Hello,
The attached LTspice simulation is a buck converter which has the same waveforms as the buck converter in the document RDR-506 by power.com……
RDR-506 report on 1.44w offline buck converter…
https://ac-dc.power.com/sites/default/files/PDFFiles/rdr506.pdf
Page 23 of this report shows the conducted EMC scan of this buck converter. However, the LTspice simulation of this buck converter , using its FFT function, does not give a graph anything like this. Do you know why not?
Pdf schem of LTspice simulation also attached
However, Another thing is that surely the conducted emissions graph on page 23 of RDR-506 looks wrong? I mean, if you look at the schematic of the buck converter on page 5 of RDR-506, it has a really heavy PI filter consisting of a 1mH inductor and a 4.7uF capacitor either side of it………for a buck converter of just 1.44W rating, that is an extremely heavy filter….how can all the Megahertz frequencies on page 23 of the RDR-506 document be there? If you look at the input current waveform, it is very smooth, there is utterly no evidence of the 10MHz waveforms which the EMC scan of page 23 suggests. Do you know what’s going on here?
The attached LTspice simulation is a buck converter which has the same waveforms as the buck converter in the document RDR-506 by power.com……
RDR-506 report on 1.44w offline buck converter…
https://ac-dc.power.com/sites/default/files/PDFFiles/rdr506.pdf
Page 23 of this report shows the conducted EMC scan of this buck converter. However, the LTspice simulation of this buck converter , using its FFT function, does not give a graph anything like this. Do you know why not?
Pdf schem of LTspice simulation also attached
However, Another thing is that surely the conducted emissions graph on page 23 of RDR-506 looks wrong? I mean, if you look at the schematic of the buck converter on page 5 of RDR-506, it has a really heavy PI filter consisting of a 1mH inductor and a 4.7uF capacitor either side of it………for a buck converter of just 1.44W rating, that is an extremely heavy filter….how can all the Megahertz frequencies on page 23 of the RDR-506 document be there? If you look at the input current waveform, it is very smooth, there is utterly no evidence of the 10MHz waveforms which the EMC scan of page 23 suggests. Do you know what’s going on here?
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