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image028&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><p /></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">Figures 9 and 10<span style="COLOR: black"> show </span>the output impedance and the transfer function of the series damped filter compared with the undamped one&#46;<s><p /></s></font></span></p><p class="MsoBodyText2" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US"><font face="Times New Roman" size="3">The two-stage filter has been optimized with the following ratios:</font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1035" style="MARGIN-TOP: 0px; Z-INDEX: 10; MARGIN-LEFT: 0px; WIDTH: 265&#46;2pt; POSITION: absolute; HEIGHT: 34&#46;8pt" o:allowincell="f" type="#_x0000_t75"><font size="3"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image030&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">The filter provides an attenuation of 80dB with a peak filter output impedance lower than 2</font></span><span lang="EN-US" style="FONT-SIZE: 12pt; FONT-FAMILY: Symbol; mso-bidi-font-size: 10&#46;0pt; mso-ascii-font-family: "Times New Roman"; mso-hansi-font-family: "Times New Roman"; mso-char-type: symbol; mso-symbol-font-family: Symbol"><span style="mso-char-type: symbol; mso-symbol-font-family: Symbol">W</span></span><span lang="EN-US" style="FONT-SIZE: 12pt; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">&#46;<span style="COLOR: blue"><p /></span></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1038" style="MARGIN-TOP: 11&#46;1pt; Z-INDEX: 13; MARGIN-LEFT: -3&#46;6pt; WIDTH: 409&#46;8pt; POSITION: absolute; HEIGHT: 215&#46;4pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image032&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p /></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><wrapblock><shape id="_x0000_s1039" style="MARGIN-TOP: 0px; Z-INDEX: 14; MARGIN-LEFT: 0px; WIDTH: 409&#46;8pt; POSITION: absolute; HEIGHT: 239&#46;4pt" o:allowincell="f" type="#_x0000_t75"><font face="Times New Roman"><imagedata src="file:///C:DOCUME~1HEJUNP~1LOCALS~1Tempmsohtml1clip_image034&#46;wmz" /><wrap type="topAndBottom" side="right" /></font></shape></wrapblock><br style="mso-ignore: vglayout" clear="all" /><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p /></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">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&#46;<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman"><span style="mso-spacerun: yes">&nbsp;</span>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&#46; <p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">CAPACITOR AND INDUCTOR SELECTION:<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">Another important issue affecting the final performance of the filter is the right selection of capacitors and inductors&#46; For high frequency attenuation capacitors with low ESL and low ESR for ripple current capability must be selected&#46; The most common capacitors used are the aluminum electrolytic type&#46;<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">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&#46;<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">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&#46;<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">At the National Semiconductor web site, </font><a href="http://power&#46;national&#46;com/"><span style="FONT-SIZE: 10pt"><font face="Times New Roman">http://power&#46;national&#46;com</font></span></a><font face="Times New Roman">, one can find all the information and tools needed to design a complete switching power supply solution&#46;<span style="mso-spacerun: yes">&nbsp; </span>On the web site are datasheets, application notes, selection guides, and the WEBENCH power supply design software&#46;<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><p><font face="Times New Roman">&nbsp;</font></p></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt"><font face="Times New Roman">REFERENCE:<p /></font></span></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt 18pt; TEXT-INDENT: -18pt; mso-list: l0 level1 lfo1; tab-stops: list 18&#46;0pt"><font face="Times New Roman"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-fareast-font-family: "Times New Roman"; mso-bidi-font-size: 10&#46;0pt"><span style="mso-list: Ignore">1&#46;<span style="FONT: 7pt "Times New Roman"">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span></span></span><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt">Rudolf P&#46; Severns, Gordon E&#46; Bloom “Modern DC to DC switchmode power converter circuits”&#46;<p /></span></font></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt 18pt; TEXT-INDENT: -18pt; mso-list: l0 level1 lfo1; tab-stops: list 18&#46;0pt"><font face="Times New Roman"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-fareast-font-family: "Times New Roman"; mso-bidi-font-size: 10&#46;0pt"><span style="mso-list: Ignore">2&#46;<span style="FONT: 7pt "Times New Roman"">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span></span></span><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt">R&#46;D&#46; Middlebrook, “Design Techniques for preventing Input Filter Oscillations in Switched-Mode Regulators”&#46;<p /></span></font></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt 18pt; TEXT-INDENT: -18pt; mso-list: l0 level1 lfo1; tab-stops: list 18&#46;0pt"><font face="Times New Roman"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-fareast-font-family: "Times New Roman"; mso-bidi-font-size: 10&#46;0pt"><span style="mso-list: Ignore">3&#46;<span style="FONT: 7pt "Times New Roman"">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span></span></span><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt">Robert W&#46; Erickson “Optimal Single Resistor Damping of Input Filters”&#46;<p /></span></font></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt 18pt; TEXT-INDENT: -18pt; mso-list: l0 level1 lfo1; tab-stops: list 18&#46;0pt"><font face="Times New Roman"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-fareast-font-family: "Times New Roman"; mso-bidi-font-size: 10&#46;0pt"><span style="mso-list: Ignore">4&#46;<span style="FONT: 7pt "Times New Roman"">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span></span></span><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt">H&#46; Dean Venable “Minimizing Input Filter”&#46;<p /></span></font></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt 18pt; TEXT-INDENT: -18pt; mso-list: l0 level1 lfo1; tab-stops: list 18&#46;0pt"><font face="Times New Roman"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-fareast-font-family: "Times New Roman"; mso-bidi-font-size: 10&#46;0pt"><span style="mso-list: Ignore">5&#46;<span style="FONT: 7pt "Times New Roman"">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span></span></span><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt">Jim Riche “ Feedback <place w:st="on">Loop</place> Stabilization on Switching Power Supply”&#46;<p /></span></font></p><p class="MsoNormal" style="MARGIN: 0cm 0cm 0pt 18pt; TEXT-INDENT: -18pt; mso-list: l0 level1 lfo1; tab-stops: list 18&#46;0pt"><font face="Times New Roman"><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-fareast-font-family: "Times New Roman"; mso-bidi-font-size: 10&#46;0pt"><span style="mso-list: Ignore">6&#46;<span style="FONT: 7pt "Times New Roman"">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span></span></span><span lang="EN-US" style="FONT-SIZE: 12pt; COLOR: black; mso-bidi-font-size: 10&#46;0pt">Bruce W&#46; Carsten “Design Techniques for the Inherent of Power Converter EMI”&#46;<p /></span></font></p>
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